Introduction of lodgepole pine in Sweden - ecological relevance for vertebrates

Several factors like vegetation structure, quality of food and protection f rom predators influence habitat utilisation by vertebrates. When an exotic tree species is introduced it has the potential to affect vertebrates in a number of ways. In the boreal region of Sweden (where Scots pine (P. sylves tris) and Norway spruce (Picea abies) are the dominant native conifers), lo dgepole pine (Pinus contorta) was introduced on a large scale about 40 year s ago. Our review of current knowledge on the lodgepole pine suggests that, in gen eral, vertebrates seem to utilise the different parts of the introduced lod gepole pine tree in the same way as they do the parts of Scots pine. Howeve r, to some extent they react to differences between the two pine species in needle morphology and chemical composition, bark structure, branch and can opy structure, as well as to differences between understory development in lodgepole and Scots pine plantations as a result of shading and soil pH. To day, we still lack knowledge about to what extent vertebrates use the seeds in lodgepole pine's serotinous cones (with their smaller size and darker c olour). Effects on vertebrates are also expected to depend on such factors as the acreage the lodgepole pine will cover, and the distribution or patch iness of the stands. We conclude that bird species composition is relativel y similar for pine stands of both species, at least at young age of the sta nds (i.e. the avian community seems to respond to differences in tree heigh t and canopy density rather than to pine species). In addition, there may a lso be a temporal dimension involved. To what extent can an animal species with a life history adapted to the native tree species utilise the new habi tat created by the introduced exotic tree species? What time is needed for this adjustment? In this paper, we discuss some of these aspects with examp les from mammals and birds in the boreal forest. (C) 2001 Elsevier Science B.V. All rights reserved.