High variability of edge effects on forest vegetation diversity
Résumé
The influence of edges on vegetation diversity in forest fragments is an important issue for biodiversity conservation because of the large part of temperate woodlands concerned. In numerous empirical studies, a general pattern has been identified; it is described as two zones: the edge where plant distribution is linked to the distance from the forest border, the core area where the variability of vegetation is not linked to this distance. We present results of a study aiming at measuring the edge effects on vegetation in forest fragments in south-western France and at identifying potential factors of their variability. Vegetation was sampled in 28 transects constituted by 20 contiguous quadrats (2x2m). Environmental conditions (soil, light) of each quadrat was measured and each transect was assigned to a type of forest border based on its orientation and adjacent land cover. Historical records on each border were also available. Multivariate ordination methods were used to analyse data to identify patterns in species distribution. Our results showed a larger variability of vegetation response to edge influence than what was expected from literature. Beta diversity between transects, and in a given transect between quadrats was high and few species appeared as associated with edge conditions. However, multitable ordination of the quadrats from the 28 transects analysed together showed a common pattern of response of vegetation, but it seemed to have several parts that had not been described before in the literature. None of the factors measured was able to explain this variability. These results underlined the variability of edge effects on forest vegetation that was often underestimated by biodiversity managers.
Domaines
Biodiversité et Ecologie
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