A tree’s rings reveal fires from years past
Like clues from an Agatha Christie my ster y novel, trees can provide secrets about past events, and their rings are especially good at providing information about fires, some of which happ ened hu ndre ds of yea rs ago , according to studies from a Texas A& M University researcher.
With wildfires often in the news, Charles Lafon, associate professor of geography, has studied the fire histor y of for es ts throu ghout the souther n and central Appalachian Mou ntains. He sa id trees can re veal ke y information abou t fire events, and some trees have a lot to tell — one tree he examined endured 14 separate fires through its lifetime. He has published th e res earch in Appl ied Vegetation Science and Physical Geography.
La fon analyzed th e tr ee rings of several pine speci es and fou nd cl ear evidenc e of “scarrin g,” a disf igur in g of the wood that is the unmistakable sign of a previous fire. More ex aminations showed that tr ees in the area ha d sustained numero us fires over the past centuries.
“We foun d one tree that has had at least 14 fires, and we found many other tr ee s that had endure d multiple fires,” he explains. By piecing together the fire- scar record from numerous trees, he and his students and collabor ators lear ne d that fires occurred frequently, about once ever y 2- 10 years. He found some trees with scars dating back to the mid- 1600s. So far, they have not discovered any trees old enough to provide a record of even earlier fires.
“The fires probably were ignited by a combination of humans and lightning strikes,” Lafon adds.
“We know that Indians often set fires to clear areas, and from records we have learned that the early settlers of the area also set fires so they could clear lands for grazing and planting crops,” he said. “Eve ntua lly, by the late 1800s and early 1900s, there was a tremendous amount of logging bec aus e Ame rica nee ded a lot of timber at that time. Devastating fires accompanied the log ging, and those fires motivat ed the fire prote ct io n campaign of the 20th century.
“The point is, there have always been fire s in fores ts. Some time s fires are a good thing because they are nature’s way of starting over and producing new grow th, and sometimes they are destructive.”
Lafon says tree rings can show if a fire occurred, and by taking several samples and cross- referencing them to other trees, it is possible to determine the pre cise yea r — and eve n the time of year — when a particular fire occurred. The trees, in turn, have adapted to fires.
“Man y tree speci es that inhabit fire- prone areas have thick, protective bark,” he pointed out.
One of Lafon’s gradua te stude nts used fir e-sca rred trees growing nea r the mal- lows to estimate how of ten fire s burned the mallows in the past. The Nature Co nservancy is using th at resea rch to guide their con- tro ll ed burnin g pro - gram.
“The bot tom line is that fire scars can tell us a lot about ecological changes,” he noted. “We can tell when a fire occurred and often how severe that fire was, and we can learn how forests changed as fire frequency varied over time. The decline in fire freque ncy during the 20 th centur y, for example, per mitted tree species like red maple to encroach into pine and oak forests. Now the pines, oaks and other fire -associa ted species like the Peters Mountain mallow are declining in abundance, reducing the com mercial va lue of the timber and diminishing the quality of wildlife habitat.
“Today, agencies like the U. S. Forest
Service, the National Park Service, The Nature Conservancy and private landowners use controlled burning to try to restore the fire- associated vegetation.
They are applying our fire histor y research to guide these efforts.”
The pro je ct wa s fund ed by th e Joint Fire Science Program, which is affiliated with the Department of the In terior and the Depar tment of Agriculture.