A new study reveals that Leonardo da Vinci's "laws of trees" - previously used by the scientific community to model the function of trees - are inaccurate for the internal vascular structure of trees. Research suggests that a misalignment of this rule with trees' vasculature may explain why large trees are more susceptible to drought and climate change.
The "law of trees" that Leonardo da Vinci used to illustrate trees has been widely adopted by the scientific community in modeling trees and their functions.
Now, researchers from Bangor University in the UK and the Swedish University of Agricultural Sciences (SLU) have found that this rule contradicts the rules that regulate the internal structure of trees.
Leonardo da Vinci's interest in painting led him to study the size proportions of different objects, including trees, in order to represent them more accurately. In order to represent trees correctly, he realized the so-called "law of trees", that is, "all branches of a tree are equal in thickness when combined with the trunk at every stage of its height."
Leonardo's "law of trees" is thought to apply to vascular channels in trees as well, with the individual channels decreasing in size in the same proportion as branches become narrower, while the trunk still increases in volume. This "rule" has been recognized as part of the metabolic scaling theory.
However, findings by scientists from Bangor University and SLU, published in the prestigious peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS), show that this model is not entirely correct when applied to the internal vascular structure of trees.
For water and nutrients to flow effectively through the tree from roots to leaf tips, the vascular system must maintain "hydraulic resistance."
Ruben Valbuena and Stuart Sopp of Bangor University and SLU calculated that for hydraulic drag to work, at a certain point the "law of trees" no longer applies.
To efficiently transport fluid from roots to leaf tips, a tree's vascular channels need to be of a certain size to maintain hydraulic resistance. Therefore, the plant must reduce in size as it reaches the end, resulting in an increase in the ratio of the capillaries to the surrounding plant body.
Dr. Ruben Valbuena (Professor Emeritus at Bangor University and now Professor at the University of Southern California) explains: "While Leonardo da Vinci provided great 'inspiration' for artists, Leonardo's laws of trees do not hold true at the microscopic level. We believe that our calculations further refine the theory of metabolic scaling and improve our understanding of plant systems as a whole. Our recalculations may also explain why large trees are more susceptible to drought and may be more vulnerable to the effects of climate change."
Co-author Stuart Sopp, who is currently studying for a PhD in environmental science at Bangor University, said: "One of our aims is to derive a ratio that can be used to estimate tree biomass and carbon content in forests. This new ratio will help calculate the global carbon capture of trees."