Edouard Le Floc'h

Biodiversity and ecosystem trajectories: first results from a new LTER in southern France

Abstract At a new long-term ecological research site in the Mediterranean climate zone of southern France, we have initiated a study of the ecological roles of biodiversity, especially plants and detritivores, at both ecosystem and landscape levels of complexity. In this paper, we describe the study site, experimental set-up, and the long-term objectives, methods and ecosystem attributes used to document the extant spatial organization of above- and below-ground biodiversity related to landscape heterogeneity and past and present land use patterns, and to monitor ecosystem response to the experimental manipulation of functional groups among plants. Baseline data are provided for plant species richness and spectrum of growth forms in six different types of land units, as well as the results of a factorial correspondance analysis of plant diversity in six discriminant classes of landscape units sampled in a total of 54 stations of 100 m2 each situated along ten toposequences. Both habitat openness (related to vegetation structure) and degree of soil degradation (directly linked to former human activities) provided highly discriminatory axes for segregation of species assemblages among the 54 stations. Relevance of the preliminary data presented is briefly discussed in terms of long-term testing of various hypotheses related to biodiversity-ecosystem functioning interactions and ecosystem ‘development’ in a Mediterranean environment with very strong anthropic influences.

Essai de synthèse sur la dynamique actuelle des châtaigneraies cévenoles et ses conséquences sur la diversité végétale

Abstract The present vegetation of the Cévennes mountains (southern France) dominated by sweet chestnut (Castanea sativa) is an outcome of an uninterrupted and frequently intense human influence existing since millennia. It is very different from the deciduous Downy oak (Quercus pubescens) forest which occupied the area at the end of the last glaciation, during a period when climate was quite similar to present day conditions in this subhumid, mid-altitude Mediterranean climate bioregion. Since human impact has been drastically decreasing for the last half century, but especially in recent years, possible vegetation trends can be envisioned for this formerly chestnut-dominated vegetation built on steep slopes and terraces. Based on experimental results in seed germination studies as well as on analysis of plant species diversity trends, we propose some possible trajectories and eventual ‘threshold crossings’ for the vegetation and landscapes of a region suffering rural exodus and agricultural abandonment. All new changes and trajectories have to be modelled taking into account a series of new constraints.