Drought and stand susceptibility to attacks by the European spruce bark beetle: A remote sensing approach

Several time-series analyses have demonstrated that after extreme summer droughtbark beetle damage increased. However, studies predicting stand susceptibility overlarge spatial extents are limited by technical constraints in obtaining detailed,spatially-explicit data on infestation spot occurrence.2. Using a unique dataset of georeferenced bark beetle infestation data, we testedwhether the spatial variation of local growing conditions of forest stands, topogra-phy, and landscape variables modified the local occurrence ofIps typographusinfes-tations after a severe hot drought in Central Europe.3. Bark beetle infestation occurrence depended on soil-related aridity intensity, eleva-tion, slope, and soil conditions. We showed that elevation interacted with growingconditions and topography. At low elevations, spruce forests growing on flat areasand wetter soils were more sensitive to the infestations. On the contrary, forestson steep slopes and soils with low water availability were rarely attacked. At thelandscape scale, bark beetle damage increased with host tree cover but decreasedwith compositional diversity.4. Our findings are generally consistent with the growth-differentiation balancehypothesis that predicts that trees growing under chronic dry conditions tend to bemore resistant against biotic disturbances.5. Spruce stands at low elevations located in homogeneous landscapes dominated byspruce were those more exposed to bark beetles in the initial phase of a drought-induced outbreak