IMPACT OF BARK BEETLES ON FORESTS AND FORESTRY IN SWEDEN

The impacts of bark beetles in Sweden and the role and management of bark beetle breeding substrate are discussed. Of the six important species damaging living trees, Tomicus piniperda and Ips typographus have the greatest impact. The damage caused by Tomicus adults feeding in pine shoots is directly related to beetle numbers, which in turn depend on the availability of non-resistant breeding substrate. Intensity of shoot pruning, tree size, and geographic region are important factors determining the extent of losses, which can amount to 45 % of the annual volume growth. The extent of tree mortality caused by Ips typographus attack depends on interactions between host tree vigour, densities of colonizing populations, and the availability of other, non-resistant breeding substrate. During the latest outbreak, the trees killed represented about 6 million cubic meters of wood. The heaviest losses were reduction of timber quality, unsalvaged timber, and the cost of control measures. The economic impact of reduced growth depends on the shortening of rotation by insect attack and on interest rates. During the 1960s and 1970s bark beetle attacks and their impact increased owing to natural causes and forestry practices. Hereafter, integrated forest protection efforts, based on research, organisation, information, and legislation, reduced bark beetle attacks to a low level.