@article {50140, title = {Small mammal herbivory: Feedbacks that help maintain desertified ecosystems}, journal = {Journal of Arid Environments}, volume = {73}, number = {73}, year = {2009}, month = {01/2009}, pages = {62-65}, chapter = {62}, abstract = {

We tested the hypothesis that herbivores contribute to feedbacks maintaining arid ecosystems in a degraded state. We studied small mammal herbivory on a subshrub, broom snakeweed (Gutierrezia sarothrae), and perennial grasses at three sites: (1) ungrazed black grama (Bouteloua eriopoda) grassland; (2) grassland degraded by intense short-duration grazing; and (3) mesquite (Prosopis glandulosa) coppice dunes. Snakeweed was browsed by herbivores primarily during dry winter months. The average percent of G. sarothrae standing crop biomass removed by browsing was 9.2 in ungrazed grassland, 7.4 in intensely grazed grassland, and 4.1 in the dunes. In ungrazed grassland, an average of 12\% of grass cover was harvested by herbivores; in the intensely grazed plots \– 80\%. Herbivore exclusion plots showed that jackrabbits (Lepus californicus) were the primary browsers on snakeweed and rodents on grasses and G. sarothrae inflorescences. Rodent removal of G. sarothrae inflorescences allows wind dispersal of seeds in disturbed and desertified areas, thereby increasing abundance of this poisonous shrub. Grass-tiller cutting by rodents provides a strong feedback that may be responsible for keeping the grass cover low on the intensely grazed areas. Jackrabbit pruning has little effect on G. sarothrae abundance at any stage of desertification.

}, keywords = {browsing, desertification, herbivory, jackrabbit, livestock grazing, snakeweed}, doi = {10.1016/j.jaridenv.2008.09.003}, url = {/files/bibliography/09-001.pdf}, author = {Roth, G.A. and Walter G. Whitford and Yosef Steinberger} } @article {50380, title = {Jackrabbit (Lepus californicus) herbivory changes dominance in desertified Chihuahuan Desert ecosystems.}, journal = {Journal of Arid Environments}, volume = {70}, year = {2007}, month = {03/2007}, pages = {418-426}, abstract = {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 tridentate) and tarbush (Flourensia cernua) were compared to shrubs not browsed by the rabbits. In the missed shrub area, herbivory on F. cernua resulted in death of 46.6\% of the shrubs, compared to only 4.8\% of L. tridentate 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 creosotebush with heavily browsed tarbush may be a factor contributing to low utilization of creosotebush stems by jackrabbits. Differential browsing by the rabbits is shifting thee ecosystems toward an L. tridentate monoculture.}, keywords = {browsing, compensatory growth, creosotebush, Flourensia cernua, Larrea tridentata, preferential feeding, tarbush}, doi = {10.1016/j.jaridenv.2007.01.009}, url = {/files/bibliography/07-016.pdf}, author = {Roth, G.A. and Walter G. Whitford and Yosef Steinberger} } @conference {50715, title = {The role of animals in desertification: Herbivory patterns in degraded grassland}, booktitle = {89th Annual Meeting, Ecological Society of America}, year = {2004}, month = {August 1, 2004}, pages = {Abstract p. 438}, address = {Portland, OR}, abstract = {We examined the contribution herbivores make to the resistance and resilience of desert grassland ecosystems following a desertification process. The study took place in the Jornada Experimental Range, New Mexico, where, historically, desert grassland has gone through the desertification process during the past century. We monitored browsing signs on snakeweed (Gutierrezia sarothrae), the dominant sub-shrub in the landscape, and on all perennial grass species. Snakeweed was monitored for browsing on a monthly basis over a period of a year, while grasses were evaluated for herbivory in a single assessment at the end of their growing season. Plots grazed by livestock for 3 subsequent years were compared with undisturbed ones. Domestic animals grazing ceased in 1998, hence all herbivory documented is related to wild rabbits and rodents. Results show clear spatial and temporal herbivory patterns on snakeweed. The animals browsed in patchy patterns and have shown significant tendency for repeated browsing on specific plants, which indicates a nonrandom feeding behavior. Relatively high browsing frequency and biomass intake were documented between November and March, which forms the dry season in the northern Chihuahuan Desert. A significant decrease in snakeweed browsing was detected with the appearance of annuals and ceased almost completelywith the availability of perennial grasses. Despite the temporal pattern detected, plant-water content failed to explain the herbivore spatial feeding preferences. Grasses had much lower initial abundance and biomass compared to snakeweed. This resulted in a significantly higher relative percentage of grass biomass consumed by herbivory. That effect strongly intensified in formerly grazed plots where initial grass cover was the lowest. By the end of their growing season almost no grass flowering tillers survived which caused insufficient seed reservoir. Our findings show that herbivores contribute to the resistance and resilience of degraded grasslands by reducing the reestablishment of grasses.}, keywords = {desert grassland ecosystems, desertification, herbivory patterns, role of animals}, author = {Roth, G.A. and Walter G. Whitford and Yosef Steinberger} }