Site factors are more important than salvage logging for tree regeneration after wind disturbance in Central European forests

Wind disturbance is the main natural driver of forest dynamics in Central and Northern Europe, but little is known regarding the general patterns of tree regeneration following windthrow in this region. On the basis of 89 windthrow gaps, we quantified natural tree regeneration 10 and 20years after wind disturbance, and identified the factors influencing tree regeneration dynamics, with a special emphasis on the post-storm management practices "salvage logging" and "no intervention". The sample encompasses gaps of ≥3ha and total overstory mortality caused by wind disturbance. The gaps date back to the two catastrophic storm events Vivian in 1990 and Lothar in 1999. Gaps covered an ecologically diverse region extending over 20,000km² and ranging from 370 to 1780ma.s.l. on the Central Plateau and in the Alps of Switzerland (Central Europe). Regeneration status was assessed on six circular sample plots per windthrow gap in 2010/2011. We recorded soil pH, organic layer, post-windthrow treatment, elevation, aspect, slope, browsing damage, and presence of predominant vegetation cover. We compared regeneration density and composition in gaps with and without salvage logging and elucidated the most important environmental factors influencing tree regeneration after wind disturbance using generalized linear models (GLMs). Ten and twenty years after wind disturbance, late-successional tree species such as beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.) frequently dominated, independent of the post-storm treatment. Salvage logging did not negatively affect pre-storm regeneration and even positively influenced post-storm tree regeneration. GLMs revealed soil pH (+) and ground vegetation cover (-) to be the most important predictors of sapling density. The findings demonstrate that site factors have a stronger effect than post-storm treatment.