Increased insect damage in Hungarian forests under drought impact
1997
Csoka, G. (Forest Research Inst., Matrafured (Hungary). Department of Forest Protection)
The increased frequency and severity of drought have played a key role in provoking serious outbreaks of several forest insects, leading to a significant expansion of the damaged territory. Populations of six species involved in this study have shown a significantly increasing trend over the last three decades. These are as follows: bark beetles on conifers, Curculio acorn weevils, Euproctis chrysorrhoea, Kermes quercus, pine sawflies, and tortricid leafrollers. All of these species are known to prefer warm and dry conditions. The yearly value of area damaged by four pests (bark beetles on conifers, Curculio acron weevils, Kermes quercus, and pine sawflies) gave highly significant positive correlations with several drought-indicating variables (yearly values, 2-, 3-, 4- year moving averages of forest drought damage and drought index). On top of the increasing damage, at least 20 species considered as thermo- and xerophilous have appeared as new forest pests in Hungary over the last two decades. Among these are Cameraria ochridella (Lepidoptera), Parectopa robinella (Lepidoptera), and Tischeria spp. (Lepidoptera). However, it should not be concluded that drought stimulates damage expansion in all forest pests. Factors other than climate can also play a significant role. These factors are for example improper human managing activities such as draining the water from the forests and planting pure and even-aged stands on sub-optimal sites. These factors and the climate extremes reinforce each others' negative effects
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