Axelrod (1958) suggested that the late Tertiary shift in regional climate -- the elimination of summer rains -- had a profound influence on the evolution of biotic provinces in the American southwest. In particular, the taxa endemic to biotic provinces characterized by summer drought, e.g., the Mojave Desert, should be derived from ancestors that likely inhabited regions of summer rain, e.g., the Chihuahuan Desert. Further, the derived features of summer-drought taxa should be related to water stress. I examined Axelrod's thesis, using a combination of phylogenetic systematics, physiological ecology, and vicariance biogeography. The first chapter is a cladistic study of the pinyon pines, 13 taxa of small trees that range from the summer-wet regions of Mexico to the summer drought regions of Nevada and California. A parsimony analysis using twenty morphological characters showed that the most recently derived pinyons are from regions of summer drought. The "summer-drought" taxa are characterized by relatively few needles per fascicle. Because fewer needles per fascicle results in a reduction in the needle surface-to-volume ratio, Haller (1965) hypothesized that fewer needles in pines is an adaptation to reduce transpirational water loss. The second chapter reports on a two year study of the xylem pressure potentials of single- and double-needled fascicles of hybrid pinyons in central Arizona. The results showed no significant differences between single- and double-needles. I concluded that either needle morphology does not effect water relations, or that the relatively high precipitation during the study did not allow significant water stress to occur. The third chapter uses the methods of vicariance biogeography to search for a common pattern of relationship between southwestern biotic provinces, as indicated by the relationships of their endemic taxa. Using a biogeographic parsimony analysis, I compared the area cladograms of six taxa -- junipers, pinyon pines, the composite Palafoxia, hedgehog cactus, desert tortoises, and gecko lizards. The most parsimonious area cladogram supports Axelrod's (1958) hypothesis, but also shows that some taxa, notably the junipers, support other patterns of area relationships, e.g., summer-drought primitive. I suggest that there is no single pattern of area relationships because of the effects of the Pleistocene (including dispersal and extinction) and vicariance events other than the Tertiary climatic change, e.g., the separation of the Baja peninsula from mainland Mexico during the Miocene.

Mine land reclamation techniques were tested in arid Southeast Arizona for their potential to enhance reclamation success on two sites at different elevations (1400- and 1650-meters above sea level) on two sandy loam soils (Arkose and Gila Conglomerate). Seedbed preparation (smooth or rough surface) and straw mulch treatments (surface mulch, mulch incorporated into the soil, or no mulch) were tested for their potential to establish vegetation and prevent erosion. Gila soil retained 12.9% more soil moisture than the Arkose soil and was preferred by the seed mix (Gila: 64.4 plants m⁻²; Arkose: 23.2 plants m⁻²). A rough surface with surface mulch was recommended. Gila soil was more susceptible to erosion likely because it contained smaller soil particles. Rock cover was associated with significantly (P=0.0138) reduced rate of soil movement (0.1588 cm soil loss or accumulation per 1 percent rock cover). Proper soil management can be critical for reclamation success.

Exurbanization is occurring where large tracts of land are being sold to developers. Typically these are ranches that are then divided into 40-acre parcels and sold by developers, avoiding subdivision regulations requiring paved streets, utilities and other amenities. The result is an unplanned subdivision with no infrastructure, and tax revenues that cannot offset the cost of providing it. Interviews with professional planners suggested there may be independent variables capable of predicting the amount of human disturbance in an exurban area: parcel size, full cash value, tenure, distance to paved roads, site-built housing, mobile homes, and presence of biological or riparian areas. A total of 7,465 acres (3,022 ha) of parcel disturbance were digitized in exurban Arivaca, acreage values were converted to a binary dependent variable and used in logistic regression analysis to test independent variables' predictive value. Four were statistically significant: parcel size, full cash value, mobile homes and site-built housing. Landscape fragmentation was also tested using the presence of the variable scoring highest in probability - site-built housing. Zones of influence with a negative ecological influence surrounded the homes - up to 5,055 acres (2,046 ha) were impacted. Interviews with an exemplary sample of residents regarding their land use ethic found all had very strong opinions on how their properties should be treated as well as undesirable land uses such as overgrazing, over-use of groundwater for short-term economic gain and use of off-road vehicles. An explanation of the small sample size of both planners and residents is warranted. Planners were limited to those working in Pima County government who had professional experience with the study area of Arivaca and were familiar with its particular situation. The number of Arivaca residents interviewed was intended to discern an exemplary group's opinions based on how large a parcel they owned, the various sizes being a typical cross-section of acreage in the study area. What these findings illustrate is (1) the difficulty of predicting human-induced disturbance, (2) land fragmentation is more than the actual areas of physical disturbance and (3) some residents are aware of impacts related to their activities, mitigating damage wherever possible.

This research applied the social network approach to unveil the social structure underlying the members of two traditional irrigation systems (TISs) in Sonora. This research used two TIS case studies representing rural communities located in arid and semiarid lands in the Sonoran Desert region, in the northwestern part of Mexico. The irrigators represented a subset of rural villages where everyone knew everyone else. The theoretical framework in this study suggested that social embeddedness of the economic activities of TIS irrigators is an important factor supporting their local institutions. Irrigators who are socially embedded posses more social capital that help them in overcoming social dilemmas. Evidence of social embeddedness is theoretically incomplete when not related to a tangible dimension of the TIS's performance. This research also dealt with the difficulty of assessing the sustainability or successfulness of a TIS. The results showed that the irrigators sharing a rural village are entangled in a mesh of social ties developed in different social settings. The most salient variable was family; cooperative ties within the irrigation system tend to overlap more than the expected by chance with kinship relationships. Likewise, irrigators had a strong preference for peers geographically close or those within the same irrigation subsector. Finally, the qualitative part of the study did not reveal the presence of severe social dilemmas. Irrigators in each community have developed successful forms of local arrangements to overcome the provision and appropriation issues typical of common pool resources. Nevertheless, the qualitative analysis revealed that there are other socioeconomic variables undermining the sustainability of the systems, such as migration, water shortages and social capacity of the systems.

Human-induced land degradation and climate change can reduce agricultural productivity and increase susceptibility to food shortages at local and global scales. Planting perennial crop species, such as fruit and nut crops, may be an intervention strategy because of their beneficial contributions to sustainable agriculture and human nutrition. Many perennial temperate fruit and nut species are however, particularly vulnerable to frost events, drought, insufficient chill hours, and disease and insect outbreaks. Modifying these species to yield harvests under a wider range of biotic and abiotic conditions may increase the value and long-term viability of perennials in agroecosystems. This dissertation examines adaptation and ecogeography in temperate perennial fruit crops, using apple (Malus sensu lato) as an example for case studies. The resilience of feral domestic apple trees in abandoned farmstead orchards throughout the southwestern U.S. indicates plasticity in adapting to local environmental conditions. Dendrochronology reveals these trees tend to persist where they have access to supplemental water, either as shallow groundwater or irrigation. While domestic apples are cultivated under a range of growing conditions, wild relatives of agricultural crops may further expand the cultivable range of the species. Crop wild relatives are species closely related to agricultural species, including progenitors that may contribute beneficial traits to crops. Sampling the genetic variation in crop wild relatives may benefit from ecological genetics and GIS theory to reveal genetic structure. The Pacific crabapple is an example of a wild apple relative that may contain genetic variation useful in apple breeding. Species distribution modeling of the Pacific crabapple identifies a narrow climatic window of suitable habitat along the northern Pacific coast, and genetic fingerprinting reveals a highly admixed genetic structure with little evidence of natural or cultural selection. While the moist coastal Pacific Northwest is not necessarily characteristic of many apple-growing regions, the species may have useful adaptations transferable to domestic apples. Genetic resources offer a promising source of raw material for adapting crops to future agricultural environments; their characterization, conservation, and use may offer important contributions to adaptation and use of perennial crops in agro-ecosystems.

No description available.

The North American Monsoon System (NAMS) is a significant weather and climate phenomenon that brings critical rainfall to the southwestern United States and northwestern Mexico. As a result of the North American Monsoon Experiment, and research efforts surrounding the field campaign, the understanding of the NAMS has increased considerably over the last 15 years. In addition questions concerning potential flash flood causing mechanisms of the NAMS have not been thoroughly investigated. This dissertation is comprised of two papers that collectively address the aspects of the literary understanding of the NAMS as we know it today and conduct an investigation into the complex interactions between various weather systems that may influence the NAMS. In the first paper, a review of the major research of the NAMS literature since the last comprehensive review 15 years ago is conducted. The results of his review are assessed for where our understanding has been improved and where future research needs to be guided for purposes of the second paper. Based upon the results from the literature review, the second paper focuses on identification of inverted troughs and gulf surges based upon lower- and mid-level atmospheric parameters for purposes of assessing the impacts on National Weather Service Storm Report flash flood dates. This research contributes to the synthesis of the current knowledge of the NAMS in general and to the specific regional impacts that do occur during periods of heavy precipitation over the NAMS region for purposes of improving meteorological predictability of flash flooding. The results can (1) gauge our understanding of the NAMS literature to date and (2) improve meteorological forecasts through the recognition of synoptic and sub-synoptic patterns related to the NAMS that are most likely to cause flash floods.

Dendrochronological research on Juniperus polycarpos growing in west and central Iran reveals that the radial growth in this species depends mainly on the amount of precipitation in the more arid regions. When the amount of rain is sufficient, i.e. above 450 mm, the prevailing summer temperature seems to become the limiting factor. Favorable conditions which prevailed during the periods 1685-1695 and 1790-1800 resulted in better width growth, while less favorable conditions which prevailed during the years 1725-1735 and 1855-1865 resulted in narrow rings.

"Last biannual progress report and final report describing work under NASA contract no. NAS5-21812."

Progress in human development is threatened by the complexities of global environmental change - a defining challenge of our time. Appropriate societal responses are needed to address disturbances and increasing vulnerability of social-ecological systems. This changing context calls current development thinking into question and requires new approaches, policies, and tools to cope with growing uncertainty. With a focus on capacities instead of vulnerabilities, an approach is needed emphasizing the role of communities in planning interventions and strengthening community resilience. This research draws on vulnerability, social-ecological systems and drylands development theory to advance an integrated understanding of resilience at community level and its role towards sustainable development. To develop a general approach for development actors to characterize a community's resilience and plan locally targeted interventions is the overall objective of this research. A participatory approach towards defining and assessing community resilience forms the basis, as it is assumed this would enable development actors to more efficiently address development concerns and empower communities to strengthen their resilience. Underlying factors that determine community resilience in selected dryland communities in Tigray, northeastern Ethiopia are identified. Here, most of the population depends on subsistence agriculture, while food insecurity and poverty persist despite concerted regional development efforts. This research compares and consolidates local perceptions of determinants of community resilience that form the basis for guidelines towards a methodological framework for determining levels of community resilience in Tigray. The guidelines were used to compare levels of community resilience of communities, with implications for operationalizing community resilience in the context of drylands development practice. Findings reflect the importance of recognizing that resilience is not about maintaining a status quo, but about addressing how societies can develop in a changing environment. Prominence of resilience thinking can promote a development practice better suited to address the challenges and opportunities that changes create for poor dryland communities. Resilience thinking does not provide quick solutions, but contributes a long-term, multi-dimensional perspective of building capacities for improved responses to current needs and future change. Resilience is not a solution in itself but can contribute towards developing more resilient trajectories for drylands development.