Impact of climate change on the population dynamics of Ips typographus in southern Sweden

Mass-propagation of the spruce bark beetle, Ips typographus, following windfalls and drought is a serious threat to mature spruce forests. Climate change will affect the population dynamics of I. typographus directly as the swarming activity and development rate are mainly controlled by temperature, and indirectly via changes in availability of brood trees. Today, I. typographus is in general univoltine in southern Sweden. In Denmark, however, the weather conditions usually support the production of a second generation. By modelling the temperature dependent population dynamics, we have evaluated the effect of regional climate change scenarios for the period of 2070-2099 on I. typographus in southern Sweden. Our results indicate that temperature increase will have a step-wise effect on the population dynamics. Earlier spring swarming and a faster development from egg to mature bark beetle increase the probability of a second swarming period during summer. A second swarming will be customary with an annual mean temperature increase of 2-3 degrees C. The thermal requirement for development of a second generation may, however, not be fulfilled every year with an annual mean temperature increase less than 5-6 degrees C. Winter is fatal for immature bark beetles, and the larger the temperature increase, the higher the probability that the second generation will complete development and survive hibernation. The temperature regime during autumn will therefore have a decisive impact on the size of the swarming population next spring. (c) 2007 Elsevier B.V. All rights reserved.