In a surprise finding that may have important implications for forest management, scientists have discovered that most species of trees speed up their growth as they age. The study was published Wednesday (Jan. 15) in the journal Nature.
“Trees keep growing like crazy throughout their lifespan,” said lead author Nate Stephenson, a forest ecologist with the U.S. Geological Survey (USGS), according to a report by Live Science.
The scientists reviewed records from studies of 403 tree species on six continents. After looking at repeated measurements of 673, 046 individual trees–some going back more than 80 years–they concluded that 97 percent of the 403 temperate and tropical species studied grow faster the older they get.
Unlike animals, whose cells malfunction and break down over a lifetime resulting in eventual death, trees apparently never suffer the ill effects of old age. Instead, only external factors such as disease, infestation, fire, or logging, can kill a tree, Stephenson said.
Until now, scientists believed older trees grew more slowly than young ones because measurements of carbon trapped by forests showed that a forest full of youngsters drew more carbon from the atmosphere than similar acreage populated by elderly trees. This gave rise to the assumption that because they seemed to consume more carbon, older trees were growing more slowly.
“But these early data weren’t measuring individual trees, and that’s where the rub comes in,” Todd Dawson, a forest biologist with the University of California at Berkeley, told Live Science. “People had this misconception because forests showed a decline in productivity as they grew older. But this is a really fun finding because it says, ‘Hey, wait a minute–that isn’t the case.’” Dawson was not involved in the study.
“I think one of the reasons [the idea that older trees grow more slowly] had such staying power is because it’s what human do,” Stephenson commented to Live Science. “We start growing slowly, then reach adolescence and have a growth spurt, then slow down again.” Trees, on the other hand, “reach that adolescent growth spurt and never stop,” Stephenson said.
The reason earlier research on a forest-wide scale showed younger forests were capturing more carbon was simply because there were more trees per square mile. But on an individual tree basis, ancient ones are much more effective at removing carbon from the atmosphere, Stephenson explained.
“We realize now the big, old trees are the ones pulling carbon most rapidly out of the atmosphere. This maybe puts an exclamation point on the importance of maintaining big, old trees,” he said.