PHYSICISTS in New Mexico say they now know why trees don鈥檛 grow more than
about 100 metres tall.
The pattern of branching vessels inside a leaf looks roughly the same as the
branches of the whole tree. Geoffrey West of the Los Alamos National Laboratory
and his colleagues used this self-similarity and the laws of fluid dynamics to
show that a gentle taper in sap-carrying channels ensures that all parts of a
tree get equal amounts of sap (Nature, vol 400, p 664).
鈥淚t democratises the tree,鈥� says West. 鈥淭he little branches at the bottom
aren鈥檛 getting all the sap.鈥� To provide this uniform supply, the channels must
get wider towards their bases. The researchers conclude that if a tree were over
100 metres tall, the entire trunk would have to be one big channel鈥攁nd
unable to support the weight of the tree.
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