Influence of selected habitat and stand factors on bark beetle Ips typographus (L.) outbreak in the Białowieża Forest

Abstract

The European spruce bark beetle (Ips typographus L.) is one of the most critical insect disturbance agents in Europe. In recent years, bark beetles have caused tremendous economic losses, and affected ecosystems over large spatial scales. In this study, we evaluated the influence of selected factors on the bark beetle outbreak in 2015, the year with the most severe drought to have been recorded in the last few decades. The main aim of this study was to develop a new approach of identifying and mapping individual trees infested by bark beetles, for more efficient bark beetle management. The study was conducted on an area occupying 62,000 ha, using airborne laser scanning, multispectral imagery data, and digital forest maps.First, an individual dead tree detection method, based on remote sensing data, was developed, which allowed the quantification of the bark beetle outbreak at an individual tree level, with accurate information on the number and location of killed spruces. Then, topography, habitat, and single tree-based variables were used to examine their influence on tree mortality. Finally, a spatial hot-spot analysis of the outbreak, throughout the 62,000 ha of the Polish part of the Białowieża Forest, was performed.For the first time, we mapped the status of the spruce bark beetle outbreak across the Białowieża Forest, using the method developed in this study. 283,166 dead Norway spruce trees were detected in the study area, supporting the fact that the current bark beetle outbreak is the largest in this area since 1945. The number of dead spruces surrounding any given dead tree was the single most important predictor in all models, with a relative contribution of 35–79% depending on the neighbourhood analysed (radius from 0 to 2000 m). Crown closure and stand age, as well as the share of dead spruce and dominant tree species were found to be the most important predictors of the development of bark beetle infestation. The method developed in this study was evaluated and proved to be suitable for the monitoring and management of the ongoing insect outbreak.