Maturation of forest edges is constrained by neighbouring agricultural land management

Abstract

Questions: (i) Do species richness and turnover across forest edges change with edge age and management intensity of adjacent lands? (ii) Does edge species composition respond to aging and landscape management and what are the environmental factors explaining this response? Location: Agricultural landscapes of the Picardy region, N France. Methods: We sampled forest edges differing in age (from a few decades to several centuries) and embedding landscape matrix (from slightly managed 'bocages' to intensively cultivated open fields). We recorded vascular plant species and a set of environment, landscape and historical variables along transects oriented perpendicularly to forest edges. We used mixed models to assess the impact of edge age and landscape type on edge species richness and turnover. We investigated the relationship between edge community composition and explanatory variables using redundancy analyses and a split-plot design. Results: Species richness decreased with both increased edge age and increased landscape management intensity, while species turnover was not influenced by any of these factors. Edge maturation was characterized by a specialization of the flora over the entire transect, which is likely a response to increased shade, litter layer thickness and soil acidity. As landscape management was more intensive, true forest species were replaced by nitrophilous and/or calciphilous non-forest species, which might be more tolerant of agrochemical and lime drift and are able to disperse through a hostile matrix. Conclusion: Although edge aging was associated with the progressive development of environmental gradients, especially light availability and litter thickness, plant communities poorly reflect these gradients under the constraint of neighbouring landscape management. On the contrary, the stronger the management intensity, the sharper the edge-interior gradient. Forest fragments are part of our contemporary agricultural landscapes. As fragments are aging, plant species accumulate and environmental gradients progressively develop at the forest edge, especially with respect to light availability and litter thickness. However, plant communities poorly reflect these gradients under the constraint of neighbouring landscape management: the stronger the management intensity, the sharper the edge-interior gradient. © 2012 International Association for Vegetation Science.