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

Authors: NIGHTINGALE LASCHE, SOPHIA - New Mexico State University; SCHROEDER, RYAN - Montana State University; MCINTOSH, MATTHEW - New Mexico State University; LUCERO, JACOB - New Mexico State University; Spiegal, Sheri; FUNK, MICAH - New Mexico State University; BECK, RELDON - New Mexico State University; HOLECHEK, JERRY - New Mexico State University; FAIST, AKASHA - Montana State University

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2022
Publication Date: 2/1/2023
Citation: Nightingale Lasche, S., Schroeder, R.W., McIntosh, M.M., Lucero, J.E., Spiegal, S.A., Funk, M.P., Beck, R.F., Holechek, J.L., Faist, A.M. 2023. Long-term growing season aridity and grazing seasonality effects on perennial grass biomass in a Chihuahuan Desert rangeland. Journal of Arid Environments. 209. Article 104902. https://doi.org/10.1016/j.jaridenv.2022.104902.
DOI: https://doi.org/10.1016/j.jaridenv.2022.104902

Interpretive Summary: Perennial grasses are essential for forage production, biodiversity, soil protection, and other ecosystem services in aird rangelands. Perennial grasses tend to grow during one "growing season" each year when conditions are warm and wet, while the rest of the year they are dormant. The amount of rainfall coupled with the intensity of livestock grazing during the growing season can affect growth and growth timing of the grasses and their related ecosystem services. In 1967-2004, an experiment was conducted in the Chihuahuan Desert, in which cattle grazed four pastures differently as follows: all yearlong, only in this fall, only in the winter/spring, or only in the summer. Reseachers measured mean annual primary productivity of the perennial grasses Bouteloua eriopoda (black grama), Aristida spp. (threeawn), and Sporobolus spp. (dropseed) in the pastures. The stocking rate was consistent across all treatments, and thus the number of cows in a pasture for a 3-month grazing season was 4-fold greater than the number of cows in the yearlong pasture. Over the 37-year study period, total perennial grass productivity decreased as aridity increased, with most severe annual decreases in the pastures with only summer and fall grazing pastures, because the higher number of cattle in the pastures during those seasons eating the black grama when it was palatable. These results agree with several other studies that have shown continuous season-long conservatively stocked pastures in arid/ semi-arid rangelands result in advantageous vegetation, livestock, and financial performance compared to those in seasonal/rotation schemes or implementing higher stocking rates.

Technical 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.