Large-scale experimental evaluation of woody plant removal outcomes in desert grassland: restoration, novelty, or degradation?

Authors: Bestelmeyer, Brandon; Burkett, Laura; James, Darren; GAMON, JUAN - Bureau Of Land Management; SCHOOLEY, ROBERT - University Of Illinois

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: The long-term effects of brush management forage plant recovery are little understood in desert rangelands. We used a field experiment carried out in plots distributed over a 6 million acre area to test the effectiveness of tebuthiuron herbicide treatments on perennial grass recovery. We monitored vegetation cover in 43 pairs of plots representing treated and untreated conditions of the same plant community and environmental setting, including measurements at baseline, 5, 10, and in some cases 15 years post treatment. We also evaluated the effects of factors including soils, recent weather, elevation, slope, and grazing management in grass responses to treatment. Woody plant removal led to increases in plant species richness and perennial grass cover, but increases were due to disturbance-adapted grasses rather than species characteristic of reference states. On average, grass cover in treatments did not attain levels observed in the reference state, and on average we observed no overall cover loss that could increase soil erosion (although plant cover loss was observed in certain treatments). Elevation, slope, and baseline cover were important predictors of treatment-associated gains in plant cover, while higher grazing intensity tended to increase richness and forb cover. Our results indicate that while woody plant removal cannot be considered to restore a reference state due to the continued absence of reference grass species, it does lead to persistent increases in overall forage cover. The best results were observed at higher elevations, on steeper slopes, and when initial (pre-treatment) cover was higher.

Technical Abstract: Woody plant encroachment into grassy ecosystems is a worldwide phenomenon that radically transforms ecosystem services. Billions of dollars have been spent to remove woody plants, but there is great uncertainty about the conditions in which such removals are beneficial. We conducted a collaborative, large-scale monitoring experiment to test whether woody plant removal restored historical states, created novel states, or exacerbated land degradation and to examine the environmental conditions in which positive outcomes were optimized. We monitored vegetation cover in 43 pairs of plots representing treated and untreated conditions of the same plant community and environmental setting, including measurements at baseline, 5, 10, and in some cases 15 years post treatment. We evaluated environmental factors that may control variation in treatment outcomes. Woody plant removal led to increases in plant species richness and perennial grass cover, but increases were due to disturbance-adapted grasses rather than species characteristic of reference states. On average, grass cover in treatments did not attain levels observed in the reference state. Negative effects of woody plant removal on total canopy cover (related to soil erosion risk) and other plant functional groups of concern for wildlife were not observed. Elevation, slope, and baseline cover were important predictors of treatment-associated gains in plant cover, while higher grazing intensity tended to increase richness and forb cover. Our results indicate that while woody plant removal cannot be considered to restore a reference state due to the continued absence of reference grass species, it does not lead to obvious land degradation. Furthermore, positive outcomes are maximized where (and when) soil moisture limitations are lowest or the cover of responding plants is highest prior to treatments. We recommend that future restoration actions be conducted as experiments that pay special attention to co-production mechanisms, standardized monitoring methods, and salient and easily measured indicators.