The cascading effect of noise on plants persists for long periods of time and after the noise is rem

Pinyon pine seedlings are taken into account during the vegetation survey. Photo: Sarah Thurmondt
Pinyon pine seedlings are taken into account during the vegetation survey. Photo: Sarah Thurmondt

Although noise can change moment by moment for humans, it has a longer-lasting effect on trees and plants.

A new Cal Poly study shows that human noise pollution affects the diversity of plant life in an ecosystem even after the noise has been removed. This is the first study to investigate the long-term effects of noise on plant communities. It was published in the journal Proceedings of the Royal Society B.

In a study conducted twelve years ago near gas wells in New Mexico, researchers found that there were 75% fewer pinyon pine seedlings in noisy locations than in quiet ones. This was most likely due to the noise fending off the Woodhouse jay scrub, which sows thousands of pine seeds, saving them to eat during the winter months.

Recently, the research team returned to these sites to find out if pinyon pine has recovered over time.

As companies change sites where they use noisy compressors to help produce natural gas, some of the previously noisy sites have become quiet. These areas had fewer seedlings and saplings compared to sites that did not have compressors added to the well pad to speed up gas production. A decrease in seedlings results in a time when the site was noisy, but a decrease in seedlings shows that pinyon pine seeds still do not germinate once the noise has been removed.

"The effects of human noise pollution are growing into the structure of these forest communities," said biology professor and senior author Clint Francis. "What we see is that removing noise does not necessarily immediately lead to the restoration of environmental function."

While it is possible that pinyon pine has declined due to a lack of production capacity, it is more likely that Woodhouse Scrub jay has not returned to a previously bustling area and is therefore not planting seeds.

"Some animals, like scrub jays, have episodic memories," says Jennifer Phillips, lead author who worked on the project while a postdoc at Cal Poly and who is currently a professor teaching at Texas A & M-San Antonio. "Animals like Scrub Jay that are sensitive to noise learn to avoid specific areas. It may take time for the animals to rediscover these previously noisy areas, and we don't know how long that may take."

The researchers also found differences in juniper seedlings and flowering plant communities depending on the current noise level and whether the noise level has recently changed because noisy compressors have been moved. Sites with more noise had fewer juniper seedlings and different plant species than quiet sites. Due to the complexity of ecosystems, the cause of these changes is still unknown.

"Our results show that plant communities change in many ways with noise reduction," Francis said. "We have a decent understanding of how and why foundational trees like pinyon pines suffer from the noise from our previous work with jays, but we also see big changes in plant communities through changes in the abundance of shrubs and annuals. These changes likely reflect the effects of noise on animals that eat plants, such as deer, elk, and various insects, as well as many pollinators that are important for plant reproduction. In essence, our research shows that the effects of noise are far-reaching and reverberate throughout the ecosystem across multiple species."

Future research may offer a more finely tuned view of how noise causes these ecosystem changes. The researchers want to learn more about which herbivores, seed dispersers, and pollinators avoid or attract noise, and how changes in insect and animal behavior collectively affect plant communities.

Based on models of more than a decade of ecosystem experiencing noise pollution, the evidence suggests that plant community may take a long time to recover from human noise exposure. However, co-author and lead botanist Sarah Termondt, a Cal Poly research affiliate, emphasizes the need to understand the full and lasting cost of noise. "Continuing to look at long-term changes in floral stocks over time will find out whether communities eventually recover from prolonged periods of noise pollution, even after it is removed from the landscape," she said.

When changes in plant communities are considered alongside growing evidence of the problems that noise creates for animals, it becomes increasingly difficult to ignore the near-absence of noise regulations across the US.

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