Search

Background: Ecological disturbance is a major driver of ecosystem structure and evolutionary selection, and theory predicts that the frequency and/or intensity of disturbance should determine its effects on communities. However, adaptations of species pools to different historical disturbance regimes are rarely considered in the search for generalizable community responses to disturbance. To explore how the severity of disturbance affects plant diversity patterns, we review studies of understorey plant community responses to wildfire in conifer forests of western North America across a gradient of departure from historical fire regimes. Review findings: We find that post‐fire plant species richness may generally be maximized at disturbance severities that match the predominant historical disturbance regime in a given ecosystem. Studies that examined multiple spatial scales indicate that plant community responses to fire are likely to be scale dependent, suggesting that post‐disturbance monitoring should consider community responses at multiple scales. Synthesis: Our review highlights that consideration of historical disturbance regimes might improve the ability to predict the effects of disturbance on communities. We discuss future research needs; quantitative studies that compare community responses to fire at multiple scales across different historical fire regimes would be particularly useful. Ultimately, consideration of disturbance as a multivariate problem is likely to lead to greater inference than traditional bivariate approaches. [ABSTRACT FROM AUTHOR]

This paper examines long-term eddy covariance data from 18 European and 17 North American and Asian forest, wetland, tundra, grassland, and cropland sites under non-water-stressed conditions with an empirical rectangular hyperbolic light response model and a single layer two light-class carboxylase-based model. Relationships according to ecosystem functional type are demonstrated between empirical and physiological parameters, suggesting linkages between easily estimated parameters and those with greater potential for process interpretation. Relatively sparse documentation of leaf area index dynamics at flux tower sites is found to be a major difficulty in model inversion and flux interpretation. Therefore, a simplification of the physiological model is carried out for a subset of European network sites with extensive ancillary data. The results from these selected sites are used to derive a new parameter and means for comparing empirical and physiologically based methods across all sites, regardless of ancillary data. The results from the European analysis are then compared with results from the other Northern Hemisphere sites and similar relationships for the simplified process-based parameter were found to hold for European, North American, and Asian temperate and boreal climate zones. This parameter is useful for bridging between flux network observations and continental scale spatial simulations of vegetation/atmosphere carbon dioxide exchange. [ABSTRACT FROM AUTHOR]

Forest management affects conditions for both early‐ and late‐seral organisms, and managers and conservationists require information for balancing the ostensibly opposing habitat needs of both these guilds. We conducted meta‐analyses that examined silvicultural systems with a range of postharvest retention and their impacts on mature‐forest and shrubland bird species densities in eastern North America during the breeding season. Densities of mature‐forest bird species generally declined as canopy tree retention and basal area decreased, although some mature‐forest species had similar densities among unharvested and partially harvested (e.g., first‐entry shelterwood) stands, and others had their highest densities in shelterwoods. We conducted a previous meta‐analysis study, which showed most shrubland bird species in the region increase with harvest intensity, but some shrubland species had similar densities in clearcuts and shelterwoods. Given the contrasting effects of harvest intensity on the two avian guilds, we used Partners‐in‐Flight conservation values to generate objective community‐wide conservation indices relative to postharvest tree retention. Clearcuts and shelterwoods typically had the highest conservation values, and unharvested and lightly thinned stands (70%–100% tree retention) had the lowest conservation scores. Many declining shrubland bird species of conservation concern are abundant in low‐retention stands, thus elevating the conservation value of these stands. Additionally, high conservation values of harvested stands with 40%–70% tree retention represent the presence of both shrubland and mature‐forest species; the latter are potentially responding to enhanced understory structure needed for avian nesting or foraging. In contrast, contemporary closed‐canopy forests in eastern North America are generally characterized by low structural diversity and are mid‐seral stands due to historical patterns of land use and tree harvesting. Although avian community conservation values were lowest in high‐retention stands and many other threatened, non‐avian taxa depend on open‐canopy, managed forests, managers should note that late‐seral, unharvested stands can provide important habitat for old‐growth‐dependent taxa and any intensive forestry should also take into account other factors. Considering the growing interest in using postharvest retention of canopy trees to meet ecological objectives, our novel synthesis can assist managers in assessing species‐specific and community‐wide avian responses to tree retention levels along the entire gradient of canopy treatments. [ABSTRACT FROM AUTHOR]