One of the most challenging questions surrounding the Clovis colonization of North America is the character and structure of terminal Pleistocene environments, including floral and faunal communities. A series of cores in the mouth of an arroyo revealed late Pleistocene - early Holocene wetland sediments buried 12 meters below surface, at the approximate elevation of the entrenched modern San Pedro River channel. A suite of ¹⁴C dates show that wetlands of the ancestral San Pedro River occupied portions of the inner valley coincident with the Younger Dryas (13,000 - 11,500 cal yr BP) and the early Holocene (10,000 - 9,500 cal yr BP). A lack of Sporormiella fungal spores indicates that mammoths were rare or absent when Clovis populations appeared in the valley around 12,800 cal yr BP. Palynological and stable carbon isotope analyses show that C₄ grasses increased at 9,940 cal yr BP, just prior to frequent burning after 9,510 cal yr BP and rapid erosion at 9,470 cal yr BP. δ ¹⁸O values from soil carbonates vary but do not record a systematic shift in precipitation source or temperature during the late Pleistocene - early Holocene transition. The establishment of C₄ grasslands in the inner valley correlates with widespread changes in the Chihuahuan Desert flora around 10,000 cal yr BP. A relatively dense accumulation of Clovis-mammoth associations in San Pedro Basin contrasts the lack of megaherbivores indicated at Palominas Arroyo. The upper San Pedro Basin of southeastern Arizona contains a minimum of four Clovis-mammoth associations, making it possibly one of the densest concentrations of human-proboscidean sites on earth in terms of time and space. I use the Younger Dryas-age stratum known as the "black mat" to compare the Clovis-age archaeofaunal record of the basin to its paleontological background in order to measure the level of human predation that created this remarkable record. This analysis indicates that Clovis people were affecting the last mammoth populations to a significant degree, a situation expected only in the presence of abundant mammoths. I argue that this condition was met in the San Pedro Basin, possibly in the form of a terminal Pleistocene refugium. If the refuge hypothesis indeed explains mammoth predation, then Clovis-mammoth associations should occur as clusters as they do in the San Pedro Basin rather than as isolates as they are known to occur elsewhere. The use of radiocarbon frequency distributions to reconstruct prehistoric human and animal populations must account for taphonomic loss and other factors that affect the archaeological and paleontological records. Surovell et al. (Journal of Archaeological Sciences, 36, 1715–1724) have recently proposed a volcanic-based correction factor for removing "taphonomic bias" from temporal frequency distributions. Analysis of 718 radiocarbon dates sampled from the alluvium of the San Pedro and Santa Cruz Rivers and their tributaries in southeastern Arizona shows that discovery and scientific biases play an equally important role in the creation of radiocarbon frequency distributions, and that "taphonomic bias" has not been systematic through time. The latter principle is further demonstrated using a sample of 123 Pliocene to Clovis-age proboscideans from the San Pedro Valley. We propose an alternative model that is based on the nature of the stratigraphic record, with discovery bias, scientific bias, taphonomic loss, and the shape of the calibration curve all operating to influence the temporal frequency distribution of prehistoric phenomena.

Desert wetlands, in particular those slow moving bodies of water known as cienegas, are important sites for biodiversity in arid landscapes and serve as indicators of hydrological functioning on the landscape-level. One of the most extensive systems of cienegas, historical or extant, in southeastern Arizona lies along Cienega Creek, located southeast of Tucson, Arizona. Satellite imagery analysis is heavily utilized to determine landscape-level trends, but cienegas present a challenge to traditional analysis methods. The Normalized Difference Vegetation Index (NDVI), the classic measure of vegetation greenness, reacts counter-intuitively to open water and is affected by open ground, both common occurrences in cienega habitats. Additional remote sensing indices have been developed that balance sensitivity to these environmental elements. This research explores these remote sensing indices at Cienega Creek applying one topographic index to current elevation data and five spectral indices to Thematic Mapper imagery from 1984 to 2011. Temporal trends were identified for all spectral indices and all indices were compared for suitability in cienega habitats. Temporal trends were analyzed for spatial clustering and spatial trends identified. The Normalized Difference Infrared Index utilizing Landsat Thematic Mapper band 5 outperformed other indices at differentiating between cienega, riparian, and upland habitats and is more suitable than NDVI for analyzing cienega habitats in such circumstances.

abstract: Las Cienegas National Conservation Area (LCNCA), located in southeastern Arizona, is a place of ecological and historical value. It is host to rare native, threatened and endangered fauna and flora. as well as the site of the oldest operating ranch in the state. The first chapter of this thesis provides a preliminary flora of vascular plants at LCNCA assembled from field collections, photographs and herbarium specimens, and published through the online database SEINet. This preliminary flora of LCNCA identified 403 species in 76 families. Less than 6% of the flora is non-native, perennial forbs and grasses are the most abundant groups, and over a third of species in the checklist are associated with wetlands. LCNCA has been the target of adaptive management and conservation strategies to preserve its biotic diversity, and results from this study will help inform actions to preserve its rare habitats including cottonwood willow forests, mesquite bosques, sacaton grasslands, and cienegas. The second chapter investigates poorly understood aspects of the life history of the endangered Huachuca Water Umbel (Lilaeopsis schaffneriana subsp. recurva. Apiaceae) (hereafter HWU). This wetland species occurs in scattered cienegas and streams in southeastern Arizona and northern Sonora, Mexico. Three studies were conducted in a greenhouse to investigate seed bank establishment, seed longevity, and drought tolerance. A fourth study compared the reproductive phenology of populations transplanted at LCNCA to populations transplanted at urban sites like the Phoenix Zoo Conservation Center and the Desert Botanical Garden (DBG). Results from the greenhouse studies showed that HWU seeds were capable of germinating 15 years in a dormant state and that HWU seeds are present in the seed banks at sites where populations have been transplanted. Also, greenhouse experiments indicated that colonies of HWU can tolerate up to 3 weeks without flowing water, and up to 2 weeks in dry substrate. Transplanted populations at LCNCA monitored in the fourth study produced a higher abundance of flowers and fruit relative to urban sites (i.e. DBG) suggesting that in-situ conservation efforts may be more favorable for the recovery of HWU populations. Findings from these studies aim to inform gaps in knowledge highlighted in USFWS recovery plan for this species. / Dissertation/Thesis / Masters Thesis Plant Biology and Conservation 2020