Human versus climatic influences on late-Holocene fire regimes in southwestern Nicaragua

Abstract

Fire regimes in the lowland Neotropics are affected both by anthropogenic land use practices and natural climate variability. In Central America it is widely recognized that fire has been used as an agricultural tool for thousands of years, but the role of anthropogenic ignition as a determinant of past biomass burning frequency and magnitude has been debated. Little is known about the effects of short-term climate variability on fire regimes in this region of the world because of both the low temporal resolution of the available charcoal records and the obfuscating effects of anthropogenic burning throughout the late Holocene. Here we reconstruct 1400 years of fire history and environmental change on Ometepe Island, Lake Nicaragua, and perform statistical wavelet analysis on multiple proxy records to identify natural cycles of environmental variability possibly related to climate forcing. Our results indicate that extensive indigenous burning and landscape modification largely mask any climate signal in the paleo-fire record from AD 580 to 1400, with the exception of the period AD 775—1000 where high wavelet power exists at scales of 2—24 years. This time period coincides with a severe, two-century long regional drought that has been identified at other locations in Central America. High wavelet power at climate-relevant scales after ~AD 1400 in the Ometepe fire record suggests that periodic drought possibly caused by the El Niño Southern Oscillation and/or high-frequency solar cycles may have played a significant role in influencing the post-contact fire regime — a role that is largely concealed in the pre-European strata because of the overriding effects of anthropogenic burning.