Saproxylic and non‐saproxylic beetle assemblages in boreal spruce forests of different age and forestry intensity

Abstract

Current clear-cutting forestry practices affect many boreal organisms negatively, and those dependent on dead wood (saproxylics) are considered as particularly vulnerable. The succession of species assemblages in managed forest habitats regenerating after clear-cutting is, however, poorly known. We compared beetle assemblages in three successional stages of managed boreal spruce forests established after clear-cutting and two types of older spruce forests that had not been clear-cut. We also assessed whether saproxylic and non-saproxylic beetle assemblages show similar biodiversity patterns among these forest types. Beetles were collected in window traps in nine study areas, each encompassing a protected old-growth forest (mean forest age approximately 160 years, mean dead wood volume 34 m3/ha), an unprotected mature forest (approximately 120 years old, 15 m3/ha), a middle-aged commercially thinned forest (53 years old, 3 m3/ha), a young unthinned forest (30 years old, 4 m3/ha), and a clearcut (5-7 years after harvest, 11 m3/ha). Saproxylic beetles, in particular red-listed species, were more abundant and more species rich in older forest types, whereas no significant differences among forest types in these variables were detected for non-saproxylics. The saproxylic assemblages were clearly differentiated; with increasing forest age, assemblage compositions gradually became more similar to those of protected old-growth forests, but the assemblage composition in thinned forests could not be statistically distinguished from those of the two oldest forest types. Many saproxylic beetles adapted to late-successional stages were present in thinned middle-aged forests but absent from younger unthinned forests. In contrast, non-saproxylics were generally more evenly distributed among the five forest types, and the assemblages were mainly differentiated between clearcuts and forested habitats. The saproxylic beetle assemblages of unprotected mature forests were very similar to those of protected old-growth forests. This indicates a relatively high conservation value of mature boreal forests currently subjected to clear-cutting and raises the question of whether future mature forests will have the same qualities. Our results suggest a high beetle conservation potential of developing managed forests, provided that sufficient amounts and qualities of dead wood are made available (e.g., during thinning operations). Confirming studies of beetle reproduction in dead wood introduced during thinning are, however, lacking.

Long-term effects of clear-cutting on epigaeic beetle assemblages in boreal forests

“…Natural forest characteristics such as predominance of large trees, amount of coarse dead wood, and multilayered stands have been reduced Östlund, 1992, 1998;Jönsson and Jonsson, 2007), leading to changes in assemblage composition in many taxa (Thor, 1998;Martikainen et al, 2000;Maeto and Sato, 2004;Dynesius and Hylander, 2007;Josefsson et al, 2010;Stenbacka et al, 2010). In Scandinavia, over 90% of the boreal forest landscape is managed and older semi-natural forests are being replaced with younger even-aged stands, regenerated after clearfelling.…”

Protection against rockfall along a maturity gradient in mountain forests

“…This is the case for bryophytes (Boudreault et al, 2002), lichens (Boudreault et al, 2002;Nascimbene et al, 2010;Troy McMullin et al, 2010), saproxylic fungi (Penttilä et al, 2004), saproxylic beetles (Martikainen et al, 2000;Similä et al, 2002;Stenbacka et al, 2010;Lassauce et al, 2011), spiders and ground beetles (Isaia et al, in press), and cavity-nesting birds (Bütler et al, 2003). Consequently, to improve biodiversity conservation, multifunctional forest management aims at restoring maturity attributes, using various strategies.…”

Post-industrial areas as successional habitats: Long-term changes of functional diversity in beetle communities

“…Species which are not associated with forest habitats show the opposite trend. Such trends are usually documented in terms of species diversity (Stenbacka, Hjältén, Hilszczański, & Dynesius, 2010). However, guilds or functional groups of arthropods can respond to the availability of specific resources and environmental factors, which may change in the course of succession.…”