In the semiarid Southwestern United States, prolonged drought conditions since the early 2000s have resulted in widespread declines of the vegetation productivity in this water-constrained ecosystem, as revealed by analyses of the Normalized Difference Vegetation Index (NDVI). However, the spatial pattern of the NDVI response to dry years is not uniform: a divergent response of NDVI to precipitation is observed between the low-lying desert and the high montane forests at elevations above 2,500 meter. Weanalyzed relationships between 15 years of Moderate Resolution Imaging Spectroradiometer (MODIS) NDVI and gridded climate data (PRISM) along elevation gradients at scales from regional to local. Our elevation-explicit analysis captures the transition from water-limited to temperature-limited ecosystems, with a sign-reversal in the correlation coefficient between precipitation and NDVI observed at about 2,500-3,000m altitude. Wesuggest warmer temperatures and less snow cover associated with drier years as explanations for high elevation gains in vegetation productivity during dry years.

The dryland ecosystems of the US Desert Southwest (SW) are dependent on soil moisture for aboveground productivity; the generation of soil moisture in the SW is dependent on both soil physical properties and climate forcing. This study is one of the first regional point-scale analyses that explores the role of soil physical properties in modulating aboveground vegetation dynamics in response to climate forcing in the SW. Soil texture accounted for significant differences in average aboveground primary productivity across the SW. However, soil texture could not account for differences in inter-annual aboveground productivity variation across the SW. Subsurface soil texture was tightly coupled with precipitation seasonality in accounting for differences in long-term average seasonal aboveground productivity in the Mojave and Sonoran Deserts. The results of this study indicate that the subsurface is a significant factor in modulating aboveground primary productivity, and needs to be included in future modeling exercises of dryland ecosystem response to climate forcing and change.

abstract: In the proposed project I simultaneously and reflexively identify and characterize social boundaries in the archaeological record by examining material culture distributions in novel ways to re-assess the scale of the Verde Confederacy, a proposed regional-scale multi-settlement alliance in Late Prehistoric central Arizona. I focus on boundaries between entities larger than villages, but smaller than regions or culture areas. I propose three innovations to better accomplish these goals. First, unlike previous conceptualizations of social boundaries as monolithic, I argue that they are better conceived of as a heterogeneous, multi-faceted phenomenon. Second, I investigate social boundaries by examining multiple lines of evidence. Previous researchers have tended to focus on one category of data at the expense of others. Third, I associate boundaries with relational and categorical collective social identification. An alliance requires regular collective actions including communication and coordinated action between large groups. These actions are most likely to emerge among groups integrated by relational networks who share a high degree of categorical homogeneity. I propose a plain ware ceramic provenance model. Seven reference groups represent ceramic production in specific geographic areas. The reference groups are mineralogically and geochemically distinct, and can be visually differentiated. With this provenance model, I reconstruct the organization of utilitarian ceramic production and exchange, and argue that plain ware distribution is a proxy for networks of socially proximate friends and relatives. The plain ware data are compared to boundaries derived from settlement patterns, rock art, public architecture, and painted ceramics to characterize the overall nature of social boundaries in Late Prehistoric central Arizona. Three regions in the study area are strongly integrated by relational networks and categorical commonality. If alliances existed in Late Prehistoric central Arizona, they were most likely to emerge at this scale. A fourth region is identified as a frontier zone, where internal connections and shared identities were weaker. As seen among the League of the Iroquois, smaller integrated entities do not preclude the existence of larger social constructs, and I conclude this study with proposals to further test the Verde Confederacy model by searching for integration at a broader spatial scale. / Dissertation/Thesis / Doctoral Dissertation Anthropology 2016

abstract: Exchange is fundamental to the establishment and maintenance of social institutions and political economies in all scales of societies. While today people rapidly exchange goods and information over great distances, in the past, long-distance exchange necessitated the mobilization of vast networks of interaction with substantial transport costs. Objects traded over long distances were often valuable and challenging to obtain, granting them multifaceted significance that is difficult to understand using traditional archaeological approaches. This research examines human interactions with scarlet macaws (Ara macao) in the United States (U.S.) Southwest and Mexican Northwest (SW/NW) between 900 and 1450 CE. This period saw large-scale cultural change in the form of migrations, rapid population aggregation, and an expansion of long-distance exchange relations in regional centers at Pueblo Bonito (900-1150 CE) in northwestern New Mexico, Wupatki (1085-1220 CE) in north-central Arizona, and Paquimé (1200-1450 CE) in northern Chihuahua. Despite the distant natural habitat of scarlet macaws, their importation, exchange, and sacrifice appear to have played integral roles in the process of placemaking at these three regional centers. Here, I use an Archaeology of the Human Experience approach and combine radiogenic strontium isotope analysis with detailed contextual analyses using a Material Histories theoretical framework to (1) discern whether macaws discovered in the SW/NW were imported or raised locally, (2) characterize the acquisition, treatment and deposition of macaws at Pueblo Bonito, Wupatki, and Paquimé, and (3) identify patterns of continuity or change in acquisition and deposition of macaws over time and across space in the SW/NW. Findings from radiogenic strontium isotope analysis indicate that scarlet macaws from all case studies were primarily raised locally in the SW/NW, though at Paquimé, macaws were procured from sites in the Casas Grandes region and extra-regionally. Variation in the treatment and deposition of scarlet macaws suggests that despite their prevalence, macaws were interpreted and interacted with in distinctly local ways. Examination of the human experience of transporting and raising macaws reveals previously unconsidered challenges for keeping macaws. Overall, variation in the acquisition and deposition of scarlet macaws indicates changing strategies for placemaking in the SW/NW between 900 and 1450 CE. / Dissertation/Thesis / Doctoral Dissertation Anthropology 2020

In the southwest United States, the current prolonged warm drought is similar to the predicted future climate change scenarios for the region. This study aimed to determine patterns in vegetation response to the early 21st century drought across multiple biomes. We hypothesized that different biomes (forests, shrublands, and grasslands) would have different relative sensitivities to both climate drivers (precipitation and temperature) and legacy effects (previous-year's productivity). We tested this hypothesis at eight Ameriflux sites in various Southwest biomes using NASA Moderate-resolution Imaging Spectroradiometer Enhanced Vegetation Index (EVI) from 2001 to 2013. All sites experienced prolonged dry conditions during the study period. The impact of combined precipitation and temperature on Southwest ecosystems at both annual and sub-annual timescales was tested using Standardized Precipitation Evapotranspiration Index (SPEI). All biomes studied had critical sub-annual climate periods during which precipitation and temperature influenced production. In forests, annual peak greenness (EVImax) was best predicted by 9-month SPEI calculated in July (i.e., January-July). In shrublands and grasslands, EVImax was best predicted by SPEI in July through September, with little effect of the previous year's EVImax. Daily gross ecosystem production (GEP) derived from flux tower data yielded further insights into the complex interplay between precipitation and temperature. In forests, GEP was driven by cool-season precipitation and constrained by warm-season maximum temperature. GEP in both shrublands and grasslands was driven by summer precipitation and constrained by high daily summer maximum temperatures. In grasslands, there was a negative relationship between temperature and GEP in July, but no relationship in August and September. Consideration of sub-annual climate conditions and the inclusion of the effect of temperature on the water balance allowed us to generalize the functional responses of vegetation to predicted future climate conditions. We conclude that across biomes, drought conditions during critical sub-annual climate periods could have a strong negative impact on vegetation production in the southwestern United States.