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