After a tree has survived a fire, scars left in the bark. If the tree survives, these scars can eventually be covered up as time goes on. However, the rings of a tree always reveal the truth about getting burned earlier in life. While these fire scars can be readily identified in trees that lived and were felled recently, they had not been observed in prehistoric trees until Bruce Byers noticed the scars on a piece of petrified wood owned by his father. The full description will appear in an upcoming issue of the journal Palaeogeography, Palaeoclimatology, Palaeoecology, and Byers presented his research in Sacramento at the Ecological Society of America's annual meeting.

Please don’t tell Smokey the Bear I said this, but there are benefits to the occasional forest fire. (That said, don’t be an asshole and start fires. That’s still not cool.) Fires clear brush and debris, removing competition of water and nutrients, allowing new plants and wildlife to come in and thrive. Fire can also eradicate disease, and is even necessary to germinate seeds in some tree species. 

While humans are responsible for about 88% of all wildfires over the last decade, nature has been starting fires with lightning, falling rocks, volcanos, or just through spontaneous combustion for about 400 million years. The evidence of those fires have been seen in charcoal, but never before in petrified wood. 

Cleo Byers, Bruce’s father, retrieved a piece of petrified wood while on a hike with his kids 28 years ago in Utah, where it was legal to obtain such the 7 kg (16 lb) memento. The tree, which lived 210 million years ago in the late triassic, served as a doorstop for Cleo’s office where he researched nuclear physics at Los Alamos National Laboratory in New Mexico. Bruce Byers, who had is a fire ecology consultant, recently recognized that this piece of petrified wood had some clues that could have indicated it experienced a fire.

Surprisingly, prehistoric trees and modern trees appear to respond to fire in a very similar manner. When a tree with rings gets a fire scar, the rings are more narrowly spaced for a time, and new growth can be seen curling and growing around it. Trees like Agathoxylon arizonicum, which is likely the species of the petrified wood, do not form rings. Instead, cells in the xylem of the tree that help deliver water, grew smaller when exposed to fire. However, after the tree had healed after the fire, the cells appeared larger than before, presumably because of the new abundance of water and nutrients from decreased competition.

Understanding more about how ancient trees responded to wildfire could help answer questions about plant evolution, particularly about the onset of flowering plants during the Cretaceous. Fires may have freed up nutrients and provided conditions necessary for angiosperms to emerge.

[Hat tip: LiveScience]