Thursday, April 22, 2004

Gravity limits tree height

Fascinating - Gravity limits tree height

FOR trees, the sky is definitely not the limit. Scientists have discovered that no tree on Earth can grow beyond about 130 metres (430ft) - no matter how ideal the conditions.

Redwood trees are the tallest on Earth, but none could ever grow beyond that limit, because gravity would prevent water reaching their top-most branches, the scientists claim.

By the reckoning of the research team involved, the "Stratospheric Giant" - a 112.7m (370ft) tree in Humboldt Redwoods State Park, California, which holds the world height record - still has a bit to go.

Dr George Koch, of the Northern Arizona State University, led a serious of climbs up five of the world’s tallest redwoods to carry out tests on their crowns.

The scientists, who report their findings in the journal Nature today, said the tallest trees struggled to get enough water to their small top leaves.

It can take 24 days for water entering the base of a redwood trunk to reach its crown.

The researchers write: "As trees grow taller, increasing water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis."

Observations show that the tallest trees, which may be more than 2,000 years old, are growing at about 25cm per year.


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