The widespread proliferation (or 'encroachment') of trees and shrubs in grasslands over the past 150 years is embedded in both natural and human systems. This dissertation addressed the following ecological and ethnoecological questions. Can seedling traits help us understand why so few woody species have encroached markedly into North American desert grasslands, and the conditions likely to promote their proliferation? What is the role of informal knowledge of the environment in efforts to manage woody plant abundance? Woody seedling survival often depends on rapid taproot elongation. In glasshouse experiments, initial water supply markedly affected taproot elongation in young seedlings. Response patterns may help explain recruitment patterns in Larrea tridentata, the principal evergreen woody encroacher in Sonoran and Chihuahuan Desert grasslands, and in Prosopis velutina and Prosopis glandulosa, the principal deciduous woody encroachers in Sonoran and Chihuahuan Desert grasslands, respectively. P. velutina and P. glandulosa showed greater sensitivity to water supply levels at the seedling stage than did the similar, related non-encroachers, Acacia greggii, Parkinsonia florida and Parkinsonia aculeata . This enabled the Prosopis species to overcome lower seed and seedling biomass to achieve similar taproot length to A. greggii and the Parkinsonia species. Consequently, population level advantages of lower seed mass, such as high seed numbers, may enhance encroachment potential in the Prosopis species without being negated by corresponding seedling survivorship disadvantages. I used semi-structured interviews to document informal rangeland monitoring by ranchers in southeast Arizona. Ranchers used qualitative methods to assess forage availability, rangeland trends and responses to woody plant suppression measures. Informal rangeland assessments informed ranchers' management decisions on sub-yearly, yearly and multi-year timescales. Informal monitoring appeared largely compatible with formal monitoring and natural science, and most ranchers integrated the two systems. Informal rangeland assessments can be valuable in planning woody plant suppression measures, particularly in light of the small number of formal long-term studies of brush suppression. Ecological studies may help predict places and periods of relatively rapid encroachment, perhaps enabling early or pre-emptive brush suppression measures. Thus, both seedling ecology and informal environmental knowledge are likely to be useful in managing woody plant populations in desert grasslands.

Borders and border barriers can be breached and boundaries and political agendas can change. The Great Walls of China, Hadrian's Wall, and the Iron Curtain have lost their strategic value. Walls are contested presently in the Middle East. And the unpopulated DMZ in Korea, while still of strategic value, is being recognized for its biodiversity and resurgence of endangered flora and fauna. Presently, the United States is building a defensive wall along the U.S.-Mexico border in the name of national security and to stem the tide of drug and human trafficking. In the process it has waived numerous environmental laws thereby putting transboundary ecosystems in danger of irreparable harm. Why should there be interest? For the reason, as put forth by Mumme and Ibáñez, that while much attention has been paid to adverse environmental effects within the United States, "little attention has been given to the potentially complicated effects of the international boundary, water, and environmental agreements to which [the United States and Mexico] are party should Mexico choose to press its rights at the level of international law. . . . As international treaties and protocols, these agreements enjoy a legal standing that may supersede the authority of most domestic legislation." The implications are far reaching. Mexico has sent diplomatic notes to the U.S. embassy in Mexico and to the U.S. Department of State, and the Secretaría de Medio Ambiente y Recursos Naturales (SEMARNAT), Mexico's environment secretariat, has held informal talks with the Department of the Interior (DOI) and with the Secretary of Homeland Security--all apparently of no avail. Canada's notes have been similarly ignored by the Department of Homeland Security. What then for the U.S-Mexico border fence? Will it eventually become a relic of past political policy? Is the United States to ignore the lessons of the past and void its environmental treaties and agreements with Mexico? Should we not be concentrating on comprehensive immigration reform and the causes of drug abuse in the United States rather than a short-term solution to long-term problems?

No description available.

With a precipitation falling to as low as 100 mm/yr, a high rate of non-renewable groundwater depletion, a growing population resulting in increased food demand and a lack of concern for water management, it is crucial to use all available tools to conserve water. One of the most important factors related to water management is crop evapotranspiration. This research examines five crop evapotranspiration models (one combination model, three radiation based models and one temperature based model) under hyper arid environment at practical field level. These models have been evaluated and calibrated using an alfalfa weekly water balance in 2010. The calibrated models have been evaluated and validated using wheat and potatoes on a weekly water balance, respectively. Based on the results and discussion, FAO-56 PM proved to be superior at estimating crop evapotranspiration while radiation and temperature based models underestimated evapotranspiration and would require subsequent local calibration. However, the drawback of FAO-56 PM is that it requires all weather data and is also significantly more complicated than other models. Important observations that were made are that calibrated Turc and Makkink models performed poorly even when they were calibrated while simple models such as calibrated Hargreaves-Samani (temperature-based) and Priestley–Taylor (radiation-based) can be adequately used for irrigation scheduling in a hyper arid environments. / Ministry of Higher Education, Saudi Cultural Bureau in Canada. Saudi Agricultural Development Company (INMA).

Thesis (PhD)--University of South Australia, 1998

In arid landscapes limited resources are concentrated into fertile patches that allow greater productivity than would otherwise be expected. Fertile patches are created and maintained by processes that modify soil topography and interrupt the flow of resources across the landscape. These processes may be abiotic or biotic in origin. Species that modify, maintain or create habitat have been termed ecosystem engineers. One group of soil disturbing ecosystem engineers creates fertile patches by modifying soil microtopography through foraging for food and creating habitat. This thesis examines the effects of soil foraging animals on resource concentration in arid environments and how effects are moderated by species and landscape. Chapter 1 provides an overview of the importance of fertile patches in arid systems and describes previous research on the effects of ecosystem engineers in arid environments. Chapter 2 examines how fertile patch creation by a well-studied arid zone engineer, the ant, varies between ant species and landforms, demonstrating that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects. Chapters 3, 4 and 5 compare the engineering effects of reintroduced native species, the Greater bilby (Macrotis lagotis) and Burrowing bettong (Bettongia lesueur) with the Sand goanna (Varanus gouldii) and the invasive European rabbit (Oryctolagus cuniculus) across three Australian landforms, revealing differences between reintroduced and invasive engineers at the both patch and landscape scales. At the landscape scale, differences in pit densities and resource concentration in foraging pits between landforms suggest that fertile patch development is not uniform. Chapter 6 examines whether the structure of the pit or the presence of litter per se explains observed increases in plant germination in foraging pits, and compares temperature and soil moisture conditions in bilby and bettong pits to the soil surface. Chapter 7 is a review that builds upon previous chapters, published and unpublished literature of the potential for reintroductions of ecosystem engineers to restore ecosystem function in degraded environments. Chapter 8 summarises the research presented in this thesis and its implications, and suggests directions for future work.

88 leaves : ill., maps, tables, photos. (part col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1976) from the Dept. of Botany, University of Adelaide

220 leaves : ill., maps, photos ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1976) from the Dept. of Botany, University of Adelaide

308 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--Dept. of Botany, University of Adelaide, 1976

Thesis (PhD)--University of South Australia, 1998