Analysing the spatial heterogeneity of emergent groups to assess ecological restoration.
Effective restoration of ecosystem structure and function needs to be built on a strong conceptual basis. The evaluation of restoration is critical in this respect, as it requires an accurate understanding of vegetation dynamics. This study was, therefore, designed to analyse how initial restoration treatments and spontaneous ecological processes act together to produce spatial heterogeneity of plant species at various scales, taking into account that species might respond differentially to these processes in accordance with their biological attributes. In a model system consisting of a large land settlement located on the banks of the river Rhône (France), 85 geo-referenced plots were located, and the abundance of all plant species and seven biotic and abiotic environmental factors that have been modified by restoration were recorded. All species were classified into emergent groups (EGs) based on 12 plant traits, and the abundance of each EG was derived for each plot. Spatial variables that explained the spatial autocorrelation of the EGs at four scales were computed. This was performed using a spatial eigenvector mapping technique. The spatial variables were then linked to a range of selected environmental factors. Large-scale patterning of EGs was explained mainly by the spatial heterogeneity of soil quality and vegetation cover. The attribute combination of the EGs that varied most at this scale suggested that the restoration had influenced vegetation development by inducing harsh physical conditions in some part of the studied area and biotic filtering (through competition) in others. A large amount of the spatial variation of EGs was not explained by the environmental factors providing some evidence for pure spatial autocorrelation effects. At the finest scale, this was linked to poor dispersal abilities of some EGs. Synthesis and applications. By combining a trait-based approach with spatially explicit methods, we explained and quantified the role of environmental changes induced by restoration and spontaneous biotic processes in structuring plant communities on different spatial scales within a large land settlement. We discuss how such an approach offers new opportunities for an improved assessment of induced and spontaneous structuring factors for restoring and for monitoring plant communities during ecological restoration.