Shrub encroachment promotes positive feedbacks from herbivores that reinforce ecosystem change

Authors: ANDREONI, KIERAN - University Of Illinois; Bestelmeyer, Brandon; SCHOOLEY, ROBERT - University Of Illinois

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2025
Publication Date: 12/2/2025
Citation: Andreoni, K., Bestelmeyer, B.T., Schooley, R. 2025. Shrub encroachment promotes positive feedbacks from herbivores that reinforce ecosystem change. Ecosphere. 16(12):e70483. https://doi.org/10.1002/ecs2.70483.
DOI: https://doi.org/10.1002/ecs2.70483

Interpretive Summary: We evaluated the roles of cattle, oryx, and native herbivores in reducing grass cover, and tested whether herbivore effects on grass cover and seedling mortality varied among ecosystem states (grassland, ecotone, shrubland). Cattle and African oryx did not contribute strongly to vegetation dynamics. However, long-term exclusion of rodents and lagomorphs led to two-to-threefold increases in perennial grass cover compared to control plots. Effects were strongest in shrub-encroached states where mesquite shrubs provided these herbivores with cover from predators.

Technical Abstract: Herbivores can be drivers of ecosystem change by triggering and reinforcing vegetation transitions. Such processes may be prevalent in drylands with low productivity where herbivore abundances are linked to climate-driven resource pulses. In the Chihuahuan Desert, ecosystems are being transformed from black grama (Bouteloua eriopoda) grasslands to honey mesquite (Neltuma [formerly Prosopis] glandulosa) shrublands. Domestic livestock, exotic African oryx (Oryx gazella), and native rodents and lagomorphs have all been implicated as drivers of these transitions through multiple mechanisms affecting different plant life stages. Across shrub encroachment gradients, we paired a long-term (21'years) herbivore exclusion experiment focused on established perennial grasses with field trials measuring herbivory risk for perennial grass seedlings. We evaluated the roles of cattle, oryx, and native herbivores in reducing grass cover, and tested whether herbivore effects on grass cover and seedling mortality varied among ecosystem states (grassland, ecotone, and shrubland). Cattle and African oryx did not contribute strongly to vegetation dynamics. However, long-term exclusion of rodents and lagomorphs led to two-to-threefold increases in perennial grass cover compared to control plots (with open access to all herbivores) in shrub-encroached states where mesquite shrubs provided these herbivores with cover from predators. Likewise, herbivory of perennial grass seedlings was highest in the shrub-encroached states and was driven by rodents. Our results indicate that native rodents and lagomorphs exert strong control over perennial grass dynamics, creating positive feedbacks mediated by changes in habitat structure that can reinforce grassland–shrubland transitions in drylands.