Forest age structure is one of the main indicators of biodiversity in temperate and boreal forests worldwide. This indicator was mainly designed for the conservation of a subset of rare or sensitive species related to the oldest age classes: it was not designed to capture variability across the entire biodiversity spectrum, but is often considered as such. In this study, we analysed alpha and beta diversity in temporary plots of western Quebec, Canada, to examine the need to develop biodiversity indicators complementary to existing forest age structure targets.
Results/Conclusions
Our analysis revealed that considered individually, stand characteristics such as cover type and height are better predictors of changes in site-level contribution to beta diversity than age. We also show that plots belonging to different age classes can be similar in terms of tree diversity. Height class was found to have a more significant impact on tree diversity than expected: height was more important than age in coniferous forests, and in deciduous and mixedwood stands it frequently complemented the impacts associated with age to better explain the observed diversity patterns. Our results suggest that forest age structure targets are unlikely to be comprehensive indicators of ecosystem sustainability and that some mature secondary stands can provide significant contributions to biodiversity. We propose that more efficient trade-offs between forest exploitation, ecosystem functioning and environmental conservation can be attained if: (i) forest age structure targets are complemented by cover type and stand height; or (ii) complementary biodiversity indicators of ecosystem sustainability are developed.