The effects of fragmentation on the susceptibility of a boreal forest ecosystem to wind damage

The clear cuts and seedling stands can speed up winds and may trigger blowdown at the edges of neighbour stands. Therefore, the height contrast of the neighbour stands and fragmentation at landscape level could be used to indicate the susceptibility of windthrow. In this study, we studied how forest fragmentation affects the susceptibility of a boreal forest ecosystem to wind damage, both at patch and landscape level based on theoretical computations. For this purpose we generated, based on real stand inventory data of a Finnish forest ecosystem, different landscape configurations of Scots pine and Norway spruce forests using Monte Carlo simulation. Thereafter, we applied a mechanistic wind damage model to predict the wind speeds needed for wind damage at forest edges. The fragmentation metrics of Contrast-Weighted Edge Density with three different height dissimilarity calculation methods were used to analyze the fragmentation at the landscape level. At the patch (stand) level, susceptibility of downwind stand to wind damage could be expressed in terms of a quadratic function, based on the tree height of upwind neighbouring stand or the height ratio between the neighbouring stands. At the landscape level, the relative risk of wind damage correlated linearly with the fragmentation despite of fragmentation metrics used. Both in single species and mixed forests, the metrics using empirical regression function based on patch level results (DS3) seemed more applicable in general than those using the ratio of tree heights between neighbouring stands (DS1) or constrained height contrast (DS2).