Managing disturbance regimes to maintain biological diversity in forested ecosystems of the Pacific Northwest (original) (raw)
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Forest management, restoration, and designer ecosystems: Integrating strategies for a crowded planet
Ecoscience, 2008
Managing for biodiversity in Pacific Northwest forest ecosystems requires a means to predict the interactive effects of natural, introduced, and altered disturbance regimes. Although disturbances are known to be a determinant of patterns of biological diversity, disturbance and diversity principles have not been consistently applied in management of forest ecosystems in the Pacific Northwest. Here we review disturbance and diversity theory and develop a synthetic conceptual model for use in predicting the effects of disturbances of any origin on biodiversity, focusing on the Pacific Northwest. Disturbance principles have traditionally been applied to understanding patterns of species diversity, but they can also be applied to understanding the broader concept of biodiversity. Our conceptual model integrates these principles, illustrating relationships among mechanisms that limit species diversity and those that enhance it. Diversity-limiting factors are: environmental stress due to high levels of disturbance relative to productivity, and competitive exclusion that can arise where disturbance has been suppressed or managed to favor a particular species' dominance. Conversely, biological diversity will be enhanced by disturbances that are not too frequent to be stressful, and that create functional heterogeneity (spatial and temporal variation in habitat structure and biological legacies that are vital for post-disturbance reproduction and growth). The three disturbance-related mechanisms that determine diversity operate over local to landscape spatial scales and ecological time scales and thus can be readily influenced by management. By comprehensively evaluating existing disturbance regimes and how they are influencing these factors, managers can help maintain or restore the ecological foundation for biodiversity. We describe management approaches to improve this foundation focusing on forests managed for multiple goals in the Pacific Northwest, where there is considerable potential for and interest in maintaining and enhancing biodiversity. #
Diversity–disturbance relationship in forest landscapes
Landscape Ecology, 2015
Context Despite decades of research, there is an intense debate about the consistency of the humpshaped pattern describing the relationship between diversity and disturbance as predicted by the intermediate disturbance hypothesis (IDH). Previous metaanalyses have not explicitly considered interactive effects of disturbance frequency and intensity of disturbance on plant species diversity in terrestrial landscapes. Objective We conducted meta-analyses to test the applicability of IDH by simultaneously examining the relationship between species richness, disturbance frequency (quantified as time since last disturbance as originally proposed) and intensity of disturbance in forest landscapes. Methods The effects of disturbance frequency, intensity, and their interaction on species richness was evaluated using a mixed-effects model. Results We found that species richness peaks at intermediate frequency after both high and intermediate disturbance intensities, but the richness-frequency relationship differed between intensity classes. Conclusions Our study highlights the need to measure multiple disturbance components that could help reconcile conflicting empirical results on the effect of disturbance on plant species diversity.
The effect of natural disturbances on forest biodiversity: an ecological synthesis
Biological Reviews
Disturbances alter biodiversity via their specific characteristics, including severity and extent in the landscape, which act at different temporal and spatial scales. Biodiversity response to disturbance also depends on the community characteristics and habitat requirements of species. Untangling the mechanistic interplay of these factors has guided disturbance ecology for decades, generating mixed scientific evidence of biodiversity responses to disturbance. Understanding the impact of natural disturbances on biodiversity is increasingly important due to human-induced changes in natural disturbance regimes. In many areas, major natural forest disturbances, such as wildfires, windstorms, and insect outbreaks, are becoming more frequent, intense, severe, and widespread due to climate change and land-use change. Conversely, the suppression of natural disturbances threatens disturbance-dependent biota. Using a meta-analytic approach, we analysed a global data set (with most sampling concentrated in temperate and boreal secondary forests) of species assemblages of 26 taxonomic groups, including plants, animals, and fungi collected from forests affected by wildfires, windstorms, and insect outbreaks. The overall effect of natural disturbances on α-diversity did not differ significantly from zero, but some taxonomic groups responded positively to disturbance, while others tended to respond negatively.
DIVERSITY–INVASIBILITY ACROSS AN EXPERIMENTAL DISTURBANCE GRADIENT IN APPALACHIAN FORESTS
Ecology, 2008
Research examining the relationship between community diversity and invasions by nonnative species has raised new questions about the theory and management of biological invasions. Ecological theory predicts, and small-scale experiments confirm, lower levels of nonnative species invasion into species-rich compared to species-poor communities, but observational studies across a wider range of scales often report positive relationships between native and nonnative species richness. This paradox has been attributed to the scale dependency of diversity-invasibility relationships and to differences between experimental and observational studies. Disturbance is widely recognized as an important factor determining invasibility of communities, but few studies have investigated the relative and interactive roles of diversity and disturbance on nonnative species invasion. Here, we report how the relationship between native and nonnative plant species richness responded to an experimentally applied disturbance gradient (from no disturbance up to clearcut) in oakdominated forests. We consider whether results are consistent with various explanations of diversity-invasibility relationships including biotic resistance, resource availability, and the potential effects of scale (1 m2 to 2 ha). We found no correlation between native and nonnative species richness before disturbance except at the largest spatial scale, but a positive relationship after disturbance across scales and levels of disturbance. Post-disturbance richness of both native and nonnative species was positively correlated with disturbance intensity and with variability of residual basal area of trees. These results suggest that more nonnative plants may invade species-rich communities compared to species-poor communities following disturbance.
Environment and Ecology Research, 2016
Aquatic biological diversity in Pacific Northwest (PNW) forests was examined after two disturbance types: natural (flooding with and without associated debris flows); and anthropogenic (canopy removal). Within the region two multi-decade studies on aquatic insects in western Oregon establish the likely upper ends of forested stream richness, with richness values of ≈300 taxa collected at Berry Creek and 449 taxa within a small watershed (Lookout Creek, 6400 ha). Therefore, compared to intensively studied sites, at least 100 to 200 species have not been documented at these sites. We examine disturbance impacts on assemblage richness in the PNW with data from three studies characterized by similar levels of sampling and taxonomic effort. Rare species were important contributors to richness, as 20 to 30% of taxa within each study area were found at only one site. Mature, clearcut, high flow, and debris flow disturbance states were compared. Ephemeroptera (p=<0.001) richness increased after debris flows and high flows, and Chironomidae (p=0.04) increased after debris flows and clearcutting. Site variability was high, with assemblage structure weakly clustered by disturbance severity as debris flow disturbance (characterized by both streambed and canopy removal) mostly separated from high flow and clearcut disturbances.
The maintenance of species diversity by disturbance
Quarterly Review of Biology, 1989
Hypotheses that relate disturbance to the production andmaintenance ofspecies diversity are reviewed. The hypotheses have been classified traditionally by the effect of the disturbance on the community: those that involve selective mortality, which maintains the species diversity ofa community in equilibrium, and those that invoke events causing random, localized, mas: mortality, which prevent the communityfrom reaching an equilibrium. Regardless of this difference, most hypothesespredict that the greatest number of species will occur at intermediate levels of disturbance.
Ecology and Evolution, 2016
Understanding species diversity and disturbance relationships is important for biodiversity conservation in disturbance-driven boreal forests. Species richness and evenness may respond differently with stand development following fire. Furthermore, few studies have simultaneously accounted for the influences of climate and local site conditions on species diversity. Using forest inventory data, we examined the relationships between species richness, Shannon's index, evenness, and time since last stand-replacing fire (TSF) in a large landscape of disturbance-driven boreal forest. TSF has negative effect on species richness and Shannon's index, and a positive effect on species evenness. Path analysis revealed that the environmental variables affect richness and Shannon's index only through their effects on TSF while affecting evenness directly as well as through their effects on TSF. Synthesis and applications. Our results demonstrate that species richness and Shannon's index decrease while species evenness increases with TSF in a boreal forest landscape. Furthermore, we show that disturbance frequency, local site conditions, and climate simultaneously influence tree species diversity through complex direct and indirect effects in the studied boreal forest.
Species' traits predict the effects of disturbance and productivity on diversity
Ecology …, 2008
Disturbance is an important factor influencing diversity patterns. Ecological theory predicts that diversity peaks at intermediate levels of disturbance, but this pattern is not present in a majority of empirical tests and can be influenced by the level of ecosystem productivity. We experimentally tested the effects of disturbance on diversity and show that speciesÕ autecological traits and community relations predicted species loss. We found that -alone or in concert -increasing disturbance intensity or frequency, or decreasing productivity, reduced diversity. Our species did not exhibit a clear competition-colonization trade-off, and intrinsic growth rate was a more important predictor of response to disturbance and productivity than measures of competitive ability. Furthermore, competitive ability was more important in predicting responses when, in addition to killing individuals, disturbance returned nutrients to the ecosystem. Our results demonstrate that speciesÕ traits can help resolve conflicting patterns in the response of diversity to disturbance and productivity.