Climate affects severity and altitudinal distribution of outbreaks in an eruptive bark beetle
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Temperature warming and the increased frequency of climatic anomalies are expected to trigger bark beetle outbreaks with potential severe consequences on forest ecosystems. We characterized the combined effects of climatic factors and density-dependent feedbacks on forest damage caused by Ips typographus (L.), one of the most destructive pests of European spruce forests, and tested whether climate modified the interannual variation in the altitudinal outbreak range of the species. We analyzed a 16-year time-series from the European Alps of timber loss in Picea abies Karsten forests due to I. typographus attacks and used a discrete population model and an information theoretic approach to compare multiple competing hypotheses. The occurrence of dry summers combined with warm temperatures appeared as the main abiotic triggers of severity of outbreaks. We also found an endogenous negative feedback with a 2-year lag suggesting a potential important role of natural enemies. Forest damage per hectare averaged 7-fold higher where spruce was planted in sites warmer than those within its historical climatic range. Dry summers, but not temperature, was related to upward shifts in the altitudinal outbreak range. Considering the potential increased susceptibility of spruce forests to insect outbreaks due to climate change, there is growing value in mitigating these effects through sustainable forest management, which includes avoiding the promotion of spruce outside its historical climatic range.
KeywordsBark Beetle Forest Damage Altitudinal Distribution Information Theoretic Approach Bark Beetle Outbreak
We thank Fabio Stergulc for its constructive comments on the manuscript, and the “Direzione Centrale delle Risorse Agricole, Naturali, Forestali e della Montagna − Regione Autonoma Friuli-Venezia Giulia” for providing raw data from the BAUSINVE project. The research was supported by the BACCARA (‘Biodiversity And Climate Change, A Risk Analysis’) project funded from the European Community’s Seventh Framework Programme (grant agreement n°226299). M.F. was partially funded by the Italian national project “2010—CPDA104007: Study of the response mechanisms to climatic change in model forest insects”. Additional support was provided by NRI/AFRI 2009-65104-05731.
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