Effects of alternative harvesting methods on boreal forest spider assemblages

Abstract

Forestry is among the most important disturbance forces in the boreal region, having caused drastic changes to the biota. Forest industries have recently introduced alternative logging techniques to better maintain forest diversity, but little is known on how these function. We studied the short-term effects of various logging methods on ground-dwelling spiders in Finland, using pitfall traps 1 year before and 2.5 years after logging. The compared logging regimes were (i) clear-cutting, (ii) retention felling, (iii) gap felling, (iv) thinning, and (v) control. We found that (1) clear-cutting and retention felling drastically changed the spider fauna. The abundance of forest species decreased with these methods, whereas most open-habitat species showed the opposite response, being caught only after logging. Moreover, multivariate analyses (nonmetric multidimensional scaling, multivariate regression trees) indicated that clear-cutting and retention felling produced similar spider faunas. (2) Increasing retention of trees caused less abrupt changes in spider fauna. Gap felling produced variable and intermediate responses, whereas thinning closely resembled control. We conclude that retention patches of a few tens of trees within clearcuts may not function as "lifeboats" for forest spiders; gap felling preserves some forest species but also supports the colonization of open-habitat species; and the studied thinning treatment well preserves the forest-floor spider assemblage. © 2008 NRC.