Plantations of fast growing exotic trees, such as hybrid poplars and hybrid larch, are increasingly used for wood and timber production, but they are also believed to impair forest biodiversity. Most studies that have assessed how such plantations may alter the diversity and composition of understorey plants were established in agricultural landscapes or have compared these plantations with old-growth natural forests. Moreover, many important aspects of biodiversity have been overlooked in previous studies, such as functional and beta-diversity. Here, we present results from a study that was aimed at quantifying alpha- and beta-diversity of understorey plant species and functional groups in exotic hybrid poplar and hybrid larch plantations located within a forested landscape of Quebec, Canada. These plantations were compared to naturally regenerated secondary forests and to functionally similar native plantations of the same origin.
Results/Conclusions
Our results indicate that exotic tree plantations do not reduce taxonomic and functional alpha-biodiversity, but may increase them, in part through the introduction of plant species that are associated with open habitats. We provide further evidence that planted forests may be as heterogeneous as naturally regenerated forests in terms of understorey plant composition. Plant species and functional composition differed slightly between stand types (naturally regenerated forests, native and exotic plantations), with native and exotic plantations offering a greater potential for colonisation by ruderal species, while being detrimental to species of closed forest habitats. Lastly, exotic plantations do not induce greater changes in understorey vegetation relative to plantations of native trees, at least during the first stand rotation.