Fine-scale spatial patterns in grassland communities depend on species clonal dispersal ability and interactions with neighbours

Non-random spatial patterns are a common feature of plant communities. However, the mechanisms leading to their formation remain unknown. The clonal dispersal ability of a species, that is, the average length of spacers between ramets, is commonly acknowledged to influence spatial patterns in clonal plants, although this relationship remains to be demonstrated. Moreover, the clonal dispersal ability of neighbouring species may influence environmental conditions and trigger modifications in clonal characteristics of a focal species. Thus, not only the clonal dispersal ability of a species, but also that of its competitors may influence the fine-scale spatial pattern of a species. In this article, we compared spatial patterns (in terms of colonization and occupation of space) of species with low (L), intermediate (I) or high (H) clonal dispersal abilities. Twelve species were classified within three groups of clonal dispersal (L, I or H) based on their average spacer lengths, and seven types of experimental assemblages consisting of species from one, two or three dispersal groups were studied. Two questions were addressed: (i) does the species clonal dispersal ability influence their spatial patterns and (ii) are species fine-scale spatial patterns affected by the clonal dispersal of neighbours? Species spatial patterns were recorded for each assemblage and were then analyzed using point pattern analysis. Despite strong species-specific effects, L-species displayed the highest level of local aggregation, which is indicative of limited space colonization, and the lowest level of local co-occurrence with other species, which is indicative of a high level of space occupation. The opposite pattern was observed in H-species, while that of I-species was intermediate. The species spatial patterns were modified by the clonal dispersal ability of competitors. Synthesis. This study emphasizes the importance not only of clonal dispersal but also of biotic interactions and, more precisely, of plant neighbour characteristics, in the spatial patterning of grassland plant communities.