By: Bentley LP, Stegen JC, Savage VM, Smith DD, von Allmen EI, Sperry JS, Reich PB, Enquist BJ (University of Arizona).
Tucson, AZ (August 6, 2013) – Researchers in the University of Arizona’s department of ecology and evolutionary biology have found that despite differences in appearance, trees across species share remarkably similar architecture and can tell scientists a lot about an entire forest.
Just by looking at a tree’s branching pattern, it turns out, scientists can gather clues about how it functions–for example, how much carbon dioxide it exchanges with the atmosphere or how much water transpires through its leaves–regardless of the tree’s shape or species.
The researchers’ results, published in the August issue of the scientific journal Ecology Letters, have important implications for models used by scientists to assess how trees influence ecosystems across the globe. Studies like this enable scientists to refine models used to assess and predict functions that cannot be directly measured for an entire forest, for example how much carbon dioxide and oxygen the forest exchanges with the atmosphere and how much water the trees lose through evaporation.
According to the authors, their study is the first empirical test of a theory UA ecology professor Brian Enquist helped develop in 1998. That theory holds that a tree’s branching structure – specifically, the width and length of its branches – predicts how much carbon and water a tree exchanges with the environment in relation to its overall size, independently of the species.
Researchers tested this prediction in five different species of trees: maple, oak, balsa, Ponderosa pine and piñon pine. They found the theory to be correct in that it allows for predictions about a tree’s function depending on its size, and also in that the theory’s principles apply across species, despite their differences in appearance.
Following is the research abstract for “An empirical assessment of tree branching networks and implications for plant allometric scaling models”:
Several theories predict whole-tree function on the basis of allometric scaling relationships assumed to emerge from traits of branching networks. To test this key assumption, and more generally, to explore patterns of external architecture within and across trees, we measure branch traits (radii/lengths) and calculate scaling exponents from five functionally divergent species.
Consistent with leading theories, including metabolic scaling theory, branching is area preserving and statistically self-similar within trees. However, differences among scaling exponents calculated at node- and whole-tree levels challenge the assumption of an optimised, symmetrically branching tree. Furthermore, scaling exponents estimated for branch length change across branching orders, and exponents for scaling metabolic rate with plant size (or number of terminal tips) significantly differ from theoretical predictions.
These findings, along with variability in the scaling of branch radii being less than for branch lengths, suggest extending current scaling theories to include asymmetrical branching and differential selective pressures in plant architectures.