Natural regeneration and early development of Scots pine seedlings after gap cutting in northern Finland

ABSTRACT

In the northern boreal region, tree growth, timber yields and economic returns are low, meaning low regeneration costs are the basis of profitable forestry. If natural regeneration is successful, it may be favoured over expensive planting or seeding. We studied the regeneration success and early growth of Scots pine in gaps in terms of seedling density and height 10 years after gap cuttings in central Finnish Lapland. Three gap sizes (diameters of 20, 40, and 80 m) were studied on patch scarified xeric and sub-xeric sites in six random blocks and a total of 18 replicates of each. The number of pine seedlings was high across the gap sizes. The proportion of empty regeneration plots (size 5 m²) was ∼ 2%. Site preparation substantially increased the number of seedlings. The growth of seedlings was faster in larger gaps, but a high proportion of exposed mineral soil decreased it. The results suggest that all studied gap sizes regenerated naturally well, and that soil scarification exposing 10–20% of the surface area or even less can be enough to achieve regeneration goals. Gaps of a diameter of 40 m or more are required to achieve an optimal balance between seedling density and growth.

KEYWORDS:

• Gaps
• site preparation
• Pinus sylvestris
• uneven-aged management
• continuous cover forestry

Acknowledgements

We would like to thank Metsähallitus for its kind contribution at all stages of the experiment. Pekka Välikangas, Pasi Aatsinki, Raimo Pikkupeura, Tarmo Aalto, Pekka Närhi, Eero Siivola, Aarno Niva, Jouni Väisänen, and Jukka Lahti among others carried out the field measurements, deserving our sincerest gratitude for their excellent work. Vesa Nivala conducted the random sampling of the points in the spatial grid. Finally, we would like to especially acknowledge Pasi Aatsinki, who processed the data proficiently for statistical analysis. Author contributions: The experiment was designed by Ville Hallikainen, who supervised its establishment and all the measurements, and performed the computations in consultation with the other authors. Janne Miettinen wrote the first draft, and all the authors edited the manuscript drafts.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was conducted at the Finnish Forest Research Institute (Metla) (later Natural Resources Institute Finland (Luke)) with funding from the Ministry of Agriculture and Forestry. This study was carried out as part of the Forward (Forest renewal by natural methods) and Transform (Tools for natural regeneration in sustainable forest management) projects funded by Natural Resources Institute Finland (Luke) and as part of the NorFor (Solving problems in forest regeneration in northern Fennoscandia) project funded by the Finnish Forest Research Institute (Metla), the Swedish University of Agricultural Sciences (SLU), Metsähallitus, and Sveaskog and as part of the ArcticHubs Horizon 2020 project (Grant Agreement No. 869580) and REBOUND -project (funded by Strategic Research Council within the Research Council of Finland, decisions No 358482 + 358497).