Ips typographus (L.) attack on patches of felled trees:: Wind-felled vs. cut trees and the risk of subsequent mortality

According to the Finnish Forest Insect and Fungal Damage Prevention Act, groups of 20 or more damaged conifers should be removed from forests. The main objective of this study was to evaluate the risks involved in leaving groups of 20 damaged spruce trees in managed forests. We also tested the effect of felling technique (natural with some remaining root connections vs. cutting) and the influence of recent forest disturbance history on Ips typographus colonization, breeding success and consequential damage to living trees. We felled groups of 20 spruce trees in 16 stands in November 2003. Half of the experimental stands were situated in southern Finland, which were damaged by autumn storms in 2001. The other half of the experimental stands was in eastern Finland, which was not affected by the storms. In this study, subsequent tree mortality occurred in only two (both in the southern study area) of the 16 experimental stands. Neither the experimental area nor the felling treatment significantly affected tree mortality. The number of colonized felled spruce trees and the densities of egg galleries in felled trees were significantly higher in the southern study area. This result indicates that population levels in the southern area were higher than in the eastern area-probably as a consequence of the autumn storms in 2001. Interestingly, there was also a significant interaction between the felling treatment and the study area, explaining the density of egg galleries in felled spruce trees. The results indicate that the population density of I. typographus affects the colonization process of felled trees, as the response to the felling treatment differed between study areas. Although there were differences in egg gallery densities, no significant differences in offspring production were found either between areas or between felling treatments. (c) 2007 Elsevier B.V. All rights reserved.