Abstract
The rise and decline of many complex, pre-European maize-farming cultures in the American Southwest coincides with the warm, climatically quiescent Medieval Climate Anomaly (MCA, ca. 850–1350 CE) and transition to the cool, hydrologically variable Little Ice Age (LIA, ca. 1350–1850 CE). The effects of drought on early subsistence agriculture in the Southwest is well studied, but the impact of temperature stress and variability on the growth of maize crops and which areas were most resilient to such stress remain open questions. We statistically downscaled outputs from a paleo-climate model experiment (CESM1 LME) to map changes to cumulative growing degree days for maize (GDD, 30/10 °C) and precipitation over Utah between 850 and 1449 CE, and downscaled GDD changes to local Fremont Culture archaeological site occupations from radiocarbon-dated contexts mapped as spatially discrete kernel density estimates of summed probability distributions (SPDs). We then analyzed correspondences between Fremont SPDs and GDD/precipitation between 850 and 1449 CE. In general, we found (1) high Fremont occupation intensity coincident with GDD that is less volatile than the long term average, and low occupation intensity coincident with, or following, periods of volatile GDD; (2) intensified occupation of high-elevation sites during the MCA, followed by a retreat to lower elevation sites coincident with a sudden rise in annual temperature volatility and increasing drought conditions; and (3) these occupation changes occurred in spite of the greater temperatures and variability in GDD at low-elevation sites. We found evidence that increased inter-annual variability of growing seasons prior to the onset of the LIA, was likely a determinant of Fremont subsistence strategy decision making, and high-elevation site occupation. The most resilient Fremont occupations in the face of these challenges were sited where growing season lengths were least variable.
Highlights
The Fremont were a maize (Zea mays) farming culture who inhabited a region roughly centered on modern Utah
We found (1) high Fremont occupation intensity coincident with Growing degree days (GDD) that is less volatile than the long term average, and low occupation intensity coincident with, or following, periods of volatile GDD; (2) intensified occupation of high-elevation sites during the MCA, followed by a retreat to lower elevation sites coincident with a sudden rise in annual temperature volatility and increasing drought conditions; and (3) these occupation changes occurred in spite of the greater temperatures and variability in GDD at low-elevation sites
Annual proxy-based temperature anomalies for the northern hemisphere correlate with the shape of cumulative kernel density estimates of Fremont radiocarbon ages during the MCA and early LIA
Summary
The Fremont were a maize (Zea mays) farming culture who inhabited a region roughly centered on modern Utah (figure 1) This placed them at the northern periphery of the well-known Ancestral Puebloan (AP) cultural complex that flourished throughout much of the American Southwest between ca. Features of environmental change that APs and the Fremont experienced, such as megadrought, warming, and variable precipitation regimes, are anticipated to arise in the region of the Southwest in the near future as a consequence of climate change (Loisel et al 2017), if they have not already (Williams et al 2020). The end of the MCA is marked by a gradual transition to a cooler, more hydrologically variable mean climatic state, known as the ‘Little Ice Age’ (LIA, from ~ 1350 CE) This transition of mean climatic state, punctuated by droughts, is associated with the decline of maize-farming occupations in the archaeological record. We infer the potential sensitivity of Fremont agriculture to early climatic changes through the use of a database of radiocarbon dated archaeological sites and growing season length estimates derived from a statistically downscaled climate model to analyze temporally and spatially the correspondences between climatic changes likely to impact maize and Fremont occupation patterns between 850 and 1449 CE
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
