Identifying reference communities in ecological restoration: the use of environmental conditions driving vegetation composition

In restoration ecology, the reference ecosystem represents a key concept which is well defined from a theoretical point of view. In practice, however, selecting reference systems, such as reference plant communities, often lacks clear methodology. In order to facilitate this selection, we provide a framework based on ecological theory, and more precisely on relationships between vegetation and environmental factors, to identify reference plant communities. The four major steps are: (1) the delimitation of a geographical zone in which habitat types similar to restoration sites occur; (2) the identification of environmental factors structuring non-degraded plant communities within this geographical zone; (3) the comparison of the environmental factors between non-degraded and degraded sites; and (4) the selection of the non-degraded sites most similar to restoration sites in terms of environmental factors to use them as references. We concept-proved our approach by identifying reference communities using environmental factor combinations for five mountain grassland sites degraded by the construction of a high-voltage line. In a multivariate analysis of 18 non-degraded sites, we identified six major environmental factors explaining plant species compositions. A second multivariate analysis including degraded sites provided environmental distances of the 18 non-degraded to each of the degraded sites. The results demonstrated that the environmentally most similar sites were not necessarily the geographically closest ones. In conclusion, the analysis of regional plant-environment interactions provides an important tool to identify reference communities or source sites for seed transfer if not available adjacent to degraded habitats.