|LONDON - Life is tough at the top, especially for very large trees.|
The tallest tree on the planet, a giant redwood that soars 370 feet into the California sky, is still growing.
But scientists say it will not grow higher than 130 meters because the taller a tree gets, the more difficult it is for water to get to the top.
\"The taller trees grow, and they do that because they are competing with other trees for light, the less able they are to grow taller,\" George Koch, a physiological ecologist at Northern Arizona University in Flagstaff, told Reuters.
\"They seem to be limited in their height growth by the influence of gravity, which makes the water held in the tree more difficult for the living cells to access.\"
Koch and his colleagues scaled five of the eight tallest trees in the world, including the world\'s biggest in Humboldt Redwoods State Park in California, to carry out tests on the increasing influence of gravity on the heights of trees.
\"Gravity is a very important constraint on height growth as trees get taller and taller,\" Koch, who reported his findings in Wednesday\'s issue of the science journal Nature, said.
The trees in the study are between 1,000 and 2,500 years old and have already adapted to climate change during their lifetimes, according to Koch.
Water reaches treetops through a process called transpiration, which pulls it into plants through their roots. The water then travels large distances through water-conducting cells, defying gravity until it reaches the top.
Koch said conditions at the top of trees resemble a desert. Leaves are small and dense because of limited water supply.
He and his team combined their treetop measurements and laboratory work to calculate the maximum height that California redwoods could reach based on the amount of water needed at the top.
\"There are a lot of ups and downs to height growth in big trees,\" he said.
Story by Patricia Reaney
REUTERS NEWS SERVICE