Livestock trampling reduces biocrust cover but not N2-fixation in southern Arizona

Question Livestock grazing is a major land use of dryland ecosystems. While the occurrence of grazing is widespread, there is high heterogeneity in grazing intensity. Biocrusts are responsible for multiple dryland ecosystem services, but livestock trampling can cause crucial disturbance to biocrust communities that may inhibit these contributions. Trampling may be particularly intense around waterpoints, with a decline in trampling with increased distance from the waterpoints. We investigated the effects of this disturbance gradient on biocrust communities. Location Santa Rita Experimental Range in southern Arizona, USA (31° 49’ N, 110° 51′ W). Methods We quantified biocrust cover and rates of N 2 -fixation along grazing gradients extending out from waterpoints. We also measured soil characteristics such as chlorophyll a (a proxy for biocrust biomass), bulk density, soil respiration, and soil water-holding capacity. Results We found that biocrust cover increased with distance from waterpoints. However, biocrust cover was not correlated with the acetylene reduction assay (an indirect measure of N 2 -fixation), δ 15 N (a direct measure of N 2 -fixation), or chlorophyll a . Conclusions These results suggest that grazing negatively affects biocrust cover. We did not find a significant difference between N 2 -fixation rates among the different distances from the waterpoints or biocrust cover.