Dryland (arid and semi-arid) ecosystems globally provide more than half of livestock production and store roughly one-third of soil organic carbon (SOC). Biogeochemical pools are changing due toshrub encroachment, livestock grazing, and climate change. We assessed how vegetation microsite, grazing, and precipitation interacted to affect SOC and total nitrogen (TN) at a site with long-term grazing manipulations and well-described patterns of shrub encroachment across elevation and mean annual precipitation (MAP) gradients. We analyzed SOC and TN in the context of vegetation cover at ungrazed locations within livestock exclosures, high-inten- sity grazing locations near water sources, and moderate-intensity grazing locations away from water. SOC was enhanced by MAP (p<0.0001), but grazing intensity had little effect regardless of MAP (p = 0.12). Shrubs enhanced SOC (300–1279 g C m2) and TN (27–122 g N m2), except at high MAP where the contribution or stabilization of shrub inputs relative to grassland inputs was likely diminished. Cover of perennial herbaceous plants and litter were significant predictors of SOC (r2 = 0.63 and 0.34, respectively) and TN (r2 = 0.64 and 0.30, respectively). Our results suggest that continued shrub encroachment in drylands can increase SOC storage when grass production remains high, although this response may saturate with higher MAP. In contrast, grazing – at least at the intensities of our sites – has a lesser effect. These effects underscore the need to understand how future climate and grazing may interact to influence dryland biogeochemical cycling.

Soil carbon and nitrogen was analyzed from soil cores collected at three sites along an elevation and rainfall gradient in southern Arizona. Within each site, there were three plots that varied in grazing intensity based on long-term exclosures that restricted grazing, long-term water points near which grazing was relatively high, and locations away from water points where grazing was reduced. Within these plots, cores were collected under woody plants and in intercanopy spaces.

Further information about the data set can be found in the "metadata" tab on the associated datasheet or in the following article:Throop, H.L., S. Munson, N. Hornslein, and M.P. McClaran. 2021. Shrub influence on soil carbon in a semi-arid grassland is mediated by climate and largely insensitive to livestock grazing. Arid Land Research and Management doi: 10.1080/15324982.2021.1952660