Study makes case for maintaining old-growth forests
By Summit Voice
FRISCO — Giant old trees play a key role in forest carbon cycles, researcher said this week, dispelling long-held misconceptions about the growth rate of trees.
In fact, trees never stop growing — as they age, their growth accelerates, even after they’ve reached massive sizes. This means that older trees play a substantial and disproportionate role in the Earth’s carbon cycle, one of the cycles that makes Earth capable of sustaining life.
The study, published in the journal Nature, was co-authored by University of Nebraska-Lincoln biologist Sabrina Russo. To reach their findings, the scientists analyzed biomass growth measurements of 673,046 trees belonging to 403 species from various temperate and tropical regions across six continents.
They concluded that for most tree species, mass growth rate continues to increase with their size, with some species’ largest trees growing by a mass equivalent to a mid-sized tree in a single year.
“Looking at data from whole forests … that is, all trees in a forest considered together as a unitm it is often found that forest productivity declines with the age of the forest, but that does not mean that the growth of the oldest trees declines,” said Russo, a forest ecologist in UNL’s School of Biological Sciences. “What turns out to be key to understanding tree growth is to examine the growth pattern of each individual, not just the forest stand as a whole.”
In addition to discovering this property of tree growth, the conclusions also contribute to understanding the global carbon cycle because trees, like all plants, take up carbon dioxide from the air and sequester it in their biomass.
“About 50 percent of a tree’s wood is carbon, so a rapidly growing, large, old tree can remove huge amounts of carbon from the atmosphere, through an enormous photosynthetic flux — far more than a younger, smaller tree can,” Russo said.
“While they are alive, these giant elders of the forest play a disproportionately important role in a forest’s carbon dynamics.”
Russo’s principal research site in Lambir Hills National Park in Malaysia on the island of Borneo also lent data to the study for 76 Southeast Asian tree species.
The study, “Rate of tree carbon accumulation increases continuously with tree size,” can be found at http://www.nature.com. In addition to Russo, the paper was authored by Nathan Stephenson and Adrian Das of the U.S. Geological Survey and Richard Condit of the Smithsonian Tropical Research Institute, along with 34 other researchers.