Beetle diversity in a matrix of old-growth boreal forest: influence of habitat heterogeneity at multiple scales

The relative contribution of compositional and structural heterogeneity on biodiversity is currently ambiguous because field studies generally integrate these two sources of habitat heterogeneity into a single index. We established the relationship between species richness of ground-dwelling and flying beetles and compositional and structural attributes of forest heterogeneity. The relationship was evaluated at two spatial scales: the scale of forest stand, corresponding to an 11.3 m radius, and the scale of landscape, corresponding to either a 400 or 800 m radius. Seventy stands were sampled in the matrix of old-growth boreal forest of the North Shore region of Quebec, Canada, during the summers of 2004 and 2005. A total of 133 ground-dwelling beetle species (range: 4-42 species per site) were captured in the pitfall traps and 251 flying species (range 16-58 species per site) in flight-interception traps. We found that the most relevant type of heterogeneity to explain variations in species richness and the significance of landscape scale information varied between groups of beetles. Compositional heterogeneity (i.e. the number of species of forest trees and shrubs) at the stand scale best predicted species richness in ground-dwelling beetles. On the other hand, it was the combined influence of structural and compositional habitat heterogeneity at stand and landscape scales that best explained richness patterns in flying beetles. Our study outlines the significance of considering multiple types and spatial scales of habitat heterogeneity when describing patterns of species richness.