800 years of vegetation change, fire and human settlement in the Sierra Nevada of California, USA

Abstract

A combination of pollen and sedimentary charcoal stratigraphies are used in conjunction with historical records to determine the relationships between climate, vegetation change and changing disturbances over the last 800 years in the Sierra Nevada, California. This period witnessed significant climate variability (the ‘Medieval Climate Anomaly’ followed by the ‘Little Ice Age’), as well as expansion of Native American, then Euro-American, populations. From c. ad 1300 to about ad 1800, the meadow was surrounded by a Pinus ponderosa–mixed conifer forest. The abundance of charcoal and carbonaceous spheres in the sediments suggests fire repeatedly burned across the meadow between c. ad 1300 and c. ad 1550, suggesting frequent surface fires. A similar pattern was noted previously in nearby Yosemite Valley, associated with a proto-historic Miwok population expansion (Anderson and Carpenter, 1991). Subsequently, cooler conditions with greater meadow soil moisture prevailed during the LIA, but with little decline in burning. We interpret this as evidence for continued Native American burning. Beginning in the mid-19th century ce, pine pollen percentages declined substantially, then rebounded somewhat during the 20th century. Grass pollen increases, and introduced herbs ( Erodium, Plantago, Rumex, Zea) increase, documenting Euro-American settlement of the local Wawona area, with harvesting of economically important trees, livestock grazing and small-scale farming. These changes are consistent with the historical record. The sedimentary record largely confirms the fire scar record, documenting the anomalous nature of the absence of fire in the vicinity, which is critical to our understanding of the importance of this process on pre-European landscapes.