There has already been a significant amount of research done into the impact human noise has on the surrounding fauna, but new research suggests that human noise may have a ripple impact on plants as well.
Published in the journal Proceedings of the Royal Society B the study was led by Clinton Francis of the National Science Foundation (NSF) National Evolutionary Synthesis Center in Durham, North Carolina, who found that because animals pollinate many plants or eat and disperse their seeds, the impact of human noise on animal colonies may also affect the plants they service as well.
In cases where noise has ripple effects on long-lived plants like trees, the consequences could last for decades, even after the source of the noise goes away, says Francis.
The researchers conducted a series of experiments within the boundaries of the Bureau of Land Management’s Rattlesnake Canyon Wildlife Area in northwestern New Mexico, home to thousands of natural gas wells that are pumped with noisy compressors that run day and night every day of the year: in other words, the perfect place to test the impact of human noise on the surrounding ecosystem.
One experiment found that black-chinned hummingbirds may in fact prefer noisy sites.
Francis and colleagues created artificial plants designed to mimic the common red wildflower located in the area known as the scarlet gilia. The researchers created three “flowers” — microcentrifuge tubes wrapped in red electrical tape — which were filled with a fixed amount of sugar and water to act as nectar. They also dusted one plant in each patch with a different colour artificial pollen.
They found that that the black-chinned hummingbird made five times more visits to the noisy sites than to the quiet ones.
“Black-chinned hummingbirds may prefer noisy sites because another bird species that preys on their nestlings, the western scrub jay, tends to avoid those areas,” Francis said.
If more hummingbird visits and greater pollen transfer translate to higher seed production for the plants, the results suggest that “hummingbird-pollinated plants such as scarlet gilia may indirectly benefit from noise,” Francis said.
More experiments reveal good news for some plants, but bad news for others.
A second set of experiments conducted in the same area focused on what the impact of human noise may be for trees, focusing on one of the dominant trees in the area, the piñon pine. The seeds from the piñon pine that aren’t plucked directly from the cones fall to the ground and are eaten by birds and other animals, often transported away and — upon passing through the animals digestive system — are fertilized and deposited some distance from the original tree.
The researchers scattered 120 piñon pine seeds at the base of 120 of the trees and — using a motion triggered camera — waited to see what animals would take the seeds. They found that after three days several animals were spotted feeding on the seeds, including mice, chipmunks, squirrels, birds and rabbits. However two animals in particular differed between quiet and noisy sites; mice, which preferred the noisier sites, and the western scrub jays, which avoided the noisy sites altogether.
Piñon pine seeds that are eaten by mice don’t survive the passage through the animal’s gut, Francis said, so the boost in mouse populations near noisy sites could be bad news for pine seedlings in those areas.
On the opposite side of the coin, however, a single western scrub jay may take hundreds to thousands of seeds, only to hide them in the soil to eat later in the year. The seeds they fail to relocate will eventually germinate, so the preference of western scrub jays for quiet areas means that piñon pines in those areas are likely to benefit.
The researchers counted the number of piñon pine seedlings in the areas and found that there were four times as many in the quiet areas as there were in the noisy ones.
It may take decades for a piñon pine to grow from a seedling into a full-grown tree, Francis said, so the consequences of noise may last longer than scientists thought.
“Fewer seedlings in noisy areas might eventually mean fewer mature trees, but because piñon pines are so slow-growing the shift could have gone undetected for years,” he said.
“Fewer piñon pine trees would mean less critical habitat for the hundreds of species that depend on them for survival.”