COMMUNICATIONES INSTITUTI FORESTALIS FENNIAE 144 DAMAGE CAUSED BY THE ROOT VOLE (MICROTUS OECONOMUS) TO SCOTS PINE IN MAN-MADE HABITATS IN NORTHERN FINLAND KIRSI-MARJA KORHONEN SELOSTE LAPINMYYRÄ METSÄTUHOLAISENA POHJOIS-SUOMESSA HELSINKI 1987 COMMUNICATIONS INSTITUTI FORESTALIS FENNIAE THE FINNISH FOREST RESEARCH INSTITUTE (METSÄNTUTKIM USLAITOS) Unioninkatu 40 A SF-00170 Helsinki FINLAND telex: 125181 hyfor sf attn: metla/ phone: 90-661 401 Director: Professor Aarne Nyyssönen Distribution and exchange of publications: The Finnish Forest Research Institute Library Unioninkatu 40 A SF-00170 Helsinki FINLAND Publications of the Finnish Forest Research Institute: Communicationes Instituti Forestalls Fenniae (Commun. Inst. For. Fenn.) Folia Forestalia (Folia For.) Metsäntutkimuslaitoksen tiedonantoja Cover (front & back): Scots pine ( Pinus sylvestris L.) is the most important tree species in Finland. Pine dominated forest covers about 60 per cent of forest land and its total volume is nearly 700 mil. cu.m. The front cover shows a young Scots pine and the back cover a 30-metre-high, 140-year-old tree. COMMUNICATIONES INSTITUTI FORESTALIS FENNIAE 144 KIRSI-MARJA KORHONEN DAMAGE CAUSED BY THE ROOT VOLE (MICROTUS OECONOMUS) TO SCOTS PINE IN MAN-MADE HABITATS IN NORTHERN FINLAND Approved, on 20.11.1987 Department of Environmental Conservation, University of Helsinki To be presented, with permission of the Faculty of Agriculture and Forestry of the University of Helsinki , for public criticism in Auditorium XII on March 2nd, 1988, at 12 noon. SELOSTE LAPINMYYRÄ METSÄTUHOLAISENA POHJOIS-SUOMESSA HELSINKI 1987 Korhonen, K.-M. 1987. Damage caused by the root vole (Microtus oeconomus) to Scots pine in man-made habitats in northern Finland. Seloste: Lapinmyyrä metsätuholaisena Pohjois-Suomessa. Communicationes Instituti Forestalis Fenniae 144. 61 p. Natural habitats of the root vole ( Microtus oecono mus) in northern Finland are seasonally flooded meadows and fens. Recent changes in land-use, such as abandoning of fields, clear-cutting and draining of peatlands, have multiplied the habitats suitable for voles. The increase in root vole numbers has resulted in damage to young Scots pines (Pinus sylvestris). Damage to seedlings on afforested fields was studied on 46 plots. Half of all the fields afforested during 1972 —1977 suffered from root vole damage. Damaged plantations were larger than undamaged ones. Also sedges and grasses were more luxurious and the soil more fertile in damaged plantations. In ploughed fields the voles used the hollow layer inside the shoulder for nesting. Damage in peatland forests of the young thinning stage was studied on 57 plots and in two line inventory areas. Half of the 3697 trees examined in drained areas were attacked, and 40 °Io of the damaged trees died within 3 years. In undrained comparison areas a total of 420 trees were examined but no vole damage was found. The luxury of the field vegetation proved to be the most important factor influencing the damage. The vegetation was classified using DECORANA and TWINSPAN analyses. Study plots were arranged according to the vegetation analyses into groups indicating the damage susceptibility. Fertilization seemed to increase the damage risk by increasing soil fertility and growth of the vegetation. Phosphorus content in the soil correlated positively with the damage degree. The damage risk also increased after heavy thinnings. Keywords: vole damage, pests, damage risk ODC 451.2+845. 4+(480.99)+149.32 Microtus oeconomus Lapinmyyrän ( Microtus oeconomus) luontaisia elin ympäristöjä ovat tulvaniityt ja aapasuot. Viimeaikaiset maankäytön muutokset, mm. peltoviljelystä luopumi nen, avohakkuiden runsastuminen ja soiden ojitus, ovat moninkertaistaneet myyrille soveltuvien elinympäristö jen määrän. Lapinmyyrän runsastuminen on tehnyt siitä huomattavan männyn tuholaisen Pohjois-Suomessa. Pienten taimien tuhoja tutkittiin metsitetyillä pelloil la 46 koealalla. Vuosina 1972-77 metsitetyistä pelloista puolella esiintyi myyrätuhoja. Tuhojen kohteeksi jou tuneet taimikot olivat laajempia kuin niiltä säästyneet. Myös sarat ja heinät olivat ensinmainituissa rehevämpiä ja maaperä ravinteisempi. Auratuilla pelloilla myyrät kaivoivat pesäkolonsa palteen sisään jäävään löyhään kerrokseen. Turvemaiden harvennusmetsien tuhoja tutkittiin 57 alalla ja kahdella linja-arviointialueella. Puolet ojitus aloilla tarkastetuista männyistä (n= 3697) oli myyrän jyrsimiä ja niistä 40 °lc kuoli 3 vuoden kuluessa. Ojitta mattomilla vertailualoilla tarkastettiin 420 mäntyä, jois ta yhdestäkään ei tavattu myyrän jyrsintäjälkiä. Pinta kasvillisuuden rehevyys osoittautui tärkeimmäksi tuho alttiutta kuvaavaksi tekijäksi. Kasvillisuus luokiteltiin DECORANA- ja TWINSPAN-analyysien avulla. Näy tealat ryhmiteltiin kasvillisuusanalyysien perusteella tu hoalttiudeltaan erilaisiksi ryhmiksi. Lannoitus näytti li säävän tuhoalttiutta lisäämällä maan ravinteisuutta ja rehevöittämällä pintakasvillisuutta. Tuhojen ankaruus oli suoraan verrannollinen maaperän fosforipitoisuu teen. Tuhoriski kasvoi myös voimakkaiden harvennus hakkuiden jälkeen. Author's address: The Finnish Forest Research Institute, Department of Forest Protection, P.O. Box 18, SF-01301 Vantaa, Finland. Helsinki 1987. Valtion painatuskeskus ISBN 951-40-0796-4 ISSN 0358-9609 473011S CONTENTS PREFACE 5 1. INTRODUCTION 7 2. ROOT VOLE DAMAGE IN AFFORESTED FIELDS 10 21. Introduction 10 22. Material and methods 12 23. Results 14 231. Vole catches 14 232. Description of the damage 15 233. Comparison of damaged and undamaged plantations 15 2331. Plantation characteristics 15 2332. Silvicultural methods 18 2333. Vegetation 18 2334. Soil 20 24. Discussion 21 3. ROOT VOLE DAMAGE IN PEATLAND FORESTS 23 31. Introduction 23 32. Study areas 25 33. Material and methods 28 34. Results 29 341. Vole catches 29 342. Description of the damage 29 343. Drainage 33 344. Fertilization and soil nutrients 34 345. Stand density 37 346. Vegetation 38 35. Discussion 42 351. Vole damage in thinning stands in other countries 42 352. Forest improvement methods and vole damage 43 353. Significance of root vole damage in forestry 44 4. GENERAL DISCUSSION AND CONCLUSIONS 46 41. Comparison with earlier studies 46 42. Old fields and peatland forests as root vole habitats 47 43. Impact of man 48 REFERENCES 50 SELOSTE 55 APPENDICES 57 To Seppo 5 Commun. Inst. For. Fenn. 144 PREFACE This study was carried out in the Department of Forest Protection, Finnish Forest Research Institute. The study is based on the author's master's and licentiate theses submitted to the Department of Environmental Conservation, University of Helsinki (Korhonen 1981, Korhonen 1985). A report on the distribution of the root vole damage (Korhonen et ai. 1983) has been published earlier. I Dr. Terttu Teivainen from the Finnish Forest Research Institute and Prof. Pekka Nuorteva from the Dept. of Environmental Conservation, University of Helsinki, pro vided valuable encouragement and advice during the years of this study. I extend my sincere thanks to them. I greatly appreciate the stimulating discussions with Prof. Erkki Annila, Mr. Asko Kaikusalo, Mr. Jouni Kitti, Dir. Erkki Numminen and many others. During the field work I have been assisted by Jaana Hiltunen, Aino Kananen and Eeva Kuhlman, and during the data handling by many helpful and patient friends in the Forest Research Institute. Katriina Huttunen, Auli Immonen, Lasse Kärnä, Pasi Pekkinen and Annikki Viitanen assisted with the typing and drawing of figures. ;r o o o y I am indepted to Mrs. N.L. Cubykina, Dr. L.N. Erdakov and Prof. A.A. Maksimov from the Biological Institute of the Academy of Sciences, Siberian Department and Prof. E.V. Ivanter from the University of Pet rozavodsk and Mrs. T.V. Ivanter from the Zoological Institute of Academy of Sciences, Karelian Department who provided valuable information about root vole biology and vole damage in the Soviet Union and kindly assisted with the literature survey, during my stay in Novosibirsk in 9.11.—16.12. 1983 and Petrozavodsk in 26.10.—1.11. 1983. My research has been financed by the Finnish Forest Research Institute and the Academy of Finland. The Committee for Scientific-technical Cooperation between Finland and the Soviet Union supported financially my stay in the Soviet Union during 24.10.—18.12. 1983. Veitsiluoto Co. and the Department of Peatland Forestry kindly allowed the use of their plantations and research areas, and made the data on silvicultural methods available. I would also like to thank Dr. Kari Heliövaara and Mr. Markku Ropo who commented on the manuscript and Mr. John Derome who corrected my English. I extend my sincere thanks to all who have cooper ated in the completion of this study. Vantaa, December 1987 Kirsi-Marja Korhonen Commun. Inst. For. Fenn. 144 7 1. INTRODUCTION The increase in forest cultivation has brought about several new forest pest f>roblems. Among the most harmful pests in orest plantations are the voles. They gnaw the bark of the seedlings and cause great economical losses to forestry during their population peak years. Vole species which are important pests in forestry in Finland are the field vole (Microtus agrestis L.), the water vole (Arvicola terrestris L.), the bank vole (Clethrionomys glareolus Schr.) and the root vole ( Microtus oeconomus Pallas). This study deals with the damage caused by the root vole in northern Finland. The damage caused by root vole is of special concern because besides in young plantations, it also occurred in forests at the young thinning stage. The root vole is a species which is distributed over the whole northern part of Eurasia, stretching from northern Scandina via and Germany to the Pacific Ocean, and in North America, the whole of Alaska and the western part of Canada. In addition to this continuous area, it also occurs in the Netherlands, Austria, Hungary and southern Scandinavia (Tast 1972). In Czechoslovakia the species is known as a very rare relict (Sladek and Mosansky 1985). In Finland the southern edge of the distribution area of the root vole is considered to be slightly south of the Arctic Circle (Siivonen 1967). In addition, the species has been reported on some islands of the Gulf of Bothnia (Kostian 1970). In Karelia the species occurs from north to south at least to the northern shore of lake Ladoga (61°30'N) (Ivanter 1986, Ivanter and Ivanter 1986). The natural habitats of root voles in Finland are of two main types: the open, watery fens occurring widely throughout northern Finland, and the seasonally flooded meadows on the shores of rivers, brooks and lakes (Tast 1966). In fens the root voles occupy the wet parts in summer and the drier hummocks in winter. In flood meadows they live within the flood range in summer and beyond it during the winter (Tast 1968 a). In spite of the differences in soil and vegetation, the ecological conditions asso ciated with flooding are so uniform in these areas, that the dominant small rodent species in both is the root vole (Tast 1966). Most of the studies carried out on the natural biotopes of the root vole have been published in the Soviet Union. The root vole is known there as the dominating small mammal throughout wide zones of the southern tundra and northern forest-tundra (Pjastolova 1971). In the forest zone the species occupies moist and swampy habitats ranging from the western border to the Kamchatka Peninsula (Dinesman 1961). In western Siberia the optimum zone of the species is considered to be the southern taiga, although it is common in all the zones ranging from the northern taiga to the southern forest-steppe, and even occurs in subalpine meadows above an altitude of 3000 m (Ravkin, J.S., Biological Institute, Siberian Dept., AN SSSR, unpubl.). The most favourable biotopes in western Siberia are moist meadows, river valleys and the edges of open bogs (Maksimov 1978). Often the species is dominating in numbers and occupies all the main biotopes: peatlands, fields with forest islands, clear-cuts (Maksi mov 1978, 1981, Maksimov and Erdakov 1985). The root vole is the most numerous species of small mammals also in the vast flooded valleys of the river Ob (Erdakov 1981 a). In northern Kazakstan the root vole occurs sporadically, but the numbers can be very high especially along the shores of lakes and large rivers (Pjastolova 1966). The root vole occupies an area unevenly. In the forest zone the species may spread out over vast areas and form large mosaic communities, while in the forest-steppe zone it occurs in small mosaic communities like separate islands (Litvin 1975). According to Silov et al. (1977), the mosaically distributed habitats of the root vole occur in moist thickets consisting of hygrophilic plants. In eastern Siberia the species has a wide range of important habitats in the forest-steppe and taiga zones: grass and herb-rich spruce forests, moss-covered pine 8 K.-M. Korhonen forests in lowlands, birch-aspen forests, thickets, meadows or bush and herb-rich bogs (Fetisov 1958). According to the data combined from the Soviet authors (Fetisov 1958, Karaseva et al. 1960, Lavrov and Zonov 1963, Ocirov 1966, Pjastolova 1974 a, Maksimov 1978, Agipaev 1979), the root vole occurs most numerously in river valleys, moist forests, meadows, open fens and in rural buildings. Summer habitats of the root vole are characterized by excess moisture and luxur ious vegetation dominated by sedges and grasses. The denser and higher the sedge cover, the better is the habitat. Root voles also occur more frequently in habitats with some sedges than in those without. Besides food the vegetation also has to provide shelter. Thus the root voles do not occur in pure stands of Trichophorum cespitosum (L.) Hartman, although this plant species is favoured by them as food. Besides large sized sedges, grasses such as Poa spp., De schampsia cespitosa (L.) Beauv., Milium effu sum L., Phragmites australis (Cav.) Trin. Steudel, Calamagrostis spp. and Molinia cae rulea (L.) Moench can also serve as the main food source of the root vole and can provide shelter, too (Tast 1966). Wintering sites or the root vole are considerably drier than its habitats during the breeding season. In peatlands the root vole prefers hummocks since it can eat the underground parts of Carex aquatilis Wah lenb., C. rostrata Stokes and Eriophorum angustifolium Honck. (Tast 1966). The root vole digs tunnels through the peat in the hummocks until they become completely hollowed out. On mineral soils the wintering sites of the root vole are situated above the flood range, along rivers, lakes and stream sides, where the underground parts of grasses and sedges are available. The runways lie above ground and the voles dig small holes to reach the roots of the plants, e.g. Deschampsia cespitosa and Calamagrostis spp. The summer food of the root vole is the green parts of sedges, cotton-grasses and grasses (Tast 1966). According to Grod zinski (1971) the species also feeds on berries and tree seeds. Tast (1974) has found that 57 % of the food eaten by the root vole during February-November is monocoty ledons, 23 % dicotyledons, 19 % Equisetum spp. and 1 % mosses. In eastern Kazakstan the root vole eats more vegetative parts of plants during the breeding season than Clethrionomys rutilus Pallas and CI. rufoca nus Sund. (Agipaev 1979). According to Karaseva et al. (1957), sedges and grasses represent more than half of the food of the root vole during the snowless period, but in April one third of the food still consists of willow bark. Fetisov (1958) has studied the food of the root voles by examining the contents of their guts and food stores in their tunnels (Appendix 1). In eastern Siberia the main rood of the species in summer are the leaves and stems of forest, meadow, peatland and subalpine plants. The winter food of the root vole is different from that of any other small rodent in Finland. According to Tast (1974), the winter food of root voles in Finnish Lapland consists almost exclusively of the underground parts of monocotyledons, es pecially Eriophorum angustifolium. Of all the mammal species occurring in Lapland, only reindeer (Rangifer tarandus L.) some times consumes similar food. However, during population peak years root voles also consume other plant species. Thus, in winter 1964 the root voles had eaten bark of Salix phylicifolia L. and S. myrsinites L. (Tast 1966). The winter diet of the root vole depends on the local conditions. In the Jaroslav region, Karaseva et al. (1957) found that 79 % of the guts examined in winter contained green grass (preserved in tunnels), more than 30 % had bark of woody plants and 20 % also seeds. In eastern Siberia the root vole eats in wintertime the remains of herbs, fallen tree leaves, bark from bushes, shrubs and fallen branches under the snow cover, and also its food reserves which consist of the rhizomes and roots of Carex spp., Calamagrostis spp., Parnassia palustris, Polygonum spp., Dentaria spp., Eranthis sibirica, and Phlomis tuberosa (Fetisov 1958). Underground parts of sedges and grasses are the main part of the winter reserves of the root vole in the Selenga river valley. In addition to these reserves, willow bark is also common in its winter diet in the area (Svecov 1970). Zonov (1962) found, near Irkutsk, that the species especially favours forest openings with flattened grass and hummocks where green shoots still emerge late in the autumn. The most common plants in the root vole 9 Commun. Inst. For. Fenn. 144 2 473011 S diet in the Irkutsk area are Carex cespitosa L., Descbampsia cespitosa and Poa spp. (Zonov 1962). Since the natural habitats of the root vole are diverse, so too are its main food and lifestyle. Erdakov (1984) found that the root voles living in flooded valleys of the Ob river and eating vegetative parts of plants have a very different daily activity rhythm than those living in the river banks and eating more concentrated food. 0 In feeding experiments the root vole has eaten the bark of the following plant species: Pinus sylvestris (Fetisov 1958, Tast 1974) Pinus cembra (Fetisov 1958) Betula spp. (Tast 1974, Teivainen 1978) Alnus spp. (Teivainen 1978) Populus spp. (Fetisov 1958, Teivainen 1978) Salix spp. (Karaseva et al. 1957, Fetisov 1958, Teivainen 1978) Vaccinium myrtillus (Fetisov 1958) A high reproductive potential is typical of the root voles in northern regions. The fecundity of females is exceptionally high, the offspring grow fast and reach sexual maturity at an early age. The females become pregnant immediately after partur ition and can reproduce throughout the whole summer (Svarc et al. 1969, Pjastolova 1971, 1974 b). When the population density reaches a certain level, young animals disperse out of the normal reproduction centers (Pjastolova and Jaskin 1975). Mobile life-style, great reproductive po tential, wide choice of food and good adaptability are natural factors which pro vide a significant potential for this species to take over new man-made habitats. In north ern Finland the root vole has occupied af forested fields and pine-dominated drained peatlands. As a consequence, it has de veloped into a pest that damages pine seedlings in afforested fields and older pine stands on drained peatlands. The aim of this study is to describe and analyze damage caused by the root vole to forestry. Since such damage has earlier been almost unknown, considerable emphasis has been placed on a descriptive study of the damaged areas. Finally, this study describes, analyzes and discusses the importance of anthropogenic factors on the history of the root vole, ranging from its natural habitats to afforested fields and eventually to drained peatland forests. The study is divided into two parts. The first part deals with the damage caused by the root vole in afforested fields, and the second part the damage in Scots pine stands on drained peatlands. The two types of damage differ from each other in the age of the damaged stands. In afforested fields the damage occurs in small seedling stands (dominant height < 1.3 m) and on drained peatlands mainly in young thinning stands (a stage which produces primarily pulp wood). The definitions of development stages are the same that have been used in the Finnish national forest inventory (Kuusela et al. 1986). The differences between undamaged and damaged afforested fields are analyzed by means of a comparison study. Line inven tory methods are used to ascertain the intensity of the damage in peatland forests, and to compare the suitability of drained and undrained peatlands as habitats of the root vole. The factors affecting the suscep tibility of different types of forest stands to root vole damage are investigated. Analyses are made of the field layer vegetation, the soil and the forest stand in damaged areas, and the results are compared to those of undamaged areas. The effect of forest cultivation methods, such as soil prepara tion, draining, thinnings, herbicide treat ment etc. on the incidence of vole damage are studied both in afforested fields and peatland forests. 10 K.-M. Korhonen 2. ROOT VOLE DAMAGE IN AFFORESTED FIELDS 21. Introduction The history of the root vole in Lapland is closely connected to the settlement of Lapland by the Finns, and the development of their agriculture. The Lapps have been living in these areas for a fairly long time, but their way of life has been based on reindeer herding, fishing and hunting, all practices which did not change the environ ment (Siuruainen 1982, Massa 1983). The Finnish settlers occupied the same habitats as the root voles: the shores of rivers and lakes (Siuruainen 1978, Vahtola 1982). Farming started in Lapland in the 16th century, but the gathering of hay in flooded meadows originates from the late 18th century and became a common practice early in the 19th century (Itkonen 1948 a, 1948 b). The Finns extended the flooded meadows and collected the hay for cattle fodder (Fig. 1). The first economic damage caused by the root vole took place in these meadows. Paulaharju (1939) describes in an ethnologi cal book the problems of meadow cultiva tion in Lapland: "Karjan eloiksi suovat rakennettiin, vaikka metsien hiiret luulivat , että heinät oli kasattu hei dän eloikseen. Ja he tulivat, söivät kohta koko suovan silppuläjäksi ja tyytyväisinä lepäilivät sil puissa". (Hay was gathered on stacks for the cattle, but the small mice from the woods thought the hay stacks were theirs. And they came, ate all the hay and rested happily among the chopped straw.) The increase in the field area has been rapid in Lapland: in 1910 the total field area was less than 15 000 ha, in 1950 almost 50000 ha and in 1969 at its greatest 87 500 ha (Fig. 2) (Lapin... 1981, 1986). Along with the expanding effect of man on nature, the root vole numbers slowly increased and the species now occupies the road banks, pasture lands and hay fields. In northern Lapland it has taken the role of the rat and lives in middens, cattle sheds, barns and houses (Tast 1968 a). In eastern Siberia, too, the root vole lives in yards, dumps, buildings and under granaries (Fetisov 1958). The root vole primarily migrates in the autumn when it can move many kilometers to winter quarters using paths for orien teering (Tast 1966, 1968 a). The growth of the field area in the 20th century in Lapland has taken place through the establishment of new farms and the clearing of river valleys, bogs and peatland forests for fields. The law which freed small tenant farmers in the 1920's was the incitement for 10 % of the farms present in Lapland today, while 13 % of the farms originated from settlement laws passed in 1922 and 1936 (Varjo 1967, Jaatinen 1982). During 1917—1945 the clearing of land for agricultural purposes was active in Lapland (Fig- 2). After World War II there was a need to replace the field area lost in Petsamo and eastern Finland by clearing forests for fields. New laws were passed: in 1940 laws covering the settling of evacuees and soldiers, and in 1944—1945 the laws covering land acquisi tion. This doubled the number of farms in Lapland up until the beginning of 1965. In Lapland there were very few fields to be redistributed and thus almost all of the new farms were established on peatland and forestland. During 1945—1964 a total of 11000 ha of new field was cleared on these new farms (Varjo 1967). Most of the new fields were cleared in southern and central Lapland (Rovaniemi, Salla, Ranua, Sodanky lä, Kittilä), primarily in peatlands, the natural biotopes of the root vole. The total area drained for fields in Lapland was 165 100 hectares during 1920—1965, 78 % of it in southern Lapland (Varjo 1967). Unlike the old villages along the sides of the rivers, the new farms were isolated in vast "aapa"-fen regions. The new farms turned out to be too small, under-productive and remote in the long run, and already in the 1950's the number of farm workers began to diminish: there were 28 300 farm workers in Lapland in 1950, but only 12 700 in 1970 (Lapin... 1975, 1986). The climate sets limits on Commun. Inst. For. Fenn. 144 11 Fig. 1. Habitats where the root vole caused economical losses for the first time were flooded meadows. Voles chopped the hay on drying frames. Kuva 1. Tulvaniityt olivat ensimmäinen ihmisen muovaama biotooppi, missä lapinmyyrä osoittautui vahingolliseksi. Myyrät silppusivat heinän haasioissa. farming in Lapland. Hay is produced on 60 % of the fields. In addition, more than half of the field area in southern and central Lapland is situated on peatlands. The root vole which, unlike other voles in Finland, changes its home range after every litter, has been able to occupy these hay fields and adapt to the yearly harvest. The real boom in the optimal habitats of the root vole has occurred since the 1960's when the abandonment of fields began (Fig. 3). In 1969 a law of field reservation was passed, which provided the farmers living on their farms with a grant for not cultivating their fields. In Lapland 17 % of the field area had come within this system by 1975 (Tutkimus... 1975, Jaatinen and Alalammi 1978, Varjo 1978). During the 1970's and 1980's migration from the countryside to industrial towns in southern Finland and Sweden has reduced the cultivated field area even more (Fig. 2) (Lapin... 1981, Häkkilä 1984). The farms are kept as summer Fig. 2. Total field area and abandoned field area in Lap land during 1910—1985 (Lapin... 1981, Lapin... 1986). Kuva 2. Kokonaispeltoala ja viljelystä poistettu peltoala Lapin läänissä Lapin maatilatalouden kehittämis neuvottelukunnan ja Lapin seutukaavaliiton tilasto jen mukaan (Lapin... 1981, Lapin... 1986). 12 K.-M. Korhonen Fig. 3. An abandoned field, a typical man-made habitat, is a most suitable habitat for the root vole. Kuva 3. Viljelystä poistettu pelto, tyypillinen ihmistoiminnan muovaama kasvupaikka, on lapinmyyrälle mitä suotui sin elinympäristö. cottages or sold to forestry companies which afforest the fields. According to the vole damage question naire and inventory results (Teivainen 1979, 1984, Korhonen unpubl.), it appears that the voles and the damage they cause in forest plantations have increased during the last few decades in northern Finland. A similar development has been observed since the late 1950's in Sweden and Norway (Larsson 1973, Christiansen 1975, Hansson and Lars son 1980) and in the Soviet Union, e.g. in the Krasnojarsk region (Svecova 1980). The highest population density peak was re corded in northern Finland during 1977— 1978, when most of the damage investigated in this study took place. 22. Material and methods The studies on root vole damage to small seedling stands were performed in 1978— 1979 in fields forested by Veitsiluoto com pany in northern Finland (Fig. 4). The root voles affected these plantations during the winter 1977—1978. In spring 1978 the com pany's foresters inventoried the vole damage on all afforested fields, totalling 87 (491.3 ha). Vole damage was observed on 34 fields (263 ha). For the study purposes the fields were divided into 40 vole damage areas (263 ha) and 68 undamaged ones (228 ha). 95 % of the seedlings which had been planted on these fields were Scots pine, but also lodgepole pine (Pinus contorta Douglas ex Loudon), Siberian larch (Larix sibirica Ledeb.) and birch (Betula pendula Roth) had been planted. The average planting density was about 2000 seedlings/ha. Data about the management methods used on the fields was collected from the forest management files of Veitsiluoto forestry division and analyzed with a VAX 11/785 computer using conventional statis tical methods. Commun. Inst. For. Fenn. 144 13 Fig. 4. Location of the fields afforested by Veitsiluoto Co. during 1972 —1977. Plantations with vole damage are indicated with (A) and undamaged with (O). Study plots in vole-damaged plantations are marked with (￿) and in un damaged plantations with (•). Kuva 4. Veitsiluoto Oy:n vuosina 1972-77 metsittämien peltojen sijainti. Myyrien vahingoittamat taimikot on merkitty (A), vahingoittumattomat (O). Myyrätut kimuksen koealat on merkitty vastaavasti: myyrätuhoalat (k), vahingoittu mattomat vertailualat (9). A more detailed study was performed on 23 plots (a total of 148 ha) which were picked randomly from among the affected afforested fields. In addition, the nearest possible field area without damage was chosen for each of these damage areas, i.e. 23 comparison plots (111 ha) (Fig. 4). Seedlings were examined with a line inventory method to determine the proportion of damaged seedlings. Vegetation analysis was made along two lines on each plot using ten systematic sample squares of 1 m 2 each. The frequency of plant species and the height of the vegetation, as well as the height of the seedlings were determined on these squares. Nomenclature of the plant species is according to Hämet-Ahti et ai. (1984). The vegetation data were analyzed by ordination, 14 K.-M. Korhonen classification and diversity methods. The or dination method used was a detrended cor respondence analysis DECORANA (Gauch 1982). In the cluster ordination produced by means of DECORANA the point value of each plot is the average of the species existing at that point, and the point value of each species is the average of those points where the species exists (Gauch 1982, Mikkola and Jukola-Sulonen 1984). j - _ / - Classification analyses were used for numerical clustering of the data by arranging the observations or variables according to special equality criteria in a data matrix. The different classification methods were tested using agglomerative, hierarchic clustering (CLUSTAN) and a dividing, hierarchic method (TWINSPAN = two-way indicator species analysis) (Mikkola and Jukola-Su lonen 1984). The diversity of the plant communities on the plots has been estimated numerically using different diversity indices. The species diversity has been calculated for each sample plot as follows: 1. Total number of species in the sample (S) s 2. Simpson's (1949) diversity index D = 1 £ p;2 3. Shannon's (Shannon and Weaver 1949) diversity index H' = p ; In p; 4. Kempton and Taylor's (1976) diversity index Q = S/2 In (R2/R,) 5. Pielou's (1966) diversity index ]' = H'/lnS where S is the number of species, p; is the coverage of the i:th species divided by the total coverage, and Rj and R 2 are the lower and upper quartiles in the species abundance distribution. Ordination, classification and diversity analyses, as well as output of the vegetation data matrix, were performed on a VAX 11/785 computer using special programmes developed for vegetation ecological studies (Mikkola and Jukola-Sulonen 1984, Mik kola, Kari, the Finnish Forest Research Institute, unpubl.). Peat samples were taken on the vegetation sample plots, a bulked, volumetric sample (> 1 1) being made of the ten subsamples from each plot. The samples were taken from the peat surface down to a depth of 20 cm. The samples were analyzed by Vilja vuuspalvelu Co. (a soil testing service). The following analyses were performed: soil type, acidity, exchangeable calcium and potassium, easily soluble phosphorus and nitrate nitro gen. The results were expressed per unit volume of the dry milled or sieved sample (mg/1). The methods and terminology are described in Kurki et ai. (1965) and Kurki (1982). The results were analyzed using conventional statistical methods. Vole trapping was carried out using snap traps, 100 traps usually being systematically set out on a plot on a single night (100 trap nights per plot). Trapping was done on a total of 961 trap nights in the vole damage areas in 1978. Trapping was not done in 1979 on the comparison plots because the vole density peak had already collapsed and the vole population was very low. The species, sex and maturity were determined. Identification of the species was checked from their teeth. 23. Results 231. Vole catches A total of 112 voles were caught in trappings performed on the damaged areas. 83 % of them were root voles and 17 % field voles (Table 1). All the field voles were caught in the southernmost part of the root vole range. The trapped root voles weighed 12—82 g (x = 31.6 g) and the field voles 12—58 g (x = 30.6 g). Of the 88 root voles examined, 42 were females and 46 males. Table 1. Number of voles caught with snap traps in July 1978 on afforested fields in different localities. Taulukko 1. Heinäkuussa 1978 pellonmetsitysaloilla suo ritettujen myyränpyyntien tulokset kunnittain. * In Kittilä 1 ex. M. oeconomus was caught during trapping of two hours with two traps. Kittilässä pyydettiin kahdella loukulla kaksi tuntia ja saatiin yksi lapin myyrä. .ocality (unta Trap nights Loukku-vrk Voles/100 trap nights Myyriä/100 loukku-vrk M. oeconomus M. agrestis iimo kuivaniemi lanua rervola Colari ialla Kittilä8' ;/100 trap nights il 100 loukku-vrk ;d fotal — Yhteensä 301 60 100 100 100 100 761 7 11.7 7 12 29 16 13.8 8.2 93 6.3 1.0 2.6 19 15 Commun. Inst. For. Fenn. 144 Half of the females were mature and half immature, but of the males only 28 % were mature and 72 % immature. Of the field voles 47 % were mature, and the female: male ratio was 10:9. The vole peak collapsed before the following summer and only trial trappings with no catches were carried out in the undamaged areas. 232. Description of the damage Voles had attacked 55 % of all the Scots pine seedlings growing on the damage plots. The damage on these seedlings (1 —5 years of age) was most frequently located in the lower parts of the stem (Table 2). Often the voles had gnawed the upper parts of the stem and top, too. In addition, they had dug holes in the peat around the tree and eaten the roots. The smallest seedlings were com pletely destroyed, only the hard pith being left (Fig. 5). Besides Scots pine, also lodgepole pine and Siberian larch, both of which are species exotic to Finland, had been attacked despite their small plantation area. Birch had been planted on a few fields only, but 94 % of the birches had been damaged by voles. Norway spruce (Picea abies (L.) Karsten) had not been planted at all on the study plots. Com pared to pine, spruce is known to be dam Table 2. Location of root vole damage in seedlings planted during 1972—77 and damaged in 1977 —78. Taulukko 2. Lapinmyyrän jyrsintäjälkien sijainti vuosi na 1972-77 istutetuissa ja talvella 1977-78 jyrsityissä taimissa. Fig. 5. The root vole often gnaws the whole pine seed ling apart from the hard pith. Kuva 5. Lapinmyyrä jyrsii pienet männyn taimet tikku kasaksi, vain kova ydinpuu jää pystyyn törröttä mään. aged by voles quite seldom (Barring 1963, Teivainen 1979). However, spruce seedlings were found to have suffered from root vole damage in Kolari on the largest of the for ested fields in Lapland (Fig. 6). The mean height of the seedlings on the affected afforested fields was 45.3 cm (SD = 3.22). Three quarters of the damaged seedlings were less than 50 cm in height. However, trees 170 cm tall had also been attacked. 65 % of the plantations estab lished I—3 years before the vole peak were damaged, but only 33 % of those planted 4—6 years before. 233. Comparison of damaged and undamaged plantations 2331. Plantation characteristics Root vole damage occurred on 37 % of all the fields afforested by Veitsiluoto Co. during 1972—1977. This was equivalent to Location of the damage Vioituksen sijainti Number of seedlings Proportion of damaged damaged seedlings, % Jyrsittyjen taimien Jyrsittyjen osuus, % lukumäärä Top Latva 22680 7.6 Top + butt Latva + rungon alaosa 36610 12.2 Butt Rungon alaosa 148130 49.6 Butt + root Rungon alaosa + juuri 41640 13.9 Root T : 9260 3.1 Juuri Whole seedling Koko taimi 40600 13.6 Total Yhteensä 298920 100 16 K.-M. Korhonen Fig. 6. Norway spruce (Picea abies) can also be attacked by root voles. Spruce seedlings with roots debarked by root voles were common in an afforested field in Kolari. Kuva 6. Lapinmyyrä jyrsii toisinaan myös kuusen taimia. Pellolle istutetun kuusen juuret on kuorittu paljaaksi (Teu ravuoma, Kolari). Fig. 7. Occurrence of the vole damage on afforested fields in accordance to the size of the plantation. Kuva 7. Myyrätuhojen esiintyminen pinta-alaltaan erikokoisissa, pelloille istutetuis sa taimikoissa. 17 Commun. Inst. For. Fenn. 144 473011 S 3 Table 3. Fields afforested by Veitsiluoto Co. during 1972—77 in different localities, and the proportion of root vole damage in these areas in 1978. Taulukko 3. Veitsiluoto Oy:n vuosina 1972-77 metsittämät pellot kunnittain ja myyrätuhojen esiintyminen niillä v. 1978. Fig. 8. Occurrence of vole damage on afforested fields according to the age of the plantation. Kuva 8. Myyrätuhojen esiintyminen eri-ikäisissä, pelloille istutetuissa taimikoissa. 53.6 % of the total afforested field area (Table 3). Damaged plantations were larger than undamaged ones, the difference being highly significant (t = 3.70, df = 49.9, P< 0.001) (Fig. 7). The same result was obtained also when using the Kruskal — Wallis test (H = 13.55, P < 0.001). Both the frequency and the severity of damage were higher in larger fields. The age of the plantations proved to be a factor depicting the damage susceptibility. The average age of the trees was 8.5 months younger in the damaged plantations than in the undamaged ones. The average time which had elapsed since planting in the damaged areas differed significantly from that of undamaged ones (t = 2.05, df = 83.7, P < 0.05 and H = 4.10, P < 0.05) (Fig. 8). Some supplementary planting had been done in both areas. Since all of the afforested fields had been planted, it was not possible to study the significance of different regen eration methods. A greater amount of the Locality Afforested fields Vole damaged areas Proportion of Kunta Metsitysalat Tuhoalat damaged areas No. ha No. ha Tuhoalojen osuus % Kpl ha Kpl ha Lapland region Lapin lääni Salla 7 77.1 6 74.0 96.0 Ranua 5 36.9 3 27.4 74.3 Simo 10 59.3 5 27.1 45.7 Rovaniemi 10 39.2 5 25.8 65.8 Sodankylä 5 31.8 3 20.5 64.5 Kittilä 4 29.8 2 18.7 62.8 Tervola 11 56.1 1 10.0 17.8 Tornio 1 6.5 1 6.5 100.0 Ylitornio 4 22.5 0 Pelkosenniemi 2 8.0 0 Savukoski 1 4.3 0 — Pello 1 3.5 0 — Kemijärvi 1 3.1 0 — — Total — Yht. 62 378.1 26 210.0 55.5 Oulu region Oulun lääni Pudasjärvi 10 56.9 6 42.8 75.2 Kuivaniemi 3 15.6 1 10.0 64.1 Kuusamo 11 39.2 1 0.5 1.3 Taivalkoski 1 1.5 0 — — Total — Yht. 25 113.2 8 53.3 47.1 Grand total 87 491.3 Kaikki yhteensä 34 263.3 53.6 18 K.-M. Korhonen seedlings in undamaged areas had been planted in pots (as opposed to bare-rooted seedlings) than in damaged areas (H = 4.68, P < 0.05). No difference was found between the origin of seedlings in the damaged and undamaged plantations, equal numbers of local and transferred provenances growing in both groups (H = 0.13, P > 0.05). 2332. Silvicultural methods The growth of grasses was heavy on nearly all of the afforested fields. However, herbicide treatment carried out less than three years before the damage appeared was more common in undamaged than in damaged plantations (H = 2.70, P < 0.1). Furthermore, the chemical control of willow bushes had been done more often in undamaged than in damaged plantations (H = 3.06, P <0.1). Soil preparation did not differ significantly in the damaged and undamaged plantations (H = 2.29, P > 0.1). Ploughing with a field plough was a common method that had been used in the undamaged areas but not in damaged ones. Ploughing with a forest plough was the prevailing method in both cases, although even more common in damaged areas. Plantations established on peatlands had been fertilized at the time of afforestation. These early fertilization treatments had no effect on the damage susceptibility of the plantations (H = 0.24, P > 0.1). 2333. Vegetation A rich coverage of grasses was typical of the young plantations on afforested arable land. In damaged plantations, where the voles had eaten the grass during winter, the proportion of withered grass ranged from a few per cent up to 90 %. Some bare ground still occurred in plots that had recently been Fig. 9. DECORANA ordination analysis of the field vegetation in forested fields. Vole damage plots are numbered from 1 to 23, and undamaged plots from 24 to 46. Kuva 9. Pellonmetsitysalojen pintakasvillisuuden DECORANA-ordinaatioanalyysi. Myyrätuho alat on numeroitu 1-23 ja vahingoittumattomat alat 24-46. 19 Commun. Inst. For. Fenn. 144 ploughed. The bottom of the furrow was in many cases under water. Elsewhere the field vegetation cover was complete, but the bottom layer was incomplete or missing. The field layer consisted mainly of grasses, with a few herbs and occasional dwarf shrubs. The most common plant species on the damaged and undamaged areas were Deschampsia cespitosa, Epilobium angustifo lium L. and Agrostis capillaris L. (Appendix 2). The frequency of mosses in the vole damage areas was 40 %, and in the undamaged areas 80 %. Only a few plant species occurred more often on the damaged plots than on the undamaged ones, such as Poa pratensis coll. and Viola epipsila Ledeb., Calamagrostis arundinacea (L.) Roth, C. lapponica (Wahlenb.) Hartman, Agrostis stolonifera L., Poa trivialis L. and Carex aquatilis occurred only in the damaged areas. Fig. 10. Classification dendrogram of the vegetation in afforested field areas obtained using TWINSPAN analysis. The plots with vole damage are marked with a T next to the plot number. Kuva 10. TWINSPAN -luokitteluanalyysin avulla muo dostettu pellonmetsitysalojen pintakasvillisuuden luo kitteludendrogrammi. Myyrätuhoalat on merkitty T-kirjaimella alanumerojen edessä. Species more common in the undamaged areas included Carex canescens L., C. magellanica Lam., C. nigra (L.) Reichard, Calamagrostis purpurea Trin., Elymus repens (L.) Gould, Luzula spp., Galeopsis bifida Boenn. and G. speciosa Miller. These species were typical of drier fields. All the species of dwarf shrubs were found more often on the undamaged than the damaged plots. Surpris ingly, the cotton grasses, Eriophorum spp. and Trichophorum cespitosum, on which root voles feed in nature, occurred somewhat more frequently in the undamaged planta tions than in the damaged ones. This is most likely due to the fact that the root voles had eaten all the cotton grasses in the damaged areas. At least half of the plant species were typical of wet and moist habitats on 43 % of the undamaged and 57 % of the damaged plots. The study plots and plant species were organized, using DECORANA ordination analysis, on two axes based on the species frequencies. No clear difference was found in the main gradients between the vegetation in the damaged and undamaged plantations (Fig- 9). TWINSPAN clustering analysis was used for the phytosociological classification of the sample plots (Fig. 10). Abundance of grasses and Epilobium angustifolium was common to all groups. Three clusters were formed on the basis of the frequency values of the plant species: I. Herb-rich plots, which were characterized by an abundance of herbs and Equisetum palustre L. Typical plants on these plots were Rubus arcticus L., Viola epipsila, Galeopsis bifida and Filipendula uimaria (L.) Maxim. The group consists of eight damaged plots and eight un damaged ones. 11. Sedge-rich plots, in which Carex magella nica, C. canescens and Eriophorum angustifolium were common. Of the plots in this group twelve were damaged and nine undamaged. This vegeta tion type is characteristic of plantations suscep tible to root vole damage. 111. Forest vegetation plots which were characterized by forest plant species. Vaccinium myrtillus, V. vitis-idaea L., Deschampsia flexuosa (L.) Trin., Melampyrum sylvaticum L. and Leontodon autumnalis L. were common. The group consisted of three damaged plots and six undamaged ones. This vegetation type could indicate those plantations which are least suscep tible to vole damage. 20 K.-M. Korhonen Table 4. Diversity analysis of the field layer vegetation on the afforested fields. Plot numbers 1 —23 damaged by voles, numbers 24 —46 undamaged. See indices on page 14. Taulukko 4. Pellonmetsitysalojen pintakasvillisuuden diversiteettianalyysi. Näytealanumerot 1-23 myyrätuhoaloja, 24-46 vahingoittumattomia aloja. Indeksien selostus sivulla 14. The classification of afforested plots was also made by means of CLUSTER analysis, but no clear groups were formed. Compari son of the diversity indices of the damaged and undamaged study plots gave no signifi cant differences explaining the damage (Table 4). 2334. Soil According to Veitsiluoto management files the root vole damage in afforested fields occurred as often on peat as on mineral soil. On the basis of the soil analysis, almost 3/4 of the area of damaged plots was peat soil Sample Näyteala Species number Lajiluku Simpson index D Shannon index H' Kempcon index Q Pielou index J_ 1 2 3 4 5 20 9 18 19 21 0.920 0.810 0.907 0.922 0.917 1.195 0.811 1.133 1.182 1.182 20.959 10.052 14.949 25.129 16.610 0.919 0.850 0.903 0.924 0.894 6 7 8 9 10 31 24 16 20 18 0.950 0.920 0.888 0.921 0.902 1.377 1.210 1.052 1.179 1.105 22.891 25.151 16.767 14.307 10.650 0.923 0.877 0.873 0.906 0.880 11 12 13 14 15 20 13 17 14 15 0.907 0.887 0.896 0.891 0.892 1.138 1.007 1.066 1.032 1.039 16.610 12.575 9.466 10.716 9.466 0.875 0.904 0.867 0.900 0.883 16 17 18 19 20 28 27 33 22 19 0.945 0.936 0.947 0.927 0.913 1.334 1.318 1.389 1.224 1.153 20.029 46.507 33.534 18.271 14.307 0.922 0.921 0.914 0.912 0.901 21 22 23 24 25 32 27 20 42 24 0.950 0.944 0.924 0.962 0.931 1.383 1.330 1.197 1.509 1.263 22.891 23.253 16.610 34.880 25.151 0.919 0.929 0.920 0.929 0.915 26 27 28 29 30 14 16 24 29 26 0.890 0.896 0.934 0.944 0.941 1.038 1.066 1.262 1.338 1.305 17.591 11.445 30.155 20.029 27.247 0.906 0.886 0.914 0.915 0.922 31 32 33 34 35 24 17 25 21 33 0.925 0.912 0.933 0.925 0.945 1.223 1.129 1.265 1.204 1.370 17.168 13.288 17.168 25.129 26.575 0.886 0.918 0.905 0.911 0.902 36 37 38 39 40 20 25 24 29 19 0.903 0.931 0.940 0.949 0.913 1.144 1.255 1.278 1.364 1.153 20.959 17.168 22.056 20.029 16.610 0.879 0.898 0.926 0.933 0.901 41 42 43 44 45 46 23 30 37 17 34 27 0.933 0.948 0.961 0.888 0.953 0.947 1.244 1.363 1.485 1.062 1.415 1.335 15.421 24.914 37.726 16.767 28.236 29.343 0.913 0.923 0.947 0.864 0.924 0.932 21 Commun. Inst. For. Fenn. 144 Table 5. Calsium, potassium and phosphorus contents of the soil in the study plots on af forested fields and the regional averages in cultivated fields. Taulukko 5. Maaperän kalsiumkalium- ja fosforipitoisuudet metsitetyillä pelloilla ja Lapin maatalousseuran sekä Perä-Pohjolan maanviljelysseuran alueiden viljellyillä pelloilla kes kimäärin. and 1/4 mineral soil. The corresponding values for the undamaged plots were 1/2 and 1/2. According to soil fertility tests carried out in 1955—1970, half of the fields in the region where damage occurred were mineral soil, and half peat soil (Lapin... 1975). The most common soil type was Sphagnum sedge peat (SCt), which occurred on half of the area of damaged plots and 40 % of the undamaged ones, but only on 10 % of all the fields in the region. The soil in both the damaged and undamaged plantations was more acid than the regional averages would indicate. The pH in the damaged areas was 5.0 and in undamaged ones 4.7 (t = 2.88, df = 45, P < 0.01), while in Kittilä, Simo and Tervo la the regional average was 5.41—5.55, in Tornio, Rovaniemi and Ranua 5.26—5.40 and in Salla 5.2 (Lapin... 1975). The nutrient contents of the soil in the study plots were below the regional averages, only calcium in the damaged areas being slightly higher. The calcium content was higher in the damaged plots than in the undamaged ones (t = 2.28, df = 43.8, P < 0.05). This was also the case with the potassium content (t = 4.59, df = 30.3, P < 0.001) and phosphorus content (t = 4.72, df = 24.6, P < 0.001) (Table 5). 24. Discussion Land use in northern Finland has gone through prominent changes during the last decades. Rapid changes have been typical of the development in agriculture: clearing of forest after World War II and the aban doning of fields in the 1970'5. Afforested fields are a new biotope which appeared to be very suitable for root voles and thus the damage to seedlings in afforested fields has been severe. The probability of a certain stand suf fering from root vole damage is not very high in general, but in the case of afforested fields and other stands with a luxurious field vegetation the damage risk is high. This study revealed that of all the fields afforested by Veitsiluoto Co. during 1972—1977, 54 % suffered from root vole damage. The damage risk seems to increase with increasing size of the forested plot. One explanation for this could be that, in large abandoned fields, the root voles can change their home ranges inside the preferable habitat, and thus the density of the vole population may increase to exceptionally high level. In addition to artificial for estation of former fields, natural regeneration Afforested fields Metsitetyt pellot AH fields Kaikki pellot Damaged areas Tuho alat mg/l Not damaged areas Vertailualat mg/l Northern Lapland region Lapin maatalous- seuran alue mg/l Southern Lapland region Perä-Pohjolan maan- vilj. seuran alue mg/l Calsium (Ca) Kalsium (exchangeable vaihtuva) 965 556 755 994 Potassium (K) Kalium (exchangeable vaihtuva) 47 25 92 88 Phosphorus (P) Fosfori (easily-soluble helppoliukoinen) 5.6 1.6 9.3 9.0 22 K.-M. Korhonen has also taken place widely. Natural affor estation of fields leads to the formation of deciduous stands rich in grasses and herbs Härvinen et ai. 1977), which are very vourable for voles. Luxurious vegetation is the main factor which makes the abandoned fields optimal habitats for voles. This was also indicated by the results of the soil analysis: damaged fields had higher nutrient contents than undamaged ones. In the afforested field areas, the damage occurred most often in fields that had been ploughed with forest machines. This is the prevailing method in the afforestation of fields (Paavilainen 1970, 1977). During this study the root voles were found to have used the hollow layer inside the ploughing shoulder as their nesting sites. The furrows served as runways for voles. The micro climate in the furrows also favours voles: temperature changes are smaller and the snow drifts build up faster. Svecova (1984) found that in furrowed areas in western Siberia 92 % of the damaged pine seedlings were growing in furrows. In addition to afforested fields, ploughing is the predomi nant method used in soil preparation on forest land in northern Finland (Pohtila 1979). Forest ploughing is mostly done on mineral soil sites, which means that the vole damage risk is mainly apparent in moist areas with a rich field vegetation. Of the other soil preparation methods, prescribed burning is the least favourable to voles but its effects are not long lasting (Larsson 1975, 1976). Similar temporary falls in vole numbers can be achieved by herbicide treatment (Sviridenko 1953, Lars son 1975, Svecova 1984, Teivainen et ai. 1986). This was also the case in some of the afforested field areas in this study. On the other hand, Larsson and Hansson (1976) found that treatment with grass herbicides seemed to increase bark consumption of the voles present in the treated areas. Commun. Inst. For. Fenn. 144 23 3. ROOT VOLE DAMAGE IN PEATLAND FORESTS 31. Introduction The economic utilization of forests began at the same time as the development of farming in Lapland. Due to the remoteness and the harsh climate of Lapland, forests in earlier times were utilized on a very small scale. The first water-powered sawmills were established at the end of the 18th century. Up until the 1870's northern water sawmills consumed altogether only 50 000 logs/year (Ahvenainen 1982). New steam saws were more effective and, with the development of river floating, larger areas were used for industrial forestry. Still in the 1930's two thirds of the number of trees felled in SW Lapland were sawtimber; this means that selective cutting was the prevailing method. The forests were in a poor condition after these cuttings. After World War II the forest industry grew rapidly in Lapland (Ahvenainen 1982, Raumolin 1982, Massa 1983) and the methods used in forestry went through a complete change during 1955—1970. In the 1950's the so-called "zero border" (the maximum distance of economic wood trans port) set limits on the expansion of clearcutting in Lapland. Already at the end of the decade, however, the amount of wood removed from northern forests was 45 % larger than the planned target (Kuusela 1979). Since then, clearcutting has been carried out in Lapland on a vast scale and, unlike in southern Finland, the total drain from forests has exceeded the recommenda tions of balanced forestry almost every year in Lapland. Industrial wood consumption in Lapland has increased 4-fold since the beginning of the 1950's (Hokajärvi 1982). The rapid increase in clearcutting and plantations has provided more and more favourable habitats for voles. Since the start of industrial forest usage was late in Lapland, the proportion of forest stands older than 100 years was 65 % in northern Finland still in the 1920'5. The rapid development of silvicultural and forest improvement methods, coupled with the growing forest industry, has caused a change in the age structure. The proportion of young stands has increased strongly, and in 1977—1980 the proportion of treeless areas was 4 %, under 20-year-old stands 11 %, 21 to 40-year-old stands 12 %, 41 to 60-year old stands 16 %, 61 to 80-year-old stands 13 %, 81 to 100-year-old stands 8 % and over 100-year-old stands 37 % of the forest land (Metsätilastollinen... 1986). Among the changes which have favoured voles, the most prominent has been the increase in commercial fellings, which in the area of root vole damage (in NE Finland and Lapland Forestry Board Districts) occurred on 78 357 hectares in 1977 and on 88 626 hectares in 1984 (Metsätilastollinen... 1979, 1986). This has led to the situation where, in the most acute root vole damage area, small seedling stands cover 3409 km 2, 30 km 2 of which are afforested fields (Kuusela et ai. 1986, Mattila 1986). The advanced seedling stands and young thinning stands cover 44 °Io of the forest land, totalling 20 059 km 2 (Table 6) (Mattila 1986). The greatest increase in the forest area in northern Finland has taken place through draining of peatlands, which started in the 1950's and reached a maximum in the late 1960's (Heikurainen 1980). By the end of 1984 the total forest drainage area was 8682 km 2 in the districts of the NE Finland Forestry Board and the southern part of the Lapland Forestry Board (Kuusela et ai. 1986), i.e. the main area where root vole damage occurred. The increase in the area drained has been rapid throughout the whole of Lapland: from 2432 km 2 in 1967 to 8902 km 2 in 1985 (Fig. 11) (Metsätilastolli nen... 1968—1986). The proposed future drainage area given by Kuusela et ai. (1986) for NE Finland and southern Lapland is 5837 km 2 of primary drainage of swamps and paludified mineral soil sites, and 1340 km 2 of supplementary drainage and cleaning of ditches. Fertiliz ation of peatlands is closely associated with drainage. Fertilization, which started in the 1960'5, was done during 1974—1984 on a 24 K.-M. Korhonen Table 6. Proportion of the different development classes of the forest land area in Lapland (Mattila 1986). Taulukko 6. Nuorten kehitysluokkien osuudet metsämaan alasta Lapin läänissä Mattilan (1986) mukaan. total of 94 000 ha of peatlands in the area susceptible to root vole damage. The maximum area of forest stands susceptible to root vole damage could include nearly all pine-dominant, small seedling stands (3000 km 2) and pine-domi nant, advanced seedling and young thinning stands on peatlands (more than 6000 km 2) in southern and central Lapland. The aim of this part of the study is to determine the effect of drainage, fertilization and other forest improvement and silvicul tural methods on the root vole damage in young thinning stands of Scots pine. Habitat changes are studied in relation to root vole damage. The vole damage dealt with in this study originated from winter 1977—1978, the time when there was an exceptionally high vole peak in Lapland. In 1981—1982 the vole densities had again become rather high, and some of the damage originated from that winter. Fig. 11. Increase in the total area drained for forestry purposes in Lapland during 1966 —1985 (Metsätilas tollinen... 1968—1986). Kuva 11. Soiden kokonaisojitusalan kasvu Lapin ja Koillis-Suomen metsälautakuntien alueilla vuosina 1966-85 (Metsätilastollinen... 1968-1986). Western Lapland Lapin metsälauta- kunnan eteläosa Eastern Lapland Koillis-Suomen metsälautakunta Total Koko alue ..ittil Koi lari Rovaniemi mlk Forest land area, ha 28490 Metsämaan ala, ha 17267 45756 4724 7037 1795 5422 Proportion of peatlands % 20 on forest land ha 5712 16 2761 19 8474 10 472 10 704 20 359 23 1247 Soita metsämaasta Area of development classes on forest land Eri kehitysluokkia metsämaan alasta 1 — Open % 5 Aukea 7 6 5 7 8 6 2 — Small seedling stand % 7 Pieni taimikko 9 7 5 6 12 8 1+2 % 12 ha 3430 16 2784 14 6214 9 440 12 867 20 359 14 737 3 — Advanced seedling stand % 19 Varttunut taimikko 20 20 15 12 19 22 4— Young thinning stand % 28 Nuori kasvatusmetsikkö 18 24 27 25 36 28 3 + 4 % 47 ha 13490 38 6567 44 20059 41 1948 38 2643 55 981 51 2748 25 Commun. Inst. For. Fenn. 144 4 473011 S Fig. 12. Research areas in peatland forests. 1 = Satta suo, 2 = Alajärvensuo, 3 = Imari, 4 = Suoloma aapa, 5 = Verkkolahdenjänkä, 6 = Teuravuoma, 7 = Pohjasenvaara, 8 = Muotkavuoma, 9 = Juola maa, 10 = Silva. Kuva 12. Tutkimusalueet turvemaiden metsissä. 1 = Sat tasuo, 2 = Alajärvensuo, 3 Imari , 4 = Suoloma aapa, 5 = Verkkolahdenjänkä, 6 = Teuravuoma, 7 = Pohjasenvaara, 8 = Muotkavuoma, 9 = Juola maa, 10 = Silva. Fig. 13. The line inventory areas in drained Teuravuo ma bog (lines 74—77) and undrained Pohjasenvaara bog (lines I—4).1 —4). Vole trapping plots are marked with an X. Kuva 13. Linja-arviointialueet ojitetulla Teuravuoman suolla (linjat 74-77) ja ojittamattomalla Pohjasen vaaran suolla (linjat 1-4). Myyränpyyntialueet on merkitty X:llä. 32. Study areas Root vole damage in advanced seedling and young thinning stands was studied in several study areas in southern and central Lapland. The effect of draining on vole damage, as well as on the distribution and severity of the damage, was studied in Kolari, Teuravuoma (67° 20' N, 23° 60' E) with the line inventory method (Fig. 12). The inventory was carried out in a drained peatland area and in a neighbouring natural, undrained peatland area, Pohjasenvaara (67° 17' N, 23° 55' E). Four parallel study lines, each 2000 m long, were surveyed in the drained area (Fig. 13). The distance between the lines was 1 km, and between plots on the same line 100 m. The study plots consisted of the five trees lying closest (less than 20 m) to the centre of the plot. A total of 361 trees in an area of 6 km 2 were examined on the 20 plots along each of the four lines. Four 1000 m-long lines were surveyed in the natural comparison area (Pohjasenvaara), the distance between the lines being 500 m (Fig. 13). The study plots were located 100 m apart, and were similar to those at Teura vuoma. A total of 150 trees were examined over an area of 1.5 km 2 in Pohjasenvaara. There was a wide range of mire site types in the area: pine bogs, small spruce swamps, almost treeless fens etc. The state of the undrained comparison area, which is pro tected by the Finnish Forest Research Insti tute as a forest reserve, was analogous to the original state of the drained peatland. It is difficult to find natural peatlands comparable to drained peatlands in northern 26 K.-M. Korhonen Finland. The Teuravuoma peatland area extends into Sweden. In Sweden there are plenty of suitable comparison areas because forest draining has not been performed this far north at all. Thus one 1000 m-long line, with plots every 50 m was surveyed in Pajala, Juolamaa bog (67° 19' N, 23° 12' E) and one 400 m-long line in Pajala, Muotka vuoma bog (67° 22' N, 23° 10' E) (Fig. 12). A total of 132 trees were examined in Pajala. The studies concerning the effect of fertilization, field vegetation and other factors on vole damage were carried out in five fertilization research areas of the De partment of Peatland Forestry, the Finnish Forest Research Institute (Appendix 3). The areas, typical of vole damage biotopes, were situated in central Lapland, earlier known as the most severely affected damage region (Korhonen et ai. 1983). Three of the study areas were located near Rovaniemi: Alajär vensuo (66° 26' N, 26° 42' E), Sattasuo (66° 27' N, 26° 44' E) and Imari (66° 29' N, 25° 31' E) (Fig. 12). One of the study areas was in Sodankylä, Suoloma-aapa (67° 21' N, 26° 32' E) and one in Kittilä, Verkkolahden jänkä (68° 00' N, 24° 19' E) (Fig. 12). In 1978, the tree stand in Alajärvensuo consisted of 42-year-old Scots pine. The stand was dense, about 1900 trees/ha, because it had not been thinned. The most common mire site type was tall-sedge pine fen (VSR) which covered 10 study plots. Four of the plots were of the herb-rich sedge birch-pine fen type (RhSR). All plots were in the 'transforming' stage. In Alajärvensuo fourteen study plots, 0.04 ha in size, were chosen along a line using systematic sampling in 1981 and 4 plots in 1982 (Fig. 14). A total of 1124 trees were examined in Alajärvensuo in 1981 and 364 trees in 1982. The tree stand in Sattasuo was not as dense as that in Alajärvensuo, about 1500 trees/ha. 40-year-old Scots pines with a few older spruces covered most of the area. Some damage by Tomicus bark beetles had occurred in the area after thinnings (Etholen and Saarnio 1977). Six study plots, 24 m x 40 m in size, were chosen systematically (Fig. 15), and a total of 859 trees were examined in 1981. The whole area was a herb-rich sedge birch-pine fen (RhSR) in the 'transforming' stage. In addition, one study plot was chosen for comparison purposes from the nearby Silva natural mire area, and a total of 138 trees were examined there. Fig. 14. The fertilization study area in Alajärvensuo and the vole damage study plots. The plots examined in 1981 are numbered as in the original fertilization experiment. The plots examined in 1982 are marked with an asterisk (￿). Fertilization data is given in A.pp. 3. Kuva 14. Alajärvensuon lannoituskoealue ja myyrätuho tutkimuksen näytealat. Vuonna 1981 tutkitut alat on numeroitu kuten alkuperäisessä lannoituskokeessa. Vuonna 1982 tutkitut alat on merkitty tähdellä (￿)). Lannoitustiedot liitteessä 3. Fig. 15. The fertilization study area in Sattasuo and the sample plots of the vole damage study carried out in 1981. Fertilization data is given in App. 3. Kuva 15. Sattasuon lannoituskoealue ja myyrätuhotut kimuksen näytealat vuonna 1981. Lannoitustiedot liitteessä 3. In Rovaniemi, Imari, the dominating stand was 20-year-old Scots pine with an admixture of birch undergrowth and some larger spruces and birches. The stand was thinned in 1973 to a density of 1600 pines/ha. The six study plots, 0.04 ha in size, were chosen beforehand from a map in order to ensure that each fertilized sector had two plots (Fig. 16). A total of 394 trees were examined in Imari. The mire site types in Imari were rather mixed: two of the study Commun. Inst. For. Fenn. 144 27 Fig. 16. The fertilization study area in Imari and the vole damage sample plots in 1981. Fertilization with PK was given in sectors 0 kg/ha, 500 kg/ha and 1000 kg/ha (numbers 0, 500, 1000 in the picture) (see also App. 3). Kuva 16. Imarin lannoituskoealue ja myyrätuhonäyte alat v. 1981. PK-lannoitus tehtiin kaistoittain 0 kg/ha, 500 kg/ha ja 1000 kg/ha (kuvassa 0, 500 ja 1000) (katso myös liite 3). Fig. 17. The fertilization study area in Suoloma-aapa and the vole damage study plots. Plots examined in 1981 are marked with the original numbers of the fertilization experiment, and the plots of 1982 with an asterisk (￿). Fertilization data are given in App. 3. Kuva 17. Suoloma-aavan lannoituskoealue ja myyrätu honäytealat. Vuonna 1981 tutkitut alat on merkitty alkuperäisen lannoituskokeen numeroin ja vuoden 1982 alat tähdellä (￿)). Lannoitustiedot liitteessä 3. plots were Carex globularis spruce-pine swamps (PsKR), two C. globularis pine swamps (PsR), one herb-rich sedge birch pine fen (RhSR) and one C. globularis spruce swamp (PsK). All plots were in the 'ditched' stage. Most of the Suoloma-aapa study area in Sodankylä was covered with 38-year-old Scots pine in 1978. The density was only 800 trees/ha since it had recently been thinned. A smaller section in the northern part consisted of different-aged pines and some spruces. The most common mire site type was tall-sedge pine fen (VSR), and in the northern part tall-sedge pine fen with Sphagnum-hummocks (VSR ram). In addi tion, plots 2, 6 and 12 were C. globularis pine swamps with hummocks (PsR ram), plot 13 a cottongrass pine bog (TR ram) and plots 7 and 8 Sphagnum fuscum pine bogs (RaR) (see Paavilainen 1978). Sixteen study plots, 20 m x 20 m in size, were chosen systematically. Thus three of each fertiliz ation combination and one plot fertilized with nitrogen alone were chosen in 1981, and four of these plots again in 1982 (Fig. 17). A total of 522 trees were examined in Suoloma-aapa in 1981 and 143 in 1982. In Kittilä, Verkkolahdenjänkä, the vole damage had occurred in 1981—1982. At that time the pure Scots pine stand was 3 m tall on the average, and 15 years old. The stand density was about 1100 trees/ha, but the density in the northeastern part especially was much lower. The proportions of different mire site types on all the study plots were as follows: herb-rich sedge birch pine fen (RhSR) 4.8 %, tall-sedge pine fen (VSR) 47.6 %, S. fuscum pine bog (RaR) 23.8 %, eutrophic flark fen (RiL) 19.0 % and herb-rich sedge fen (RhSN) 4.8 %. The peat thickness varied between 80—100 cm and all the plots were in the 'ditched' stage. In 1982 twelve vole damage study plots, 0.04 ha in size, were chosen systematically along three lines in order to give two plots for each fertilization combination (Fig. 18). Plot number 100 had no trees and thus number 93 was chosen instead. However, no damage was found on 93. A total of 437 trees were examined in Verkkolahdenjänkä. 28 K.-M. Korhonen Fig. 18. The fertilization study area in Verkkolahden jänkä and the root vole damage study plots (num bered). Fertilization data are given in App. 3. Kuva 18. Verkkolahdenjängän lannoituskoealue ja myy rätuhotutkimuksen näytealat (numeroitu). Lannoi tustiedot liitteessä 3. 33. Material and methods The studies were carried out in 1981 in Alajärvensuo, Sattasuo, Imari and Suoloma aapa. Some of the plots in these areas were re-examined in 1982. The studies in Verkko lahdenjänkä were performed in 1982, and re examined in 1983 and 1986. The line inventories were done during 1983—1985 in the Teuravuoma, Pohjasenvaara and Pajala areas. Vole trappings were performed in 1977—78 and on a small-scale in 1981. A total of 3697 trees were examined on drained areas and 420 trees on undrained ones. The height and diameter at breast height of each tree growing on the study plots were measured. All of the trees were examined by exposing the butt, root neck and a part of the root system in order to detect any gnawing signs of root voles. Damage signs on the butt of the mire pines of development class 3 and 4 are clearly visible for many years. Recent root damage is also easy to recognize after some digging, but earlier damage to the roots is not so easy to detect. In contrast to the situation above the peat surface, the resin does not dry out and turn white. It is easy to see that these trees are suffering, but the damaging agent may be difficult to detect. The trees on the study plots were classified into two groups: 1) trees gnawed by voles and 2) ungnawed trees. The gnawed trees were further divided into two sub groups: la) trees killed by voles and lb) trees damaged by voles. Trees under 1 m tall were excluded from the study. The propor tion (%) of gnawed trees out of all the trees on a plot is referred to further on in the text using the expression "damage degree". In this study the mire site types of the drained plots were determined according to their original site type because the plots were in the 'ditched' or 'transforming' stages, but not yet 'transformed'. This is typical in Lapland where the development of drained swamps toward mineral soil forest types is slow: of all the drained peatlands 39.7 % are in the ditched stage, 54.6 % transforming and only 5.7 % transformed (Kuusela et ai. 1986). The vegetation and soil analyses were done with the same methods as for the afforested fields, although only five 1 m x 1 m squares were used on each 20 m x 20 m plot. In addition to the species frequency, the coverage percentage was also determined. Analyses were performed on all fertilization study plots in 1981, and in 1985 on four plots in the drained Teuravuoma line inven tory area and on eight plots in the natural Pohjasenvaara. Two vegetation analysis plots were also chosen from natural peatlands in Pajala, Sweden (Fig. 12). The mire and forest site types were determined on the basis of the field-layer vegetation (Kujala 1979, Heikurainen 1986). In cases where the mire type had been determined earlier by the 29 Commun. Inst. For. Fenn. 144 Dept. of Peatland Forestry, their results were used as an aid in the determinations. English terminology is according to Laine et ai. (1986). Recovery of the trees after vole attack was studied in Verkkolahdenjänkä. 23 pines suffering from vole damage were marked in 1982. These trees had all been attacked by voles during the previous winter, but at the time of marking they appeared healthy. The height, diameter at breast height and the proportion of the butt circumference gnawed were measured. The recovery capacity was estimated in 1983, and the trees examined and measured again in 1986. The trees on the line inventory plots were examined in order to detect any signs of vole attack. The severity of the damage to a tree was estimated as the proportion of the circumference gnawed at the butt or root neck of the tree. Vole trapping was done with snap traps using the same methods as in afforested fields. Voles were trapped during a total of 1590 trap nights from September 1977 to September 1978. Trappings were performed by Mr. Asko Kaikusalo in Kolari, Sodanky lä, Muonio and Rovaniemi (Fig. 12). The data were analyzed on a VAX 11/785 computer using conventional statistical ana lyses and special vegetation analysis pro grams (Jukola-Sulonen 1983, Mikkola and Jukola-Sulonen 1984). 34. Results 341. Vole catches A total of 493 voles were caught during 1590 trap nights. 48.5 % of them were root voles, 2.0 % field voles, 40.6 % bank voles, 0.4 % grey-sided voles and 8.5 % lemmings (Lemmus lemmas L.). The root vole was the most numerous species in all regions (Table 7). In drained pine bogs it was the dominant species, although bank voles were also caught there. In natural peatlands, a few field voles and lemmings were caught in addition to root voles and bank voles. The bank vole was the dominant species in spruce forests on mineral soil, although root voles and a few lemmings and grey-sided voles were also caught there. No water voles were caught in any of the biotopes, no traces of them being found at all. In Kolari trapping was done in the line inventory areas on drained and undrained peatlands. Only root voles were caught in the Teuravuoma drained pine fen in Sep tember, 1977 (Table 7). The root vole population density had increased throughout the summer and autumn of 1977. A great number of voles survived winter 1978, causing damage. The root vole density in Teuravuoma was high also during summer 1978, but bank voles were caught then, too. In Pohjasenvaara undrained pine bog the root vole numbers were lower especially in autumn 1977 (Table 7). 342. Description of the damage Vole damage occurred on half of the Scots pine trees growing in the study areas in drained peatlands, 40 % of the gnawed trees being dead three years after the damage. The damage degree of the study plots in young thinning stands varied from 16 % to 85 %. The voles had gnawed the thick bark at the butt of the pines (Fig. 19), and debarked the upper parts of the roots (Fig. 20). Of the 568 affected pines examined in 1982, 33 % had root damage only, 52 % stem damage only and 15 % both. The results of this re-examination indicated that some of the trees with only root damage had not been noticed in the studies of 2899 trees performed in 1981. The proportion of trees with damage on both the root and stem may have been higher, because the roots of trees with clearly visible stem injury were not examined thoroughly. This assumption was supported by the results of the inventory done on the Teuravuoma drained peatland in 1985. The corresponding values for Teuravuoma (243 damaged pines) were 54 %, 11 % and 35 %, respectively. Trees with roots damaged by voles had become suscep tible to wind damage (Fig. 21). The root vole had attacked, in addition to pines, only two spruces on the plots in young thinning stands and advanced seedling stands. A fallen spruce, with roots badly damaged by voles, was also found outside the study plot area. Although the root vole is known to feed on older deciduous trees (Kaikusalo, Asko, the Finnish Forest Research Institute, 30 K.-M. Korhonen Table 7. Number of voles caught with snap traps during the period July 1977 to September 1978 in older Scots pine stands in Lapland. Taulukko 7. Myyränpyyntien tulokset heinäkuun 1977 ja syyskuun 1978 välisenä aikana mäntyä kasvavilla aloilla Lapissa. unpubl.), no damaged deciduous trees were found in the thinning stands of this study. Three years after the damage the mean height of the trees (n = 2899) growing on the plots in the fertilization study areas was 4.0 m (1.3 —14.0 m), and the mean diameter at breast height 5.6 cm (1 —27 cm). The trees mortally damaged by voles (n = 686) were 3.2 m (1.3 —8.5 m) tall in the average and 4.2 cm (1 —17 cm) in diameter, while those less severely damaged by voles (n = 827) were 4.7 m (1.3 —9.6 m) and 6.8 cm (1 —21 cm), Locality Kunta Month, year Biotope Kk, vuosi Biotooppi Trap nights Loukku-vrk Microtus oeconomus Voles/100 trap nights — Myyriä!100 loukku-vrk Microtus agrestis Clethrionomys Lemmus Clethrionomys glareolus lemmus rufocanus Kolari Teuravuoma 9.77 Abandoned field Pakettipelto 100 32 9.78 Abandoned field Pakettipelto 100 18 9.77 Drained pine bog Ojitettu räme 80 13.8 9.78 Drained pine bog Ojitettu räme 50 24 8 Kolari Pohjasen- vaara 9.77 Dwarf shrub pine bog/ open bog IR/neva 80 5 2.5 9.78 Dwarf shrub pine bog/ open bog IR/neva 100 19 4 5 9.77 Vaccinium myrtillus type spruce forest MT-kuusikko 80 1.3 26.25 9.78 Vaccinium myrtillus type spruce forest MT-kuusikko 100 3 51 Sodankylä 9.77 Pine bog/spruce swamp Räme/korpi 100 11 2 4 7.78 Pine bog/spruce swamp Räme/korpi 100 29 3 9 9.78 Spruce swamp — Korpi 40 12.5 22.5 7.5 9.78 Pine bog — Räme 60 35 6.7 3.3 Muonio 9.78 Clear-cutting/pine bog Avohakkuu/räme 100 39 5 Rovaniemi 7.78 Hylocomium-M yrtillus type I — HMTI 50 20 7.78 Abandoned field Pakettipelto 50 22 9.77 Hylocomium-M yrtillus type 11 — HMT II 100 13 1 23 7 7.78 Hylocomium-Myrtillus type II — HMT II 170 2.9 22.9 12.9 9.78 Hylocomium-Myrtillus type II — HMT II 130 3.8 10.8 6.2 1.5 x/ 100 trap nights x 1100 loukku-vrk 15.8 0.56 12.0 2.1 0.08 SD 12.27 1.20 13.33 3.80 0.35 Total — Yhteensä 1590 239 10 200 42 2 31 Commun. Inst. For. Fenn. 144 Fig. 19. Root vole debarking in older pines is clearly visible when it is located at the butt of the tree. Kuva 19. Suurten mäntyjen tyveliä sijaitseva lapinmyy rän jyrsintäjälki on helppo havaita. respectively. Three years after the damage the difference between the mean height of the gnawed and ungnawed trees was not significant (F = 0.636, df = 1,82, P > 0.05), and the mean diameter was the same in both groups because tree growth is slow on peatlands in Lapland. The trees at Verkkolahdenjänkä were measured during the summer following the outbreak of damage. The average height of all the trees (n = 437) was 2.9 m (1.3—7.5 m), and the mean diameter at breast height 4.4 cm (I—l 3 cm). The corresponding values for killed trees (n = 39) were 2.8 m (1.3—6.1 m) and 3.8 cm (I—9 cm), and for less severely damaged trees (n = 182) 3.1 m (1.3—7.5 m) and 4.9 cm (I—l 3 cm). The correlation between the height of the gnawed trees and the damage degree of the plots (n = 52) was not significant, while that between the mean diameter at breast height and the damage degree was (r = 0.296, P < 0.05). Recovery of the trees after vole attack depended on the proportion of the stem and root circumference gnawed. The trees examined in 1982 were distributed according to the severity of damage as follows: 13 % of the trees with less than half of the circumference eaten were dead, 36 % of those with 50—99 % of the circumference eaten were dead, and 84 % of those gnawed Fig. 20. Root vole debarking is often located on roots and thus not seen above the peat Kuva 20. Lapinmyyrän jyrsintäjälki sijaitsee usein juurissa eikä näy turpeen päälle. 32 K.-M. Korhonen Fig. 21. Typical appearance of a pine stand attacked by the root vole. Absence of older needles and a tendency to lean over are characteristic to trees with root damage. Kuva 21. Lapinmyyrän aiheuttamat tuhot mäntyjen juurissa ilmenevät neulaskertojen vähäisyytenä ja puun kallistu misena tuulen ja lumen vaikutuksesta. Teuravuoman ojitusalueen tuhoja. all around the butt were dead. Pines that had been gnawed all around the stem but which were still alive had all been attacked the previous winter. These trees will also die sooner or later. Of 361 trees examined in the Teuravuoma line inventory, 7 % were totally debarked, 10 % were debarked over 50—99 % of the circumference, and 14 % under half of the circumference. Only root damage was found in more than 1/3 of the trees, and root damage in addition to stem damage in more than 1/4 of the trees. 1/3 of the trees were undamaged. Repeated recovery surveys were done in Verkkolahdenjänkä. 23 of the pines attacked by voles during the previous winter were marked. One year after marking one of the study trees had fallen down, but the others were still alive. Four years after marking 26 % of the trees were dead but still standing, and 13 % had fallen down. The estimations done one year after the marking (and damage) proved to be fairly successful (Table 8), but were slightly optimistic. Four years after the damage had occurred, all those trees which had been gnawed only on the roots or on less than 20 % of the stem circumference were still assessed to be probably or possibly recovering (Table 9). All those trees on which at least 80 % of the stem circumfer ence had been gnawed were dead or likely to die soon. Recovery of the trees on which 20—80 % of the stem circumference had been gnawed depended on other factors such as the total area debarked, root connections and insect attack. The growth of the trees was also negatively correlated (r = 0.417, n = 23, P < 0.05) with the proportion of the stem circumference debarked. 33 Commun. Inst. For. Fenn. 144 Table 8. Recovery of the trees debarked by the root voles in Verkkolahdenjänkä. Taulukko 8. Lapinmyyrän jyrsimien puiden toipuminen Verkkolahdenjängällä. Table 9. Proportion debarked in trees of different con dition classes and the height increment of them during the 4-year-period after the damage. Taulukko 9. Puiden terveydentila suhteessa jyrsityn kuo ren osuuteen ja neljän vuoden pituuskasvuun myyrä tuhon jälkeen. 343. Drainage The root vole damage in advanced seedling and young thinning stands occurred almost entirely on drained peatlands. Despite the extensive surveys, only a few damaged trees were found growing on mineral soil in habitats such as the edges of abandoned fields and inside reindeer fences. Damage was also rare on natural undrained peatlands, occurring only along streams with flooded meadows. In a comparison study of drained and undrained peatlands, a total of 361 pines were examined in a line inventory of the Teuravuoma drained peatland and a total of 150 pines on the undrained Pohjasenvaara. The comparison area of Pohjasenvaara is a part of the same vast peatland as the Teura vuoma drainage area. Mire site types of the two areas were as follows: Drainage had converted some of the pre vious open fens into pine fens in Teuravuo ma. The mean height of the pines was 4.5 m (SD = 1.27) on drained peatlands, and 3.8 m (SD = 1.77) on undrained ones. The mean diameter at breast height was 6.8 cm (SD = 2.41) on drained, and 6.2 cm (SD = 4.20) on undrained peatlands. No damage was found on the trees on undrained peatlands, but on drained peatlands 67 % of the pines examined had been attacked by voles, 14.5 % of them being dead in 1985. The damage degree of the study plots did not correlate with either the height (r = 0.080, P>o.l) or the diameter at breast height (r = 0.010, P>o.l) of the trees. The damage intensity was different on different mire site types (Fig. 22). The lowland of Teuravuoma reaches far to the west. Since no forest draining has been done at Pajala, Sweden, this area appeared to be suitable for comparison. A total of 132 pines were examined, but no vole damage was found. Condition of the trees Juiden terveydentila >ne year after the damage 1 v tuhon jälkeen n % *our years after the damage 4 d tuhon jälkeen n % Dead, fallen Kuolleita, kaatuneita 1 4 3 13 Dead, standing Pystyyn kuolleita 0 6 26 47 % 61 Dying — Kuolevia 6 26 3 13 Most likely dying Todennäköisesti kuolevia 4 17 2 9 Unknown — Ei tietoa 2 9 9 % Most likely recovering Todennäköisesti toipuvia 7 31 5 22 44 % 39 Recovering — Toipuvia 3 13 4 17 Total — Yh teensä 23 100 Condition of the trees ''uiden terveydentila Debarked % of the Height increment circumference dm/4 years Syöty °Io ympärys- Kasvu, dm/4 v. mitasta x x SD Dead, fallen Kuolleita, kaatuneita 60 0 0 Dead, standing Pystyyn kuolleita 75 0.8 1.0 Dying — Kuolevia 85 3.3 5.8 Most likely dying Todennäköisesti kuolevia 50 4.0 5.6 Most likely recovering Todennäköisesti toipuvia 36 5.2 3.6 Recovering — Toipuvia 14 7.5 4.1 Mineral soil sites Pine fens Spruce swamps )pen ri tens 21 10 58 15 50 18 6 100 drained fndrain< 34 K.-M. Korhonen Fig. 22. Occurrence of different types of vole damage in pines growing on different mire site types in Teura vuoma drained peatland. 1 = Hylocomium-Myrtillus site type, 2 = productive pine bogs, 3 = low pro ductive pine fens, 4 = spruce dominated swamps, 5 = birch dominated sedge fens. Kuva 22. Myyrätuhojen jakaantuminen tuhotavoittain eri suotyypeillä kasvavissa männyissä Teuravuoman ojitusalueella. 1 = HMT, 2 = hyväkasvuiset rämeet, 3 = kitukasvuiset rämeet, 4 = korvet, 5 = koivuval tainen RhSR. 344. Fertilization and soil nutrients Root vole damage was very common in the older fertilization study areas. Half of the 3336 trees examined in these areas were damaged by voles. The mire types in the damaged fertiliz ation study plots were as follows: The damage on the fertilized plots occurred most frequently on the richest Fig. 23. The proportion of pines damaged by voles on different peatland site types in advanced seedling and young thinning stands. RhSR = herb-rich sedge birch-pine fen, PsK(R) = Carex globularis spruce (and pine) swamp, RiL = eutrophic flark fen, VSR = tall-sedge pine fen, PsR = C. globularis pine swamp, RaR = Sphagnum fuscum pine bog. Kuva 23. Myyrän jyrsimien puiden osuudet eri suotyy peillä riuku- ja kasvatusmetsissä. peatland types: herb-rich birch-pine fens and spruce-pine swamps (Fig. 23). The damage degree in different mire site types differed significantly from each other (F = 4.05, df = 5,46, P < 0.005). The relationship between fertilization and root vole damage was studied by comparing the damage in the fertilization study plots (Figs. 14—18). Interpretation of the results was made difficult by the fact that the fertilizers used in the different areas were not the same (Table 10). In any case, the average damage degrees of the different study areas did not differ significantly from each other (F = 2.00, df = 4,47, P > 0.05). In the pooled data the average damage degree of plots unfertilized with macro nutrients was 43.6 %, the damage degree of plots given PK, PK + ash and PK + micro nutrients 61.3 % and on NPK, NP and N plots 45.7 %. The averages differed from each other significantly (F = 5.14, df = 2,49, PC0.01). The most common soil type in the damaged areas was Sphagnum- peat (St), accounting for 3/4 of the study plots. The average pH of the soil on the study plots was 4.8 (SD = 0.34), the lowest values occurring in Imari and the highest in northern Suoloma-aapa, Sattasuo and SW Alajärvensuo. The correlation between acid ity (pH) and damage degree was not significant (r = 0.081, P > 0.1). VSR RhSR PsR PsK(R) RiL RaR Total 46 35 6 5 5 3 100 35 Commun. Inst. For. Fenn. 144 Table 10. Root vole damage on the fertilization study plots in drained peatland forests. Taulukko 10. Lapinmyyrätuhojen esiintyminen eri tavoin lannoitetuilla aloilla ojitetuilla tur vemailla. The main factor indicating the effect of fertilization on vole damage is the amount of nutrients in the soil. The nutrient analyses were made in 1981, three years after the damage had occurred, and the contents were thus lower than during the damage year. However, the analyses revealed that the available phosphorus and potassium con tents were higher on plots fertilized with PK than on unfertilized ones. The highest contents of phosphorus were recorded in Suoloma-aapa, and the lowest in Alajärven suo. The positive correlation between the phosphorus content and the damage degree was significant in Suoloma-aapa (r = 0.874, P < 0.001), in Alajärvensuo (r = 0.661, P < 0.01) and in Sattasuo (r = 0.842, P < 0.05), but negative in Imari (r = 0.901, P < 0.05). The average damage degree of the different study areas did not differ from each other significantly (F = 2.49, df = 3,38, P > 0.05), while the P content did (F = 16.22, df = 3,38, P < 0.001). The positive correlation between the phosphorus content and damage degree on all the plots was highly significant (r = 0.499, n = 42, P < 0.001) (Fig. 24). This positive correlation was also found when non-parametric corre lation was determined (r s = 0.478, t = 3.44, df = 40, P < 0.005). Fig. 24. The correlation between root vole damage in tensity (proportion of gnawed trees in a study plot) and the phosphorus content (mg/1) of the soil (r = 0.499, n = 42, P < 0.001). Kuva 24. Myyrätuhojen (jyrsittyjen puiden %-osuus alan puista) ja maaperän fosforipitoisuuden välinen korre laatio (r = 0,499, n = 42, P < 0,001). ; ertilization lannoitus No. of plots Aloja, kpl No. of trees Puita, kpl Proportion of damaged trees, % Myyrän jyrsimien osuus, % Porportion of killed trees, % Myyrän tappamien osuus, % >fo fertilization li lannoitusta 10 495 39.6 10.1 dicronutrients iivenseos 3 114 39.5 8.8 ish — Tuhka 1 44 52.3 6.8 »K 14 1272 65.0 28.9 'K + micronutrients 'K + hivenseos 4 123 61.8 16.3 'K + ash — PK + tuhka 1 57 50.9 8.8 'K + urea 2 82 31.7 6.1 sTPK 8 666 42.8 25.2 vTPK + micronutrients JPK + hivenseos 3 95 52.6 16.8 NTP 5 357 44.5 20.7 1 31 58.1 19.4 "otal — Yhteensä 52 3336 52.0 21.7 36 K.-M. Korhonen Table 11. Some physical and chemical properties of peat in young thinning stands on drained and undrained peat lands. Taulukko 11. Turpeen fysikaalisia ja kemiallisia ominaisuuksia harvennusikäisissä metsiköissä ojitetuilla ja ojittamat tomilla soilla. St = Sphagnum peat, LSt = Lycopodium-Sphagnum peat, Ct Carex peat, Mm Mull, Mr Till, Hk Sand St = Rahkaturve, LSt Metsärahkaturve, Ct = Saraturve, Mm Multamaa, Mr = Moreeni, Hk = Hiekka Fig. 25. The correlation between root vole damage intensity and A) potassium content of the soil (r = —0.152, P > 0.05) and B) calcium content of the soil (r = 0.158, P > 0.05). Kuva 25. Myyrätuhojen ja A) maaperän kaliumpitoisuuden (r = —0,152, P > 0,05) ja B) maaperän kalsiumpitoisuu den (r 0,158, P > 0,05) välinen korrelaatio. irea I lue N Electricial conductivity Johtoluku 10 X mS/cm x SD Acidity — pH Cultivated layer M uokkauskerros x SD Exchangeable calsium Ca vaihtuva mg/1 x SD Exchangeable potassium K vaihtuva mg/l x SD Easily-soluble phosphorus P helppoliuk. mg/1 x SD Exchangeable magnesium M g vaihtuva mg/1 x SD Teuravuoma (drained damaged area ojitettu tuhoala) 4 0.48 0.17 4.7 0.21 550 255 33.8 4.79 3.2 4.50 48 28 All damaged areas (drained) Kaikki tuhoalat (ojitusalueet) 46 0.68 0.16 4.8 0.32 779 312 35.6 17.1 5.5 2.79 — Pohjasen vaara (undrained, not damaged — ojittamaton, vahingoittumaton) 8 0.48 0.23 5.1 0.46 1178 1010 54.4 21.1 2.0 0.95 219 183 Pajala (undrained, not damaged — ojittamaton, vahingoittumaton) 2 0.60 0.00 4.8 0.42 550 70 42.5 3.54 2.1 0.42 95 14 All undrained, not damaged comparison areas — Kaikki ojitta- mattomat, vahingoittu- mattomat vertailualat 11 0.79 0.21 5.0 0.48 995 902 50.4 19.1 2.2 1.1 All damaged areas Kaikki tuhoalat No. — Lkm. % St 32 70 LSt 2 4 CSt 3 7 Soil type — Maalaji SCt LSCt LCt Ct 2 — 22 4 — 44 Mm HkMm HkMr HHK Total Yht. 1 1 1 — 46 2 2 2 — 100 All undrained, not damaged comparison areas — Kaikki ojittamattomat vertailualat No. — Lkm. % 4 36 1 9 11 2 — 9 9 18 1 — — 1 11 9 — — 9 100 37 Commun. Inst. For. Fenn. 144 The highest potassium contents occurred in Imari and the SW part of Alajärvensuo, and the lowest in Suoloma-aapa. The correlation between the potassium content and the damage degree was non-significant in all areas: rsu = 0.156, = — 0.169, rg a = 0.556, rjm = —0.659, and in the pooled data (r = 0,152, n = 42, P>0.05) (Fig. 25 A). The highest calcium contents occurred in northern Suoloma-aapa and Sattasuo, and the lowest in Imari. The correlation between the calcium content and damage degree was significant only in Sattasuo (r = 0.959, n = 6, P < 0.01), but in other areas and in the pooled data non-significant (r = 0.158, n = 42, P > 0.05) (Fig. 258). The nitrate contents were under 10 mg/1 on all the plots, and could not be analyzed with the methods used by Viljavuuspalvelu. The soil analysis results tor the vole damage areas were compared to those of undamaged comparison areas. The analyses revealed that the phosphorus content of the soil in drained peatlands was higher than that in undrained ones, but the calcium, potassium and magnesium contents were lower (Table 11). 345. Stand density The correlation between stand density and degree of vole damage was not signifi cant (r = -0.202, n = 52, P > 0.1) (Fig. 26). On the other hand, in Alajärvensuo where the stand was rather dense the negative correlation between stand density and dam age degree was significant (r = 0.677, n = 14, P < 0.001). No correlation was found in the less dense stand at Verkkolah denjänkä. The relationship between vole damage and stand density was not linear. Most damage occurred on plots with a mean density of between 1400—1700 pines/ha. The damage degree was lower when the density was higher or lower than this value. Many of the areas had been thinned I—3 years before the damage occurred. Heavy thinning carried out according to a thinning model (Vuokila 1971) had preceded the damage in Teuravuoma. Thinnings had also been done in Suoloma-aapa and in some of the plots in Rovaniemi. The stand density was rather low in the fertilization study areas. The average density of all the study plots was 1363 trees/ha before the damage occurred. Three years Fig. 26. Correlation between root vole damage intensity and the density of the stand (stems/ha) in advanced seedling and young thinning stands on peatlands (r = —0.202, P > 0.1). Kuva 26. Myyrätuhojen ja puuston tiheyden (runkoa/ha) välinen korrelaatio riuku- ja kasvatus ikäisissä metsissä turvemailla (r = - 0,202, P >0,1). 38 K.-M. Korhonen Fig. 27. The stand density of the fertilization study areas, prior to (whole column) and after the vole damage. Kuva 27. Puuston tiheys lannoituskoealueilla ennen (ko ko pylväs) ja jälkeen myyrätuhojen. after the vole damage the density of living trees was 1104 on the average, but only 695 trees/ha for undamaged trees (Fig. 27). The difference between the stand density before the damage and the density of the trees alive after the damage had occurred differed significantly from zero (t = 7.34, df = 51, P < 0.001), as did the difference between the density before the damage and the density of undamaged trees (t = 14.66, df = 51, P < 0.001). According to the instructions of the Central Forestry Board, pine stands are considered to be understocked and under productive if the number of stems is less than 60 % of the number recommended (Takala 1986). The recommendation for thinning stands varies between 1000—1300 stems/ha in northern Finland, depending on the fertility of the site. According to this classification, Sattasuo, four plots in Alajär vensuo and one in Verkkolahdenjänkä be longed to the group with a minimum of 1300 stems capable of development/ha; Imari, ten plots in Alajärvensuo, 14 plots in Suoloma-aapa and five in Verkkolahdenjän kä to the group of 1200 stems/ha, and four plots in Verkkolahdenjänkä and two in Suoloma-aapa to the group of 1000 stems/ha. Thus, prior to the damage, only Suoloma aapa and part of Verkkolahdenjänkä were understocked, but after the vole damage all of the areas were underproductive (Fig. 27). 346. Vegetation The field layer vegetation on the drained peatlands had changed as a result of ditching. Betula nana L. was more abundant and luxuriant on the drained peatlands than on the undrained ones. Vaccinium vitis idaea and lichens were also more numerous on the drained peatlands, while Andromeda polifolia L. and Equisetum fluviatile L. dominated on undrained ones. The changes in plant cover in the fertilization study areas originated from draining, fertilization and thinning. As a whole, the vegetation was characterized by dwarf shrubs. The propor tion of grasses and herbs varied from rather scarce to abundant. The degree of vole damage was related to the occurrence of some plant species on the study plots. The occurrence of Eriophorum vaginatum L. was positively correlated with the damage degree, while the occurrence of Empetrum spp., Vaccinium uliginosum L. and Andromeda polifolia was negatively correlated with the damage degree (Table 12). The degree of vole damage was also compared to the vegetation according to physionomic plant groups (Kalliola 1973). The abundance of sedges and grasses was positively correlated with the damage degree (r = 0.371, n = 42, P < 0.05). On the other hand, the more dwarf shrubs there were, the lower the damage degree (r = 0.463, n = 42, P < 0.001) (Table 13). Dwarf shrubs in any Table 12. Correlations between the intensity of the vole damage (proportion of trees damaged by voles) and the abundance of some common plant species. Taulukko 12. Myyrätuhojen (jyrsittyjen puiden %-osuus koko puustosta) ja eräiden kasvilajien runsauden vä liset korrelaatiot. 'lant species kasvilaji Correlation Significant coefficient at the risk level Korrelaatio- Merkitsevä (n — 42) kerroin riskitasolla r 'actinium vitis-idaea 'actinium uliginosum 7. oxycoccos L. (+ microc.) ietula nana indromeda polifolia impetrum spp. ,eaum palustre L. 4enyanthes trifoliata L. lubus chamaemorus L. Ipilobium angustifolium Zalamagrostis purpurea Zarex chordorrhiza L. fil. -0.183 -0.452 -0.243 0.213 -0.376 -0.600 -0.157 -0.044 -0.130 0.184 0.088 0.262 1 % 5 % 0.1 % 10 % 39 Commun. Inst. For. Fenn. 144 Table 13. Correlations between the intensity of the vo le damage (proportion of trees damaged by voles) and the abundance of physionomic plant groups. Taulukko 13. Myyrätuhojen (jyrsittyjen puiden %-osuus) ja fysionomisten kasviryhmien esiintymisen väliset korrelaatiot. case were very abundant on all the damaged plots. However, the degree of damage diminished in cases where the abundance of dwarf shrubs restricted the occurrence of other plant groups. The total number of plant species was 51 in the field layer and seven in the bush layer. Mosses and lichens occurred in the ground layer. Highly significant positive correlation was found between the number of plant species and the damage degree on the plots (r = 0.535, n = 42, P < 0.001). The damaged plots resembled each other according to diversity analysis (Table 14). The Shannon index correlated positively with the damage degree on the plots (r = 0.384, n = 42, P < 0.05). No correlation was found between the total coverage of the field layer and the damage degree. A vegetation table was produced using a special vegetation table program (Appendix 4) (Mikkola, unpubl.). The study plots and Table 14. Diversity analysis of the vegetation in the young thinning stands damaged or not damaged by voles. Damaged areas include the fertilization study areas numbers 1-10, 12—43 and Teuravuoma drained peatland numbers 54—57. Undamaged areas include Silva-plot number 11, Pohjasenvaara undrained peatland numbers 44—51, Muotkavuoma 52 and Juolamaa 53. Taulukko 14. Pintakasvillisuuden diversiteettianalyysi kasvatusmetsien myyrätuhoaloilla ja vahingoittumattomilla vertailualoilla. Tuhoaloihin kuuluvat lannoituskoealat (1-10, 12-43) ja Teuravuoman ojitusalueen alat (54-57), vahingoittumattomiin Silva-ala (11) ja Pohjasenvaaran alat (44-51) sekä Muotkavuoma (52) ja Juolamaa (53). Plant group Kasviryhmä Correlation Significant coefficient at the risk level Korrelaatio- Merkitsevä (n = 42) kerroin riskitasolla r Zquisetum spp. — Kortteet -0.048 >edges and grasses larat ja heinät 0.367 5 % rrees and bushes ja pensaat 0.188 ■ierbs — Ruohot 0.059 3warf shrubs — Varvut -0.463 1 % bosses — Sammalet -0.228 Jchens — Jäkälät -0.287 10 % neld layer Kenttäkerros -0.181 v :u„ bitter — Karike Sample Näyteala number Lajiluku limpson index D ihannon index H' Lempton index Q Pielou index J' Sample Näyteala Species number Lajiluku Simpson index D index H' Pielou index r 1 2 3 4 5 27 25 19 22 17 0.724 0.674 0.884 0.688 0.690 1.855 1.680 2.403 1.801 1.603 0.000 0.000 4.343 7.935 7.282 0.563 0.522 0.816 0.583 0.566 31 32 33 34 35 23 26 22 19 13 0.810 0.645 0.814 0.681 0.589 2.199 1.632 2.103 1.637 1.217 8.656 0.000 10.013 14.427 8.656 0.701 0.501 0.680 0.556 0.475 6 7 g 9 10 16 20 16 14 22 0.728 0.781 0.717 0.657 0.748 1.690 1.897 1.604 1.466 1.877 4.971 5.139 7.282 3.907 15.870 0.609 0.633 0.578 0.556 0.607 36 37 38 39 40 18 19 18 18 16 0.681 0.637 0.830 0.713 0.675 1.713 1.709 2.144 1.786 1.501 6.492 5.581 4.625 12.984 11.542 0.593 0.580 0.742 0.618 0.542 11 12 13 14 15 13 14 17 17 13 0.583 0.724 0.660 0.676 0.675 1.331 1.668 1.594 1.578 1.657 3.728 3.366 7.282 7.282 3.728 0.519 0.632 0.563 0.557 0.646 41 42 43 44 45 23 18 11 17 20 0.727 0.656 0.710 0.842 0.914 1.876 1.670 0.608 2.188 2.626 7.456 5.023 2.606 4.900 5.974 0.598 0.578 0.671 0.772 0.877 16 17 18 19 20 14 18 17 16 17 0.650 0.631 0.681 0.731 0.682 1.455 1.540 1.564 1.778 1.749 3.907 5.592 0.000 3.031 4.971 0.551 0.533 0.552 0.627 0.617 46 47 48 49 50 19 15 19 19 27 0.899 0.833 0.907 0.890 0.907 2.489 2.103 2.619 2.465 2.727 4.809 3.970 15.810 5.581 8.276 0.845 0.777 0.890 0.837 0.827 21 22 23 24 25 19 13 15 17 18 0.673 0.632 0.707 0.696 0.722 1.642 1.313 1.573 1.692 1.633 9.102 8.656 4.465 4.111 12.984 0.558 0.512 0.581 0.597 0.565 51 52 53 54 55 21 21 11 14 15 0.823 0.900 0.834 0.864 0.810 2.241 2.528 2.067 2.197 2.057 6.213 4.551 7.610 4.916 4.028 0.736 0.830 0.862 0.833 0.759 26 27 28 29 30 13 20 19 18 19 0.697 0.759 0.853 0.697 0.714 1.573 1.973 2.279 1.683 1.788 2.885 4.809 5.139 5.023 5.139 0.613 0.659 0.774 0.582 0.607 56 57 13 14 0.830 0.870 2.081 2.226 4.269 3.616 0.811 0.843 40 K.-M. Korhonen Fig. 28. DECORANA ordination analysis of the drained peatlands and undrained comparison areas. Ordination of sample plots in two axes according to the frequencies of plant species. Plot numbers 1-10, 12—43 and 54 —57 damaged by voles, underlined numbers 11 and 44 — 53 undamaged. The clusters formed by TWINSPAN classification are shown with broken lines. Kuva 28. Turvemaiden ojitusalojen ja ojittamattomien vertailualojen pintakasvillisuuden DECO RANA-ordinaatioanalyysi. Näytealojen ordinaatio kahdella akselilla laskettuna kasvilajien esiintymisfrekvenssien perusteella. Myyrätuhot esiintyivät aloilla 1-10, 12-43 ja 54-57, tuhoja ei esiintynyt aloilla 11 ja 44-53 (alleviivatut). TWINSPAN-luokittelun avulla muodostetut ryh mät on erotettu katkoviivoin. plant species were organized using DECO RANA ordination analysis into two pairs of axes (Fig. 28). The analysis was made using species frequencies (eigenvalue = 0.404) and coverage (eigenvalue = 0.247). The threshold value for statistical significance in the analysis is considered to be 0.200. The main trend in the ordination was related to the moisture conditions, rather than to trophic levels. The plant species characterizing different peatland sites (Eurola and Kaaki nen 1978) formed a continuum from spruce swamps to open fens (Fig. 29). Vegetation on the damaged plots differed from that on the undamaged plots and was associated with increasing moisture conditions. The order of the damaged plots did not corre spond with either the damage degree or the phosphorus content of the soil. 1 I Phytosociological classification of the material was done by CLUSTER and TWINSPAN analyses using species fre quencies and coverages. CLUSTER analysis did not produce any relevant clusters. The best results for this material were given by TWINSPAN analysis based on species frequencies (Fig. 30). According to the TWINSPAN dendrogram, the plots were divided into two groups: 41 Commun. Inst. For. Fenn. 144 Fig. 29. Continuum formed by the plant species indicating different peatland site types (see Eurola and Kaakinen 1978) in the DECORANA ordination analysis based on the species frequencies. Plant species indicating pine bogs marked with R, spruce swamps with K, open bogs with N, open fens with L and forests with M. Kuva 29. Eri suotyyppejä indikoivien kasvilajien (ks. Eurola and Kaakinen 1978) muodostama jatkumo DECORANA-ordinaatioanalyysissä lajien esiintymisfrekvenssien mukaan. Rämeitä indikoivat kasvilajit on merkitty R, korpia indikoivat K , nevoja N, lettoja L ja metsäisyyttä M. I. Eriophorum group (38 plots) with two subgroups consisting of a) 12 plots at Alajärven suo and one at Imari and b) one plot at Alajärvensuo, all of the plots at Sattasuo, the Silva comparison plot, one of the plots at Imari and all of the plots at Suoloma-aapa. 11. Ledum group (19 plots) with two subgroups consisting of a) one plot at Alajärvensuo, four at Imari, all of the damaged plots and four of the undamaged plots at Kolari and b) six undamaged plots at Kolari and Pajala. The plant species were divided into two groups according to the results of fre quency-based TWINSPAN and DECO RANA analyses. Plant species typical to group I more or less indicated damage susceptibility. Such plants were Eriophorum spp., Betula pubescens Ehrh., Potentilla palustris (L.) Scop, and Salix myrtilloides L. Plant species more typical of the undamaged plots were Ledum palustre and Vaccinium myrtillus. Common species on all peatland study plots, both undamaged and damaged by voles, were Betula nana, Vaccinium uliginosum , Andromeda polifolia and Rubus chamaemorus. The coverage based analysis showed that Betula nana was more luxurious in drained (damaged) peatlands and Andro meda polifolia in undrained (undamaged) ones. The results of the ordination analyses were in agreement with the linear correla tions between plant species and damage degree. 42 K.-M. Korhonen Fig. 30. TWINSPAN classification dendrograms of the drained and undrained peatland study plots based on frequencies of plant species. The plots with vole damage are marked with a T next to the plot number. Kuva 30. Turvemaiden ojitusalojen ja ojittamattomien vertailualojen TWINSPAN-luokitteludendrogram mit kasvilajien esiintymisfrekvensseistä laskettuna. Myyrätuhoalat on merkitty T-kirjaimella alanumero jen edessä. 35. Discussion 351. Vole damage in thinning stands in other countries The damage caused by the root vole in drained peatland forests has earlier been described in Finland only in the form of a minor report by the author of this manu script (Korhonen et ai. 1983). No reports of similar damage have been made from either northern Sweden or the Kola peninsula, except for a few observations in the Tor nionjoki valley by Erkki Numminen (the Finnish Forest Research Institute, unpubl.). It may be that damage signs have not been found there. However, it is more likely that damage does not occur there to the same extent. The peatlands north of the Arctic Circle have not been drained in Sweden. Furthermore, in comparison to Finland there are less abandoned and cultivated fields in northern Sweden and on the Kola peninsula. In most cases voles damage rather small seedlings such as those in the afforested fields in this study. Damage to older trees has usually been caused by climbing species such as Clethrionomys glareolus and CI. rufocanus (Saalas 1949, Teivainen 1979, Nakatsu 1982, Timcenko 1983 a, 1983 b). In the Far East, as much as 90 % of the seedlings in pine plantations were damaged by voles during the peak year 1977—1978 (Timcenko 1986). The grey-sided vole had gnawed the bark above ground, and the far eastern vole underground (Timcenko 1986). In western Siberia the main vole species causing damage to both agriculture and forestry is the water vole, Arvicola terrestris (Maksimov 1977). Severe damage has also occurred in 20-year-old pine plantations, where water voles have gnawed the roots and bark at the butt (Nikolaeva 1971). In 1983 I was able to see damage of this kind in western Siberia and, although it appeared that the habitats were quite unlike those in Finland, the character of the gnawing resembled that of root vole damage in Finland. The water vole can cause minor damage in Finnish Lapland, too, but de barking of the butt is not typical of its behaviour in Finland. In British Columbia, Canada, Townsend voles ( Microtus townsendii Bachman) have caused damage in Douglas fir (Pseudotsuga Commun. Inst. For. Fenn. 144 43 menziesii Mirb.), western white hemlock ( Tsuga heterophylla Sarg.) and western white pine (Pinus monticola Dougl.) stands less than 40 years of age by removing bark and cambium from stems, branches and roots (Harper and Harestad 1986). A common feature in the damage caused by Townsend voles in British Columbia and by root voles in northern Finland is that in most cases thinnings had preceded the damage. 352. Forest improvement methods and vole damage The total area drained for forestry in Finland has been very much higher than that in the neighbouring countries (Braekke 1978). In Sweden, drainage is not considered to be profitable north of the Arctic Circle, and thus there are no drained peatlands in the range of the root vole. This may be the main reason why damage caused by the root vole has not been found in young thinning stands in Sweden. The present study indicated that the root vole damage in advanced seedling and young thinning stands is a problem of drained peatlands. The fertilization of peatlands increased the damage susceptibility of pine stands. However, it is difficult, on the basis of the results, to distinguish between the effect of fertilization and drainage because both measures had been used on most plots. In any case, it is not possible in practice to raise a commercial forest on peatlands without using PK fertilization. Nitrogen (N) is used on peatlands less than phosphorus and potassium. Nitrogen application is recommended only together with PK fertilization (Kaunisto and Paavi lainen 1977). On the other hand, most of the information concerning the effect of fertilization on the susceptibility of trees to herbivores is about nitrogen fertilization. Nitrogen fertilization has been found to increase hare damage (Sullivan and Sullivan 1982, Bryant et al. 1983, Rousi 1983) and moose damage (Laine and Mannerkoski 1980, Löyttyniemi 1981). In the present study the NH4 nitrogen contents of all the plots were lower than the critical values indicating a need for nitrogen fertilization (Kaunisto 1982). Besides the heavy damage on PK fertilization plots, damage was also found in this study inside reindeer fences, where the field vegetation had become grass rich due to the fertilizing effect of reindeer grazing. As well as increasing the growth of trees, draining and fertilization also increase the growth of the field vegetation: herbs, grasses and dwarf shrubs (Järvinen et al. 1977). The field layer vegetation retains 36 % of the nitrogen, 7 % of the phosphorus and 19 % of the potassium given as fertilizer (Heiku rainen 1980). Fertilizing with phosphorus has strongly increased the plant biomass, the increase correlating directly with the in crease in phosphorus. Nitrogen has only slightly increased the plant biomass, but the strongest effect was given by NPK fertiliz ation (Heikurainen 1980). The coverages of Eriopborum vaginatum and Epilobium an gustifolium increased both with increasing NPK fertilization and a narrower ditch spacing (Heikurainen and Laine 1976). The coverage of the shrub layer was not affected, but the height of the shrubs increased with more intense fertilization and narrower ditch spacing. The low temperature sum in northern Finland has a similar increasing effect on shrub growth (Heikurainen and Laine 1976). This explains the typical luxurious dwarf shrub layer of drained peatlands in northern Finland. Schneider and Westman (1987) found that community trophic status correlated strongly with the phosphorus content of the peat. In their study on sedge pine fens, DECOR AN A ordination gave the trophic gradient as axis 1, and a hydrological gradient could not be interpreted. According to Heikurainen (1980), the biomass of the field vegetation is at its greatest 3—4 years after fertilization. The changes in plant species composition caused by fertilization include an increase in species that rapidly utilize the added nutrients, at the expense of those species with a slow util ization ability (Chapin 1983). The changes in appearance, vegetation and ground water level due to draining and fertilizing are permanent. Dense stands of birch and willows appear along the ditches. The effect on Eriopborum spp. lasts for a long time, while that on herbs is shorter. On the other hand, the changes induced by draining are rather slow. Even in southern Finland the development towards transformed, heath type vegetation lasts at least 30—40 years (Sarasto 1952). 44 K.-M. Korhonen The results of the present study are in agreement with earlier reported effects of fertilization on the field vegetation. The main change in the habitat, due to draining and fertilization, was the increasing luxur iousness of the vegetation, which made a dense population of root voles possible. The most prominent difference between natural bogs and the drained fens and bogs was the richness of dwarf shrubs and some sedges and grasses. The essential feature of a vole habitat is in fact the sufficiency of food and shelter. Before draining, many of the study plots had been natural pine bogs and swamps where root voles did not occur. Some of the plots had originally been flark fens, which are natural habitats of the root vole. In both cases, the habitat provided enough food and shelter after draining to attract voles and to make the increase in numbers possible. A very high root vole population rather rapidly destroys the sedge and grass vegeta tion, as was found to be the case in the afforested field areas. Consequently, the scarcity of high quality food in winter, combined with the normal tendency of voles to vary their food source, is the reason why the tree bark was eaten. During the snowless period the scarcity of food leads to the dispersion of young animals. The effect of fertilization and even draining is not only a question of a change in habitat, but also a change in tree chemistry. Voles, as other herbivores, choose their food on the basis of both the nutritional quality and the presence of harmful substances in plants (Batzli 1983). The effect of harmful secondary compounds on feeding habits of mammalian herbivores has been emphasized in many recent studies (Löyttyniemi and Hiltunen 1978, Bryant and Kuropat 1980, Haukioja et ai. 1983, Palo et ai. 1983, Palo 1984, Bryant and Chapin 1985, Bryant et ai. 1985, Tahvanai nen et ai. 1985, Helle et ai. 1986, Lindroth and Batzli 1986). According to Dethier (1977), salt deficiency drive many vertebrates to use abnormal food while, on the other hand, hypersalinity in the plant has repelling effects. In any case, the changes in the trees brought about by fertilization favour the voles: both the nutrient content increases and the levels of harmful substances de crease. 353. Significance of root vole damage in forestry The pines completely debarked around the stem by root voles during the winter still looked healthy the following summer. Later on the needles turn brown in colour and the trees will die. Although the trees with minor injuries remain more or less green for many years, the older needles are shed. This is the reason for the characteristic appearance of such a damage (Fig. 21). Recovery of the damaged trees depends on the size of the debarked area, the root connections between trees and the condi tions prevailing after damage. Timcenko (1983 b) states that all trees with at least 90 % of the stem circumference debarked will die, and trees with more than 50 % debarked will suffer from retarded growth. Lodgepole pine (Pinus contorta), which is damaged by voles more than Scots pine (Hansson and Boström 1979), has a better ability to recover after vole damage than Scots pine (Hansson 1984). Even so, a reduction in growth and losses in timber quality took place in even slightly damaged seedlings (Hansson 1984). The partially damaged trees are suscep tible to secondary insect pests and diseases. The debarking scars initiated by voles may serve as entry ports for disease. The storm in autumn 1982 blew down great numbers of vole-damaged pines on peatlands. In western Siberia the water vole damage to older pines brought about the Dentroctonus micans (Kugelann) damage which rapidly killed the vole-damaged trees (author's own observa tion). The severe climate in northern Finland, cold winters and coolness and shortness of the growing season especially, can prevent the numbers of secondary insects ( Tomicus spp., Pissodes spp.) from increasing, despite the availability of breed ing material (Saarenmaa 1981). In peatland forests consisting of ad vanced seedling and young thinning stands, thinnings are needed to ensure the growth of a commercial stand. Kuusela et ai. (1986) proposed immediate (next 10-year-period) thinnings on a total of 60 km 2 in small seedling stands, and 1329 km 2 in advanced seedling and young thinning stands in the NE Finland and southern Lapland Forestry Board Districts. In 1977, the year preceding root vole damage, thinnings were carried out Commun. Inst. For. Fenn. 144 45 on a total of 800 km 2 in Lapland (Metsäti lastollinen... 1979). After heavy silvicultural measures and pre-commercial thinnings the field vegetation often becomes rich in grasses and herbs, which leads to the development of a favourable habitat for the root vole. In the present study the Teuravuoma drained peatland was a typical example of an advanced seedling stand, which had been thinned pre-commercially according to the instructions. Now, following the root vole damage, it has a too low stocking density. Most of the fertilization areas in this study had also been thinned a few years before the damage. Also Virtanen et ai. (1984) state that very severe vole damage has occurred after thinnings on study plots sited on peatlands in northern Finland. Recently Ikäheimo and Norokorpi (1986) stated that the amount of vole damage to the butt of trees on thinned study plots was 2—3 times higher than that on the plots not thinned. Besides the changes in habitat quality, the greater incidence of debarking by voles in thinned stands may have occurred because of the increased vigor of the trees. The Townsend vole has also been found to debark naturally regenerated Douglas-fir in thinned stands more than in unthinned ones (Harper and Harestad 1986). In this Douglas-fir study there were over 10 000 stems/ha in unthinned stands and 625—1225 in thinned. Some recent studies carried out on peatlands in Finland support the present recommendations, i.e. no more than 2000— 2500 seedlings/ha (Kaunisto and Tukeva 1986). This does not take into account the risk of vole damage. On the other hand, Kaunisto and Päivänen (1985) recommend denser stands on peatlands in northern Finland due to the damage risks. As a result of vole damage, Scots pine stands became under-productive: Sattasuo, Verkkolahdenjänkä and Suoloma-aapa even below the level (500 —700 stems/ha) at which there is a reasonable certainty of raising a stand (Hyvärinen 1986). Thus root vole damage can be of considerable economic importance. Draining, fertilization and silvi cultural measures are expensive in remote forests and, if the forest becomes under stocked and is no longer worth growing after 20—30 years, economical losses are high. The risk of root vole damage depends on the luxury of the field layer vegetation in the stand. Afforested field areas are thus very vulnerable at a young age. The pine stands regenerated on open fens by means of draining and fertilizing are susceptible later on at the advanced seedling and young thinning stages. All silvicultural measures, such as heavy thinning and fertilization, which promote the luxurious growth of field vegetation, increase the risk of vole damage. 46 K.-M. Korhonen 4. GENERAL DISCUSSION AND CONCLUSIONS 41. Comparison with earlier studies The importance of the root vole as a damaging agent of forest trees, ranging from the small seedling stage to the thinning stage, was revealed in this study. Earlier studies on vole damage in Lapland have shown that the most prominent damage in plantations occurred during 1973—1974 and 1977—1978, but less in the 1980's (Teivai nen 1979, Korhonen et ai. 1983). According to our knowledge of the feeding habits of voles (e.g. Kalela 1957, 1962, Koskina 1957, Myllymäki 1959, 1975, Tast 1968 b, Tast and Kalela 1971, Hansson and Zejda 1977, Teivainen 1978), the root vole, the field vole, the grey-sided vole, the bank vole and the water vole can be potential damaging agents of forest trees in northern Finland. To date, only the root vole has caused damage to coniferous trees on a considerable scale in this region. Vole catches obtained on the study plots of this study, as well as those elsewhere by Kaikusalo (unpubl.), revealed that most of the damage in afforested field areas and drained peatlands is caused by the root vole. In addition, during the peak in 1977—1978 the root vole was found to be the most common vole species on abandoned fields ranging from northern Lapland to Simo and Kuivaniemi, 100 km to the south of the pre viously known edge of its distribution range (see Siivonen 1967). Feeding experiments have shown that, compared to most of the other vole species, the root vole eats a lot of roots (Tast 1974, Teivainen 1978). The results of this study are in good agreement with this. The proportion of bark in the diet of the root vole has often been underestimated, due to the fact that the root vole eats bark almost exclusively during the winter. Most authors who have studied the winter food of the root vole have stated that bark makes up an important proportion of its winter diet (Barabas-Nikoforov 1946, Karaseva et al. 1957, Fetisov 1958). The appearance of the study plots in the present study indicated a deficit of food plants during wintertime before the popula tion decline. This can mean that tree bark is eaten mainly during starvation conditions. In addition to the amount of food, the accessibility of the food is also vital. Thus the conditions during the winter, especially the structure of the snow, become im portant. During such winters when other food, e.g. green shoots preserved under the snow becomes scarce or hard to reach, the voles eat much more bark. Dinesman (1961) has found that eating of bark in winter by the social vole ( Microtus socialis Pallas) is affected by the previous growing season as follows: Winter Characteristics of grass Role of woody plants in growth during previous summer winter food of voles and state of the vegetation in winter 1950/51 Growth of steppe vegetation Depression in vole ceased in summer. numbers. No diet study. 1951/52 Growth of steppe vegetation Depression in vole was normal. numbers. No diet study. 1952/53 Summer and autumn growth Vole diet consisted of of the steppe vegetation was vegetative parts and exceptionally good. Grasses seeds of grasses. Woody stayed green under snow. plants were eaten rarely. 1953/54 Drought caused a stop in Proportion of woody the growth of the steppe plants was 13—20 % of vegetation during summer. the winter diet. 1954/55 Drought halted the growth Woody plants were of the grasses in eaten very often, summer. 1955/56 Grasses withered out at the Main food of the voles end of May. No autumn was woody plants, growth of the grasses existed. An ice layer, 5—12 cm deep, covered the ground in winter. Timcenko (1983 b) states that, in the Far-East, the grey-sided vole causes damage to forest trees especially during winters when the snow layer is thick and the temperature conditions in the burrows of the vole colonies are optimal. Thus a large proportion of the population overwinters and, after eating up the high-calorific food available, starts debarking trees (Timcenko 1983 b). This could be the explanation for the fact that root vole damage does not always coincide with high vole populations. On the other hand, there is some evidence that voles eat bark in spring in spite of the 47 Commun. Inst. For. Fenn. 144 availability of other food, e.g. seeds of trees and bushes (Timcenko 1987). It can also be thought that a proportion of the root voles is specialized in eating bark. Ecomorpholo gical differences of this type are found in western Siberia between lake, bog, and meadow phenotypes of the water vole (Nikolaeva 1981). Voles, as well as hares, usually prefer broad-leaved trees to coniferous trees. During this study, however, mountain hares (Lepus timidus L.) were rather often found to have eaten the bark above the snow level of the same pines which the root vole had gnawn under the snow. The explanation for this is unknown. Earlier reports of the root vole as a damaging agent of forest trees are scarce. In Poland the species caused damage to seed lings of broad-leaved trees on drained peatlands with a rich growth of grasses (Gebczynska 1969, Buchalczyk et al. 1970). In contrast to this study, Scots pine was not gnawed at all. In the Krasnojarsk region vole damage has also occurred in pine and spruce fir plantations (Svecova 1984). Stomach and leftover analyses of voles showed that the species responsible for the damage were the root vole, the field vole, the grey-sided vole, the narrow-skulled vole (Microtus gregalis Pallas) and the bank vole (svecova 1980, 1984). 42. Old fields and peatland forests as root vole habitats The present study deals with root vole damage in two rather different habitats: abandoned fields and pine forests on peat bogs. Abandoned fields seem to be optimal biotopes for root voles. The vole population can survive there during depression years, and their reproduction centres are also situated there. In older fields the root voles reproduce quickly and the population den sity can grow to over 400 voles/ha (Mäenpää 1985). In afforested fields voles obtain all the food they need. Grasses, sedges and herbs in summer, underground organs of plants, green shoots preserved under the snow and the bark of willows and trees in winter are present in amounts sufficient to support a growing population. As a result of the lux urious growth of grass and often ploughing with forest machines, the afforested fields also provide plenty of cover for nesting burrows and runways. Dispersion from overcrowded field populations most often occurs during the autumn when the root voles move to new wintering sites. The root vole moves more often and over longer distances than other vole species. Even the female changes its home range after every litter, the distance between different nesting sites being 15—140 m. Males have been found to move around an area of 5000 square meters during a single summer month (Tast 1966). The distance between summer and winter habitats is usually 20—200 meters, but young animals may migrate several kilometers (Tast 1966, Balahonov 1976). According to Tast (1966), most of the young root voles leave their native bogs before the end of the summer. Erdakov (1981 b) has found that mature root voles orientate themselves to a new habitat quicker than young ones, but young voles move around actively to explore the new area. In fact the root voles also change their range in winter. The root vole communities examined once every two weeks near Irkutsk had changed their site each time, and old exits had disappeared under the snow (Zonov 1962). These earlier studies support the idea that the root voles moving out from abandoned fields cause damage in peatland forests. It is still unknown whether the voles migrating from the surrounding areas cause the damage or whether it is their offspring which has become abundant on the drainage areas. Some of the habitats on drained peatlands were dominated by grasses and sedges, e.g. the drained fens in Suoloma-aapa and Verkkolahdenjänkä. In most of the damaged stands the vegetation was characterized by luxurious dwarf shrubs, e.g. in Alajärvensuo and Teuravuoma. For large animals such as the moose (Alces alces L.) and for game birds these areas are very inaccessible, but voles which move under shrubs and along ditches profit from the good cover. In addition, the slopes of the ditches provide good nesting sites. The food selection on peat bogs is rather different from that on fields. Sedges, grasses and herbs are more scarce, and hence the amount of green summer food is restricted. On the other hand, the bark of 48 K.-M. Korhonen woody plants is abundant and the varying snow cover with plenty of holes maintains a supply of green shoots well through the winter. Compared to natural biotopes, the old fields are equal to flooded meadows and flark fens. In old fields, however, the root vole can stay all year and does not need special summer and winter habitats. The vegetation in hay fields is usually higher than that on aapa-fens, and hence the abandoned fields are more optimal for the root vole than their natural habitats. The drained peatlands resemble shrublands along river shores and the hummocks of open aapa-fens, i.e. the natural winter habitats of the root vole. Furthermore, the vole catches indicated that drained peatlands serve as winter biotopes for root voles which have migrated from surrounding meadows, flark fens and abandoned fields, while on the afforested fields the catches were high during winter and summer. During summer 1981 when root voles were abundant in optimal grass land habitats in Rovaniemi, no voles of any species were caught, despite trapping on 200 trap nights, in the less optimal Sattasuo and Alajärvensuo study plots nearby. Although the differences in field vegetation between afforested fields and drained pine fens were clear, the luxurious growth of the field layer vegetation, typical for both habitats, distin guishes the damaged areas from most habitats on mineral soil sites in Lapland. The survival of overwintering voles de pends on the snow cover. If the snow is less than 20 cm deep, it will not provide enough cover for voles in an air temperature of 20° C (Timcenko 1986). The snow forms drifts on both ploughed afforested fields and drained peatlands, and even in winters with little snow it is deep enough in places. In many winters the depth of the snow cover in southern and central Lapland even exceeds the minimum needed for winter reproduc tion of the root vole (Tast and Kaikusalo 1976). The age of the damaged trees was the most prominent difference between the afforested fields and drained peatlands. In the fields, damage was the heaviest to small seedlings, while in peatland stands the damage occurred on trees ranging from 1 10 m in height, no strong preference being shown for tree size or age. In British Columbia the Townsend vole showed a similar pattern, no preference for size and age occurring over the DBH range of o—l 9 cm and age of 8—33 years (Harper and Harestad 1986). The most important feature common to the afforested fields and drained peatlands was that both of them were man-made biotopes. New ecological niches are always filled, new habitats will be occupied sooner or later by animal species with a good adaptive capacity. The changes in vegetation and other conditions regulate this phenom enon. When man-made habitats are created and exploited for economic activities, new invading species will most likely cause damage of some significance. 43. Impact of man In northern Finland the most prominent changes in land use have been the clearing of forest for fields after World War 11, the abandoning of fields in the 1970'5, the sudden increase in clear-cutting and artificial reforestation, as well as draining of peatlands for agriculture and forestry. All these habitat alterations have taken place during a period of some 20—30 years. As a con sequence the voles have become a major problem for modern forestry. Similar development in the Krasnojarsk region, Siberia, has led to a total change in the species composition of small rodents. Up until 1966 the area of plantations accounted for 20 % of the forest land in Krasnojarsk, but in 1973 it was more than 40 % (§vecova 1980). As a result, the previously common ruddy vole (Clethriono mys rutilus) became rare and other species {Microtus oeconomus, M. agrestis, M. gregalis, Cl. rufocanus and CI glareolus) occupied the new habitats (§vecova 1980). Equal effects on small mammal communities as a result of changes in land use are known from all over the world (Hansson 1975, 1978, Larsson 1976, Marcström 1977, Bejcek 1981, 1982, Monthey and Soutiere 1985, Happold and Happold 1987.) One of the most striking habitat alter ations due to human influence has occurred in the Krusne Hory mountains in Czecho slovakia where air pollution has killed the conifer forests. Increased light under the 49 Commun. Inst. For. Fenn. 144 canopy has changed the field layer vegeta tion totally into grassland. The plantations of Picea pungens Engelm., the only conifer which has tolerated heavy emissions, have as a consequence suffered from damage caused by the field vole, a species earlier very rare in the area (Tichy 1987 and the author's own observations 1985). The numbers of voles and their damage to forest plantations have increased throughout Fennoscandia since the end of the 1950's (Larsson 1973, Christiansen 1975, Teivainen 1979). According to Christiansen (1979), the increase in vole damage in Norway is connected with changes in land use such as the increase in the afforestation of fields and the start of artificial reforestation. Timcen ko (1986) states that the vast areas of clear-cutting and abundance of plantations in the Far East have caused changes in field vegetation, thus bringing about the increase in vole numbers. The vegetation on clear-cut areas on mineral soil resembles that of afforested fields. Light-demanding species dominate and short-lived growth of Epilo bium angustifolium, Rubus idaeus L. and Vaccinium vitis-idaea is usual. In the mesic dwarf shrub type the transition from V. myrtillus to the grass Deschampsia flexuosa is typical after clear-cutting (Marcström 1977). The changes in the peatland habitats caused by forest improvement measures, draining and fertilization, are as deep-going. 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Annales Zoologici Fennici 3: 127—171. 1968 a. The root vole, Microtus oeconomus (Pallas), in manmade habitats in Finland. Annales Zoologici Fennici 3: 230—240. 1968 b. Influence of the root vole, Microtus oecono mus (Pallas), upon habitat selection of the field vole, Microtus agrestis (L.) in northern Finland. Annales Academiae Scientiarum Fennicae (A IV) 136. 23 p. 1972. Lapinmyyrä. In: Siivonen, L. (Ed.). Suomen Nisäkkäät I. Keuruu, p. 404 —414. 1974. The food and feeding habits of the root vole, Microtus oeconomus in Finnish Lapland. Aquilo, Series zoologica 15: 25—34. & Kaikusalo, A. 1976. Winter breeding of the root vole, Microtus oeconomus, in 1972/73 at Kilpisjärvi, Finnish Lapland. Annales Zoologici Fennici 13: 174—178. & Kalela, O. 1971. Comparisons between rodent cycles and plant production in Finnish Lapland. Annales Academiae Scientiarum Fennicae (A IV) 186. 14 p. Teivainen, T. 1978. Eräiden poppelikloonien myyrätu hoalttius ruokintakokeiden mukaan. Summary: Re sistance of some poplar clones to vole damage through feeding experiments. Folia Forestalia 339. 12 P — 1979. Metsäpuiden taimien myyrätuhot metsän uudistusaloilla ja metsitetyillä pelloilla Suomessa vuosina 1973 —76. Summary: Vole damage to forest tree seedlings in reforested areas and fields in Fin land in the years 1973—76. Folia Forestalia 387. 23 p. 1984. The damage risk and the extent of vole damage in forest plantations in Finland. Proceedings of a Conference on the Organisation and Practice of Vertebrate Pest Control. 30 August 3 Septem ber 1982, Elvetham Hall, Hampshire, England, p. 573—587. , Jukola-Sulonen, E.-L. & Mäenpää, E. 1986. Pinta kasvillisuuden kemiallisen torjunnan vaikutus pel tomyyräpopulaation kehitykseen. Summary: The effect of ground-vegetation suppression using her bicide on the field vole, Microtus agrestis (L.) popu lation. Folia Forestalia 651. 19 p. Tichy, V. 1987. Drobni mysoviti hlodavci v lese a obra na proti nim. Abstract: Small mouse-like rodents. Lesnicka Prace 2: 70—75. Timcenko, L.I. 1983 a. Attraktivno-biologiceskij metod ogranicenija cislennosti mysevidnyh gryzunov. Les noe Hozjajstvo 2: 56—57. 1983 b. Povrezdenija kedrovo-sirokolistvennyh lesov mlekopitajuscimi na Dal'nem Vostoke. Ekologija i zascita lesa. Mezvuz. Sbornik Naucnyh Trudev: 65—69. 1986. Povrezdenie derev'ev i kustarnikov zivotnymi na Dal'nem Vostoke. Lesnoe Hozjajstvo 1: 64—66. 1987. Massovoe povrezdenie aralii Man'czurskoj izjubrami i gryzunami v Habarovskom krae. Lesnoe Hozjajstvo 3: 66—67. Tutkimus pellonvaraustilojen käytöstä Lapin läänissä. 1975. Lapin maatilatalouden kehittämisneuvottelu kunta. Rovaniemi. 51 p. Vahtola, J. 1982. Lapin talonpoikaisasutuksen kehitys 1600-luvun loppupuolelle asti. In: Aho, S. & Heik kola, L. (Eds.). Lapin plakaatista tilojen autioitumi sen aikaan. Oulu University, Research Institute of Northern Finland. Series C, 42: 135—155. Varjo, U. 1967. Lapin maatalous 1950-59. Lapin seutu suunnittelun kuntainliitto. Rovaniemi. 75 p. 1978. Problems facing rural life in northern Finland. Nordia 12(1): 79—86. Veijalainen, H. 1974. Metsänparannettu ja luonnonti lainen suo eläinten talvisena elinympäristönä. Sum mary: Winter habitat preferences of wild animals on improved and virgin peatlands. Metsäntutkimuslai toksen suontutkimusosaston tiedonantoja 3. 10 p. Virtanen, J., Norokorpi, Y. & Kaunisto, S. (Eds.). 1984. Metsänuudistamisen ja taimikonhoidon peri aatteet. Metsäntutkimuslaitoksen tiedonantoja 135. 12 , - Vuokila, Y. 1971. Harvennusmallit luontaisesti synty neille männiköille ja kuusikoille. Summary: Thinning models for natural pine and spruce stands in Fin land. Folia Forestalia 99. 18 p. Zonov, G.B. 1962. O zimnem pitanii polevki-ekonom ki. Doklady Irkutskogo Protivocumnogo Instituta 4: 137—138. Total of 166 references Commun. Inst. For. Fenn. 144 55 SELOSTE Lapinmyyrä metsätuholaisena Pohjois-Suomessa Johdanto ja tutkimuksen tarkoitus Myyrät ovat osoittautuneet merkittäväksi nykyaikai sen metsätalouden ongelmaksi erityisesti Fennoskandi assa ja Siperiassa. Jyrsimällä taimien kuorta ne ovat ai heuttaneet tuhoja pellonmetsitys- ja metsänviljelyaloil la. Tämä tutkimus käsittelee Pohjois-Suomessa esiinty viä myyrätuhoja, joiden pääasialliseksi aiheuttajaksi to dettiin lapinmyyrä, Microtus oeconomus Pallas. Lapinmyyrän luontaisia esiintymispaikkoja ovat jo kien ja järvien tulvarannat sekä tulvivat aapasuot. Näil tä laji on vuosisatojen ja erityisesti viime vuosikymme nien aikana levinnyt mitä erilaisimmille ihmistoiminnan muovaamille biotoopeille. Pääosa lajin esiintymistä ja ravintoa koskevista tutkimuksista on julkaistu vain Neuvostoliitossa. Pohjois-Suomessa viime vuosikymmeninä tapahtu neista maankäytön muutoksista huomattavimpia ovat olleet sodanjälkeinen metsien ja soiden raivaaminen pel loksi, peltojen hylkääminen 1970-luvulla, avohakkuiden ja metsänviljelyn nopea runsastuminen sekä laajamittai nen soiden ojitus. Näiden seurauksena on syntynyt uu sia ihmisen luomia biotooppeja varsinkin Etelä- ja Kes ki-Lappiin. Tutkimus koostuu kahdesta osasta. Ensimmäisessä osassa tutkitaan lapinmyyrän aiheuttamia tuhoja pelloil le istutetuissa taimikoissa, toisessa osassa tuhoja turve maiden mäntymetsissä. Lapinmyyrätuhojen syntyyn vaikuttaneita tekijöitä ja tuhojen seurauksia selvitetään. Koska aikaisempia tutkimuksia aiheesta ei juuri ole, huomattava osa tutkimuksesta on tuhojen kuvaamista ja analysointia. Tarkoituksena on selvittää, mitkä teki jät vaikuttavat myyrätuhojen syntyyn, mikä on eri met sänuudistus- ja metsänparannusmenetelmien merkitys ja ovatko myyrätuhot seurausta ihmisen toiminnan ai heuttamista muutoksista Pohjois-Suomen metsissä. Lapinmyyrätuhot metsitetyillä pelloilla Pellonmetsitysalojen myyrätuhoja tutkittiin 11 kun nan alueella Etelä- ja Keski-Lapissa Veitsiluoto Oy:n vuosina 1972—77 metsittämillä 87 pellolla. Lapinmyy rätuhoja esiintyi 37 %:lla pelloista, mikä vastasi 54 % metsitettyjen peltojen pinta-alasta. Kenttätutkimukset suoritettiin vuosina 1978 ja 1979. Kenttäkoealoiksi va littiin 23 tuhojen kohteeksi joutunutta taimikkoa ja yh tä monta vertailutaimikkoa, joissa tuhoja ei esiintynyt. Taimikoiden perustamis- ja hoitotoimenpiteitä sekä pintakasvillisuus- ja maa-analyysien tuloksia vertailtiin tuhoalojen ja vahingoittumattomien alojen kesken. Alat luokiteltiin pintakasvillisuuden perusteella ryhmiin TWINS PAN-ja DECORANA-analyysien avulla. Myy riä pyydystettiin tappoloukuin 961 loukkuvuorokaute na myyrätuhoaloilla. Pääosalla pelloista lapinmyyrä oli ainoa laji, mutta eteläisimmiltä tuhoaloilta saatiin myös f>eltomyyriä. Kaikkiaan 112 pyydystetystä myyrästä oli apinmyyriä 83 % ja peltomyyriä 17 %. Lapinmyyrien jyrsintäjäljet sijaitsivat taimien tyvellä ja/tai juurissa. Pienimmät taimet oli jyrsitty lähes ko konaan silpuksi. 95 % istutetuista taimista oli mäntyjä, joten pääosa tuhoistakin oli männyissä. Tuhojen koh teeksi joutuneet taimikot olivat pinta-alaltaan keski määrin suurempia kuin tuhoilta säästyneet taimikot (t = 3,70, df = 49,9, P < 0.001). Keski-iältään tuhoalo jen taimikot olivat 8,5 kk nuorempia kuin vahingoittu mattomat taimikot (t = 2,05, af = 83,7, P < 0,05). Niinikään tuhon kohteeksi joutuneista taimikoista oli suurempi osa istutettu käyttäen paljasjuurisia taimia (H = 4,68, P < 0,05), ja heinäntorjuntaa oli niissä tehty vähemmän kuin tuhoilta säästyneissä taimikoissa (H = 2,70, P < 0,1). Kaikkien pellonmetsitysalojen pintakasvillisuutta val litsivat heinät. Märkien ja kosteiden kasvupaikkojen la jit olivat yleisempiä tuhoaloilla kuin vahingoittumat tomilla aloilla. Näytealat ja kasvilajit järjestettiin DE CORANA-ordinaatioanalyysin avulla akseliparille kas vilajien esiintymisfrekvenssien perusteella, mutta muu tossuunnissa ei havaittu eroja tuho- ja vertailualojen vä lillä. TWINSPAN-analyysin avulla muodostetuille kas visosiologisille ryhmille oli yhteistä heinien ja maito horsman runsaus. Tuhoalttiimmiksi todettiin saramai sen kasvillisuuden luonnehtimat alat, vähiten alttiiksi metsäkasvien luonnehtimat alat. Pintakasvillisuus oli tuhojen kohteeksi joutuneissa taimikoissa yhtenäisem pää kuin vahingoittumattomissa taimikoissa ja niiden Shannon diversiteetti-indeksit erosivat merkitsevästi toisistaan (F = 4,97, df = 1,44, P < 0,05). Metsitetyillä pelloilla maan ravinnepitoisuudet olivat alempia kuin alueen viljelyksessä olevilla pelloilla. Maaperän fosfori-, kalium- ja kalsiumpitoisuudet olivat tuhon kohteeksi joutuneissa taimikoissa merkitsevästi korkeampia kuin tuhoilta säästyneissä taimikoissa (fosfori: t = 4,72, df = 24,6, P < 0,001; kalium: t = 4,59, df = 30,3, P < 0,001; kalsium: t = 2,28, df = 43,8, P < 0,05). Lapinmyyrätuhot turvemaiden metsissä Turvemaiden metsien lapinmyyrä tuhoja tutkittiin Etelä- ja Keski-Lapissa vuosina 1980—85. Pääosa tuhoista oli syntynyt talvella 1977—78, vähäisempi osa talvella 1981 —82. Tuhojen esiintymistä ojitetuilla ja ojittamat tomilla turvemailla selvitettiin linja-arvioinnilla Kolarin Teuravuoman ojitusalueella ja viereisellä luonnontilai sella suolla. Muut tutkimukset tehtiin Metsäntutkimus laitoksen suontutkimusosaston lannoituskoealueilla. Kasvillisuus- ja maa-analyysit sekä puustomittaukset tehtiin 46 tuhoalalla ja 11 vertailualalla, samoin mene telmin kuin pellonmetsitysaloilla. Tulokset käsiteltiin VAX 11/785 tietokoneella BMDP- ja kasvillisuusana lyysiohjelmia käyttäen. Myyriä pyydettiin 1590 loukku vuorokauden ajan vuosina 1977—78. Kokonaissaalis oli 493 myyrää, joista lapinmyyriä oli 49 %. Lapinmyyrä oli yleisin laji kaikilla pyyntibiotoopeilla lukuunottamatta HMT-kuusikkoa, jossa metsämyyrä oli yleisin. 56 K..-M. Korhonen Turvemaiden metsissä tuhot kohdistuivat ojitusalu eiden harvennusikäisiin mäntymetsiin. Ojitetuilla alueil la tarkastettiin ja mitattiin yhteensä 3 697 puuta, ojit tamattomilla vertailualueilla 420 puuta. Tuhojen koh teeksi joutuneilla ojitusaloilla puolet puista oli myyrän jyrsimiä. 40 % jyrsityistä puista oli kuollut kolmen vuoden kuluttua vioituksesta. Ojittamattomien soiden puissa tuhoja ei esiintynyt. Myyrät olivat jyrsineet kuo ren puiden tyveltä ja/tai juurista. Jyrsittyjen puiden keskipituus oli 4 m (1,3—10,0 m) ja rinnankorkeuslä pimitta 6 cm (1—21 cm). PK- ja PK+tuhka/hivenlannoitetuilla aloilla myyrän jyrsimien puiden osuus oli 61 %, NPK-, NP- ja N-lan noitetuilla 46 % ja pääravinteilla lannoittamattomilla aloilla 44 %. Erot olivat tilastollisesti merkitseviä (F = 5,14, df = 2,49, P < 0,01). Eri koealueiden tuhoas teiden välillä ei ollut merkitsevää eroa (F = 2,00, df = 4,47, P > 0,05). Turpeen fosforipitoisuus oli tuho aloilla korkeampi ja kalium-, kalsium- ja magnesiumpi toisuudet alhaisemmat kuin vertailualoilla. Turpeen fosforipitoisuuden ja tuhon ankaruuden välinen positii vinen korrelaatio oli erittäin merkitsevä (r = 0,499, n = 52, P < 0,001). Sen sijaan kalium- ja kalsiumpitoi suudet eivät korreloineet merkitsevästi tuhoasteen kanssa. Pääosa tuhoista esiintyi aloilla, missä puuston tiheys oli 1400—1700 mäntyä hehtaarilla. Puuston keskitiheys oli tuhojen kohteeksi joutuneilla aloilla ennen tuhoja 1363 mäntyä/ha. Kolme vuotta tuhon jälkeen eläviä puita oli 1104 hehtaarilla, mutta kokonaan tuholta sääs tyneitä vain 695 runkoa/ha. Parittaiset keskitiheyksien erotukset erosivat merkitsevästi nollasta (t = 7,34 ja t = 14,66, df = 51, P < 0,001). Kaikilla tutkimusalueilla myyrätuhot olivat aiheuttaneet puuston vajaatuottoi suuden, Sattasuolla, Verkkolahdenjängällä ja Suoloma aavalla jopa alle jatkokasvatuksen kannattavuusrajan (500—700 runkoa/ha). Ojitettujen alojen pintakasvillisuus poikkesi ojitta mattomien vertailualojen pintakasvillisuudesta, vaikka alkuperäiset suotyypit vastasivat toisiaan. Tuhojen an karuudessa eri suotyypeillä oli merkitsevä ero (F = 4,05, df = 5,46, P < 0,005). Ojituksen ja lannoituksen seu rauksena varpujen rehevyys ja korkeus oli lisääntynyt, heinät ja sarat olivat runsastuneet. DECORANA-ordi naatioanalyysiä käytettiin ilmaisemaan kasvisosiologisia muutossuuntia aineistossa. Päävaihtelusuunnaksi osoit tautui kosteuden, eikä ravinnetason muutos. Aineiston kasvisosiologiseen luokitteluun käytettiin TWINSPAN -analyysiä. Sen avulla koealat jaettiin kahteen ryh mään: 1) Tupasvilla-ryhmä (38 alaa) ja 2) Suopursu ryhmä (19 alaa). Kasvilajeista tupasvilla, hieskoivu, kurjenjalka, vaivaiskoivu ja juolukkapaju olivat tyypilli siä tuhoaloille kun taas suopursu, suokukka ja mustikka vahingoittumattomille aloille. Tulosten tarkastelu Lapinmyyrätuhot esiintyivät kahdella hyvin erilaisella biotoopilla: metsitetyillä pelloilla ja ojitetuilla turve mailla. Pelloilla myyrätuhon kohteeksi joutuivat pienet taimet. Sen sijaan ojitusalueilla tuhot esiintyivät suuris sa puissa. Metsitetyt pellot ovat myyrille erittäin suo tuisa elinympäristö, jossa ne voivat lisääntyä silloinkin kun kanta on hyvin vähäinen. Ojitetuilla turvemailla la pinmyyriä esiintyi vain kannan ollessa hyvin runsas. Suotuisissa oloissa ne lisääntyivät ojitusaloilla ja aiheut tivat tuhoja. Turvemaiden mäntymetsissä ojitus oli rehevöittänyt pintakasvillisuutta ja muuttanut kasvupaikat myyrille suotuisiksi. Samalla tavalla olivat vaikuttaneet useissa tapauksissa tuhoja edeltäneet harvennushakkuut. Myös lannoitus näytti lisäävän männiköiden myyrätuhoalt tiutta. Tulosten perusteella on kuitenkin vaikea erottaa lannoituksen ja ojituksen vaikutuksia toisistaan, sillä molemmat toimenpiteet oli tehty lähes kaikissa tuhon kohteeksi joutuneissa metsiköissä. Käytännössä ta lousmetsän kasvattaminen ojitetuilla soilla lienee mah dotonta ilman PK-lannoitusta. Ojitus muuttaa pinta kasvillisuutta hitaasti ja suon kuivuminen turvekan kaaksi kestää kymmeniä vuosia. Sen sijaan lannoitus ja harvennushakkuut aiheuttavat nopeamman ja lyhyt aikaisemman muutoksen pintakasvillisuudessa. ....— r — - Metsitetyillä pelloilla taimikot jouduttiin myyrätuho jen vuoksi täydennysistuttamaan useitakin kertoja. Oji tetuilla soilla tuhot sattuivat pääosin yhden tavallista korkeamman myyrien esiintymishuipun aikana, mutta niillä on pitkäaikaiset vaikutukset metsikön tuottoon. Lapinmyyrän aiheuttamien tuhojen lopullinen merkitys ilmenee kasvutappioina, laatuvikoina ja mahdollisina seuraustuhoina vasta vuosien kuluttua. Myyrätuhojen riski tulisi ottaa huomioon laskettaesssa ojituksen ja lannoituksen kannattavuutta Pohjois-Suomessa. Tur vemaiden taimikoissa nykysuosituksia korkeammat kasvatustiheydet vähentäisivät myyrätuhoriskiä ja tuho jen seurauksia. Myös harvennushakkuiden ja jatkolan noitusten ajoitus myyräkannan romahdusvaiheeseen vä hentäisi tuhoja. KORHONEN, K.-M. 1987. Damage caused by the root vole (Microtus oeconomus) to Scots pine in man-made habitats in northern Finland. Seloste: Lapinmyyrä metsätuholaisena Poh jois-Suomessa. Communicationes Instituti Forestalis Fenniae 144. 61 p. 57 Commun. Inst. For. Fenn. 144 Appendix 1. Food of the root vole according to Fetisov (1958). +++ = eaten very often, ++ = eaten moderately, + = eaten seldom. Liite 1. Lapinmyyrän ravintokasvit Fetisovin (1958) mukaan. Syönnin aste: +++ = paljon, ++ = kohtalaisesti, + = vähän. lani spec: .es-1 .ssues ea* :en-! iasv: .nosal Intensity Syönnin voimakkuus Cquisetum fluviatile L. , Equisetum spp. heads-tähkät ￿ ￿ > inus cembra L. shoots-versot ￿ J inus sylvestris L. bark of fallen branches ￿ pudonneiden oksien kuori lilium effusum L. leaves-lehdet + canina L. leaves-lehdet spp. stem, leaves-varsi,lehdet ￿ + Wena sativa L. seeds-siemenet ￿ aquatica (L.) Beauv. leaves-lehdet ￿ Slyceria lithuanica Gorski stem, leaves-varsi.lehdet ￿ 'arex spp. roots- juurakot ￿ ￿ + 'arex spp. stems ,leaves-varret,lehdet + ￿ 2riophorum spp. stems ,leaves-varret.lehdet »alix myrtilloides L., Salix sp. bark , twigs-kuori ,oksat 5 opulus tremula L. bark,fallen leaves in winter ￿ + kuori,pudonneet lehdet 5 opulus spp. bark,fallen leaves in winter + ￿ kuori,pudonneet lehdet 3 olygonum viviparum L. stems ,leaves-varret,lehdet Polygonum viviparum roots in stores- juurakot + Polygonum alopecuroides Turcz. roots in stores- juurakot Polygonum bistorta L. roots in stores- juurakot + + \triplex patens Litw. stems ,leaves-varret,lehdet ￿ + Jilene spp. stems ,leaves-varret,lehdet + rrollius asiaticus L. leaves-lehdet Cranthis sibirica DC roots in stores-juurakot Anemone crinita Juz. leaves-lehdet sibirica L. stem, leaves-varsi,lehdet )entaria tenuifolia Ledeb. roots in stores- juurakot hapsella bursa-pastoris (L.) Medicus leaves ,stems-lehdet.varret iergenia spp. leaves-lehdet spp. leaves-lehdet ianguisorba officinalis L. leaves-lehdet ￿ ["rifolium repens L. ,T. pratense L. leaves-lehdet .athyrus spp. stems ,leaves-varret,lehdet ￿ Jeranium spp. roots in stores- juuret ilrodium cicutarium (L.) L'H6r. roots in stores- juuret )arum carvi L. roots in stores- juuret spp. leaves-lehdet ￿ )ornus sibirica Lodd. bark-kuori faccinium myrtillus L. twigs in winter-varvut + + Jalium spp. ,leaves-varret,lehdet laianthemum bifolium (L.) F.W. Schmidt stems ,leaves-varret,lehdet 'rientalis europaea L. stems .leaves-varret,lehdet ￿ »arnassia palustris L. roots in stores- juuret )ryas oxidontha Juz. leaves, stems-lehdet.varret ￿ .innaea borealis L. leaves ,stems-lehdet,varret + »hlomis tuberosa L. roots in stores- juurakot + + + 58 K.-M. Korhonen Appendix 2. Vegetation analysis of the afforested field areas. Comparison of plots with or without vole damage. The plant species are ranked according to their frequencies (f, %). Liite 2. Metsitettyjen peltojen pintakasvillisuusanalyysi. Myyrätuhoalojen ja vahingoittumattomien alojen vertailu. Kasvilajit on järjestetty esiintymisyleisyyden (f, %) mukaan. Spec ies - Lajit F C temaged plots - Tuhoalat Not damaged plots - Vertailualat j,.?..?..-----^.- 7 , [P. 11_ 12_ -13- 1 f,. 1.5. 16 17 18 19 20 21 22 B 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 41 1 40 EPIL ANGU 1 95.3 I 11 OCSC CCSP I 93.! ! 9 AGRO CAPI I 93.! ! 20 Rlht ACCT I 84.J I 14 FEST RtBR I 84.( I 13 POA PRAT I 82. ( I 50 ACHJ MILL I 76.1 1 62 S«LI SP 1 69.( ! 61 BCTU PUBE 1 67.4 ! 87 OR£ 1 65.2 ! 29 RAMJ ACRI I 63.C I 30 RAW REPE I 60.5 ! 21 RIK ACLA I 58.3 ! 81 EPIL PALU ! 54.: I 49 ACHI PTAR 1 54.: I 26 CERA FCNT 1 43.! I 90 CALA PW I 39.1 ! 8 PHI PRAT I 37 .C 1 73 POTI PALU 1 28. I 92 TRIE EIPO I 28. ! 5 LUZU KJLT I 28. I 35 TR IF REPE I 28. 1 93 Via EPIP 1 26.1 ! 95 CALA STRI 1 26.1 ! 24 sm GRAM 1 26.1 ! 55 TARA SP ! 26.1 ! 66 RHIN MI» ! 23.5 ! 32 R18U AfiCT ! 23.5 l 53 CIRS »€1I I 23.5 1 3 PINU SYIV ! 23.5 I 58 Via PALU 1 21.3 I 34 FILI UUtt 1 21.3 1 88 EOJI PALU ! 21.3 ! 60 JK FILI 1 21.3 1 54 LEON AUTU I 21.3 ! 47 GALI ULIG I 21.3 ! 41 G*LE BIFI 1 17.4 ! 89 ERIO AK3J ! 17.4 ! 91 CARE Mflff ! 17.< ! 4 CARE SP I 17.4 ! 59 PICE ABIE I 17.4 ! 16 ELYM REPE 1 15.2 I 23 STR >£DI ! 15.2 ! 84 OCSC FLEX ! 15.2 ! 6 LUZU PALL I 15.2 I 76 VACC MlRT 1 15.2 1 56 VACC VITI I 15.2 I 48 Sai VIRG I 15.2 1 98 E>PE NIGR 1 13.C 1 85 EQUI RUV 1 13.C 1 36 TRIF PRAT 1 13.C I 77 CARE HIGR I 10.5 1122 RCR1 PALU 1 10.5 I 43 GALE SPEC 1 10.5 !104 >£Nr TRIF 1 10.5 I 2 EOJI SYIV ! 10. ! 22 0€N ALBU 1 10. ! 118 H1ER HUE I 10. I 65 AN3E SYIV I 10. ! 69 CALA AftUN 1 8. ! 124 ERIO VAGI I 8. ! 57 VERO LONG ! 8. I 1 EQUI ARVE ! 8. 1131 RUBU OW1 ! 8. I 97 VACC ULIG l 8. ! 12 PCA TRIV 1 8. ! 19 RIK LONG ! 8. 1105 BETU ! 8. ! 133 VICI CRAC 1 8. ! 25 SILE OIOI 1 8. I 86 VALE OFFI I 6. 1 7 ANTH OXR I 6. ! 46 SYIV I 6. ! 67 PILO OFFI I 6. I 78 CARE ROST 1 6. ! 44 VERO SERP ! 6. I 71 fCLA PRAT 1 6. I 52 CIRS PALU ! 6. 1 10 AGRO CANI I 6. ! 83 GALI PALU 1 6. 1116 LEUC VULG 1 6. I 68 JUNI CChM 1 6. 1107 AGRO STa 1 4. 1119 OACT GLCM I 4. ! 75 LUZU PILO I 4. 1106 CARE AQUA I 4. I 64 GEIH R IVA 1 4. ! 127 LEDU PALU 1 4. I 15 FEST PRAT 1 4. I 38 LATH PRAT I 4. 1 63 LYSI VaG 1 4. ! 70 JUNC EFFU ! 4. ! 31 BAR8 VULG ! 4. 1132 CAM3 ROTU ! 4. ! 106 POA AMU ! 4. 1128 TRIC CESP ! 2. 1135 HrtJS ARVE I 2. 1129 ERYS OCI ! 2. ! 39 EPIL SP 12. 1126 POTE EREC 1 2. ! 37 VICI SEPI 1 2. 1134 GHAP SYIV 1 2. ! 99 CALA LAPP ! 2. I 72 PEUC PALU I 2. I 27 SPER ARVE 1 2. 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I • 3.5 1 30 10 40 10 . . 10 M in 1 " 1 1° • • 30 • • • 10 : : M 10 : : : : : : : 10 : 1 : : : 10 : : 36 : H • • • ■ • 10 20 10 .. 20 10 30 ... 40 ?■; • • • IS 60 .101010 10 .1 i'5 ... 20 20 10 10 .. 10 10 30 . I It'll ' ' ' ™ 10 . 30 .... 10 ..... 10 10 20 . 10 . ! H ' ' ™ 20 ' * 20 . . 10 . . . 40 . . 10 . 10 fn . . 30 . . 30 10 10 .... 10 i'2 30 20 .... 10 10 10 10 H 10 . . 40 . . 40 20 . . : 40 H 10 90 30 10 .. 10 ... I In in 10 .... 50 20 10 . I ! ?•? ..... 20 10 40 10 ... 10 . K • • • • 20 ... io .. 30 io ; ; i »•5 10 . 10 ... JO . 10 .... 10 } 3 ,A .A .A 10 10 ... 10 10 .20 . i :§ ::::::::::::: :'?!°o :4ö»46 2010 ■ ■ I : 56 :::::::26 : : : W ,6 X : : : : : 10 : : : : : , 6 : : i 20 ! : : l6 : :::::::::::: 40 10 ::: .a : ,ö4ö : : ,ö : : 20 : : :! : '• io : .o ::::::: io ::::::: : :« 10 : : : : : : 132C }• 10 20 10 .... 10 . . ! }•} 10 20 ... 10 10 ! H ,A 10 . . 10 . . . . 20 . 10 . ! ?*! 10 10 • • • • 10 10 ... I ! }•? ! 20 X 20 ... ! J J*5 J • 20 20 30 i I 1.3 1 ... 30 20 . 10 ... . ! I 1.3 I 10 40 : 10 I 1.3 I • • 40 . . 10 ' ' 10 I 1.1 I 10 10 . . 30 ! 0.9 1 : iö :: iö :::::: 20 :::::: ::::::: : I 0.9 1 20 10 10 1 0.7 1 io io io j o.7 j io io . io !!.!!!!!!' i: I 0.9 I 30 m I 0.7 I 20 * * * ' 10 i o.7 I . ... io ... 20 .... I !!!!!!! 10 I 0.7 1 'in on ' i o.41 ::::: Jo :::::::: : in 20 • I 0.4 l 10 10 . 1 0.4 1 . . 10 .10 i I 0.4 1 .... 10 in I \ll\ «6 ' !o!4 i go " ' 30 j 1 0.4 1 20 . . • : 1 0.4 1 20 I 0.4 I 20 I 0.4 1 20 I 0.4 1 20 i o.21 . iö : I 0.2 1 .... 10 . 1 0.2 1 10 I 0.2 1 .10 I 0.2 1 .... .10 ......... I 0.2 1 10 • o.21 iö : : : :::::::::::::::: i Commun. Inst. For. Fenn. 144 59 Appendix 2. Continued. Liite 2. Jatkoa. Species - Lajit F C Cömaged plots - Tuhoa la t Not danaged plots - Vertailualat . i . - - - . 2. . 5.. L. . Z.. 2. . L i}.«.i?.if. 1L}LiZ.if 19 20 21 22 23 24 25 26 27 28 29 30 3 1 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 fill FEST CVIN I ! 112 CARE BRUM I 1113 Ai.CH SP I 1114 CAU VULG I 1115 CAf-P PATU 1 ! 51 TUSS FARF J 1117 CIRS VULG I ! 33 POTE HD'\V ! I 79 PCÄ PAL'J I 1120 par LAPA I 1121 POLY SP I I 80 via RIVI I 1123 TAM VULG I I 94 SALTS ALPI I 1125 SCUT GALE I ! 45 VERO ARVE I ! 96 TRIC ALPI ! I 82 G#LE SP ! ! 17 ALNU INCA 1 1133 CARD CRIS ! I 18 IRTI DICE I 1100 CARE OCR I 1101 CRTH SECU ! !102 PARN PALU I 1103 SELA SELA 1 1136 PCÄ SP ! ! 137 TRIP INCD ! 1138 BOU PDO I 1139 PLAN MM) ! i o. 1 0. 1 0. 1 0. I 0. ! 0. I 0. i 0. 1 0. I 0. I 0. ! 0. ! 0. ! 0. I 0. I 0. 1 0. 1 0. ! 0. I 0. I 0. I 0. I 0. ! 0. 1 0. i 0. ! 0. ! 0. I 0. j Y . i J— I . 16 I I I i 60 K.-M. Korhonen Appendix 3. The basic data of the fertilization study plots used in the vole damage research. Liite 3. Turvemaiden lannoituskoealojen perustiedot. ') Phf = Fine-ground rock phosphate bienofosfaatti, Psf = Super phosphate superfosfaatti, Prf = Rock phosphate raakafosfaatti, Pkf = Potassium phosphate kaliummetafosfaatti (Sokli). 2) N = Oulu saltpeter Oulunsalpietari (27,5), P Rock phosphate raakafosfaatti (33), K = Potassium salt kalisuola (60), Micro = Mixture of micronutrients + borate hivenseos ■+ lannoiteboraatti. 3) PK Granular phosphorus-potassium fertilizer of peatland forests suometsien PK-lannos, rakeinen (0-20-20), Urea = Urea (46,3), Micro = Mixture of micronutrients hivenseos, Ash = Dry ash kuiva tuhka. >tu< ady area, >t numbers lization experiment Lannoituskoe ementary fertilization J atkolannoitus Draining Perusojitus fforestation Metsitys runnings, year Harvennus- musalue, numerot Year Plot size Vuosi Ruutukoko Fertilizers — Lannoitteet kg/ha Year Vuosi Fertilizers Lannoitteet kg/ha Year Vuosi Spacing Sarkaleveys Year Vuosi Method Tapa Alajärvensuo 8, 23,31 4, 20, 39 7,21,30 11, 27, 42 6, 25, 36 10, 19, 33 13, 22, 37 9, 15, 35 14, 17,38 12, 18, 29 1, 24, 41 5, 26, 34 3, 16, 32 2, 28, 40 1965 potassium salt kalisuola 65—195 urea 200 phosphorus fosfori 50-150 0.04 ha 1975" Phf Psf Prf Pkf K20 N 50 — — — — 100 100 — — — — 100 150 — — — — 100 — 50 — — 120 100 — 100 — — 120 100 — 150 — — 120 100 — — 50 — 120 100 — — 100 — 120 100 — — 150 — 120 100 — — — 50 120 100 — — — 100 120 100 — — — 150 120 100 — — 100 — 120 100 1936 70 m 1936 broad- cast sowing haja- kylvö 1975 , 4 !, 5 1,6 1970 0.2 ha PK/ PK/ PK/ April May June huhtik. toukok. kesäk. 500 — — — 500 — — 500 1933 45 m naturally regenerated metsittynyt luontaisesti 1970, 1974 Imari 1968 strips kaistat PK-fertilizer PK-lannos 0 1000 1956 5— 300 m 1973 2, 4,5 1,3,6 Suoloma-aapa 1,27 32, 46 6, 11, 28, 37 42 26 47 21, 34 7, 25, 41 2, 24, 33 1964 0.04 ha phosphorus fosfori 700 potassium kalium 200—370 19762 > N 357 357 357 357 P 357 357 357 357 357 K 178 178 178 micro- nutrients hiven 110 110 110 110 110 1939 40 m 1939 patch sowing ruutu- kylvö 1975, 1976 Verkkolahden- jänkä 27, 56, 74 19, 42, 88, 93 65 2, 24, 28, 67 7 1968 0.04 ha PK-fertilizer PK-lannos 400—500 19783 > PK 500 500 500 500 micro- dry nutrients ash urea hiven tuhka 250 — — — 100 — — — 10000 — — 10000 1968 30 m 1978 12, 66, 69, 100, 111 Commun. Inst. For. Fenn. 144 61 Appendix 4. Vegetation analysis of the vole damage areas (numbers I—lo,1 —10, 12—43, 54 —57) on drained peatlands and the comparison areas (numbers 11, 44 —53) on undrained peatlands. Plant species and study plots are organized according to the TWINSPAN analysis. The groups produced by TWINSPAN are separated with lines. Liite 4. Ojitettujen turvemaiden myyrätuhoalojen (1-10, 12-43, 54-57) ja ojittamattomien vertailualojen (11, 44-53) pintakasvillisuusanalyysi. Kasvilajit ja näytealat on järjestetty TWINSPAN-luokitteluanalyysin mukaan. TWINSPANilla muodostetut ryhmät on erotettu viivoin. 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