A 7500-year record of fire and precipitation dynamics from Clear Pond, South Carolina, USA

Abstract

We analyzed a 2.38 m sediment core from Clear Pond, South Carolina, to reconstruct fire and effective moisture over the past 7500 years in a Pinus-Quercus forest. Our record of macroscopic charcoal, reconstructed precipitation isotopes from δ²H_n-alkane analysis, and other geochemical indicators provides a high-resolution record of the interplays between fire and effective moisture on the Atlantic Coastal Plain (ACP). Our work complements and updates an existing pollen and microscopic charcoal record from Clear Pond with additional analyses, including reconstructed effective moisture. δ²H_n-alkane values are indicative of soil moisture isotopic values, which are controlled by precipitation δ²H values and fractionation during evaporation and transpiration. Our results show that from ca. 7500–3670 cal yr bp, effective moisture was higher than modern conditions at Clear Pond, but fires were frequent. Our δ²H_n-alkane record of effective moisture indicates that conditions remained mesic from ca. 3670 cal yr bp until 2350 cal yr bp, but macroscopic charcoal data indicate that fires were much less frequent than before. This pattern is in opposition to several nearby records on the ACP, where much of this timespan was apparently somewhat dry with frequent fires. After ca. 2350 cal yr bp, effective moisture slightly increased, and frequent fires returned to the landscape. These conditions persisted until about ca. 860 cal yr bp, when δ²H-derived effective moisture values reached their most positive values, indicating xeric conditions, and charcoal data indicate a declining importance of fire on the landscape. Over the past 7500 years at Clear Pond, there is an apparent decoupling of reconstructed paleomoisture indicators and macroscopic charcoal records, which indicates that fire is not largely controlled by climate on the ACP and that landscape burning by Native Americans may be an important control on Holocene fire regimes at Clear Pond, especially from ca. 7500–2350 cal yr bp.