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Nama L. is a genus of approximately 50 species of herbs and subshrubs that occurs in habitats ranging from arid deserts to mesic woodlands in the New World and the Hawaiian Islands. The group has historically been divided into five or six subgeneric groups based on habitat as well as on the morphology of the anthers, styles, leaves and seeds. At least 14 species of Nama from the Chihuahuan Desert Region are either facultatively or obligately endemic to gypsum deposits. This dissertation examines interspecies relationships within Nama from a molecular phylogenetic perspective in order to evaluate historic morphology-based subgeneric classification systems of the genus and to examine the origins of facultative and obligate gypsophily within the genus. DNA sequence data from the chloroplast regions matK and ndhF and from the nuclear ribosomal region ITS were collected from 46 species of Nama as well as from four new species and several outgroups. Data were analyzed using maximum likelihood and Bayesian methods. Phylogenetic analyses recover seven strongly supported major lineages within Nama. These lineages do not correspond to traditionally recognized subgenera, although they are largely congruent with an informal system based on ultrastructural observations of seeds. Four of the seven major lineages include gypsophilous species; these range from two lineages that include a single facultative gypsophile each, to one lineage that is almost entirely comprised of gypsophiles. Gypsum endemism in general, as well as facultative and obligate gypsophily in particular, has arisen multiple times in Nama. Parametric bootstrapping rejected the hypothetical monophyly of gypsophiles across the genus as a whole and within each of the two clades that contain multiple gypsophiles. Because approximately 20 species have been described since the last major revision of Nama nearly 80 years ago, detailed morphological observations of herbarium specimens were made in order to produce a comprehensive key to the species of Nama as well as the revision of a lineage comprising eight gypsophiles and one limestone endemic. / text

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Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 202-224). Available also in a digital version from Dissertation Abstracts.

This thesis investigated the interaction of complex vegetation with wind flow and sediment transport at a creosote shrubland located in New Mexico and formed part of a larger on-going study to improve wind erosion modeling techniques. Directionally dependent roughness densities, λ, were computed and compared to mean wind speed ratios (WSRs) derived from anemometry data. A significant relationship existed among decreasing WSRs and increasing λ, indicating that shelter to the ground changed depending on the orientation of the wind. WSRs were larger on the west, more sparsely vegetated side, than in the east, demonstrating that distribution and plant size have a significant effect on near surface winds. Comparison of these data to a similar study completed in a mesquite coppice dune field demonstrated weaknesses in the roughness density parameter. These results have application for improving the understanding of interactions between wind flow and vegetation in complex rangeland environments.

Many grasslands in arid and semi-arid regions are undergoing rapid changes in vegetation, including encroachment of woody plants and invasive grasses, which can alter the rates and patterns of fire and sediment transport in these landscapes. We investigated the spatial distribution of sediments at the scale of vegetated microsites for three years following a prescribed fire using a multiple rare earth element (REE) tracer-based approach in a shrub-grass transition zone in the northern Chihuahuan desert (New Mexico, USA). To this end, we applied REE tracers – holmium, europium, and ytterbium on shrub, grass, and bare microsites, respectively in March 2016. Soil samples were collected from both burned and control (not burned) sites before (March) and after (June) the annual windy season, from 2016 through 2018. Results indicate that although the horizontal mass flux (HMF) of wind-borne sediment increased approximately threefold in the first windy season following the fire, and the HMF of both plots were not significantly different after three windy seasons. Comparing REE concentrations in sediments from both plots over the three years and three annual windy seasons, we observed a post-fire shift in source and sink dynamics of sediments. The tracer analysis of wind-borne sediments indicated that the source of the HMF in the burned site was mostly derived from shrub microsites following the fire, whereas the bare microsites were the major contributors for aeolian sediment in control areas. The shift in sources and sinks, and the spatial homogenization of REEs indicate that the removal of shrub vegetation resulted in sediment redistribution to the bare microsites even three years after the prescribed fire. The findings of this study will improve our understanding of post-fire geomorphic processes at a microsite scale in a grassland ecosystem undergoing land degradation induced by shrub encroachment. / Geology

This dissertation presents an evaluation of coprolite specimens from the Lower Pecos canyonlands as records of individual dietary decisions. Prior studies of coprolites from this region have greatly expanded our knowledge of Archaic subsistence patterns, but have not taken full advantage of the record of individual dietary decisions recorded in each coprolite specimen. The menu, or dietary combinations, reflected in individual coprolite specimens are assessed through the identification of several congruent botanical components derived from the same food resource, phytoliths, fiber ultimates, and epidermal sheets. The data is analyzed with hierarchical cluster analysis, an exploratory statistical technique. The resultant menus reflected in these clusters are evaluated with reference to the diet-breadth model developed for the known staple resources of the canyonlands as well as the seasonal subsistence patterns observed in the ethnohistoric record of modern-day Mexico and Texas. This same technique is also applied to the coprolite data available from previous studies in the Lower Pecos canyonlands. Overall, the combined dietary data available for the Lower Pecos canyonlands presents a similar dependence on desertic plant resources throughout the Archaic. Three main menus are apparent in the specimens. The first menu consists of prickly pear (Opuntia sp.) cladodes, or nopales, and was principally, although not exclusively, consumed in the late spring. This menu is primarily consumed when other resources were not readily available and may be considered a dependable but undesirable meal. The second menu consists of pit-baked lechuguilla (Agave lechuguilla) and sotol (Dasylirion sp.) caudices, or hearts, common throughout the cool season. This menu entails high processing costs, but would provide a reliable caloric return. The third menu exhibits a monolithic reliance on prickly pear fruits, or tunas, during the summer. The ease of harvest and consumption is reflected in the seasonal dominance of this resource, which was assuredly a highly desirable meal. The dietary patterns recorded in the coprolite specimens from the Lower Pecos canyonlands demonstrate a seasonally variable diet-breadth that incorporated low-ranked resources during times of seasonal scarcity as well as a monolithic dependence on high-ranked resources when they were available in the local landscape.

abstract: Population growth within drylands is occurring faster than growth in any other ecologic zone, putting pressure on already stressed water resources. Because the availability of surface water supplies in drylands tends to be highly variable, many of these populations rely on groundwater. A critical process contributing to groundwater recharge is the interaction between ephemeral channels and groundwater aquifers. Generally, it has been found that ephemeral channels contribute to groundwater recharge when streamflow infiltrates into the sandy bottoms of channels. This process has traditionally been studied in channels that drain large areas (10s to 100s km2). In this dissertation, I study the interactions between surface water and groundwater via ephemeral channels in a first-order watershed located on an arid piedmont slope within the Jornada Experimental Range (JER) in the Chihuahuan Desert. To achieve this, I utilize a combination of high-resolution observations and computer simulations using a modified hydrologic model to quantify groundwater recharge and shed light on the geomorphic and ecologic processes that affect the rate of recharge. Observational results indicate that runoff generated within the piedmont slope contributes significantly to deep percolation. During the short-term (6 yr) study period, we estimated 385 mm of total percolation, 62 mm/year, or a ratio of percolation to rainfall of 0.25. Based on the instrument network, we identified that percolation occurs inside channel areas when these receive overland sheetflow from hillslopes. By utilizing a modified version of the hydrologic model, TIN-based Real-time Integrated Basin Simulator (tRIBS), that was calibrated and validated using the observational dataset, I quantified the effects of changing watershed properties on groundwater recharge. Distributed model simulations quantify how deep percolation is produced during the streamflow generation process, and indicate that it plays a significant role in moderating the production of streamflow. Sensitivity analyses reveal that hillslope properties control the amount of rainfall necessary to initiate percolation while channel properties control the partitioning of hillslope runoff into streamflow and deep percolation. Synthetic vegetation experiments show that woody plant encroachment leads to increases in both deep percolation and streamflow. Further woody plant encroachment may result in the unexpected enhancement of dryland aquifer sustainability. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2017