The Effects of Climate and Population Density on Agricultural Production

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The transition to food production represents one of the most significant events in human history. Growing evidence for the persistence of agriculture through periods of population collapse and environmental change suggests that the transition to food production is a tipping point from which human populations cannot return, but at least one case study provides evidence to the contrary. The Fremont in the Basin-Plateau region of Western North America farmed maize for nearly a millennium, from about 1550-650 years ago (AD 450-1350), then abandoned agriculture and their farming villages a few centuries prior to European contact. Farming ceased earlier in some regions of the Fremont landscape than in others but by AD 1350 most of the characteristics of settlement pattern that identified the Fremont as an archaeological complex were no longer present. At European contact groups living in the eastern Great Basin and on the northern Colorado Plateau had returned to mobile hunting and gathering. Reasons for both the origin and demise of Fremont farming have been hotly debated, but a consensus is lacking. This project will generate extensive data on diet, climate and demography in order to address the rise, spatiotemporal variation in reliance on maize and fall of the Fremont complex, which will serve as a model system to explore the dynamics that lead to agricultural collapse. Several approaches will be used to reconstruct the variables that likely determined the investment of Fremont populations in maize agriculture and their decision to return to foraging. Demography - the size and distribution of human populations - is one critical factor. Summed radiocarbon dates from Fremont contexts will be used as a proxy for prehistoric population densities. Research has shown population growth puts pressure on wild resources and can be a driver of reliance on domesticates. Thus, variation in the size and structure of local Fremont populations may address variation in reliance on maize. Modeling agricultural suitability will further inform this work. Key climatic variables that affect maize productivity such as precipitation, growing degree days, soil moisture and soil chemistry are critical to the success of maize farming. Modern data will be temporally adjusted with tree-ring chronologies to reconstruct paleo-climate across the Fremont region. Finally the bone chemistry of a large collection of Fremont individuals will be analyzed to determine spatiotemporal variation in the dietary importance of maize. Once all the data are assembled the relative influence of each factor will be evaluated. The resulting analyses will examine how an individual's reliance on maize agriculture varied as a function of each explanatory variable while holding time, space and other confounds constant.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.