Jackrabbit (Lepus californicus) herbivory changes dominance in desertified Chihuahuan Desert ecosystems

This study addressed the question: can herbivory by a medium size herbivore, black-tail jackrabbits (Lepus californicus), change dominance in desertified ecosystems dominated by two species of shrubs. Shrubs that were pruned by jackrabbits in plant communities dominated by creosotebush (Larrea tridentata) and tarbush (Flourensia cernua) were compared to shrubs not browsed by the rabbits. In the mixed shrub area, herbivory on F. cernua resulted in death of 46.6% of the shrubs, compared to only 4.8% of L. tridentata shrubs. There was no evidence of jackrabbit browsing of dead F. cernua in a tarbush monoculture area. The canopy volumes of F. cernua plants that survived repeated browsing were significantly smaller than predicted based on unbrowsed plants with the same basal stem areas. Jackrabbit browsing resulted in increased canopy volume of creosotebush shrubs. Creosotebush average canopy volume significantly exceeded predicted values because of compensatory growth of stems from nodes below the severed point. Close spatial association of lightly browsed creosotebushes with heavily browsed tarbush may be a factor contributing to low utilization of creosotebush stems by jackrabbits. Differential browsing by the rabbits is shifting these ecosystems toward an L. tridentata monoculture.