@article {JRN55184, title = {Herbivory Effects on Ephedra spp. in the Chihuahuan Desert}, journal = {Open Journal of Ecology}, volume = {10}, year = {2020}, month = { February 2020}, pages = { 37-44 }, abstract = {

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.

}, keywords = {Desert Cottontail Rabbits (Sylvilagus auduboni), desertification, Ephedra torreyana, Ephedra trifurca, Exclosures, Jackrabbits (Lepus californicus)}, doi = {10.4236/oje.2020.102003}, url = {files/bibliography/20-007.pdf}, author = {Walter G. Whitford and Yosef Steinberger} } @article {51313, title = {Desertification and animal biodiversity in the desert grasslands of North America}, journal = {Journal of Arid Environments}, volume = {37}, year = {1997}, month = {1997}, pages = {709-720}, abstract = {

Studies of breeding birds and small mammals were conducted at a series of sites that form a gradient of severity of desertification. Desert grassland sites represented the least changed landscape units and mesquite coppice dunes represented the most severe degradation, an irreversibly degraded landscape unit. The hypothesis that desertification reduces species diversity was not supported by the data. Species richness and diversities (Shannon-Weaver H') of breeding birds were higher in the desertified areas than in the grassland with one exception. Data from a site dominated by the exotic African grass, Eragrostis lehmanniana, in south-eastern Arizona showed that breeding bird diversity was lower at that site than at a site in the same region that was dominated by native grasses. Species richness, diversity (H'), and abundance of small mammals were also higher in desertified areas than in desert grassland. Most grassland species of birds and mammals persist in the desertified habitats and species that are characteristic of shrublands colonize desertified desert grasslands. This accounts for the increases in species richness. However some species such as the banner-tailed kangaroo rat, Dipodomys spectabilis, are eliminated when grassland degrades to mesquite coppice dune or eroded creosotebush communities. These data suggest that other measures of faunal biodiversity such as keystone species may be better measures of the impact of desertification on animal biodiversity.

}, keywords = {biodiversity, breeding birds, desert grasslands, desertification, exotic species, rodents}, doi = {10.1006/jare.1997.0313}, url = {/files/bibliography/600.pdf}, author = {Walter G. Whitford} } @conference {51465, title = {Persistence of desertified ecosystems: explanations and implications}, booktitle = {International Symposium and Workshop on Desertification in Developed Countries: Why Can{\textquoteright}t We Control It?}, year = {1994}, month = {October 24-29, 1}, pages = {18-19}, address = {Tucson, AZ}, abstract = {

Desertification in much of the southwestern U.S. and northern Mexico has resulted in the replacement of perennial grasslands with desert scrublands. Scrublands dominated by C3 shrubs exhibit long-term persistence, resist control efforts, and are resilient in areas where control and revegetation with grasses have been attempted. Experiments using 5 consecutive years of summer drought using \"rain-out\" shelters and 5 consecutive years of approximately doubling the summer rainfall resulted in no significant changes in annual net above-ground primary production of creasotebush, barren tridentata, in either of the treatments. There were significant changes in species composition and above-grind net primary production of spring annual plants and some reduction of perennial grasses and fortis in droughted plots. There were small changes in decomposition rates and nitrogen mineralization potential but no quantitative differences in the Studies of shrub water budgets demonstrated that between 6 percent and 25 percent of the intercepted rainfall was translocated to deep soil storage by stemflow and root channelization. Nutrient minerals in stemflow water on creosotebush were 5 to 10 times more concentrated in stemflow than in thrnttghfsli and bulk precipitation. These data demonstrate that once shrubs are established, islands of resource enrichment of water and nutrients develop under the shrubs. The result is self-reinforcing systems that are resistant to disturbance. The characteristics of the shrub-dominated ecosystems documented in the experiments demonstrate that they are likely to persist with climate change. The data from these studies suggest that management of desertified landscapes in North America should focus on maintaining the residual grasslands and on the economic uses of the shrub-dominated ecosystems.

}, keywords = {desert scrublands, desertification, desertified landscapes, maintaining grasslands, management}, author = {Walter G. Whitford and G. Martinez-Turanzas and E. Martinez-Meza} }