Charcoal stored in preserved guano gives helps reconstruct regional fire histories

by

Editors' notes

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility:

fact-checked

peer-reviewed publication

proofread

A group of bats hangs on a rocky cave ceiling, as seen from below. One of them has its mouth wide open in a yawn. Credit: R. Andrew King/USFWS, Public Domain

With wildfires growing more frequent and more intense in many parts of the world, scientists are looking to the past to better understand where and when fires have burned. Lakes and wetlands, which capture airborne charcoal particles when they fall from the atmosphere, have provided most records of ancient fires, or paleofires. Now, researchers have found a new tool to help reconstruct fire history: bat poop.

Bats can collect charcoal on their fur as they fly and by brushing up against plants on which charcoal has settled. As they roost in caves and groom themselves, which they do for at least an hour per day, they can ingest—and then poop out—charcoal. Other charcoal particles also may fall to the cave floor, where guano accumulates.

Though some previous research has used pollen and nitrogen preserved in bat guano to reconstruct vegetation records and learn more about past climates, no one had used guano records to examine fire histories.

To test whether bat guano accurately recorded fires, Alexandra Tsalickis and colleagues collected a 2-meter core of guano buildup from a limestone cave in central Tennessee. Radiocarbon dating revealed that the guano mound started building up around 1952. They analyzed the core centimeter by centimeter, dated the tiny pieces of charcoal they found, and compared that charcoal record to data from historical wildfires and prescribed burns in the area.

The findings are published in the journal Geophysical Research Letters.

(a) Cripps Mill Cave is located in the southeastern USA. (b) Located in central Tennessee, Cripps Mill Cave is in a region with both wildfire and prescribed fire. (c) Historically, annual area burned within 200 km of Cripps Mill Cave has varied considerably, as has the relative area burned by wildfire (red), prescribed fire (orange), and fires of unknown cause (gray). In this paper, we focus on the period of 1998–2018 CE (green box) to calibrate charcoal preserved in Cripps Mill Cave guano as a paleofire proxy. Credit: Geophysical Research Letters (2024). DOI: 10.1029/2024GL112045

The dates from charcoal in the bat poop core matched up with those from the historical fire data, providing the first evidence that guano can be used for paleofire reconstructions. However, because bats hibernate in winter, the records are reliable only for nonwinter fires.

In addition, bat poop charcoal dates correlated more strongly with dates of prescribed burns than of wildfires. That could be because bats flee wildfires (and thus are not in the area to poop out records of the fires) or intentionally seek out prescribed burn areas for foraging (as has been found in previous studies) or a combination of both.

The study gives scientists a new tool for reconstructing paleofire histories where lakes are absent and for distinguishing between human-caused fires and wildfires.

More information: Alexandra Tsalickis et al, Fire in Feces: Bats Reliably Record Fire History in Their Guano, Geophysical Research Letters (2024). DOI: 10.1029/2024GL112045

Journal information: Geophysical Research Letters

Provided by Eos

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.