Abstract
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.
Highlights
Species diversity is influenced differently by environmental heterogeneity acting across multiple scales [1]
As the forest understory is the most common environment, we argue that beta-diversity was greatest in heterogeneous landscapes overall, giving partial support to the heterogeneity–diversity relationships (HDR) hypothesis for this species group
Our work provides evidence that landscape spatial heterogeneity influences woody species diversity in the balsam fir/yellow birch bioclimatic domain
Summary
Species diversity is influenced differently by environmental heterogeneity acting across multiple scales [1]. A hierarchical approach to understanding the patterns of biodiversity includes consideration of the roles of factors that act as filters to species coexistence at different spatial and temporal scales [2,3]. Both biotic and abiotic conditions determine habitat quality and temporal variation, which influences local species persistence. Environmental heterogeneity in abiotic conditions provides the underlying fabric over which different ecosystem trajectories are manifested, generating a mosaic of community assemblages that shift due to landscape disturbance regimes and succession [4,5]. Tree mortality continuously reshapes forest structure at different scales, contributing to spatiotemporal heterogeneity in resources
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