Natural regeneration and development of Scots pine seedlings in continuous cover forestry in northern Finland

Continuous cover forestry (CCF) is expected to enhance the overall production of ecosystem services compared to even-aged rotation forestry. CCF is relying on natural regeneration and the ingrowth of seedlings in small gap and selection cuttings. However, the factors affecting their success in CCF remain poorly understood, especially under the challenging climatic conditions and sparse stand structures typical in northern boreal forests. Here, we examined the natural regeneration and development of Scots pine (Pinus sylvestris L.) seedlings and the factors influencing them following selection cuttings across Northern Finland. The cuttings were done with varying intensity at 27 experimental sites between 1985 and 2007. The establishment and height growth of new Scots pine seedlings were inventoried in 2019. We used generalised linear mixed modelling to evaluate the establishment of new Scots pine seedlings in 50 m2 study plots, and log-normal linear mixed modelling to evaluate their post-cutting height growth, and the affecting factors affecting them. In a post-cutting field inventory, it was found in the study plots on average, 2144 new pine seedlings ha–1, about 20 % of the plots having no new seedlings. By comparison, the constructed models underestimated this number (on average, 1700 seedlings ha–1). An increase in basal area, tree stock volume and number of overstory trees reduced both the number of seedlings and their height. A thick humus layer reduced the number of seedlings. Denser moss and herb cover reduced the number of seedlings but increased their height. Also, the seedlings were shorter in the northern regions due to the harsher growing conditions.