Exploring the Early Anthropocene Burning Hypothesis and Climate-Fire Anomalies for the Eastern U.S.

Abstract

This review explores the long-term role of climate versus human activity on vegetation and fire dynamics in the eastern U.S. Early Holocene warming resulted in a conversion of Picea (boreal) to temperate Quercus and Pinus forests when indigenous populations were sparse but charcoal abundances were relatively high, underscoring the importance of climate. Pyrogenic trees also dominated during the middle Holocene Thermal Maximum period, associated with increasing indigenous populations and high charcoal abundance on most sites. During Neoglacial Cooling (3300 to 150 BP) charcoal levels and pyrogenic trees remained high in the central and southern regions apparently due to Native American and early European burning trumping colder climate. In northern regions, oak-pine and charcoal abundance were distributed on intermittent dry and/or Native American sites. High levels of charcoal and pyrogenic species during the early Holocene and Neoglacial Cooling represent important anomalies in the ecological history of the eastern U.S. While the importance of warmer and drier climate is evident throughout, the Early Anthropocene burning hypothesis is plausible for the eastern U.S. where extensive lightning fires are rare, outside of the southeast coastal plain. The cessation of Native American burning and other early European disturbances were transformative to the ecology of the eastern U.S.

Is climate an important driver of post‐European vegetation change in the Eastern United States?

“…Commensurate with a precipitation–moisture gradient from west (dry) to east (moist), the historical structure of component ecosystems generally graded from open savannas to closed‐canopy forests. The fact that oaks and associates were able to maintain dominance eastward under progressively wetter conditions (where the competitive effect of shade‐tolerant species is stronger) underscored the importance of human ignitions in presettlement times (Guyette et al ., ; Abrams & Nowacki, , ).…”

“…It was intentional human ignitions who largely drove fire regimes in the presettlement times in much of the eastern United States and without those ignitions fire occurrence would have been greatly reduced (Guyette et al ., ; Abrams & Nowacki, ), even under somewhat warmer and drier conditions. There is little evidence to support widespread lightning‐caused fires in the eastern United States, outside of Florida, due to a lack of dry lightning (Abrams & Nowacki, , ). The true ecophysiological requirements of species and the pivotal role of historical fire need to be better integrated into future climate change scenarios (inputs, outputs, interpretations) to improve the predictive power of models and their ecological relevance (e.g.…”

Wave of fire: an anthropogenic signal in historical fire regimes across central Pennsylvania,USA

“…). Paleoecological (pollen, charcoal) studies suggest that, during the late Holocene, anthropogenic fire use overrode climatic controls on vegetation at broad scales (Abrams and Nowacki ). Prehistoric increases in sedimentary charcoal in the eastern USA have been shown to be coincident with periods of cultural transition (Hart and Buchanan ); however, the roles of human and lightning ignitions continue to be debated (Parshall and Foster , Nowacki and Abrams , Matlack ).…”

People, El Niño southern oscillation and fire in Australia: fire regimes and climate controls in hummock grasslands

“…Anthropogenic fire regimes thus emerge from dynamic interactions between people and climate and are clearly detectable at landscape-level scales, but would not be predicted in an analysis that decouples climate and human drivers of fire regime dynamics. Rather, as some are beginning to point out [63,64], climate affects not only plants and animals, but human populations, mobility and land/ resource use decisions as well, which in turn have significant effects on fire and vegetation at landscape scales.…”