Spatial interactions between storm damage and subsequent infestations by the European spruce bark beetle

Disturbances such as storm damage and bark beetle infestations are key factors for the development of forest ecosystems. Infestations of the European spruce bark beetle (Ips typographus), which is the most devastating biotic disturbance agent in forests of central Europe and Scandinavia, are often triggered by storm damage. However, our understanding of spatio-temporal bark beetle dynamics at fine scales is still limited. In order to assess future risks of I. typographus infestations, we analyzed spatial interactions of the infestation pattern in a 180 km2 study region in central Switzerland. We computed neighborhood characteristics of bark beetle dispersal and fitted Poisson models to the spatial point patterns of bark beetles and storm damages. Infestations of I. typographus were found to be clustered at short distances (<500 m). In contrast, the spatial distribution of storm damages followed an inhomogeneous Poisson distribution that was explained by environmental covariates. Increasing topographic exposure, south- and west-facing slopes as well as increasing proportions of Norway spruce enhanced the probability of storm damage and bark beetle infestations. Our study is a contribution towards quantifying important ecological drivers in a spatially explicit manner that helps assessing predisposing factors for future bark beetle infestations.