Washington: The mathematical explanation for the phenomena – the taller the tree, the smaller its leaves – also sets a limit on how tall trees can grow, researchers say.
For the study, Kaare Jensen from Harvard University and Maciej Zwieniecki from the University of California, Davis, compared 1925 tree species with leaves ranging from a few millimetres to over 1 metre long and found that leaf size varied most in comparatively short trees.
According to Jensen, the explanation lies in the plant’s circulatory system – 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.
However, 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 taller, New Scientist reported.
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, thereby creating a bigger bottleneck.
This equation describing the relationship shows that as trees get taller unusually large or small leaves both cease to be viable, the range of leaf size narrows and at around 100 m tall the upper limit matches the lower limit.
The study has been published in the journal Physical Review Letters.