RESEARCH ART ICLE
Climate change mitigation potential of restoration of
boreal peatlands drained for forestry can be adjusted by
site selection and restoration measures
Anna M. Laine1,2,3 , Paavo Ojanen4,5, Tomi Lindroos6, Kati Koponen6, Liisa Maanavilja7,
Maija Lampela7, Jukka Turunen7, Kari Minkkinen4, Anne Tolvanen8
Peatland restoration is seen as a key nature-based solution to tackle climate change and biodiversity loss. In Europe, nearly
50% of peatlands have been drained during the last decades, which have shifted their soils to carbon dioxide (CO2) sources.
Soils of forestry-drained peatlands are known to vary from CO2 sources to small sinks depending on their fertility and wetness.
When peatlands are restored, it can be expected that rates of CO2 and methane exchange will vary depending on site fertility
and wetness. We generated seven restoration pathways with different starting and end points and assessed the climate impacts
of them. The GHG emission coefficients were compiled from literature, and radiative forcing was calculated for a 500-year time
period since restoration. All seven restoration pathways improved carbon sink capacity; however, the climate impact differed
from cooling to warming. The highest cooling impact occurred in a pathway leading from nutrient-rich drained peatlands
toward tree-covered spruce or pine mires. Warming impacts occurred in a pathway leading from nutrient-poor drained peat-
lands toward open peatlands. The results of this study can be used to help identify peatland sites and restoration targets to max-
imize climate change mitigation from restoration. In practice, however, restoration has to fulfill other targets, such as
biodiversity safeguarding, improvement of hydrological conditions, and socio-economic aspects. Fulfilling all targets simulta-
neously requires compromises on all targets.
Key words: carbon storage, climate change mitigation, forestry drainage, GHG emission, peatland, rewetting
Implications for Practice
• As carbon dioxide and methane emissions in forestry-
drained and restored peatlands vary based on site condi-
tions (fertility, water table level, and vegetation type),
the selection of restoration sites and measures influences
the climate mitigation potential of restoration.
• Climate change mitigation potential is at its greatest when
nutrient-rich forestry-drained peatlands are restored
toward tree-covered spruce or pine mires where the water
level is below the peat surface.
• Climate change mitigation potential is smallest when
nutrient-poor drained peatlands are restored toward open
peatlands where water level is near the peat surface.
• The results of this study can be used to identify potential
peatland restoration sites to maximize their climate
change mitigation.
Introduction
Peatlands store around 30%, or 644 Gt of the planet’s terrestri-
ally available carbon (Yu et al. 2010). As the carbon storage
capacity is strongly dependent on land use, particularly drainage
state, the role of peatland management in climate change mitiga-
tion is important (UN Environment 2019; UN Decade on
Ecosystem Restoration 2020–2030; Convention on Biological
Diversity 2021; Lehtonen et al. 2021). Globally, 12% and in
Europe, nearly 50% of peatlands have been drained and
degraded (UNEP 2022). Rewetting of peatlands is seen as a
potential means to mitigate climate change, as it efficiently
Author contributions: AML conceived the ideas and designed study; AML, PO, KM
contributed to data acquisition; AML, TL, KK analyzed the data; AML led the writing
of the manuscript; all authors, including LM, ML, JT and AT, contributed critically to
the drafts and gave final approval for publication.
1Environmental Solutions, Geological Survey of Finland, Viestikatu 7A, POBox 1237,
Kuopio FI-70211, Finland
2School of Forest Sciences, University of Eastern Finland, PO Box 111, FI-, 80101,
Joensuu, Finland
3Address correspondence to A. M. Laine, email anna.laine-petajakangas@uef.fi
4Department of Forest Sciences, University of Helsinki, PO Box 27, 00014, Helsinki,
Finland
5Natural Resources Unit, Natural Resources Institute Finland (Luke),
Latokartanonkaari 9, Helsinki 00790, Finland
6Carbon Neutral Solutions, VTT Technical Research Centre of Finland, PO Box 1000,
Espoo FI-02044 VTT, Finland
7Environmental Solutions, Geological Survey of Finland, Vuorimiehentie 5, PO Box
96, Espoo FI-02151, Finland
8Service Groups, Natural Resources Institute Finland (Luke), Oulu, Finland
© 2024 The Author(s). Restoration Ecology published by Wiley Periodicals LLC on
behalf of Society for Ecological Restoration.
This is an open access article under the terms of the Creative Commons Attribution
License, which permits use, distribution and reproduction in any medium, provided the
original work is properly cited.
doi: 10.1111/rec.14213
Supporting information at:
http://onlinelibrary.wiley.com/doi/10.1111/rec.14213/suppinfo
September 2024 Restoration Ecology Vol. 32, No. 7, e14213 1 of 13
slows down peat decomposition (Leifeld & Menichetti 2018;
Humpenöder et al. 2020). Yet, the restoration techniques
(Zak & McInnes 2022) and the initial state of the drained site
(Ojanen & Minkkinen 2020) may strongly impact the rate of
mitigation. For example, in boreal forestry-drained peatlands,
carbon dioxide (CO2) and nitrous oxide (N2O) emissions are rel-
atively low when compared to agriculturally used peatlands or
peatlands located in warmer climate, and typically the drained
peatlands emit low amounts of methane (CH4), except from
ditches that typically cover a small proportion of the land
(Ojanen & Minkkinen 2020; Rissanen et al. 2023).
In Finland, the main objective of restoration of forestry-
drained peatlands has been to restore the structure and function
of the peatland ecosystem by improving the quality of species’
habitats and biotopes, fulfilling the goals of ecological restora-
tion (Aapala & Similä 2014). In practice, this means filling in
or blocking the ditches and managing tree cover so that it resem-
bles the native reference system. Restoration experiments in
boreal forestry-drained peatlands show promising results
in recovering vegetation. In most cases, the peat-forming vege-
tation, namely Sphagnum mosses, dwarf shrubs, and sedges,
recovers within 5–10 years because many of these generalist
species remain in drained peatlands in small quantities even
decades after drainage (e.g. Laine et al. 2011; Hedberg
et al. 2012; Haapalehto et al. 2017). The reestablishment of the
more demanding species of inundated or forested habitats or
specific nutrient conditions (rich fen species) has been more dif-
ficult (Mälson et al. 2010; Hedberg et al. 2012; Maanavilja
et al. 2014).
The studies in which greenhouse gases have been measured
from restored boreal forestry-drained peatlands show that CO2
and CH4 exchange returns to a similar range as in undrained
peatlands (e.g. Urbanov
a et al. 2013; Laine et al. 2019; Purre
et al. 2019). However, the rate of green house gas (GHG) emis-
sions and restoration mitigation potential varies between drained
peatland types (Ojanen & Minkkinen 2020). Some of the boreal
nutrient-poor forestry-drained peatlands have quite low soil CO2
and N2O emissions (Ojanen et al. 2013; Minkkinen et al. 2020;
Alm et al. 2023), while the growing trees are binding CO2 more
efficiently than the low-stature vegetation of pristine peatlands if
the harvest of trees is not considered. In addition, due to the low
water table level, the CH4 emissions are small except for the
ditches (Ojanen et al. 2010; Rissanen et al. 2023). As long as
the tree stand is alive and not harvested, the climate impact of
forestry drainage in such habitats is mostly cooling (Ojanen
et al. 2013). Restoring such a site likely increases CH4 emissions
and removes the carbon sink formed by the trees (Wilson
et al. 2016; Ojanen & Minkkinen 2020), limiting the climate
impact of the restoration of nutrient-poor drained peatlands.
Nutrient-rich sites, on the other hand, have considerable soil
CO2 and N2O emissions (Minkkinen et al. 2020; Alm
et al. 2023) and thus have more potential for climate change mit-
igation by restoration (Ojanen & Minkkinen 2020).
As is the case with boreal forestry drained peatlands, the
CO2 and CH4 gas exchange of restored peatlands also varies.
It may be expected that the variability is similar as between
undrained peatland types. Generally, in an average year,
undrained peatlands take up and store CO2 from the atmo-
sphere (e.g. Lund et al. 2010). There are some differences in
the long-term C accumulation between peatland types with
nutrient-poor types offering more stable accumulation
(Turunen et al. 2002). The CH4 emissions tend to vary more
between peatland types so that increasing wetness, nutrient
availability, and in case of the boreal peatlands, the amount
of aerenchymous plants all cause higher emissions (Turetsky
et al. 2014; Zhang et al. 2021). More simply, the open wet
sedge-dominated fens tend to have much higher CH4 emis-
sions than the drier Sphagnum and shrub-dominated bogs and
the drier pine and spruce mires (Turetsky et al. 2014; Zhang
et al. 2021; Table S2).
In addition to the above-mentioned differences in GHG
exchange between boreal peatland types, the radiative effects
and the atmospheric lifetimes of CO2, CH4, and N2O differ, all
together affecting the climate impact of different peatland types
over time. Due to the lifetime differences between the gas spe-
cies, the time frame chosen for inspecting the climate change
mitigation potential of restoration is crucial. The shorter the time
frame, the greater the impact the increased CH4 emissions have
compared to reduced CO2 emissions. Therefore, if the aim of
restoration is climate change mitigation, the type of peatlands
to be restored (starting point for restoration) and the end point
of restoration, that is, whether restoration aims at wet open peat-
land habitat or drier habitat that remains covered by trees after
restoration, affect the effectiveness of the restoration. The larg-
est climate benefits may be achieved by restoring those drained
habitats that produce the highest emissions in their drained state,
or alternatively, by steering restoration toward habitats that pro-
duce lower CH4 emissions. So to say, the key to maximize the
climate benefits of peatland restoration is to maximize the differ-
ence in climate effects between the status quo trajectory and the
restoration trajectory. Previously, the climate mitigation poten-
tial has been evaluated based on a rather coarse division of peat-
lands into nutrient-rich and poor types, without a focus on the
restoration end point (Wilson et al. 2016; Ojanen &
Minkkinen 2020).
The aim of this study was to evaluate the climate change mit-
igation potential of the restoration of boreal forestry-drained
peatlands. We asked how much we could manage the climate
impact of restoration by selecting nutrient-rich or nutrient-poor
peatland sites to be restored and by choosing different restora-
tion end points (open and tree-covered). All restoration end
points considered here are natural peatland habitats in Finland,
namely fens, bogs, pine mires, and spruce mires. These native
references are analogous to Gann et al. (2019), yet they may
not fully represent the historical reference, that is, the peatland
type existing before drainage. We generated seven restoration
pathways and assessed the climate impacts of each. The study
was limited to boreal Finland, where more than half of the orig-
inal 10 Mha of peatlands have been drained for forestry
(Turunen & Valpola 2020). In addition to biodiversity losses,
peatland drainage has impacted water quality, caused peat deg-
radation, and CO2 emissions. It is estimated that drainage has
decreased the carbon storage of Finnish peatlands by 0.17–
0.51 Gt C (Turunen & Valpola 2020).
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We compiled published estimates for soil CO2, CH4, and N2O
emission coefficients for forestry-drained and undrained boreal
peatland types from Finland and nearby boreal areas. As the
available data from restored peatlands does not yet allow for
metanalysis but indicates that gas exchange is similar to
undrained peatlands (e.g. Wilson et al. 2016), we use the
undrained peatland data for restored peatlands. To incorporate
the radiative effects and atmospheric lifetimes of the three green-
house gases, we used the REFUGE 4 tool (Lindroos 2023) to
calculate the radiative forcing for a 500-year time period since
restoration. REFUGE model results show the time dynamics
that different restoration pathways (nutrient-rich or nutrient-
poor peatlands, restoration toward treeless or tree-covered state)
have on the global radiative forcing. We discuss the climate
impact results relative to habitat biodiversity value.
Methods
Restoration of Peatlands in Finland
Nearly all peatland restoration in Finland has been carried out on
forestry-drained peatlands in nature conservation areas. The
main objective has been to restore the structure and function of
the native peatland ecosystem by improving the quality of spe-
cies’ habitats and biotopes, fulfilling the goals of ecological res-
toration (Aapala & Similä 2014). The first peatland restoration
experiments were performed in the 1970s and 1980s to protect
exceptionally valuable species and habitats, while the launch
of EU Life funding in the 1990s marked the beginning of
large-scale restoration using heavy machinery and accompanied
by monitoring and scientific research (Fig. 1; Aapala &
Similä 2014). Currently, the restored peatland area exceeds
55,000 ha (Fig. 1, Metsähallitus 2023, personal communication)
with a growing share also in private lands.
Peatland Site Types and Restoration Pathways
To estimate the impact of restoration on GHG exchange, the
first step is to pair the restoration starting points, that is, the
forestry-drained peatland site types, with the potential native
restoration end points, that is, the type of peatland that the
restoration practices aim for. Here, we use peatland site type
classification for the pairing. In the case of forestry-drained
peatlands, this is a prominent tool, as the drained sites often
still carry some characteristics and plant species from the
time before drainage. The Finnish peatland site type classifi-
cation is based on vegetation communities and habitat wet-
ness, and the forestry-drained types have been paired with
undrained natural peatland types with similar nutrient status
(Laine et al. 2018). In this study, we expect that with restora-
tion, it is possible to create habitats similar to undrained nat-
ural peatland site types (Table S1) and use them as potential
restoration objectives (Laine et al. 2018).
While in Finnish tradition, the forestry-drained peatlands are
divided into 5–10 categories based on the nutrient and moisture
status (Laine et al. 2018), in this paper, we follow Wilson et al.
(2016) by using two categories: nutrient poor and nutrient rich.
The literature estimates on soil GHG emissions support this
division to be efficient, while there is currently not enough
knowledge to support further division (Ojanen et al. 2010; Oja-
nen & Minkkinen 2019; Minkkinen et al. 2020).
Figure 1. Annual peatland restoration area (ha) in Finland carried out by Metsähallitus, the managing body of the state-owned lands responsible for most of the
peatland restoration executed in Finland.
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The restoration outcomes are defined based on native
undrained peatland site types (Laine et al. 2018) that are pooled
into five categories (tree-covered spruce mires, tree-covered
pine mires, open eutrophic or mesotrophic fens, open oligotro-
phic fens, and open ombrotrophic bogs) based on nutrient status
and wetness. The division is based on nutrient status and
wetness-driven differences in CH4 emissions. The defined resto-
ration pathways are shown in Figure 2.
In the pairing of drained peatland habitats and native refer-
ences, the emphasis is on the similar nutrient status of the site,
while wetness can be modified by the restoration practices. As
the two drained and five undrained categories include several
gradually displacing site types, more than one potential
restoration pathway is possible (Fig. 2). As an example, in the
nutrient-rich drained category of habitats, tree species range
from broadleaved trees to Norwegian spruce and Scots pine,
while the nutrient status ranges from eutrophic to the high
end of oligotrophic. The nutrient-poor drained peatlands
quite solely grow Scots pine and are weakly oligotrophic to
ombrotrophic.
Soil GHG Emission Estimates for Different Peatland Types
To evaluate the climate impacts of different restoration path-
ways (Fig. 2), GHG emission estimates (g gas m
2 a
1) for
each peatland category, namely the two forestry-drained and
five restoration outcomes (Fig. 2) were derived from the litera-
ture as follows.
For the two nutrient status classes of forestry-drained peat-
lands, we obtained soil CO2, CH4, and N2O emission rates from
Finnish studies targeting the different forestry-drained peatland
site types. N2O emissions are from Minkkinen et al. (2020).
CH4 soil emissions are from Ojanen et al. (2010), but emissions
from ditches (2.5% of the area) come from Rissanen et al.
(2023). Soil CO2 emissions are derived from Ojanen and Min-
kkinen (2019). CO2 emission estimates are complemented by
adding the amount of C that has arrived as deposition and not
through plant photosynthesis (2.5 g C m
2 a
1) (Lindroos
et al. 2007), while for C leaving the peatland as dissolved
organic carbon (DOC) emission (10.5 g C m
2 a
1)
(Sallantaus 1994) 90% is expected to be emitted into atmo-
sphere as CO2 (Evans et al. 2014; Hiraishi et al. 2014), while
10% is stored in other ecosystems.
For the GHG emission estimates of restoration outcomes,
we made the assumption that the gas fluxes at restored sites
will be similar to those at undrained peatlands and that the
effect of rewetting on the emissions of CO2, CH4, and N2O
will be immediate and constant for 500 years. These assump-
tions were made because only a few short-term studies on gas
fluxes from restored forestry-drained peatlands are available
(Komulainen et al. 1998, 1999; Juottonen et al. 2012;
Urbanov
a et al. 2013; Koskinen et al. 2016; Laine
et al. 2019; Purre et al. 2019). In addition, Wilson et al.
(2016) showed that the average rates after rewetting are close
to those of undrained peatlands.
To derive CO2 estimates for the five different undrained peat-
land classes (Table S1; Fig. 2), we used long-term average C
accumulation rates measured from Finnish peatlands (Turunen
et al. 2002). This study by Turunen et al. (2002) is the only
one spanning all major peatland types and with replicated sites.
In addition, using the long-term accumulation rates decreases
the impact of varying weather conditions for CO2 exchange.
The long-term C accumulation was converted into CO2 follow-
ing Equation (1).
CO2exchange¼
Caccumulation þ 0:1 DOCemissionð
þ CH4 C emission 
 C
depositionÞ  3,664 gCO2=gC½ 
ð1Þ
For C that has arrived as deposition and not through plant
photosynthesis, we used a value 0.5 g C m
2 a
1 (Lindroos
et al. 2007). Of the DOC-emission (9.5 g C m
2 a
1; Sallan-
taus 1994) 90% is expected to be emitted to the atmosphere as
CO2 (Evans et al. 2014, Hiraishi et al. 2014), while 10% is stored
in other ecosystems. The part of accumulated carbon that is
emitted as CH4 is specific for each peatland type (see below).
For CH4 emission estimates, we carried out a literature survey
looking for all published values from Finland and the nearby
boreal region (Table S2). We searched for studies from which,
in addition to seasonal or annual CH4 emission it was possible
to conclude the peatland site type. In the case of seasonal values
(usually given for the period May to September), we estimated
the winter emission to be 15% of the seasonal emission, similar
to Saarnio et al. (2007).
Climate Impact Calculations
The climate impact of restoration for each restoration pathway
(Fig. 1) was calculated (1) as the change (from drained to
restored state emissions) in carbon balance in the atmosphere
(including change in CO2 and CH4 fluxes, measured as C),
(2) as the change in total emissions (CO2 equivalent emissions
including the change in CO2, CH4, and N2O in 100- and
500-year time frame), and (3) by using the REFUGE 4 tool to
estimate the additional radiative forcing for a 500-year time
period since restoration.
REFUGE 4 tool calculates time-dynamic impacts of user-
given emission scenarios. It follows the Intergovernmental
Panel on Climate Change (IPCC)1 AR6 methodology, covers
CO2, CH4, and N2O, and can handle both positive and nega-
tive emissions of these gases. The tool was developed in
1993 by Korhonen et al. (1993) and updated in 2000s
(Monni et al. 2003) and 2010s (Pingoud et al. 2012). The
fourth version, REFUGE 4, has been published as an open
access tool, including documentation and validation
(Lindroos 2023).
REFUGE 4 calculates the change in the atmospheric concen-
tration of gases. Peatland restoration creates an impact on atmo-
spheric carbon balance and consequently changes the carbon
fluxes to land and ocean sinks. REFUGE calculates these behav-
iors and illustrates them in result figures. REFUGE 4 results show
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Figure 2. Potential restoration pathways. Restoration is targeted for forestry-drained peatlands that are divided into two classes based on their nutrient
status. Peatland vegetation is dependent on ecohydrology, namely quantity and quality of water; therefore, with restoration practices (by affecting the
amount and quality of water directed to the restoration site), it is possible to guide their development toward forested or open peatland habitats and in
some cases, even impact the nutrient availability. In addition, the habitats within the two drainage groups vary, and some habitats at the poorer end of
the nutrient-rich group (those that before drainage were wet open peatlands) grow pine and have nutrient imbalances due to which it may be more
feasible to direct their development toward pine mire or oligotrophic fen. For these reasons several restoration outcomes are suggested for nutrient rich
and poor sites. Drained peatland site types of photos in the upper row from left to right: Vaccinium myrtillus type, V. vitis-idaea type, and Cladonia
type; natural peatland sites types in the lower row from left to right: Spruce mire, Tall sedge fen, Dwarf shrub pine bog, and Sphagnum fuscum pine
bog. Photos by J. Laine.
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time dynamics arising both from the warming effect of different
gases and possible variations by years in emission scenarios.
Absolute Global Forcing Potential (AGFP) results describe
the warming effect of the emission scenarios. The AGFP results
are in watts per square meter for the surface of Earth and are typ-
ically studied as annual values and time-integrated values.
Time-integrated results are very similar to global warming
potential (GWP)-methodology which studies time-integrated
AGFP of pulse emissions and compares them to the impact of
CO2 pulse. As the unit of AGFP (W m
2) is quite unintuitive,
REFUGE aims to concretize this by converting time-integrated
AGFP into more regularly used units, MtCO2-eq. The conver-
sion is done by comparing results to a constant annual 1 Mt
CO2 emission scenario. A more detailed description of the
AGFP and conversion to constant annual CO2 emissions are in
the REFUGE documentation (Lindroos 2023).
Here, we calculate estimates for politically important emis-
sion reduction target years 2035 and 2050 (16- and 31-year
horizons). Finland aims to be carbon neutral by 2035 (Finnish
Climate Act 423/2022), and the EU has a carbon neutrality tar-
get for 2050 (European Climate Law 2021/1119). In addition,
we calculate results with 100- and 500-year time horizons,
where 100/500-year time-integrated results can be compared to
GWP 100/500 results (Table 1).
Results
Carbon and Greenhouse Gas Balance
Restored peatlands are larger CO2 sinks and have quite variable
CH4 emissions and negligible N2O emissions. The CH4 emis-
sions depend on wetness and vegetation type, being highest at
the wet sedge fens (open oligotrophic). Restoration improves
the atmosphere’s C balance (i.e. makes it more negative by
increasing the soil C sink) in most restoration pathways
(Table 1). Yet, due to the high CO2 emissions of forestry-
drained nutrient-rich class, their restoration has a stronger
Figure 3. Impact on the atmosphere’s C content (g C/restored m2) of the seven restoration pathways (NP, nutrient poor; NR, nutrient rich).
Figure 4. Constant annual CO2-eq emission  SE of different restoration pathways starting from nutrient rich forestry-drained peat soils (NR) or nutrient poor
forestry-drained peat soils (NP). The tree stand CO2 sink is not included in the calculations. Constant annual CO2-eq emission is calculated from reference
emission scenarios that have constant annual CO2 emissions of x tCO2/year and the samewarming effect with a given time horizon. It is a time-dynamic version of
static CO2-eq emissions calculated with, e.g. GWP100 factors.
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impact on C balance compared to the restoration of nutrient-
poor peatlands.
Impacts on the atmosphere’s carbon balance are smaller when
taking into account changes in the carbon land and ocean sinks
and impacts on processes in the atmosphere (Fig. 3). After
100 years, the amount of C in the atmosphere is approximately
45% lower when calculated with REFUGE (Fig. 3) compared
to simplified calculations (Table 1) due to land and ocean sinks
absorbing carbon from the atmosphere.
CO2-Equivalent Emissions
When summing emissions with GWP100 factors, most restora-
tion pathways increase the total GHG emissions; however, the
uncertainty of the estimates is large due to relatively large uncer-
tainties in all components of GHG emissions (Table 1). With
GWP100 factors, high CH4 emissions from restored peatlands
have a much larger impact on total CO2-equivalent emissions
than the reduced CO2 emissions. The restoration pathways that
improved the emission balance calculated at the 100-year time
frame were nutrient-rich drained peatlands restored toward
tree-covered peatland types, that is, spruce mires and pine mires.
For nutrient-poor drained peatlands, restoration pathway aiming
at pine mire slightly increases emissions when summed with
GWP100 factors (Table 1). When considering a longer time
frame of 500 years, only the restoration pathway from
nutrient-poor drained peatland to open oligotrophic fen leads
to increased CO2-equivalent emissions.
The more detailed calculations of emission dynamics by
REFUGE show that the warming impact of nutrient-rich
forestry-drained peatlands restored toward spruce mires would
correspond to the warming impact of an emission scenario that
has constant annual emission reduction of 250 g CO2-eq for
each square meter of restored land in the 16-year horizon and
330 g CO2-eq m

2 a
1 reduction in the 100-year horizon; how-
ever, the uncertainties of the estimates are high (Fig. 4). All res-
toration pathways have a cooling impact when the time horizon
increases due to the longer lifetime of CO2 in the atmosphere
than CH4. However, restoration pathways that increase the
amount of CH4 emissions have a significantly higher warming
effect with shorter time horizons (Table 1).
Radiative Forcing
Results from the REFUGE tool show the time dynamics that dif-
ferent restoration pathways have on the global radiative forcing
(measured as AGFP). Positive impact means that the measure
warms the planet, while negative values indicate cooling.
All four restoration pathways for nutrient-rich forestry-
drained peatlands are more beneficial in long term than in the
near term (Fig. 5). Spruce mire pathway has the lowest emis-
sions and reduces the global radiative forcing from the begin-
ning of the inspected time horizon. Open oligotrophic
restoration pathway shows increasing annual radiative forcing
up to 2080, and the cumulative impact on global warming is pos-
itive despite the small reduction toward the end of the 500-year
horizon.
Figure 5. Time-integrated additional Absolute Global Forcing Potential (AGFP) caused by restoring forestry-drained peatlands to different types of peatland
habitats (restoration outcomes) starting from nutrient rich (NR) forestry-drained peatland types and nutrient poor (NP) forestry-drained peatland types. m2 refers
to global m2, not m2 in the peatland. The impact is calculated for 1 m2 of restored area. The tree stand CO2 sink is not included in the calculations.
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Restoration pathways of nutrient-poor forestry-drained peat-
lands have a significantly longer period of increasing AGFP than
those for nutrient-rich peatlands (Fig. 5). The cumulative impact
of all studied restoration pathways for nutrient-poor peatlands
showed a warming impact over the studied 500-year horizon.
The order of the restoration pathways was the same as in the case
of nutrient-rich soils: the drier pine mire pathway had the lowest
warming impact, while the open oligotrophic pathway led to the
highest warming. Based on the radiative forcing dynamics, we
formed three climate response groups: (1) from nutrient rich
toward spruce and pine mires; (2) from nutrient rich toward open
peatlands and from nutrient poor toward pine mire; and (3) from
nutrient poor toward open oligotrophic or ombrotrophic
peatlands.
The different GHG’s, CO2, CH4, and N2O have different
impact on annual AGFP over time and depending on the restora-
tion pathway (Fig. 6). The additional impact of reduced CO2
emissions increases over time, while that of increased CH4 emis-
sions saturates after a first decades. The differences in AGFP
between restoration of nutrient-rich and nutrient-poor forestry-
drained peatlands is caused by the level of CO2 emissions miti-
gated by restoration. The differences between the restoration
outcomes, however, are caused by the rate of CH4 emissions ini-
tiated by restoration, being clearly higher at open peatland types
than at spruce or pine mires (Fig. 6).
Discussion
The results show that the climate impact of peatland restoration
depends on the restoration pathway, that is, the site characteris-
tics before restoration and the end point of restoration. Here, we
focused on impacts based on changes in soil and underground
vegetation GHG emissions and excluded the dynamic tree stand.
Our results highlight that restoration of forestry-drained peat-
lands is not just one or two incidents (as the nutrient poor and
nutrient rich categories in Wilson et al. 2016), but the choices
of which types of peatlands to restore and toward which status
in terms of tree cover and wetness are crucial if restoration is car-
ried out to support climate change mitigation.
All seven restoration pathways have the potential to improve
carbon storage and sink capacity, however, the climate impact of
the pathways differs. We defined three climate response groups
among the seven pathways. The first group, from nutrient rich
toward tree-covered spruce and pine mires shows fast climate
cooling impact soon after restoration. The second group, from
nutrient rich toward open peatlands and from nutrient poor
toward tree-covered pine mires, shows a warming impact after
restoration due to increased CH4 emissions. As time passes,
however, the additional AGFP first saturates, and finally the
impact turns to climate cooling. The third type, from nutrient
poor toward open oligotrophic or ombrotrophic peatlands,
shows increasing annual additional forcing after restoration that
saturates but remains high for decades. The difference in climate
impact between restoring nutrient-rich and poor drained peat-
lands is mostly down to the amount of CO2 emissions that resto-
ration mitigates, but when comparing the different restoration
outcomes within the two groups, the differences in climate
impact are caused by the rate of CH4 emissions initiated by
restoration.
When purely concentrating on climate benefits, the best res-
toration option would be to restore nutrient-rich drained peat-
lands (that have high soil CO2 emissions) toward tree-
covered spruce mires. Pristine spruce mires have low CH4
emissions (Nilsson et al. 2001; Huttunen et al. 2003;
Figure 6. Annual impact of different restoration pathways on the AGFP by different greenhouse gases (A) nutrient-rich forestry-drained peatlands, (B) nutrient-
poor forestry-drained peatlands. The overall impact of reduction pathways is calculated as an integral from 2020 to studied end point in Figure 5. m
2 refers to
global m
2, not m
2 in the peatland. The impact is calculated for 1 ha of restored area.
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Minkkinen et al. 2007), which makes the potential climate
cooling impact immediate. In Finland, such spruce mires are
among the most threatened peatland types, with high conserva-
tion value (Kontula & Raunio 2019), and therefore, this resto-
ration pathway would have high benefits for biodiversity. As a
downside, restoration of drained spruce-dominated peatlands
is challenging due to their complicated hydrology. Despite
intensive planning and skilled operations, failures may occur.
If restoration fails, there is a risk for very high CH4 emission
and water pollution (Koskinen et al. 2016, 2017). When resto-
ration is conducted outside conservation areas and on private
land, also socio-economic constraints need to be considered
(Andersen et al. 2017; Zak & McInnes 2022). Private land-
owners likely have little interest to restore such highly produc-
tive, drained peatlands. More so, even the forestry-drained
spruce sites are relatively rare compared to other peatland types
in Finland (Korhonen et al. 2021) and therefore if concentrated
on this pathway, the restoration area in any case would remain
quite modest.
Climate-wise the second-best option is to restore the
nutrient-rich pine-dominated drained peatlands toward tree-
covered pine mires, again a pathway leading to high CO2
emission mitigation and low CH4 emissions (Nykänen
et al. 1998; Minkkinen et al. 2007). In practice, this restora-
tion pathway demands minimal effort, as only partial tree
removal and ditch infilling are needed. Restoration of such
site would have long-term benefits for water quality
(Menberu et al. 2017). However, pine mires are among the
most typical peatland types in Finland, and therefore restor-
ing them do not offer great biodiversity wins in terms of rare
habitats or species (Kontula & Raunio 2019). While the area
of drained pine-dominated peatlands would offer large areas
for restoration, the landowners may be reluctant to restore
such sites as they typically support productive tree stands.
Climate-wise, fewer gains are received when restoring
nutrient-poor forestry-drained peatlands. Such sites are likely
the most available ones for restoration in Finland, as drainage
has led to approximately 0.8 milj. ha (Laiho et al. 2016) of
low-productive forest stands. As the value of these for land-
owner is low, they are likely more willing to offer such sites
for restoration. While large climate or biodiversity gains are
not achieved by restoration, it does have long-term benefits for
water quality (Menberu et al. 2017).
Climate-wise, the worst pathway is to restore the nutrient
poor drained sites toward wet, sedge-dominated peatlands. Pris-
tine sedge fens have higher CH4 emissions than other peatland
site types (Zhang et al. 2021), and the same can be expected
for restored habitats with similar characteristics. Such habitats,
however, have high biodiversity value in Finland and offer hab-
itat for most of the peatland obligate red list species (Hyvärinen
et al. 2019). In addition, restoration has benefits for water quality
(Menberu et al. 2017).
Our results give insight into the potential restoration path-
ways for climate change mitigation. In practice, restoration has
to fulfill many simultaneous objectives and support the provi-
sion of several ecosystem services (Table 2). The most widely
recognized ecosystem services provided by peatlands are cli-
mate regulation, biodiversity and habitat provision, and water
flow and quality regulation (Kimmel &Mander 2010). As drain-
age is the most significant factor in the decline in the provision
of these services, restoration is paramount to improve the status
of peatlands (e.g. Humpenöder et al. 2020). Nevertheless, socio-
economic aspects and public acceptance must also be taken into
account. It is not realistic to restore only certain types of peat-
lands with certain type of management practices. Although the
restoration of nutrient-rich forestry-drained peatlands would
have the greatest potential for climate change mitigation, these
peatlands also have high forestry potential. Thus, a variety of
needs have to be reconciled when planning the management
of peatlands (Table 2).
Limitations of the Study Approach
This study is based on published literature estimates of soil GHG
emission of drained peatland site types. The estimates are based
on data from several study sites, yet the gas exchange likely var-
ies from year to year according to weather conditions. We also
did not account for the tree growth C sink and storage that
decreases to some extent when forestry-drained peatlands are
restored. The dynamic and unstable C sink of trees is also
strongly affected by management practices. It may also be
argued that increasing albedo due to removal of trees may coun-
terbalance the decreasing tree C sink (Lohila et al. 2010); how-
ever, more studies on the subject are needed.
In addition, the GHG estimates for restored peatlands were
taken from literature-based values of pristine peatland types
Table 2. Impact of different restoration pathways starting from nutrient-rich (NR) or nutrient-poor (NP) forestry-drained peatlands on climate, biodiversity, and
water quality; risk level for restoration measures to fail; availability of land for restoration depends on willingness of landowner to restore forestry-drained land.
Green color indicates positive impact, low risk and high availability, red color is the opposite.
Restoration pathway
Climate change
mitigation potential Biodiversity
Water
quality
Risk level for failure in
restoration measures
Availability for
restoration
NR! spruce mire
NR! pine mire
NR! open mire
NP! pine mire
NP! open mire
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toward which they are expected to develop. After restoration,
the peatland vegetation undergoes succession and correspond-
ingly, the gas exchange likely changes over the years. Unfortu-
nately, there are no long-term studies on gas exchange at
restoration sites, and even long-term monitoring of vegetation
is limited to a few sites and years. Therefore, we are currently
unable to include successional changes in gas fluxes following
restoration in this study.
All GHG estimates for the forestry-drained and restored site
types have relatively high uncertainties, making the uncertainty
of the estimated climate impacts (i.e. CO2-eq emissions in dif-
ferent time frames) high. More uncertainty in the estimates is
caused by the ongoing climate change; gas exchange of both
drained and pristine/restored peatlands is likely to change.
Increasing CO2 emissions are projected for drained peatlands
due to higher temperatures (Alm et al. 2023). There is evidence
that global warming has already increased the peat decomposi-
tion rate, DOC and CO2 emissions in boreal-drained peatlands
(McCarter et al. 2021). It may be expected that with ongoing cli-
mate change, the decomposition will further increase in the
future. The response of pristine and restored peatland to
increasing temperature and drier conditions seems less
straight-forward. While decomposition will likely increase, in
some habitats net CO2 uptake may increase due to vegetation
change-derived increased productivity (Laine et al. 2019; Köster
et al. 2023). Therefore, projecting climate impacts to the unsure
future is complicated. One crucial impact of climate change is
the increased risk of forest fires (Davies et al. 2013; Wilkinson
et al. 2023). A fire in drained peat soil may release large amounts
of carbon stored in peat soil and trees, and it may expand to large
areas as peat fires are difficult to stop. Rewetting prevents/slows
down peat decomposition and prevents forest fires, as wet peat is
significantly less inflammable than dry peat (McCarter
et al. 2021).
Acknowledgments
The study was funded by Ministry of Agriculture and Forestry,
Finland (Catch the Carbon Programme, LandUseZero and Tur-
vahiili projects). AML acknowledge the funding by Academy of
Finland Flagship for ACCC (grant No. 337550).
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Supporting Information
The following information may be found in the online version of this article:
Table S1. Undrained peatland site types included in the five restoration outcome
classes.
Table S2. Data used for calculating methane emissions of restored (i.e. pristine) peat-
land site type groups.
Coordinating Editor: Norbertas Noreika Received: 2 February, 2024; First decision: 27 March, 2024; Revised: 3 June,
2024; Accepted: 3 June, 2024
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