January 16, 2014 at 3:46 pm #41847
A most recent study claims trees do not stop growing, but they just get stronger when they grow older.
As tress age, they do not grow weaker, but they continue to grow at an even faster rate and process carbon dioxide even better than their younger counterparts do, according to the researchers from University of Nebraska-Lincoln.
“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.
A team of researchers collected growth measurements of 673,046 trees belonging to 403 tree species from tropical, subtropical and temperate regions across six continents. Some of the trees used for the study were more than 80 years.
They concluded that 97 percent of the trees assessed grow faster the older they get.
Some trees grew so fast that they were able to add the size-equivalent of an entire other mid-sized tree in a single year.
Unlike animals, trees apparently never become weaker nor suffer the ill effects of old age. Instead, only external factors such as disease, infestation, or fire, can destroy a tree, the researchers said.
For many years, scientists have viewed trees through a human perspective. That is why they believed that older trees grew more slowly than young ones because measurements of carbon trapped by forests showed that a forest full of young ones drew more carbon from the atmosphere than similar acreage populated by elderly trees, assuming that older trees were growing more slowly.
The new research proved the opposite: trees grow faster as their size increases.
“Looking at data from whole forests – that is, all trees in a forest considered together as a unit – 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 UNL biologist Sabrina Russo.
“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.”
Massive sized trees and older trees play a disproportionately large role in the carbon cycle. The same conclusions that found the accelerated growth rates help scientists better understand the carbon cycle on a global scale.
“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.
Older tree’s leaves process carbon dioxide less efficiently, although this is relieved by its much larger canopy and leaf area.
“The apparent paradoxes of individual tree growth increasing with tree size despite declining leaf-level and stand-level productivity can be explained, respectively, by increases in a tree’s total leaf area that outpace declines in productivity per unit of leaf area and, among other factors, age-related reductions in population density,” according to the authors.January 17, 2014 at 3:04 pm #41848
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