Herbivory Effects on Ephedra spp. in the Chihuahuan Desert

Two species of Ephedra: E. trifurca and E. torreyana inhabit shrub and grassland habitats in the northern Chihuahuan Desert. E. torreyana is limited to black grama grasslands where grasses are taller than the shrub. E. torreyana is heavily browsed by vertebrates and E. trifurca is browsed during some years. We established an experiment with cylindrical exclosures that excluded rabbits and rodents, rabbits but accessible to rodents, for comparison with E. torreyana plants available to all herbivores. Plants accessible to all vertebrate herbivores were significantly smaller with shorter stem lengths than plants in exclosures. We concluded that E. torreyana in black grama grassland are largely hidden from vertebrate herbivores and that intense herbivory reflects the degraded state of the study site which makes the E. torreyana evergreen shrubs apparent to vertebrates.