Climate change and insect pests.

Chapter 14 (Page no: 248)

Effects of new forest management on insect damage risk in a changing climate.

Recent findings suggest that damage by forest insect pests will increase as a consequence of climate warming. Here, we ask whether changes in forest management can alter and possibly mitigate the increased risk of damage and outbreaks. We focus mainly on conditions in northern Europe, particularly Sweden, but conclusions should be valid for northern temperate forests. Three types of insect pests are considered; the regeneration pest, Hylobius abietis (pine weevil), defoliators and the bark beetle, Ips typographus. We compare the expected effect of new management methods with the presently predominant method of even-aged stands, which are thinned two to three times before final harvest by clear-felling. Continuous cover forestry (CCF) is the method most different from the present practice. CCF would lead to a drastic decrease in pine weevils, and also less damage by defoliators, but this latter prediction is uncertain. For the bark beetle, the uncertainty is even greater. In mixed forests, all three insect pest types are expected to become less of a problem. Putative mechanisms involve more abundant and diverse natural enemy fauna, and a more scattered distribution of food resources. A shorter rotation period (including no thinning) is expected to increase the damage by pine weevils, as it will result in more abundant breeding material. For defoliators, it is difficult to foresee the effects. A shorter rotation period will decrease the risk of bark beetle outbreaks, as storm-fellings will be less frequent and young stands more common. The effects of exotic tree species and clonal forestry are complex and will depend on several factors. A general conclusion is that forest management may be used to mitigate the anticipated risk of insect pest damage as a consequence of climate warming, but more research is required to certify these indications.

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