Forest growth may look chaotic, but University of Arizona professor Brian Enquist is finding that trees, plants and, ultimately, forests develop according to patterns of branching. COURTESY OF EDWARD GRAY

The way trees grow and forests form might seem completely random, but a University of Arizona scientist and his team have discovered it's a lot more calculated than you might think.

In a first-of-its-kind series of studies, Brian Enquist and his team discovered what governs size, shape and other features of trees and plants.

His work, published in a series of recent papers, has allowed him to make accurate predictions about how much carbon dioxide forests assimilate, how much carbon they store and how much water and nutrients they use.

His work has allowed him to accurately predict how forests will grow. But more than that, it may allow us to understand important concepts in global climate change, as well as assisting in agriculture, conservation and restoration.

Enquist, a professor in UA's Department of Ecology and Evolutionary Biology, said that though trees look complicated, their structure can be explained through simple math. The rules he's discovered govern metabolism - the "fire of life" that dictates our pace of living: how fast something grows and how long it lives.

His work uncovered that these rules create a branch hierarchy and relate to how the branch radius and length change as one moves from the base of the tree to its tip. The rule creates a repeating pattern in trees, where a branch grows to a particular length and then sprouts a new limb at a particular spot.

Leonardo da Vinci was the first to look at tree patterns, which allowed him to draw them realistically, Enquist said. Da Vinci's rules, such as consistent branching ratios, are still used to draw trees accurately.

Enquist has gone on to look at these patterns in plants, as well. The same rules that govern trees also govern the internal tissues of plants, he said.

These systems exist in trees because evolution by natural selection has shaped how they obtain and transport resources, Enquist said. Selection has apparently acted on organisms to help them make maximum use of resources like light and water. At the same time, they've adapted to transport those resources at minimal cost and time - moving them to where they are metabolized.

The rules aren't unique to plants.

While Enquist applied these rules to forests, branching systems can be applied to most of biology, and that includes mammals - even humans.

"If you think about your lung or cardiovascular system, they're branching vascular systems," he said. "It's a network that branches to the rest of your body. If you look at a lung, it's a treelike network. And think about real trees: There's a hierarchical branching network that starts with a base and branches out to terminal ends."

Biology professor James Brown of the University of New Mexico said Enquist's work will help with planning and conservation in forestry, agriculture and other areas because it will give researchers a solid baseline for their work.

Brown said that if someone is interested in evaluating different outcomes for a restoration program, Enquist's research helps provide an accurate prediction of results no matter the species.

Brown said Enquist's work is getting international attention, and specifically from Chinese scientists who have visited with Brown.

"They're interested in applying this theory to better understand and manage applied systems in China, either forests or agriculture ecosystems," Brown said.

"What density do you plant different feeds at? In some cases, we know because there's lots of experience with the fundamental varieties of corn and wheat and so forth, but for alternative crops, it's not clear what that is."

Brown said companies don't want to spend a significant amount of money to plant seeds more densely than necessary. Overseeding can cause the plants to die, or the competition may cause the plants to be stunted, creating reduced yields, he said. Brown said Enquist's work will help avoid these sorts of problems.

Enquist also is conducting research in Costa Rica, where he's been observing a tropical forest.

"We've been following the dynamics and fate of every single tree within a long-term monitoring plot," he said. "We're very much interested in understanding what influences which trees live or die, which species do well here, and also the functioning of entire forest."

The group is attempting to understand what controls growth and mortality rates so members can build more predictions about how forests work.

"These mathematical rules are enabling us to develop a deeper understanding of how differing tree species, as well as the functioning of the entire forest, will respond to a changing climate," he said.

Victoria Blute is a NASA Space Grant intern. E-mail her at