Long-term effects of stocking rate, year, and weather on honey mesquite canopy cover and density

TitleLong-term effects of stocking rate, year, and weather on honey mesquite canopy cover and density
Publication TypeConference Proceedings
Year of Publication2022
AuthorsMcIntosh MM, Holechek JL, Spiegal S., Cibils AF, Estell RE, Steele C, Jeon S., Bestelmeyer BT
Conference NameSociety for Range Management
ARIS Log Number399045
Keywordsand density, canopy cover, honey mesquite, Long-term effects, stocking rate, weather, year

Abiotic (precipitation, temperature) and biotic (grazing) factors are thought to be important drivers of undesirable woody shrub encroachment in arid rangelands. Woody encroachment has pervaded global rangelands over the past century, but the relative impacts of either grazing or climate are still not fully understood. We sought to evaluate the long-term (25 years; 1995-2019) effects of stocking rate (light: 25-30% and conservative: 35-40%; key forage species use rate), year, and the interaction of stocking rate by year to explore the impacts of grazing and annual weather fluctuations on percent cover and density of honey mesquite (Prosopis glandulosa), a native but invasive shrub, at the Chihuahuan Desert Rangeland Research Center (CDRRC) in southern New Mexico. Precipitation data were collected continuously at the CDRRC; temperature data were collected at the neighboring USDA-ARS Jornada Experimental Range. Drought occurred in 12 of 25 study years and mean ambient summer temperature increased from 15.1 ± 0.15 to 15.4 ± 0.27°C between the first and last 12 years of the study period. We found that stocking rate and the interaction of stocking rate by year had no effect on mesquite percent cover or density (% cover: P = 0.70; density: P = 0.10), although year had a significant effect (% cover: P < 0.01; density: P < 0.01). Mesquite canopy cover increased by 3% from 3.8 to 7.1% cover and mesquite density increased by 175% (P < 0.01) from 284 ± 53 plants*ha to 782.08 ± 35 plants*ha between the last vs first three years of the study. Our preliminary results support a growing body of literature that suggests the overriding effects of climate (increased temperatures and prolonged droughts) will continue to drive undesirable shrub encroachment on Chihuahuan Desert rangelands even when animal stocking rates are kept at historically sustainable levels.