Ips typographus population development after a severe storm in a nature reserve in southern Sweden

Large-scale natural disturbances pose challenges for the management of protected areas and may have undesirable consequences for commercial plantations nearby. A storm, which felled nearly 10 000 m 3 of spruce forest in the Osaby nature reserve in southern Sweden, allowed us to study the subsequent population development of the spruce bark beetle (Ips typographus L.). Two summers after the storm, an exceptionally high proportion (74%) of wind-felled trees had been successfully colonized by the bark beetle, and all living spruce trees had been killed. On standing trees, colonization density was three times higher, and reproductive success one-fourth, that on wind-felled trees. The negative relationship between colonization density and reproductive success indicates that intra-specific competition is one of the main mechanisms reducing I. typographus population growth when the beetles switch from wind-felled to standing trees after storm disturbances. Indeed, there was no significant difference in beetle production between wind-felled and standing trees. Furthermore, there were no differences in colonization density, reproductive success or production at different heights in standing trees; however, a higher proportion of the new adults emerged at the tree-tops rather than lower down before overwintering. Our results also demonstrate that a large proportion (ca. 50%) of the 1. typographus population that developed in the storm-fell area apparently overwintered under the bark of standing trees.