Early natural tree regeneration after wildfire in a Central European Scots pine forest: Forest management, fire severity and distance matters

Abstract

In the last years, several wildfires destroyed large areas in Central European forest stands and the risk for fires is predicted to increase in the future. However, little is known about post-fire succession including the effect of forest management for this region. We studied recolonization patterns of natural regeneration of the pioneer tree species Betula pendula Roth (silver birch), Pinus sylvestris L. (Scots pine), Populus tremula L. (European aspen) and Salix caprea L. (goat willow) on 200 plots in a large, 334 ha burned pine forest stand two years after a severe wildfire. Natural regeneration in general was high, reaching higher densities than artificial regeneration on most plots. The influence of fire severity, post-fire forest management (complete and partial salvage logging and soil disturbance like skidder traffic, ploughing and raking) and distance to the next potential seed source on the number of tree regeneration was tested with multiple linear regression. High fire severities decreased abundance of pine, aspen and willow. The regeneration of all four investigated tree species was influenced by forest management. High birch regeneration was predicted for completely salvage logged plots in combination with skidder traffic or early ploughing and plots without any forest management. Pine regeneration was predicted to be highest on completely salvage logged and sites without any salvage logging. Forest management which includes partial salvage logging showed mostly lower predicted regeneration of birch, pine and aspen as probably an effect of timing. Willow regeneration was promoted by forest management which includes late ploughing. Regeneration of birch and pine decreased with increasing distance to the next potential seed tree, while aspen and willow sapling densities were not affected by distance due to their excellent dispersal by wind. For birch and especially pine, close seed trees are crucial for sufficient natural regeneration. Recolonization of burned areas is a highly dynamic process dependent on several factors. However, natural regeneration provides a fast, cost-effective way of reforestation which can be facilitated by suitable silvicultural treatments. We recommend to keep survived trees as green islands on site to provide close seed sources. To avoid seedling disturbance, forest management activities should be complied according to life cycles of naturally established tree seedlings. We also suggest using the benefits of deciduous pioneer trees in forestry in order to establish more diverse, less fire-prone forests after wildfires in the long term.