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.