Intensive forestry filters understory plant traits over time and space in boreal forests

Because of their scarcity, protected areas alone cannot maintain biodiversity. Therefore, it is necessary to create conditions appropriate for plants and wildlife in managed landscapes. We compared the effects of different intensities of forest management on functional responses of vascular understory plants using the fourth-corner method. We analysed functional community composition along a management gradient that spanned semi-natural forests to extensively managed forests (naturally regenerated cuts) to intensively managed forests (planted forests) in Canada. Results showed trait filtering along the gradient of forest management intensity. In natural and extensively managed forests, where forest retention was high in time and space, persistence traits (e.g. perennial geophytes or chamaephytes, non-leafy stem foliage structure) were maintained. At the opposite end of the gradient, in intensively managed plantations where forest retention elements (e.g. amount of dead wood) were reduced, trait filtering led to species associated with colonization, such as tall species with limited lateral extension. These results suggest that intensive forestry conducted over a large extent may change the functional composition of understory plants.