Norway spruce susceptibility to bark beetles is associated with increased canopy surface temperature in a year prior disturbance

Abstract

Forest pest infestation is a major driver of tree mortality, altering ecosystem functioning, changing microclimates, and causing significant woodland loss globally. We examined environmental effects on Picea abies susceptibility to bark beetle Ips typographus before and during a multi-year severe outbreak in a protected, natural, Norway spruce-dominated mountain forest in Central Europe. In contrast to recent publications that focus on identifying spectral signatures related to the early (“green”) beetle attack stage, we investigated large-scale signals indicating the predisposition of stands to herbivore infestation in the year preceding the outbreak, using remotely sensed (RS) climate and ecological data. Through partial least square regression, we analyzed interactions between microclimate variables related to susceptible, infested, and healthy spruce stands. Using RS classification maps, we reconstructed the annual forest area changes from 1985 to2020 and linked it to previous climate events.Our findings indicate that the surface temperature in stands subsequently attacked was higher compared to intact stands in the year prior colonization. Over the research period, the forest’s original cover decreased by 50%, with an average annual change of 1.5%. The recorded episodes of above-average tree mortality were linked to extended summer warming and short-term winter temperature declines, accompanied by windstorms. We argue that the use of remotely sensed temperature data can aid in predicting landscape scale spruce susceptibility to bark beetle outbreak one year before the actual attack occurs. This prediction could substantially improve management of forest disturbance, by providing more time to implement preventive or protective measures.