tree-environment relationships/modeling, dendrochronology theory
Historically, Dr. Dean’s research has featured an integrated and evolving emphasis on human ecology in the broadest sense and on human behavioral adaptation to environmental stability, variability, and change in the American Southwest in a more specific sense. The fine focus on the Southwest – which is blessed with unusually high quality paleoenvironmental, archaeological, and anthropological data – provides refined local and regional studies that illuminate the universal principles and processes involved in the general case. This research has progressed from particular to more general issues and from simple to increasingly complex considerations. Given this trajectory, the research has employed data from a broad range of disciplines and benefited from collaboration with scholars representing several dendrochronological sub-disciplines, anthropology, archaeology, geology, alluvial geomorphology, hydrology, palynology, archaeobotany, physics, chemistry, political science, artificial life, complexity, and computer modeling. This eclectic approach dictates emphasis on all three aspects of archaeological dendrochronology: chronology, behavioral analysis, and environmental reconstruction. Since 1999, several investigations have been directed at these research themes.
The crucial importance to human paleoecology of establishing exact time relationships between past human and natural events drives the chronological research. A major component of this effort is the analysis of all archaeological tree-ring samples from the Southwest, an endeavor that has enjoyed 23 consecutive years of NSF support (1985-2007). In the last seven years, this project derived 6,563 dates from 40,946 samples; expanded archaeological tree-ring dating in the Great Basin, the Great Plains, the Sonoran and Chihuahuan Deserts, and Alaska; and produced numerous local tree-ring chronologies. More localized research has involved intensive dating programs to illuminate social organization, intergroup relationships, and environmental adaptation among the Anasazi of Mesa Verde, Chaco Canyon, and Tsegi Canyon and among the Navajos of northwestern New Mexico. Chronological work also involves an empirical characterization of the magnitude of the “old wood problem” (the degree to which the use of dead wood for fuel and construction can skew archaeological radiocarbon and tree-ring dates) in northwestern Colorado and in general.
Behavioral research has been focused on the wood use and adaptive patterns of Anasazi and Navajo populations in the Four Corners region. These studies elucidate the evaluation of archaeological tree-ring dates and illuminate the ways in which different societies respond to environmental variation and change. Considerable attention has been given to how wood use behavior affects the distribution of tree-ring dates and to archaeological dating theory. Two studies using strontium isotope ratios in forest surrounding the San Juan Basin and in construction timbers from archaeological sites in Chaco Canyon document the extraction of spruce and fir constructions beams from mountain ranges up to 70 km from the Canyon and of ponderosa pine beams from a wide are to the north and west of the Canyon. In addition to illuminating the environmental impact of prehistoric logging, these results testify to the Chacoan social system’s ability to mobilize large groups of people for communal projects.
Dean’s environmental research has emphasized reconstructing past climatic variability across the Southwest, combining dendroclimatic reconstructions with other paleoenvironmental indicators, and assessing the potential effects of environmental change on the human populations of the region. This effort produced a geographical network of 30+ dendroclimatic reconstructions that illuminate local and regional variability in climate during the last two millennia. Current research is focused on characterizing the effects of precipitation and temperature variability on the agricultural populations of the Zuni, Tsegi Canyon, Mesa Verde, and Flagstaff areas over the last 2,000 years. A cooperative study is attempting to refine the dating of the eruption of Sunset Crater to better understand the impact of this major natural event on the prehistoric human inhabitants of the San Francisco Peaks area of northern Arizona.
All these concerns are integrated in an effort – in cooperation with scientists from the Arizona State Museum, Santa Fe Institute, Brookings Institution, the University of Massachusetts, and the School of American Research – to model environmental impacts on socio-cultural systems. The agent-based modeling of human subsistence and settlement behavior uses paleoenvironmental data to recreate annual potential crop-yield variability in Long House Valley in northeastern Arizona and simulates the behavior of households (agents) on this changing production landscape. Comparing the results of the simulation to archaeological data on the Anasazi occupation of the area allows objective assessment of all aspects of the model including the paleoenvironmental input and the demographic properties of and behavioral rules for the agents. This process isolates problems with the model and indicates ways in which it can be improved to more accurately replicate real human behavior and enhance understanding of universal aspects of sociocultural adaptation, change and evolution.