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A comparison of the experiences of Side, Saint-Exupery, and Camus in North Africa and the Sahara Desert, and an assessment of the affect of these experiences on their lives and work. / Thesis / Master of Arts (MA)

Plant communities that occur on edaphically heterogeneous landscapes are ideal systems for exploring questions of niche and community assembly. Species with affinity for harsh substrates often have well-defined edaphic niches and are ideal models for testing ecological and evolutionary theory. While plants on substrates such as serpentine and gypsum have received much attention, those on other harsh substrates, including on vertic clay soils, have gone unstudied. Vertic clay soils are both chemically and physically challenging to plant establishment and productivity. Plant communities associated with vertic clay soils of the San Joaquin Desert appear to have a distinctive mosaic pattern of species distribution that reflect differences in soil properties across the landscape. I conducted fieldwork and a pot study with 12 native annual plant species with an affinity for vertic clay soils to determine whether the vertic clay soils at two sites in the San Joaquin Desert were heterogeneous, whether soil heterogeneity predicted the pattern of species distributions observed, and to examine the competition effects of an invasive annual grass (Bromus madritensis) on these species. I found that the vertic clay soils at both of my sites are internally heterogeneous, that soil heterogeneity does appear to shape the patchy distribution of species at both these sites, and that these species have different realized edaphic niches. I utilized treatment soils spanning a gradient of chemical stress present at both study sites in my pot study and found that competition from B. madritensis reduces biomass for all species, and that the effect of competition differed between soil types. Further, I found that species’ edaphic niche optima shift when competition is present, and that competitive ability differed across the gradient of edaphic stress in my treatment soils.

The microorganisms that live in and on a host (the microbiome) influence host phenotype, health, and behavior in plants and animals. However, the effects of the host and environment on the composition of microbiome communities are unclear. This is especially true in arid and semi-arid environments such as deserts that filter many microorganisms. This study investigated variation in phyllosphere microbiotal bacterial assemblages of prickly pear cactus (Opuntia) across differing spatial scales, ecoregions, and taxa throughout Texas at two timepoints. I expected bacterial assemblages to differ significantly among Texas ecoregions and among species. Results support significant influences on bacterial assemblage composition including ecoregion, taxonomy, and potentially seasonal time of sampling. The dry season timepoint yielded high microbial diversity and abundance across species and ecoregions, with different species and ecoregions harboring unique microbial communities. The rainy season timepoint yielded significantly lower levels of microbial diversity and abundance across species and ecoregions.

This paper will report the results of a study commenced in 1935, at the Desert Experimental Range, Pine Valley, Millard County, Utah, to determine the relative effects of various grazing treatments upon the plant members of the shadscale [Atriplex confertifolia (Torr. And Frem.) S. Wats.] - winterfat [Eurotia lanata (Pursh) Moq.] plant association. Results of this study indicate that distinct vegetational changes have occurred within that plant association during twenty-three years of controlled grazing by sheep.

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No description available.

Hydrologic and material dynamics of ephemeral rivers were investigated in the Namib Desert to assess how hydrologic regimes shape the physical habitat template of these river ecosystems. An analysis of long-term hydrologic records revealed that the variation in mean annual runoff and peak discharge were nearly four times higher than the global average, rendering the rivers among the most variable fluvial systems yet described. Further, a pronounced downstream hydrologic decay characterized all of the rivers. The high spatio-temporal variability in flow was reflected in patterns of material transport. Retention of woody debris increased downstream, in contrast to patterns typically reported from more mesic systems, largely attributable to hydrologic decay. Woody debris piles were the principal retentive obstacles and played an important role in channel dynamics. They were also key microhabitats for various organisms, forming "hotspots" of heterotrophic activity analogous to patterns reported from perennial streams. Large amounts of fine particulate and dissolved organic matter (FPOM and DOM) deposited in the lower reaches of the rivers serve to fuel this heterotrophic biota. As a result of the hydrologic decay, sediment concentration (both organic and inorganic) increased downstream and the lower reaches of these rivers acted as sinks for material exported from their catchments. FPOM and DOM concentrations were among the highest reported for any aquatic system, and, contrary to patterns reported from more mesic systems, FPOM dominated the total organic load transported in these rivers. Inorganic solute concentration also increased downstream, resulting in a downstream increase in soluble salt content in floodplain soils. Soils within the river's lower reaches served as effective long-term integrators of hydrologic variability. The mean extent of floods entering the lower river was defined by an alluviation zone, evident from the convexity exhibited in the lower section of the rivers' longitudinal profiles. A downstream increase in the proportion of silt within floodplain soils is associated with increased sediment deposition. Silt deposition had a positive influence on moisture availability, plant rooting, and habitat suitability for various organisms, including fungi and invertebrates. In addition, a strong positive correlation was observed between silt, organic matter, and macronutrients. Thus, the hydrologic control of transport and deposition patterns has important implications for the structure and function of ephemeral river ecosystems. Finally, an examination of the influence of elephants upon riverine vegetation highlighted the importance of these systems as isolated resource patches interspersed in an arid and hostile landscape. Further, it illustrated that flooding was a key ecological process and that hydrologic alterations would affect the fluvial ecosystem as well as the regional landscape they drain. / Ph. D.

A house is pulled apart into its separate rooms and joined in the out-of-doors. This collection of rooms is recognized as a camp. This move is in agreement with the site of the house, which is the foothills of the Rincon Mountains, twenty miles east of Tucson, Arizona, and bordering along Saguaro National Monument. The collection of structures that make up the buildings of the camp are joined by a path that encircles the camp, and also describes the active life of the camp. The design of the camp is informed by studies in geometry and proportion in a few modern houses, information gathered from the site--particularly as it relates to climate and geography, and studies of the form of architectural elements. Simultaneously, the design of the camp is informed by ideas that evolved in form through the course of the design, namely, a pulling apart of space and material, sitting lightly on the ground, and bringing light into a room between the roof and wall. / Master of Architecture