Patterns of secondary succession in calcareous grasslands: can we distinguish the influence of former land uses from present vegetation data?
Résumé
We performed a comparative analysis of two neighbouring chalk hillsides, constituted of mosaics of patches of different secondary successional ages but differing with respect to recent land use history (stable vs. variable). A survey on plant communities was performed with similar design for each site. Multivariate analyses were performed to study the relationships between vegetation and environmental variables so as to interpret the present vegetation variability. Co-inertia analyses show that, in both sites, (1) secondary succession dominates the general pattern of composition gradients in plant communities and (2) succession gradient is strongly connected with soil depth. While soil features are linked to natural variables (altitude) in one site, such link is absent in the other site, suggesting the potential role of past land uses. In order to test this last hypothesis, we performed a partial canonical correspondence analysis (CCA) on an additional data set. Two issues are discussed in the context of a conservation LIFE program: (1) the importance of historical data for the definition of ecosystems of reference, seen as target for restoration and (2) the importance of assessing the long-term influence of past land uses for the definition of conservation management plans