1 Saproxylic insects, a functional group dominated by beetles, are dependent on dead or moribund trees as habitat elements. 2 Although there are few studies of saproxylic insects from the North American boreal zone, European studies demonstrate that forest harvest can lead to a biologically significant decrease in saproxylic beetle diversity. 3 We studied saproxylic beetles in the North American boreal mixedwood forest using flight intercept traps established on naturally dead and girdled trembling aspen and spruce trees along a successional gradient of undisturbed stands from deciduous to coniferous overstory trees. 4 Composition and diversity of beetle assemblages differed among forest successional types. 5 Snag age class was an important determinant of composition for saproxylic beetle assemblages. 6 Multivariate regression analysis of these data indicated that saproxylic beetles are responding to changes in coarse woody debris, and not to the relative densities of canopy tree species, although these variables are strongly correlated. 7 Coarse woody debris management should be a primary concern in forest management plans seeking to conserve saproxylic organisms and the critical ecosystem functions (i.e. nutrient cycling) in which they participate.Keywords Coleoptera , coarse woody debris , habitat associations , insect conservation . are also influenced by canopy composition ( Siitonen, 2001 ). In some areas of the boreal mixedwood forest, canopy composition can be generally related to succession because stands with proportionally more deciduous canopy trees represent earlier successional stages, and coniferous trees begin to dominate older stands further in time from the most recent disturbance event ( Rowe, 1994 ).Recent work in aspen-dominated stands in Canada has shown that CWD qualities influence saproxylic beetle assemblages, and there is a distinct succession of species during the breakdown of CWD in early successional stages ( Hammond, 1997;Hammond et al. , 2001Hammond et al. , , 2004. By contrast, boreal coniferous and mixedwood stands have received little attention in North America. In the present study, we examine saproxylic assemblages in undisturbed stands spanning the succession gradient from deciduous dominated to coniferous dominated stands, and assess the relative influence of CWD quality and quantity on saproxylic beetle species diversity and composition. Because of the close association of saproxylic beetles and CWD, we hypothesize that the greatest difference will occur between deciduous and coniferous trees, and beetle communities in forest stands close in the successional gradient will be more similar than those farther apart. Materials and methods Study sitesThe field work was conducted at the Ecosystem Management Emulating Natural Disturbance (EMEND) research site in northern Alberta, Canada (56°46 Ј 13 Ј N, 118°22 Ј 28 Ј W). The elevation on the site ranges from 677 -880 m a.s.l., and the soils there are fine-textured lacustrian ( Work et al. , 2004 ). EMEND includes relative...

Recovery of biodiversity and other ecosystem functions to pre-disturbance levels is a central goal of natural disturbance-based approaches to ecosystem management. In boreal mixedwood forests, green-tree retention has been proposed as an alternative approach to traditional clearcutting that may minimize initial displacement of species assemblages and speed recovery of the biota. Here we evaluated the effectiveness of six levels of dispersed greentree retention for conservation of ground beetle biodiversity in four boreal mixedwood cover types that span a gradient of stand development following wildfire. Each cover type X treatment combination was replicated three times in an operational scale experiment using 10-ha compartments. Ground beetle assemblages (59 species and 45 419 individuals) responded to increasing levels of dispersed, green-tree retention, but even relatively high levels of retention (up to 50% retention) did not retain species assemblages characteristic of uncut forest stands. This latter effect was most pronounced in compartments in later successional stages; i.e., those with developing conifer understories, or mixed and/or conifer-dominated overstories. Beetle assemblages in high levels of retention (50-75%) were statistically similar across all cover types, although we detected modest differences among the 5-year recovery of assemblages, based on initial cover type differences. Thus, recovery to initial conditions likely will be slower in mixed and conifer stands than in deciduous stands. We suggest that recovery of beetle assemblages is strongly linked to stand reinitiation through deciduous "suckering" post-harvest. Increasing levels of harvest appear to homogenize carabid assemblages across the four dominant cover types, and thus higher levels of retention (>50%) will be required to preserve assemblages of later successional stages. Regional renewal of assemblages, however, will require landscape-level planning.

Saproxylic insect assemblages inhabiting dead wood in Canadian forests are highly diverse and variable but quite poorly understood. Adequate assessment of these assemblages poses significant challenges with respect to sampling, taxonomy, and analysis. Their assessment is nonetheless critical to attaining the broad goals of sustainable forest management because such species are disproportionately threatened elsewhere by the reductions in dead wood generally associated with commercial exploitation of northern forests. The composition of the saproxylic fauna is influenced by many factors, including tree species, degree of decay, stand age, and cause of tree death. Wildfire and forest harvesting have differential impacts on saproxylic insect assemblages and on their recovery in postdisturbance stands. Exploration of saproxylic insect responses to variable retention harvesting and experimental burns is contributing to the development of prescriptions for conserving saproxylic insects in boreal forests. Understanding of processes that determine diversity patterns and responses of saproxylic insects would benefit from increased attention to natural history. Such work should aim to provide a habitat-classification system for dead wood to better identify habitats (and associated species) at risk as a result of forest management. This tool could also be used to improve strategies to better maintain saproxylic organisms and their central nutrient-cycling functions in managed forests.

Forest fires are among the most important natural disturbances in the boreal region, but fire-initiated succession is increasingly often interrupted by salvage logging, i.e., post-fire removal of burned trees. Unfortunately, very little is known about the ecological effects of this practice. To address this knowledge gap and to examine other factors affecting the abundance of two fire-associated carabid species (Sericoda quadripuntata and S. bembidioides) we conducted three field studies based on pitfall trapping in recent burns in Alberta, Canada. The results suggest that the abundance of both species drastically decreased from the first to the third post-fire year and that fire severity was positively associated with abundance of both species. The combined effects of wildfire and forest harvesting were associated with higher catches of S. quadripunctata, but lower catches of S. bembidioides. We discuss these findings in the contexts of salvage logging and species ecology.