This study evaluated the influence of Lehmann lovegrass (Eragrostis lehmanniana Nees) on the densities and spatial distributions relative to mesquite (Prosopis velutina Woot.) of two native grasses, Arizona cottontop (Digitaria californica (Benth.) Henr.) and Rothrock grama (Bouteloua rothrockii Vasey), in the semi-desert grassland. Also evaluated were the affects of independent variables range site, elevation, and proportion mesquite cover on these relationships. General Linear Model analyses showed no association between Lehmann lovegrass and either the densities or the distributions of the native species. Arizona cottontop showed an affinity for mesquite cover, while Rothrock grama and Lehmann lovegrass both showed an aversion to mesquite canopy. The relationship of Rothrock grama to mesquite cover was affected by range site. The relationship of Lehmann lovegrass to mesquite cover became less averse with increasing elevation and as its density increased. These results contradict suggestions that Lehmann lovegrass is associated with declines in native grasses.

Lehmann lovegrass (Eragrostis lehmanniana Nees.), a perennial bunchgrass, has established itself well since its introduction from South Africa. Arizona cottontop (Digitaria californica (Benth.) Henr.) is a native perennial bunchgrass that sometimes appears on the same sites and soils as Lehmann lovegrass. In a greenhouse, emergence was evaluated using line-source irrigation which simulated natural summer precipitation on two soil types collected from the Santa Rita Experimental Range (SRER). Density and cool-season growth of each species were monitored along transects located at the SRER on three different soils. I found that although Lehmann lovegrass and Arizona cottontop emerge similarly on two soils, Arizona cottontop un-emerged caryopses had a better percent survival rate. Also, Lehmann lovegrass plants had more green above-ground biomass from November to May than Arizona cottontop, and Lehmann lovegrass was able to greenup more rapidly following rain. This study showed these species have similar emergence characteristics, but that their cool-season greening differs.

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Pastoral nomadism in arid and semiarid regions has evolved over many centuries as a rational response to uncertain climatic conditions and fragile ecosystems. Nomads are the main inhabitants of the bast area of marginal rangeland in Saudi Arabia. However, in the past few decades, modernization, in the form of improved transportation and access to water, combined with government subsidy of supplemental barley to the nomads of regions such as At-Taisyiah in the northern part of Saudi Arabia have provided the nomadic tribes with a buffer against uncertain climatic conditions and against the consequences of increasingly aggressive grazing of the range. In this study, an integrated approach is adopted to assess the impact of modernization and government intervention on the nomads and on the health of rangelands in At-Taisyiah. The approach consisted of interview with nomads in the region, a socio economic study of the region's nomadic lifestyle, analyses of several range capability assessment studies, and utilization of stochastic simulation models. Three major areas were identified in need of major improvements. These are the nomads' perception of range land resources, use of rangeland, and government policies towards nomads and rangeland. Improvement in these areas will play a major role in slowing the acceleration of desertification of marginal range lands in Saudi Arabia. comparison of Monte-Carlo simulations of four different grazing intensity scenarios and 12 different levels of government subsidies confirmed that lower grazing intensities provide the only means for sustainable utilization and for the combating of desertification of the rangelands in At-Taisyiah region.

There are thousands hectares of abandoned farmlands in Arizona. Research on practical methods for establishing native plants and wildlife on abandoned farmlands is under way at the Desert Botanical Garden of Phoenix and the University of Arizona. This research is aimed at improving understanding of the primary variables affecting restoration of abandoned farmlands. These variables include: water treatments, planting dates, mulch and water catchment, seasonal planting and plant species composition. The objectives of the study is to investigate the effect of land restoration practices on nitrogen, protein, fiber (NDF and ADF), ash and dry matter contents of three Atriplex species under different management and site conditions. The amount of nutrient contents in Atriplex species growing on abandoned farmlands under irrigation and conservation practices is higher when compared to no irrigation or control in Casa Grande research site. Atriplex species growing under mulch and water catchment condition had significantly higher nutrient content compared to other treatments. Furthermore, seasonal planting in abandoned farmlands affected the nutrient contents of Atriplex cultivars at the University of Arizona farm. The Atriplex cultivar planted in the winter had higher nutrient contents when compared to those planted in the summer and irrigated with a sprinkler irrigation system for some cultivars. A better understanding of how these variables affect nutrient contents of Atriplex species used in this restoration study will play an important role in directing public interest towards the revegetation of abandoned farmlands in southern Arizona for food production.

Atriplex canescens (Pursh) Nutt., Atriplex polycarpa (Torr.) Wats., and Atriplex lentiformis (Torr). Wats. have been considered candidate perennial shrubs for revegetation of abandoned farmlands in southern Arizona. Objectives of the 1992-1994 field studies were to investigate the establishment characteristics of populations of these species and to estimate water requirements for establishing transplants and/or seedlings under a line-source sprinkler irrigation system. During the summer on a sandy loam soil, seedling establishment occurred at total water amounts greater than 200 mm but was absent at amounts less than 150 mm The poor stand establishment was attributed to high soil temperatures at 1 to 3-cm depth which were not optimum for seed germination. Transplant survival percentages were greater than 89% except for accessions of A. canescens var. linearis (S. Wats.) Munz, which were affected by rabbit herbivory. Transplants were successfully established by planting into a wet soil profile followed by cumulative precipitation amounts of 60 to 70-mm. Establishing Atriplex taxa during the summer using transplants was more promising than direct-seeding. On a silt loam soil during the 1993 winter, stand establishment was not increased under cumulative precipitation and irrigation amounts greater than 100 mm compared to 66 mm of precipitation. On a clay loam soil during the 1994 winter, supplemental irrigations increased the probability of seedling emergence and stand establishment was higher under total water amounts greater than 100 mm. Differences between years in response to the line-source irrigation gradient were attributed to the number of consecutive days when soil moisture at 1 to 3-m depth was high for optimal seedling emergence. During the winter, plant heights were not affected by total water amounts between 182 to 248-mm (1993) and between 119 to 150-mm (1994), whereas heights were reduced at total water amounts less than 100 nun in 1993, and less than 90 mm for all species in 1994 except A. polycarpa. In southern Arizona where precipitation is erratic in amount and timing, supplemental irrigations may increase the probability of successful seedling establishment of Atriplex shrubs.

I investigated the effects of prescribed fire on Agave palmeri , an important seasonal food source of the federally Endangered bat, Leptonycteris curasoae yerbabuenae. Three different treatments were randomly assigned to plots containing agaves within a burn unit: plots were burned with extant fuel, plots were left unburned, and plots were burned with an augmentation of fuel. Agaves were surveyed before the fires, immediately after the fires, and one and two years after the fires. Mortality and survivorship with the fuel load, agave size and the type of clusters in which the agaves grew. Agaves near mesquite and acacia trees or dead, dried agaves experienced higher mortality than agaves growing elsewhere. Agaves in plots with added fine fuels also had higher rates of mortality. One year post-fire, mortality was low in all treatments and recruitment was higher on augmented and burned plots than on unburned plots. Two years post-fire, mortality of small Agave palmeri was associated more strongly with rainfall than with fire treatment, while mortality of larger height classes of agaves exhibited a delayed response to fires.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

The invasive Chinese tallow tree (Sapium sebiferum) is difficult to control because of its large seed bank and ability to resprout from cut stumps. I performed laboratory and field experiments to evaluate the effectiveness of mulching live trees for restoring invaded prairies. Herbicide use was limited to manual application to cut stumps. I manipulated mulch depths and types in the field and measured soil temperatures beneath them. At depths of as little as 5 cm, Sapium mulch damped soil temperature fluctuations and reduced seedling emergence. Reduced seedling emergence was not the result of allelopathic compounds in Sapium mulch because other mulch types suppressed emergence similarly. Substantial regrowth of native vegetation occurred through the mulch. Independent manipulations of mulch depth and temperature fluctuations in a lab experiment confirmed that mulch suppressed seed germination indirectly via soil temperature effects. This prairie site can now be managed by mowing or burning.

Re-introducing heterogeneity to native North American rangelands is imperative to maintaining grassland biodiversity, and it has been suggested that using a variety of cattle grazing intensities on the landscape could accomplish this. I used generalized linear mixed models to describe the effects of grazing intensity on vegetation structure, plant species diversity and plant communities over four years. I used the Mantel test and non-metric multidimensional scaling to illustrate changes in plant communities with varying grazing intensities and over time. Effects of grazing were cumulative and changed over time, upland and lowland habitats responded differently to grazing intensity, and heterogeneity was maximized at the landscape scale under a variety of grazing intensities. When conservation is the primary goal, a variety of grazing intensities on the landscape can be used to increase heterogeneity, and therefore grassland biodiversity.