Scars on trees left by fires hundreds of years ago are helping scientists understand past wildfire trends across North America and giving clues to how blazes might unfold with further climate change.
Fire scars are small wounds made when fires burn near trees but don鈥檛 kill them. They provide rich details about past wildfires and their underlying causes, says at the University of Colorado, Boulder.
鈥淔or dendrochronologists examining fire scars, every tree and every site tells a story about the past forest 鈥� its age, how climate influenced its growth and productivity, how fire spread through and influenced the forest and how people augmented or disrupted its function,鈥� he says.
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Guiterman and his colleagues studied a database of fire scars in North America that聽was established in 2022 to enable scientists to learn about past forest fires using physical data stored in trees. Most trees in this database have around six fire scars.
The researchers focused specifically on scars from 1750 to 1880. This window precedes widespread industrialisation and the modern era of forest fires.
Results showed that many areas that experience severe wildfires today, including western parts of Canada and the US, had frequent, widespread fires over 150 years ago.
Like those of today, pre-modern fires were influenced by many factors, including climate, vegetation and people, says Guiterman. Soil moisture and fire scar data revealed a particularly clear connection between periods of drought and subsequent fires.
Most pre-modern fires were significantly less severe than those today. Beginning in the 20th century, forest fires were largely suppressed across North America. This created a surplus of vegetative fuels that, in turn, increased fire size and severity.
鈥淗ad historical fire regimes continued to present, modern fires 鈥� even under 鈥榚xtreme鈥� conditions 鈥� would likely be quite manageable and beneficial to forests,鈥� says Guiterman.
The study serves as a reminder that fires were common and extensive following drought, and we can expect to see more severe droughts as a result of climate change, he says.
鈥淲hen fire activity is synchronised by regional drought, firefighting resources are quickly spread too thin and exhausted,鈥� says at the University of Arizona. 鈥淭he overall findings highlight the danger of extreme fire occurrence years, especially in western North America.鈥�
Guiterman worries that fire-scarred trees, stumps and logs will eventually disappear from our forests, so they should be collected and studied now. 鈥淭he urgency is huge, because people, climate and fire are removing, degrading and burning the evidence of past fire regimes, and we still have so much more to learn,鈥� he says.
Global Ecology and Biogeography
