Noise Pollution Affects Plants, Too

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Trees in the foreground of San Francisco's financial district. Research shows that trees and other plants are being affected by noise.

THE GIST

- Scrub jays avoid noisy sites, preventing them from doing the important job of dispersing pine tree seeds.

- Some hummingbirds flock to noisy areas, possibly helping them pollinate more flowers in those places.

- A fifth of our nation is impacted by noise pollution, but we still know little about how animals are affected.

Facing an ever-increasing din of background noise from traffic and other human activities, many animals are adapting by changing their behavior or just moving to quieter locales.

In turn, noise pollution is altering the landscape of plants and trees, which depend on noise-affected animals to pollinate them and spread their seeds.

Some plants do worse in noisy areas, a study found, while others seem to do better, depending on how the community of creatures around them changes. Either way, the ripple effects can be far reaching and long lasting, especially for trees, which often take decades to grow from seedlings into adults.

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And the results likely apply to any ecosystem where animals are affected by noise.

"Most of the literature on the impacts of noise on surrounding natural communities has really focused on what a single species is going to do because it can't communicate," said Clinton Francis, an evolutionary ecologist at the National Evolutionary Synthesis Center in Durham, N.C.

"But what we have to realize is that if we see a disturbance in a species that is really important for the community, it is going to have these cascading effects throughout the ecosystem. And we might see some really large-scale changes due to the responses of one or two important species."

With the growth of superhighways, air traffic, construction and other machine-based activity, the globe has been growing louder and louder over the last century. Only recently have scientists started to document the ways that individual species respond to the racket.

In loud places, studies have found in the last few years, some birds sing at higher frequencies. Bats can have trouble finding prey. Frogs can struggle to find mates. And whales seem to be vocalizing with more volume to communicate with each other.

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To find out how noise might be affecting entire communities instead of just single species, Francis and colleagues built upon research they had already done, which showed that western-scrub jays avoid noisy areas while black-chinned hummingbirds prefer to build their nests amidst the din. (One theory for why is that loud places are safer for hummingbird nests because the birds don't need to worry about predation by scrub jays there).

Scrub jays are important dispersers of piñon pine tree seeds. Each fall, a single bird picks up thousands and thousands of seeds and then hides them in various stashes. Throughout the winter, when other food becomes scarce, the birds feast on hidden seeds. But some seeds never get recovered. Instead, they sprout and form the next generation of trees.

In a woodland area of New Mexico, the researchers scattered 20 seeds under each of 12 piñon pines -- six in quiet spots and six in loud areas near natural gas wells. Every day for three days, the team came back to each tree to see how many seeds had been eaten and to replenish the stashes. Motion-triggered cameras revealed which animals were eating the seeds.

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Under the quiet trees, the researchers report today in the journal Proceedings of the Royal Society B, jays collected seeds along with other animals. But jays didn't ever show up under noisy trees, where mice ended up doing most of the seed chomping.

Because mice eat seeds instead of hiding them and because seeds don't survive the trip through a mouse's digestive tract, the results suggest that noise might interfere with the ability of piñon pines to survive from generation to generation.

In fact, compared to loud areas, the researchers counted four times as many piñon pine seedlings in quiet sites.

On the other hand, similar experiments showed that hummingbirds visited and tried to pollinate artificial flowers in noisy sites five times more often than they visited quieter flowers. So, some plants might actually do better where noise levels are high if that's where their pollinators thrive.

As much as a fifth of all land area in the United States is impacted by noise. Yet we still know very little about how all that noise is affecting most animals, said Gail Patricelli, an evolutionary ecologist at the University of California, Davis.

The new findings suggest that it's not just animals that we have to worry about when it comes to noise. To protect the entire ecosystem, it might be important to spend more money in order to use quieter versions of technologies for transportation, drilling and other applications.

The study "gives us hints that the impacts that noise has on animals may magnify up the community structure and have effects across the board in the entire ecosystem," Patricelli said. "These are absolutely huge areas we're having an impact on. And we don't understand it much at all."