Trees Use Roots to Fight Off Other Trees, Says Study

Photo: Joshua Rappeneker / CC

There's nothing quite as relaxing as a nap in the shade of a majestic old tree, or strolling down some quiet forest path flanked by towering columns of wood and bark. But while all may appear tranquil and quiet, for the trees themselves things might be a bit more reminiscent of fighting for space in the front row of a heavy-metal show -- visible roots and all. In fact, after studying tree growth patterns, researchers from Princeton recently concluded that trees are actually quite demanding of their personal space.Evidently in the soil beneath trees, there's some fascinating competition going on. Ecologists have found that trees not only send out roots to collects water and nutrients, but to ward off other trees from gaining ground nearby. In other words, trees aren't merely expending energy keeping themselves alive -- they're doing their best to keep away the competition, too, says the study.

The New York Times spoke with one of the study's authors, plant ecologist Ray Dybzinksi, to get the lowdown on the quiet conflict trees are in underground:

Using computer software to predict the growth patterns in forests over time, Dr. Dybzinski and his colleagues are now reporting that the overabundant roots act as weapons to prevent other trees from growing.

Creating roots takes energy, and optimally every tree would have just enough roots to capture the nutrients and water it needs.

Instead, the scientists write in The American Naturalist, the trees create excess roots -- probably not to help them grow more successfully, but rather to cause other trees to grow less successfully.

In the resulting system, trees that produce fewer roots (or too many roots) lose out.

Dr. Dybzinski points out that not all tree-battles are subterranean. In forests, trees are in a constant struggle to survive by capturing sunlight, with those caught in the shade losing out. In fact, if there was no competition, trees would have no particular motivation to grow so tall at all. "If they could somehow agree to cooperate and not compete, they could all stay closer to the ground and do something else with that energy, like create seeds," Dybzinksi told The Times.

Interestingly enough, it's not just other plants feeling squeezed out by pushy trees. Bulging roots have been known to crack and raise more than few a sidewalks and driveways as well -- but some humans are a bit more willing to deal with encroaching roots than others.

Recently the fate of a 130-year-old elm tree on a street in Back Bay, Boston was called into question by locals complaining that its roots were buckling the sidewalk, making it difficult to traverse, particularly for folks with disabilities. The grand old tree had gone too far with its rooting ways; federal law requires that walkways be accessible -- so it seemed the elm would have to go.

Nearby residents, many of whom had spent decades enjoying the hardy tree, gathered for a meeting to save it from the saw, reports The Boston Globe. Finding a sidewalk that could handle the tree's persistent roots would be difficult, but then they found a contractor who had an idea.

An asphalt supplier from Hyde Park recommended a process in which crushed rock is layered with liquid asphalt to create a durable yet flexible surface that would gently slope over the tree roots. He would use a type of rock, quarried in Pennsylvania, whose color almost exactly matched the red brick of the sidewalk, and the supplier, Paul Fulmore of Riverside Asphalt Services, offered to provide the materials and labor free of charge.

...In the Back Bay, the American Elm is now secure, its roots no longer a problem for a well-trod part of the sidewalk. Supporters hope they've bought the elm at least another 50 years.

While roots may be quite unwelcoming at times, especially when used to keep away other plants, some people are more than happy to deal with it. "It had become a friend,'' Back Bay resident James Paradis said of the reprieved elm. There is a chance that trees may be equally understanding of their pushy peers' need for a little personal space, but unfortunately none could be found to comment.

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Tags: Biology | Evolution