Jennie L. Pearce

Can a trait-based multi-taxa approach improve our assessment of forest management impact on biodiversity?

Harvest impact on forest biodiversity has been widely studied, but for managers confronted with a need for integrated cross-taxa assessment, application remains a significant challenge. Using post-harvest boreal forest succession as a model system, we investigate the usefulness of a trait-based multi-taxa approach to improve our understanding of the community dynamics after disturbance. We assess the strength of response to forest harvesting and recovery patterns of four taxa with contrasting attributes (vegetation, carabids, spiders and birds) along a post-harvest chronosequence of jack pine stands in the boreal forests of Canada. We used a complementary set of functional and taxonomic diversity metrics to identify commonalities and dissimilarities in the community assembly processes and sensitivities to harvesting among taxa. Despite the overall similarity of community response for most pairs of taxa and metrics, the strength of cross-taxa congruency varied greatly among metrics, illustrating the complexity of taxa response to harvest as well as the necessity of including a variety of biodiversity metrics in impact assessments. Of the four selected taxa, spiders were found the most sensitive to harvesting, with a strong response to environmental changes after harvest and a slow community recovery process. Birds and carabids showed highly congruent response patterns, with a strong response to harvest followed by a marked recovery process. Ground vegetation was the most resilient to harvesting. We discuss the management implications of these contrasting recovery processes, outline the current limitations of this method and suggest steps toward the implementation of effective integrated multi-taxa monitoring programs.

Effects of spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks on boreal mixed-wood bird communities.

This study examined the influence of a spruce budworm (Choristoneura fumiferana (Clem.)) outbreak on a boreal mixed-wood bird community in forest stands ranging in age from 0 to 223 yr. We asked if (1) patterns of species response were consistent with the existence of spruce budworm specialists, i.e., species that respond in a stronger quantitative or qualitative way than other species; (2) the superabundance of food made it possible for species to expand their habitat use in age classes that were normally less used; and (3) the response to budworm was limited to specialists or was it more widespread. Results here indicated that three species, specifically the Bay-breasted Warbler (Dendroica castanea), Tennessee Warbler (Vermivora peregrina), and Cape May Warbler (Dendroica tigrina), had a larger numerical response to the budworm outbreak. They responded with increases in density of up to tenfold over 4 or 5 yr. No other species responded with more than a twofold increase in the same time period. These species also showed a functional response by breeding more frequently in young stands aged 1-21 yr and intermediate stands aged 22-36 yr as budworm numbers increased. Our data also suggested that many species profited to a lesser extent from budworm outbreaks, but that this effect may be too subtle to detect in most studies. We found evidence of a positive numerical effect in at least 18 additional species in one or two stand-age categories but never in all three for any one species. Given the numerical response in many species and the potential influence of budworm on bird populations because of the vast extent of outbreaks, we believe that the population cycle of spruce budworm should be considered in any evaluation of population trends in eastern boreal birds.

Dynamic landscape meta-population models and sustainable forest management

This chapter proposes a model-based approach to assessing sustainability using indicator species of ecosystem condition to provide timely feedback to managers about the sustainability of current and alternative forest management options, and to support the development of better-targeted and more relevant monitoring systems. Dynamic landscape metapopulation (DLMP) models integrate spatial models of forest change (also known as landscape dynamic models or forest succession models) with metapopulation models, which describe demographic and biological attributes of species, and the dynamic consequences of dispersal, and habitat change. DLMP models have the potential to play an important role in assessments of sustainability, and such models should be considered as fundamental adaptive management tool. Such models will complement monitoring studies by providing a context for interpreting observed population fluctuations, identifying sensitive parameters and biologically important effect sizes, thereby supporting ecologically meaningful and cost-effective monitoring systems. DLMP models of indicator species appear to be useful for assessing and ranking the sustainability of management options, quantifying the stresses placed on ecosystems by particular management activities, and targeting future research and data collection.