Are habitat islands islands? Woodliving beetles (Coleoptera) in deciduous forest fragments in boreal forest



Modern forestry has changed the fire dynamics in the boreal forest and as a result the size and number of deciduous forest patches have been reduced as well as the number of deciduous trees within the coniferous forest This has exaggerated the insularity of deciduous forest patches within the boreal coniferous forest zone In this paper I examine whether the diversity of beetles living in dead stems of deciduous trees follows the relationship with patch area to be predicted from island biogeographic theory, and to what extent the species assemblages differ between large and small patches and single deciduous trees within managed coniferous forests Three larger patches of deciduous forest (>120 ha) arisen as successions after forest fires in the late 1880's are compared with 6 small (<20 ha) patches of similar origin No difference in diversity could be detected between large and small patches A statistically significant difference between assembly composition was detected using matrix regression between a matrix of observed assembly similarities and a hypothetical similarity matrix based on the type of area in which the plot was situated (large- small or matrix) Finally I examined the distribution of the 56 most common beetle species over the habitat types investigated Thirty four species did not show any Significant habitat preference, 12 were found more often in clear-cut areas than expected 5 were over-represented in small patches, and 4 in large areas My explanation to this apparent lack of insularity effects is the relative recent commencement of intensive forestry in these areas and the fact that the matrix is of rather high quality that is inhabitable for numerous beetle species Thus the patches may be viewed as incipient islands still exchanging biota with their surroundings