The state of change of Erica scoparia L. heathland through cattle grazing and oak colonization

In: Revue d'Ecologie, Terre et Vie, 2009, 64 (1), pp.3-17. Our aim was to ascertain whether changes in plant species richness and other vegetation features occur in heathland dominated by Erica scoparia L. (besom heath) through the impact of cattle grazing and oak colonization. Our study took place in the Brenne Regional Natural Park (center of France) where this cricaceous species, locally called 'brande', is now considered of patrimonial interest and protected at regional and European level. We selected 10 sites in a private property, covering I wide range of ecological conditions (shallow and deep soils, grazed and non-grazed besom heath, pure and oak-colonized besom heath). Vegetation (percent occupancy of plant species) wits sampled in May-June 2006 (105 samples, 1m2) each) and the impact of shrub and tree vegetation on plant biodiversity was assessed by correspondence analysis (CA) and total and partial Mantel tests (Monte-Carlo procedure). An environmental gradient of decreasing light incidence from grazed heath to old heath to oak-wood was depicted, along which a number of ecological, morphological and physiological plant traits (growth habits, Ellenberg values, Grime strategies, Tolerance Index of the plant community) were observed to vary. Species richness decreases when ericaceous or, although to a lesser extent, oak cover increases and it increases under low to moderate cattle grazing. Consequences for the sustainable management of 'brande' are discussed.