Climate and human impact on vegetation and fire in an arid Colorado Plateau ecosystem in Western North America

Abstract

Understanding how arid western North American environments have responded to past climatic conditions can help predict how they respond to anthropogenic climate change. Unfortunately, millennial-length continuous paleoecological records in these regions are scarce. Here we evaluate the human-environmental history of Utah's Grand Staircase-Escalante National Monument (GSENM), USA, back to the Middle Holocene (ca. 7350). Our study presents new records of stratigraphic pollen and charcoal recovered from two sediment cores and pollen recovered from eleven Neotoma (packrat) middens. Our records cover an elevational gradient within pinyon-juniper woodlands, with one core (LP-12-03) recovered from a high elevation site (Lake Pasture) and one core (MC-12-03) and the eleven packrat middens recovered from a low elevation site (Meadow Canyon). Both of these sites contain archaeological records spanning from the Archaic to the Historic with increased occupation during the Formative. We analyze these paleoecological records with the goals of determining how vegetation and fire histories differ over an elevational range, what the records reveal about prehistoric agriculture, and the relative impact of natural climate variability and human land use on the environment through time in southern Utah. Our records provide pinyon-juniper vegetation and fire histories spanning back to the Middle Holocene (ca. 7350 years), evidence of agriculture from Terminal Archaic through Late Prehistoric times (ca. 178–1550 CE) in Meadow Canyon, the utility of non-invasive methods of archaeology in the form of sediment cores and packrat middens, and support for National Register of Historic Places eligibility for archaeological sites surrounding each core location. We conclude that the records of vegetation and fire differ markedly between the high and low elevation sites, the low elevation site contains direct evidence of prehistoric agriculture whereas the high elevation site does not, and that the climate-fire relationship at each site has been buffered by prehistoric land use.