Do newcomers stick to the rules of the residents? Designing trait-based community assembly tests

QuestionsHow similar or dissimilar must a species be to the resident plant community in order to successfully colonize grassland communities that vary in land-use intensity? Is land-use intensity an environmental filter that affects the survival rate of newcomers? Do species that are more likely to co-occur with the resident species show higher survival rates than those that are more similar/dissimilar to the resident community or randomly chosen species? LocationSchwabische Alb, Hainich and Schorfheide, Germany. MethodsWe planted different species from the regional grassland species pool into extant grassland communities exposed to different levels of land-use intensity. Species composition was recorded across 54 sites comprising meadows, mown meadows and grazed grasslands located within the Biodiversity Exploratories' project areas in three different regions of Germany. New species were selected for enrichment planting in the plots according to four different scenarios: species with highly similar or dissimilar traits, species with the highest degree of co-occurrence (derived from vegetation records held in the German vegetation reference database) and randomly chosen species. The changes in community mean trait distances brought about by enrichment planting and the transplant survival were related to land-use intensity. Results and ConclusionLand use was found to be an important environmental filter, as mean trait distance consistently declined with increasing land-use intensity across all scenarios. The planted species with the highest probability of co-occurrence with the resident species did not change the mean pair-wise trait distances across all plots, which indicates that they reflected the same degree of environmental filtering as the resident species. Accordingly, the species that commonly co-occur with the resident species survived best. These findings open a new avenue for using vegetation databases to assess the relative importance of environmental filtering.