Gauging the relative effects of mammalian herbivores on shrub encroachment at Jornada Basin

Kieran Andreoni

Grassland-to-shrubland state transitions can impose inconsistent but often significant effects on ecosystem services and biodiversity of drylands.  Mammalian herbivores can play an important role in determining such states because they connect higher a (i.e., predator) and lower (i.e., plant) trophic communities.  Cattle, rodents, and lagomorphs have been shown to often contribute to such transitions in the northern Chihuahuan Desert.  Likewise, exotic African oryx have dispersed into the Jornada Basin, preferring grassland habitats to shrublands, highlighting a need to understand their role in grassland-to-shrubland state transitions. Through a combination of exclosure treatments, seedling herbivory experiments, and dietary analysis we aim to expand our understanding of herbivory effects on state transitions by integrating potential impacts of livestock and native small mammals with that of oryx.  We hypothesize that certain mammal taxa will contribute more strongly to the triggers and feedbacks of shrub encroachment.