Beetle diversity in timberline forests: a comparison between old-growth and regeneration areas in Finnish Lapland

Abstract

We compared beetle fauna among six types of forests: (1) old-growth pine, (2) old-growth spruce and (3) old-growth mixed forests; (4) 1-year-old and (5) 15-year-old seed-tree cut pine forests, and (6) 15-year-old clear-cut spruce forests using window trapping. In the old-growth forests, species richness was explained by site productivity, amount and quality of coarse woody debris (CWD), and tree species composition. Many of the explaining variables, e.g., site productivity, volume of living timber and volume of CWD were intercorrelated. Beetle assemblages varied according to the site fertility and successional stage. The species compositions of non-saproxylic species were rather similar in the seed-tree-cut areas and in the old-growth pine forests, but the species composition of saproxylics differed between the two forest types. On the contrary, the species compositions of both saproxylics and non-saproxylics differed distinctly between the old-growth spruce forest and clear-cut sites. Species colonising recently died trees, soil-dwelling open-habitat species and some polypore-living cisids were more abundant in regeneration areas than in old-growth forests, whereas species of many other mycetophagous beetle families were practically absent from the logged sites. Compared with old-growth forests, the proportion of nationally rare saproxylic species was high at the recently cut sites, but clearly lower at the old regeneration sites. This indicates that in the long run the changes in the amount and quality of CWD may have detrimental effects to rare saproxylic species in the regeneration areas.