Aging giant sequoia trees are growing faster than ever, with some of the oldest and tallest trees producing more wood, on average, in old age than they did when they were younger. (Read about giant sequoias in National Geographic magazine.)
A 2,000-year-old giant sequoia is just cranking out wood, said Steve Sillett, a professor at Humboldt State University in California who has conducted recent research on the big trees.
Other long-lived trees like coast redwoods and Australia's Eucalyptus regnans also show an increase in wood production during old age, according to an article Sillett published in the journal Forest Ecology and Management.
That may be because a tree's leaf area increases as its crown expands over a long life span. The leaves produce more sugars through photosynthesis, Sillett said, and these sugars build wood across a growing cambium, or the living surface separating bark and wood in trees.
"What we're finding," Sillett said, "is that the rate of wood production in some species doesn't slow down until a tree gets to the end of its lifetime."
Sequoias Active in Old Age
Sillett's team recently measured the President, a 3,200-year-old giant sequoia tree in California's Sequoia National Park. By climbing and measuring the tree, they calculated that the 247-foot-tall (75-meter-tall) giant holds more than 54,000 cubic feet (1,500 cubic meters) of wood and bark, earning it the ranking of second largest tree on Earth, as reported in National Geographic. (Watch video: Photographing the President.)
"Eventually every tree will suffer structural collapse and fall apart," said Sillett, who is also a National Geographic explorer. "All Earthlings have finite life spans, but some trees live more than a thousand years without slowing down." (National Geographic News is part of the National Geographic Society.)
(Interactive gallery: The creatures that call giant sequoias home.)
Sillett is also co-leading the Redwoods and Climate Change Initiative group investigating how climate changes may affect tree growth. They've established long-term monitoring plots throughout the geographic ranges of both redwood species in California and have recorded growth histories of over a hundred trees.
Because the trees are still alive, Sillett said, they can go back to specific trees and evaluate predictions about their growth responses to climate variation.
"Annual rings provide a wonderful, long-term record of a tree's performance," Sillett said. "By studying a tree's rings, we can, in a sense, translate what it knows about the forest."