This research focused on the development of an agent-based model of livestock herds in semi-arid rangeland and its application in view of the sustainable use of natural resources and effects of climate change.

Higher stocking density under seasonal-rotation grazing is expected to increase plant abundance because expanded animal distribution and reduced selective grazing on forage species will reduce the spatial variation and competitive advantage of non-forage species compared to yearlong grazing. Rangeland scientists struggle with how long rangeland experiments must continue in order to detect grazing treatment effects, particularly in semi-arid ecosystems with slow responses and high spatio-temporal variability. My first study investigated grazing system effects on plant abundance (cover and density) over the short-term (12yrs) or long-term (22 or 34yrs) after accounting for covariates (mesquite and precipitation gradients). My second study assessed how grazing systems affected spatial variation in grass abundance over 22 or 34 years after accounting for precipitation gradient. The first study was a course resolution approach, looking at grazing impacts on plant abundance. The second study was a finer resolution assessment of the underlying assumption that rotational grazing systems reduce selective grazing. Using split-plot analysis of variance, with year as the split, changes in mean plant abundance and variance in grass abundance were compared between two grazing systems (yearlong vs. seasonal rotation), after accounting for covariate(s). Variance of grass abundance among sample locations within an experimental pasture was the measure of spatial variability and was expected to increase with selective grazing. Grazing systems did not influence plant abundance or spatial variation of grasses. The absence of grazing effect may be due to overriding influences of grazing intensity, large pasture sizes, temporal variation in precipitation, and few replicates. Specific to spatial variation, the absence of grazing system effect may be due to discrepancies in transect representation across ecological sites and spatial variation of grasses occurring at scales different than the 30-m transect size. Like earlier research, my studies failed to substantiate the fundamental premise for implementing rotational grazing systems. This exposes challenges that confront rangeland scientists when implementing grazing studies in spatio-temporally heterogeneous ecosystems. I recommend that research shift from comparing rigid schedule-driven grazing systems to more adaptive management approach where there are comparisons between different levels or different designs of flexible systems.

Rangelands comprise between 40 and 50 percent of all U.S. land and serve the nation both as productive areas for wildlife, recreational use, and livestock grazing and as watersheds. The health and management of rangelands have been matters for scientific inquiry and public debate since the 1880s, when reports of widespread range degradation and livestock losses led to the first attempts to inventory and classify rangelands. Scientists are now questioning the utility of current methods of rangeland classification and inventory, as well as the data available to determine whether rangelands are being degraded. These experts, who are using the same methods and data, have come to different conclusions. This book examines the scientific basis of methods used by federal agencies to inventory, classify, and monitor rangelands; it assesses the success of these methods; and it recommends improvements. The book's findings and recommendations are of interest to the public; scientists; ranchers; and local, state, and federal policymakers.

This book is open access under a CC BY-NC 2.5 license. This book provides an unprecedented synthesis of the current status of scientific and management knowledge regarding global rangelands and the major challenges that confront them. It has been organized around three major themes. The first summarizes the conceptual advances that have occurred in the rangeland profession. The second addresses the implications of these conceptual advances to management and policy. The third assesses several major challenges confronting global rangelands in the 21st century. This book will compliment applied range management textbooks by describing the conceptual foundation on which the rangeland profession is based. It has been written to be accessible to a broad audience, including ecosystem managers, educators, students and policy makers. The content is founded on the collective experience, knowledge and commitment of 80 authors who have worked in rangelands throughout the world. Their collective contributions indicate that a more comprehensive framework is necessary to address the complex challenges confronting global rangelands. Rangelands represent adaptive social-ecological systems, in which societal values, organizations and capacities are of equal importance to, and interact with, those of ecological processes. A more comprehensive framework for rangeland systems may enable management agencies, and educational, research and policy making organizations to more effectively assess complex problems and develop appropriate solutions.

Cum laude graduation (with distinction).

Grazing by wild and domestic mammals can have small to large effects on plant communities, depending on characteristics of the particular community and of the type and intensity of grazing. The broad objective of this report was to extensively review literature on the effects of grazing on 25 plant communities of the southwestern U.S. in terms of plant species composition, aboveground primary productivity, and root and soil attributes. Livestock grazing management and grazing systems are assessed, as are effects of small and large native mammals and feral species, when data are available. Emphasis is placed on the evolutionary history of grazing and productivity of the particular communities as determinants of response. After reviewing available studies for each community type, we compare changes in species composition with grazing among community types. Comparisons are also made between southwestern communities with a relatively short history of grazing and communities of the adjacent Great Plains with a long evolutionary history of grazing. Evidence for grazing as a factor in shifts from grasslands to shrublands is considered. An appendix outlines a new community classification system, which is followed in describing grazing impacts in prior sections.

Soil scientists and rangeland ecologists are increasingly making range management decisions based upon projected impacts to soil health but disagreement persists regarding the direction, magnitude, and rate of potential soil health changes. According to the United States Department of Agriculture - Natural Resources Conservation Service (USDA NRCS), soil health is defined as the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans. Thus, it is important for soils to be managed sustainably for future generations. Soil health is complex and measured by its physical, chemical, and biotic properties all of which interact. Examples of these soils properties are: structure, nutrient content, and microbial activity. All are closely related to organic matter - an excellent indicator of soil health. Grazing lands represent ~40% of the earth’s terrestrial surface and have tremendous potential to sequester carbon while cattle, numbering ~1 billion head worldwide are one of the main grazers upon them. Within the state of Wyoming USA, cattle outnumber people 2.5:1 and anthropogenic management of their grazing likely has an effect on soil health. Unfortunately, the majority of research and data obtained from grazing studies have not occurred at working cattle ranches and may be hindering producer adoption. Furthermore, soil monitoring, soil health criteria, and expectations have generally been constrained to row cropping systems in mesic climates, not the semi-arid rangelands of the western US, and have been secondary to forage quality and animal performance. We conducted field research at two physical sites in Wyoming supplemented by systematically reviewed literature at the global scale to identify any research “gaps” with the intention of providing credible information and advice to regional producers seeking input. At our physical sites, located in McFadden and Lingle, Wyoming, different Animal Day pasture categories, grazing regimes, and densities are being utilized to understand the effects of cattle grazing on Wyoming’s native rangelands. The McFadden site is a working ranch located on a high-elevation steppe that rotationally grazes three herds of ~300 Angus/Simmental/Gelbvieh crossbred cows. Eleven native upland pastures of 167 to 367 acres (68 to 149 ha) were sampled in order to understand the relationship between grazing time per pasture and soil and plant quality. The Lingle site is a traditional research design at the University of Wyoming’s James C. Hageman Sustainable Agriculture Research Facility (UW SAREC) on a northern mixed-grass prairie, consisting of twelve 1 acre (0.405 ha) paddocks and three grazing densities; notably ‘not grazed’ (NG), ‘moderate rotationally grazed’ (MRG), and ‘ultra-high density rotationally grazed’ (UHD), replicated spatially four times each in a randomized complete block design. Our Chapter 1 global literature review resulted in 42 studies with an average publication date of 2010 from four continents. Cattle were utilized as the main grazer in North America while sheep were the main grazer in Asia. The majority of the research was conducted at research facilities, and organic matter’s response to grazing was generally neutral. Chapter 2 ranch-scale research conducted at Sims Ranch in McFadden, Wyoming determined that organic matter may be an indicator of time in pasture and established a soil health baseline for future research. Chapter 3 grazing density research at UWSAREC revealed time of sampling and environment interactions and established a soil health baseline for continued research.

The New Forest in southern England is an area of mixed vegetation set aside as a Royal Hunting Forest in the eleventh century and since that time subjected to heavy grazing pressure from large herbivores. The entire structure of the Forest and its various communities has been developed under this continued history ofheavy grazing, with the estab lishment of a series of vegetational systems unique within the whole of Europe. The effects of large herbivores in the structuring of this eco system in the past, and the pressure of grazing continuing to this day, have in turn a profound influence, indeed the dominating influence, on the whole ecological functioning of the Forest system. Because of its assemblage of unique vegetation types, the area is clearly of tremendous ecological interest in its own right. In addition, its long history of heavy grazing ani the continued intense herbivore pressure make the New Forest an ideal study-site for evaluation of both short-term and long term effects of grazing upon temperate ecosystems. The N ew Forest (some 37,500 ha in total area) currently supports a population of approximately 2,500 wild deer (red, roe, sika and fallow); in addition 3,500 ponies and 2,000 domestic cattle are pastured on the Forest under Common Rights.