You can’t get to the moon by climbing successively taller trees

Monday, 28 January, 2013

Once a tree exceeds 100 metres in height, such as the coast redwoods in California, one of which is some 115 metres tall, they have difficulty producing leaves, that in turn prevents them growing any higher.

Sugars produced in leaves diffuse through a network of tube-shaped cells called the phloem. Sugars accelerate as they move, so the bigger the leaves the faster they reach the rest of the plant. But the phloem in stems, branches and the trunk acts as a bottleneck. There comes a point when it becomes a waste of energy for leaves to grow any bigger. Tall trees hit this limit when their leaves are still small, because sugars have to move through so much trunk to get to the roots, creating a bigger bottleneck.

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