Influence of the spatial variability of soil type and tree colonization on the dynamics of Molinia caerulea (L.) Moench in managed heathland
Résumé
European heathland communities on acid, nutrient-poor soils have a high ecological value due to their special environmental conditions. Natural succession (tree colonization and the emergence of grasses) poses a threat to this type of habitat and different types of management strategy must be considered if it is to be maintained. A previous study on a dry heathland area located in the Fontainebleau forest (France) showed a gradual shift from a pure ericaceous stand to a mosaic of grasses and Ericaceae, despite the application of measures such as removal of woodland species to sustain the habitat. Habitat change was due to local expansion of a grass, Molinia caerulea (L.) Moench. The present paper aimed to identify factors responsible for the expansion of M. caerulea and the subsequent decrease in ericaceous heath. We focused our study on spatial variability of soil properties (soil horizons, pH, water content) and reforestation (density of birch individuals and proximity to woodland) as a suite of possible factors promoting the expansion of M. caerulea. We show that the development of grasses was correlated with thin soil E horizon and spatial distribution of old shoots of birch, Betula pendula Roth, which are regularly cut and then resprout. These results suggest that new methods to avoid tree colonization must be introduced if typical heathland is to be maintained.
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