Search Results (4)

Species respond to environmental changes at different rates, resulting in no change, increased, or decreased resemblance among species assemblages. We explored the patterns of rate of change in bird diversity in five ecoregions of the United States across 30 years. We characterized the rate of change in breeding avian biodiversity using measures of species richness and assemblage dissimilarity, detecting changes in the same for 50% and 70% of the assemblages, respectively. Fast richness declines and species replacement were associated with rapid biotic differentiation within ecoregions, while rapid increases in richness and slowed species replacement were tied to high within-ecoregion biotic homogenization rates. Further, it was exceedingly rare for any biodiversity measured to change slowly over time; most changes were rapid. For the species assemblages studied here, changes in assemblage dissimilarity patterns were more common than changes in species richness, even though species richness has received more research attention. These results underscore the need to combine measures capturing different aspects of biodiversity (e.g., species richness and assemblage differentiation) to provide greater insight into the underlying mechanisms and pathways driving changes in biodiversity patterns. Full article

White oak mortality is a significant concern in forest ecosystems due to its impact on biodiversity and ecosystem functions. Understanding the factors influencing white oak mortality is crucial for effective forest management and conservation efforts. In this study, we aimed to investigate the spatial pattern of WOM rates across the eastern US and explore the underlying processes behind the observed spatial patterns. Multicycle forest inventory and analysis data were compiled to capture all white oak plots. WOM data were selected across plot systems that utilized declining basal areas between two periods. Ripley’s K function was used to study the spatial pattern of WOM rates. Results showed clustered patterns of WOM rates at local and broad scales that may indicate stand-level competition and regional variables affecting white oaks’ dynamics across southern and northern regions. Results also indicated random patterns at broad scales, suggesting variations in topographic and hydrological conditions across the south and northern regions. However, the central region indicated both clustered and random patterns at the local scale that might be associated with inter-species competition and the possibility of environmental heterogeneity, respectively. Furthermore, uniform patterns of WOM rate at a broad scale across all regions might suggest regions with spatially homogeneous environmental factors acting on the dynamics of white oaks. This research might be helpful in identifying impacted areas of white oaks at varying scales. Future research is needed to comprehensively assess biotic and abiotic factors at various spatial scales aimed at mitigating WOM. Full article

Human-induced climate- and land-use change have been affecting biogeographical and biodiversity patterns for the past two centuries all over the globe, resulting in increased extinction and biotic homogenization rates. High mountain ecosystems are more sensitive to these changes, which have led to physiological and phenological shifts, as well as to ecosystem processes’ deformation. Glacial relicts, such as arctic-alpine taxa, are sensitive indicators of the effects of global warming and their rear-edge populations could include warm-adapted genotypes that might prove—conservation-wise—useful in an era of unprecedented climate regimes. Despite the ongoing thermophilization in European and Mediterranean summits, it still remains unknown how past and future climate-change might affect the distributional patterns of the glacial relict, arctic-alpine taxa occurring in Greece, their European southernmost distributional limit. Using species distribution models, we investigated the impacts of past and future climate changes on the arctic-alpine taxa occurring in Greece and identified the areas comprising arctic-alpine biodiversity hotspots in Greece. Most of these species will be faced with severe range reductions in the near future, despite their innate resilience to a multitude of threats, while the species richness hotspots will experience both altitudinal and latitudinal shifts. Being long-lived perennials means that there might be an extinction-debt present in these taxa, and a prolonged stability phase could be masking the deleterious effects of climate change on them. Several ex situ conservation measures (e.g., seed collection, population augmentation) should be taken to preserve the southernmost populations of these rare arctic-alpine taxa and a better understanding of their population genetics is urgently needed. Full article

Partial disturbances enhance spatial heterogeneity through the diversification of forest structure, which contributes to niche partitioning and consequently to species diversity. However, this heterogeneity–diversity relationship may differ between groups of species, and is potentially modified by biotic interactions at the community level. We propose that shrub diversity will be greater in heterogeneous landscapes, while tree diversity will be lower in those same landscapes, due to the biotic interactions of shrub competition. We conducted field sampling in the balsam fir/yellow birch bioclimatic domain in western Québec, a forested ecosystem disturbed by natural and anthropogenic partial disturbances. We selected 12 forested landscapes (1 km²), four in each of three classes of landscape heterogeneity (heterogeneous, moderately heterogeneous, homogenous). Shrub and tree species regeneration abundance was measured in three different size classes of canopy gaps and the forest understory. Gap proportions were assessed in each landscape using aerial LiDAR data. Tree and shrub alpha-diversity significantly responded to landscape heterogeneity, shrubs being more diverse while tree seedlings were less diverse in heterogeneous landscapes. Heterogeneous landscapes showed highest species accumulation rates for shrubs in medium-sized gaps. For tree seedlings, species accumulation rates were highest in heterogeneous landscapes in the forest understory. Our study thus supports the heterogeneity–diversity relationship with shrubs having higher alpha and beta diversity in heterogeneous landscapes whereas local-scale tree diversity was higher in homogenous landscapes. Full article