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Climate, Fire, and Native Americans: Identifying Forces of Paleoenvironmental Change in the Southern Sierra Nevada, California
AdvisorMensing, Scott A.
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Humans have altered landscapes across North America for millennia, changing vegetation composition and fire frequency through clearing land, grazing livestock, and fire suppression (Anderson and Moratto, 1996; Beaton, 1991; Bowman et al., 2011; Cronon, 1983; Gayton, 1948; Kroeber, 1959, 1925; Lewis, 1973; Lightfoot and Lopez, 2013; Lightfoot and Parrish, 2009a; Martin and Sapsis, 1992; Voegelin, 1938). Though there is general agreement that they influenced the composition of the western United States’ landscape through use of fire (Denevan, 1992; Boyd, 1999; Vale, 2002; Whitlock & Knox, 2002; M.K. Anderson, 2005; Bowerman et al., 2011), the extent of that modification is unclear. Some researchers argue for minimal impact, with disturbance being limited to the areas immediately surrounding permanent settlements (Vale, 2002a; Whitlock and Knox, 2002a). Others argue that Native American influence on the environment was at the landscape scale, especially through the use of fire (Denevan, 1992; Boyd, 1999; M.K. Anderson, 2005; Bowerman et al., 2011). Native Americans have inhabited California since the terminal Pleistocene. California’s Native Americans were proto-agriculturalists, relying not on crops such as maize, but on managed native taxa such as oak and pine (Anderson and Moratto, 1996; Anderson, 1999; Gayton, 1948; Kroeber, 1959, 1925; Lewis, 1973; Voegelin, 1938). Disentangling paleoclimatic versus anthropogenic vegetation change in relation to fire history is difficult, especially in the absence of clearly anthropogenic plant manipulation (e.g. maize cultivation). I use two mid-elevation sedge meadows in Sequoia National Forest (Holey Meadow and Trout Meadow), within the southern Sierra Nevada of California as study sites to identify climatic versus Native American-influenced changes in forest structure and composition. This dissertation uses data from multiple lines of evidence (paleoecology, ethnographies, archaeology, plant ecology, and landscape modeling) to explicitly examine whether Native American use of fire altered forest structure to the point that it can be observed in the paleoecological record, or whether climate and natural processes overwhelm any impact Native Americans had on the environment. This dissertation addresses the following questions:1. Can we identify the impact of Native American-set fires on the paleolandscape?2. Are these impacts local or at a landscape-scale?3. Could climate alone have produced the forest composition observed in the paleorecord, or was the addition of cultural burning necessary?To answer these questions, the paleolandscape at these two sites was reconstructed using a combination of pollen analysis (vegetation), charcoal analysis (fire history), and process-based landscape modeling. Charcoal analysis demonstrated consistency with regional fire reconstructions, which is expected given that charcoal is typically produced by severe, fast-moving crown fires. Anomalous periods of vegetation change were identified at both sites by comparing changes in climatic and fire-sensitive taxa (Abies and Quercus) with annually reconstructed paleoclimate data. Anomalies between vegetation and climate were most evident at Holey Meadow. Paleolandscape modeling at Holey Meadow further supported a Native American-influenced fire regime at the site.This research provides support for the hypothesis that Native American-set fire can be identified through the paleoenvironmental record, and that these high-frequency, low intensity fires were necessary to produce the forest composition observed in the pollen record. Both study sites demonstrate periods of local anthropogenic influence not explained by climate. These results, combined with three previously studied sites in mountainous areas of California begin to hint at spatially dispersed Native American influences on Sierra Nevadan forests. While this research increases our knowledge of potential periods of climatic and anthropogenic-influenced fire regimes in the southern Sierra Nevada, replication of this cross-disciplinary methodology throughout the Sierra Nevada is necessary to help determine the geographic extent of this land-use pattern.