A continental comparison indicates long-term effects of forest management on understory diversity in coniferous forests

Promotion of species diversity has become a major goal in forestry. This requires an understanding of the impacts of management disturbance on species diversity relative to natural drivers such as climatic or edaphic conditions on the relevant temporal scales, i.e., centuries. We examined the effects of long-term management disturbance on understory plant diversity in coniferous forests by comparing structure types (ages since disturbance) between regions with comparable abiotic settings but contrasting management history, i.e., management for centuries in central Europe versus the first logging in primary forests in western Canada. We systematically sampled three age classes after disturbance and compared their alpha diversity and species composition. The structure types (age classes) showed similar differences in alpha diversity in both landscapes, while the response of species compositions differed between the two. Fewer late-successional specialists occurred in the European landscape. Within the setting of our study, the structure types, which reflect the time since major forest management disturbance, affected understory species richness and composition at least as strongly as environmental conditions such as climate, soil, and tree layer diversity across the broad altitudinal gradients that we sampled. Our results suggest that forest management affects the diversity of coniferous forests, with management for centuries disadvantaging late-successional specialists. Furthermore, it appears that human action is becoming the major determinant of diversity of coniferous forests, emphasizing the need for sustainable management schemes.