I investigated whether rapid-maturing medics (genus Medicago) could establish and produce seed under the relatively dry winter conditions of southern Arizona. Hardseededness is common in many medics and may limit germination before fall rains. Therefore, I was also interested in the amount of medic germination that occurred following summer rainfall. Five accessions from four Medicago species (laciniata, polymorpha, truncatula and littoralis) were sown with or without a companion grass (Oryzopsis hymenoides) and grown with or without weekly 2 cm irrigation. While single-plant forage yields were over 8 times higher with irrigation, each accession established and produced up to 14 seeds for every seed sown under rainfed conditions. The companion grass had no influence on medic performance. Natural reestablishment occurred in all accessions from pods. Seedlings established in summer did not survive to flowering. M. littoralis appeared particularly well adapted to establishment under rainfed conditions in this environment. (Abstract shortened with permission of author.)

I measured digestible protein consumed by 4 (2 M, 2 F) captive desert mule deer (Odocoileus hemionus crooki). Deer were fed native forage collected from the Belmont Mountains, Arizona. Intake of forage differed significantly (P < 0.05) between sexes in every season. Intake of digestible protein for both sexes was highest in fall, lowest in the spring and summer for males and females, respectively. Significant (P < 0.05) differences of forage biomass were recorded among all vegetation associations and seasons in the Belmont Mountains. The most forage biomass was available in winter, the least in spring. Desert mule deer in the Belmont Mountains are close to the nutritional carrying capacity of the range. Other efforts to increase the deer population may not be effective if the forage base is not increased.

Germination of 10 native and exotic grasses was compared for temperature regimes representing abruptly and gradually fluctuating minimum and maximum wet seedbed temperatures in summer, spring, and winter, respectively, in the desert grassland. Gradually fluctuating temperatures produced similar total percent germination but more rapid germination than abruptly alternating temperatures and constant 25 degrees C. Lehmann lovegrass (Eragrostis lehmanniana) and 7 native grasses were sown into stands of Lehmann lovegrass that were left intact, burned, sprayed with herbicide and left standing, or sprayed and mowed. In 1992 mow and dead standing treatments reduced Lehmann lovegrass seedling density and improved establishment of cane beardgrass (Bothriochloa barbinodis), Arizona cottontop (Digitaria californica), green sprangletop (Leptochloa dubia), and plains bristlegrass (Setaria leucopila) compared to burn and control treatments. In 1993 the burn treatment reduced mature Lehmann lovegrass and enhanced establishment of sideoats grama (Bouteloua curtipendula), Arizona cottontop, green sprangletop, and plains bristlegrass compared to the other treatments.

A nearly monospecific stand of Lehmann lovegrass (Eragrostis lehmanniana Nees.) was grazed by cattle during two summer growing seasons to simulate short duration grazing. Grazing treatments were timed to coincide with preboot, boot to early inflorescence and hard seed phenological stages. During each treatment, grazing intensity on individual plants included heavy, moderate or light intensities. In 1990 maximum regrowth occurred when plants were grazed during boot to early inflorescence and at a light grazing intensity. In 1991, plants grazed during preboot or boot to early inflorescence and at a light or moderate intensity produced higher regrowth amounts than the other treatments. Plants grazed during boot to early inflorescence recovered significantly faster than plants grazed during preboot in 1990 and 1991. In 1990 lightly grazed plants recovered biomass faster than plants grazed at heavier intensities. In 1991 plants grazed at light and moderate grazing intensities recovered significantly faster than heavily grazed plants. Heavily grazed plants never produced enough regrowth to resemble moderately or lightly grazed plants within one growing season.

Tannins are polyphenolic compounds which precipitate, or conjugate, with proteins to make them indigestible. Tannins appear to confer anti-herbivore defense in shrub live oak (Quercus turbinella), a common browse in the interior chaparral of Central Arizona. The results of the present study indicate that the rumen microflora in goats can adapt to tannin rich diets thereby increasing in vitro dry matter digestibility of shrub live oak leaves. Major digestion inhibitors of shrub live oak appear to be fiber content (NDF, ADF, and lignin) and presence of condensed tannins in the leaves. In vitro dry matter digestibility of oak leaves appears to be higher in rumen microflora from goats than in rumen microflora from cows, although further research is needed to determine digestive efficiency among these species.

A prototype spatial decision support system for rangeland watershed management was developed to simplify the process of incorporating advances in technology into the decision process. The application utilizes an open framework by using Web services that are components that communicate using text-based messages, thus eliminating proprietary protocols. This new framework provides an extensible, accessible, and interoperable approach for spatial decision support systems. An important input into the SDSS is digital elevation data where data are produced using different methods, and with different accuracies and resolutions. Six digital elevation models were compared with survey data to evaluate accuracies at different locations in the Walnut Gulch Experimental Watershed. The sensitivity of the SDSS was evaluated using six management systems that were ranked based on minimizing sediment yield. The sensitivity of the DEM, contributing source area value, and precipitation event size on management system rankings was evaluated. Results provide assistance for users in selecting these data and modeling values. This research illustrated that recent advances in information technology can be effectively utilized in watershed decision support technology. The Internet-based SDSS provides core functionality required for rangeland watershed management education and decision-making. In comparing digital elevation data of different sources and resolutions with survey data, the DEM data approximated surfaces well, with the higher resolution data producing lower root mean square error values. And finally, different digital elevation models, contributing source area values, and precipitation event sizes produced different management system rankings. (Abstract shortened by UMI.)

Effects of weaning on metabolic profiles and hepatic IGF-1 mRNA of beef dams (Trial 1), and diet effects for early-weaned (EW) steers on response to an infectious bovine herpesvirus-1 (BHV-1) challenge (Trial 2) were investigated. Trial 1 treatments were arranged in a 2 x 2 factorial and included 14 heifers and 14 cows assigned randomly to one of two treatment regimens: EW (average age of 114 ± 13 d) or normal-weaned (NW, average age of 197 d). Heifers with calves EW experienced a greater increase (parity x weaning; P = 0.02) in BW over heifers with calves NW, but no change in BW due to weaning was observed for cows (P > 0.71). Early weaning (vs. NW) increased (P < 0.05) body condition (BC) and change in BC of all dams. No parity x weaning or parity x weaning x d interactions (P > 0.14) were observed for serum IGF-1, NEFA, or urea nitrogen (SUN). A parity x d interaction (P < 0.05) for hepatic IGF-1 mRNA, serum IGF-1, and SUN was observed, but no differences (P > 0.10) were detected between heifers and cows within d. For Trial 2, backgrounding treatments included a bermudagrass hay diet (CTRL); bermudagrass hay plus soybean meal (SBM) fed at 0.175% of BW (as-fed); bermudagrass hay plus SBM at 0.35% of BW; or a 70% concentrate (CONC) diet. During the receiving phase, all steers were fed CONC and intranasally challenged with BHV-1. Treatment x d interactions (P < 0.01) were observed for serum NEFA, total protein, SUN, glucose, immunoglobulin G (IgG), insulin, and rectal temperature. Three d after the BHV-1 challenge, IgG was greater (P < 0.05) for forage-fed steers vs. CONC. Three and 4 d after the challenge, rectal temperature was greater (P < 0.01) for protein supplemented steers vs. CTRL. Therefore, EW can increase BW and BC of first-calf heifers and decrease SUN in first-calf heifers and mature cows, and a higher quality diet fed to EW steers during a backgrounding phase enhances ADG and G:F, and increases febrile response (measured by rectal temperature) to an infectious BHV-1 respiratory challenge.

The main objective of this study was to describe the relationship between rangeland condition and land tenure system. Other management and biophysical variables were also analyzed. The data for this study were obtained from range condition studies done during the period of 1973 to 1993 in the State of Sonora, Mexico. The sample of 480 cases, included ejidos and private properties and covering an area of 1,774,479 hectares. The information was analyzed using simple tabulation, contingency analysis, correlation analysis, and multiple regression, using range condition as the dependent variable and the land tenure and management and biophysical variables as the independent variables. No direct linear relationship between rangeland condition and land tenure system was observed, but the chi-square result showed different rangeland condition distribution for both land tenure systems. The only variables linearly related to range condition were infrastructure condition and precipitation. Rangeland condition was most strongly related to precipitation in the year of survey, where higher condition ratings were observed in wetter years. Rangeland condition ratings for ejido holdings were higher than private holdings because the surveys on ejidos were performed in wetter years than private lands. Variables like precipitation are almost impossible to modify, but they should be taken into consideration in cattle management. People can modify some variables. For example, improving the infrastructure condition and attaining a better grazing distribution could help both types of properties to improve rangeland condition. Because precipitation level is so strongly related to rangeland condition in any one year, it is important that land managers, administrators, lenders, and policy makers demand many years of rangeland condition surveys, that include wet and dry years to evaluate all rangeland management practices, including the land tenure system.

Vegetation change, particularly from the grass to shrub lifeform, is a critical issue on the world's rangelands. The plant community present on a site is the primary determinant of the land's value for watershed protection, wildlife habitat, livestock production, and recreation. Studying past vegetation composition can help separate natural from anthropogenic sources of change and guide natural resource conservation and management decisions. Stable carbon isotope (δ¹³C) values and associated radiocarbon ages from soil organic matter (SOM) were used to evaluate vegetation change across five landscape positions at a small enclosed basin in southeastern Arizona. The utility of the carbon isotope method was verified for this site based on the clear and wide separation in δ¹³C values between grasses having the C₄ photosynthetic pathway and shrubs having the C₃ pathway. The direction and timing of vegetation dynamics differed with landscape position along a gentle elevation gradient from the basin outlet to a nearby volcanic ridge top. Warm-season C₄ perennial grasses have dominated the basin outlet, center, and toe slope landscape positions since at least 5000-6000 yr BP, except for a dramatic increase in C₃ plants at the bottom of the outlet excavation around 5000 yr BP. This isotopic change is associated with rounded cobbles that may have been a stream channel, suggesting the presence of C₃ herbaceous or woody riparian vegetation. On mid-slope and ridge top landscape positions, where semidesert shrubs now dominate, warm-season perennial grass, composition decreased from approximately 60% as recently as 400 yr BP to only 1.5% now. SOM density separates were also analyzed. The youngest SOM is represented by the <2 g/cm³ density fraction that turns over in a few years to several decades and has a post-bomb radiocarbon age. For the ridge top landscape position, this fraction yielded 39% C₄ vegetation, suggesting that the conversion from grass to shrub vegetation occurred recently.

Attempts to establish native grasses in revegetation projects in semidesert grasslands in the Southwestern United States often fail whereas revegetation of non-native lovegrasses (Eragrostis spp.) is frequently more successful. The reasons for differential establishment are unclear. Species may be differentially vulnerable to variable patterns of soil moisture availability during germination and seedling growth. Field experiments described within this dissertation investigated the effects of planting date and species on germination, emergence, mortality, survival, and seedling growth of native and non-native warm-season perennial grasses seeded in southeastern Arizona. Native species [Sideoats grama (Bouteloua curtipendula (Michx.) Torr.), cane beardgrass (Bothriochloa barbinodis (Lag.) Herter), green sprangletop (Leptochloa dubia (H.B.K.) Nees), and Arizona cottontop (Digitaria californica (Benth.) Chase)] germinated rapidly, produced a few, large cohorts of seedlings, and retained limited residual germinability following initial rain events. In contrast, Lehmann lovegrass (Eragrostis lehmanniana Nees) germinated more slowly, produced more, smaller cohorts throughout the growing season, and retained more residual germinable seeds following initial rains. Mortality of all species was highest in the first week following emergence. Early development of adventitious roots and relatively high rates of biomass accumulation exhibited by Lehmann lovegrass are potentially advantageous under variable environmental conditions. Establishment of fast-germinating native species is favored by rainfall patterns that support early seedling growth subsequent to initial rains; the risk of seeding failure for these species increases when lengthy dry periods follow initial rain events. Years in which summer soil moisture conditions are highly variable would tend to favor Lehmann lovegrass establishment. Gradual depletion of the seedbank, early seedling growth characteristics, and rapid production of seed in response to drought increase the probability that at least one cohort will establish or will survive long enough to replenish the seedbank for subsequent years. In southeastern Arizona, the probability of intermittent dry periods decreases as rainstorm frequency increases near the end of July, yet the recommended time to reseed is early summer. Adjusting the planting date to late July or early August may improve the potential for successful revegetation of native species that germinate rapidly and produce few cohorts following initial rains.