Trends in Outbreaks of Defoliating Insects Highlight Growing Threats for Central European Forests, and Implications for Eastern Baltic Region

Ingars Siliņš,Olga Miezīte,Āris Jansons,Annija Kārkliņa

doi:10.3390/f12060799

Abstract

To identify general patterns in the effect of climate-driven changes in the outbreak frequency of forest defoliating species, we examined 60 years of records (1950–2010) of outbreaks of five defoliating species. Data on Lymantria dispar, Lymantria monacha, Bupalus piniarius, Panolis flammea, and Operophtera brumata from five Central European countries (Slovakia, Czech Republic, Austria, Hungary, and Germany), where the current climate is comparable with the projections of climate for the Eastern Baltic region by the end of the 21st century, were analyzed. Time series approach was applied to estimate the linkage between outbreaks and climate warming. Mean annual, summer, and winter deviations for the period of 1850 to 1900 were assessed as proxies of warming. To estimate the legacy effect, warming proxies were lagged by one year. Among those tested, warming proxies showed a linkage with outbreaks. Three significant outbreaks occurred in the analyzed period (at the beginning and end of the period). During the middle part of the analyzed period, the frequency and magnitude of outbreaks were low, implicating a higher insect outbreak risk with warming in Central Europe. In the latter part of the analyzed period, more frequent yet smaller outbreaks occurred, which supports the outbreak linkage with one-year lag, summer, and annual temperatures.

Highlights

The defoliating lepidopterans—Lymantria dispar, Lymantria monacha, Bupalus piniarius, Panolis flammea, and Operophtera brumata, which are widespread in Central and Northern Europe and have similar development cycles, cyclic population dynamics, and frequent outbreaks—were selected
The climate conditions of the Eastern Baltic region are to become comparable to the current climate of Central Europe conditions by the end of the 21st century [24,27], and similar trends in defoliator behavior might be expected
This is supported by the comparable composition of forests in Central Europe and the Eastern Baltic region [28]

Summary

Introduction

Natural disturbances are key processes of forest ecosystem dynamics that change forest structure at the spatial and temporal scales [1] Disturbances such as storms, fires, and insect outbreaks are an inherent part of forest ecosystems [2]. The ongoing climate change shifts the frequency and/or severity of natural disturbances as well as the means and amplitude of meteorological parameters and has direct and indirect effects on insects and trees [3,4]. Global warming can promote insect outbreaks; the ongoing increase in optimum temperature might lead to the disruption of diapause requirements and spring development of insects. This might lead to a decrease in outbreak frequency and severity [6]. An indirect effect of warming could influence the spatial distribution of host trees and their suitability to insects [6,7]

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