Experimental treatments for increasing perennial grass cover in a shrub-invaded grassland in the Southwestern Borderlands region of Arizona and New Mexico

Abstract

The density of mesquite (Prosopis spp.) and other woody species has increased on desert and semidesert grasslands in the southwestern United States. This increase in woody species has been associated with the decline of native herbaceous plants and a loss of biological diversity and productivity. There have been numerous attempts to reverse this situation. The effort reported here employed crushing the woody species with heavy equipment, with and without seeding native perennial grasses, and the use of prescribed fire. The treatments were not expected to kill the woody species but to reduce their dominance on the rangeland. The mechanical treatments significantly reduced the cover of woody plants compared to the untreated control plots on two ranchland sites and the effect lasted 9 years. On these ranches, perennial grass cover, particularly plains bristlegrass (Setaria macrostachys), and production were higher on crush + seed treatments for 2 or 3 consecutive years until the severe drought of 2003 negated the treatment effects. On pasture at a third site, woody cover was lower on treated plots compared to the control plots. The seeded and residual grass cover was not sufficient to carry the prescribed fires without supplemental ignitions. Though the fires initially reduced the crown cover of woody species on the treated plots, most recovered within 3 years. The treatments were not successful under severe drought conditions. A test under wetter conditions or with a more drought-tolerant mix of seeded grasses might produce different results. Continued, periodic fire treatments might reduce woody plant cover and competition with the grass stand. Additional fire treatments should be attempted in any future experiments.

Citation

Gottfried, Gerald J.; Turner, David; Bemis, Ronald J.; Neary, Daniel G.; Sundt, Peter; Traphagen, Myles B.; Edminster, Carleton B.; Decker, Donald D. 2020. Experimental treatments for increasing perennial grass cover in a shrub-invaded grassland in the Southwestern Borderlands region of Arizona and New Mexico. Gen. Tech. Rep. RMRS-GTR-417. Fort Collins, CO: U.S. Department of Agriculture, Forest Service. 35 p.