Recovery of Mediterranean steppe vegetation after cultivation: Legacy effects on plant composition, soil properties and functional traits

Questions Are the vegetation structure and soil properties of fallows similar to adjacent species-rich Mediterranean steppe communities 35 years after abandonment? Is there a spontaneous redevelopment towards the original steppe vegetation after reintroduction of the traditional grazing system? Can differences in functional trait composition be identified according to different land-use types? Do traits of selected species affect the ability to recolonize fallow land? Location Mediterranean steppe of La Crau (Southeastern France). Methods We conducted 80 vegetation surveys and soil analyses in the steppe and adjacent fallow land in six locations in La Crau in 2015; for three locations, data from 2001 were included. To compare the functional composition of steppe vs fallow land, community-weighted means (CMW) of specific leaf area (SLA), leaf dry matter content (LDMC) and canopy height were calculated. To test whether trait variability is associated with the recolonization success of 12 selected target species, we measured SLA, LDMC, canopy height, plant width and aboveground biomass on eight replicate individuals per site and species. Results Fallow land was characterized by lower species richness and elevated phosphorus and potassium content in the soil. Comparing vegetation releves between 2001 and 2015 revealed that the fallows were developing towards steppe vegetation. CWMs of SLA were significantly lower and CWM of LDMC higher in steppe than in fallow land. There was no similarity in trait composition between steppe species that successfully recolonized the fallow-land community, and no evidence that intraspecific trait variability is associated with recolonization success of these species. Conclusions Even after decades of abandonment and reintroduction of the grazing system, the vegetation structure, soil properties and plant functional trait composition of fallows differ from those of adjacent steppe communities. These results illustrate the need for active restoration to accelerate the recovery of former arable land to the target steppe communities.