Drought initialised bark beetle outbreak in Central Europe: Meteorological factors and infestation dynamic

Abstract

Extreme events, such as extreme droughts and intense temperatures, have become more frequent and severe, contributing to increased mortality rates in Norway spruce (Picea abies) due to bark beetle attacks. In particular, the most devastating outbreak of the spruce bark beetle in Central Europe began after the extreme drought year of 2018. This drought event also corresponds to the peak of the outbreak of the Eurasian spruce bark beetle (Ips typographus L.) in the study area - the School Forest Enterprise in the area surrounding the town of Kostelec nad Černými Lesy (Czech Republic). The study covers the period from 2012 to 2022, when there was a significant tree cover loss of 845.4 ha (15% of the spruce dominated area) that was caused by bark beetle. The primary objectives of the study were to identify the key meteorological variables affecting annual tree cover loss, bark beetle damage spot initiation, and spreading. We used the Global Forest Change dataset and meteorological data from the nearest weather station. The predictor variables were modelled in two ways: Generalised Additive Models (GAMs) regression and ridge regression. The study found that different climatic variables influenced the initialisation and spreading of bark beetle infestations. The most important climatic factor for initialisation is the duration of solar radiation in April of the previous year. The average annual air temperature in the current year plays an important role in the spreading of bark beetle spots. The higher area of spot initialisation occurred in the initial beetle outbreak phase, while the area of spreading of bark beetle spots started to increase at the peak, and was higher in later phases. Regarding annual tree cover loss, the most important factors are the duration of solar radiation in June and September of the current year, as well as the average annual precipitation of the previous year.