Long-term growing season aridity and grazing seasonality effects on perennial grass biomass in a Chihuahuan Desert rangeland

Abstract

Growing season aridity and livestock grazing seasonality can influence primary productivity of perennial grasses in dryland systems. For this study, we used a long-term dataset (1967–2004) to investigate the independent and joint effects of growing season aridity and season of grazing (yearlong continuous, fall, winter/spring, or summer season grazing) on the mean annual primary productivity of the perennial grasses Bouteloua eriopoda (black grama), Aristida spp. (threeawn), and Sporobolus spp. (dropseed) in a southwestern United States Chihuahuan Desert rangeland system. Over the 37-year study period, total perennial grass biomass decreased as aridity increased, but the extent of this relationship depended upon season of grazing and specific grass taxon. Aridity-related decreases in total perennial grass biomass were most severe in the summer grazing treatment. Our findings indicate that over time, summer and fall grazing can potentially exacerbate the negative effects of increasing aridity on perennial grass biomass. As arid and semi-arid rangelands globally face increasing aridity associated with a changing climate, land managers can modulate the season of grazing, dependent on dominant taxa present, to minimize these effects. Our study and those from other arid land locations indicate continuous grazing at light to conservative intensities can better sustain key perennial grasses than strategies involving concentrated seasons of grazing. However, growing season aridity levels must also be taken into consideration.