Man-made noise disrupts the growth of plants and trees

Pinus edulis foliage and cones (c) snowpeak via wikimedia commons The Pinon pine could suffer from high levels of artificial noise

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It alters birdsong and can make it difficult for some predators to hunt, and now it seems that man-made noise also affects plants.

A US team found that industrial noise disrupted the behaviour of animals that pollinate plants and disperse seeds.

This, they suggest, could be slowly transforming our landscape, especially by changing the dispersal of slow-growing trees.

The study is published in the Royal Society Proceedings B.

The team, led by Clinton Francis from the National Evolutionary Synthesis Center (NESCent) in North Carolina, tested the effects of industrial noise on wildlife in Rattlesnake Canyon Habitat Management Area (RCHMA), New Mexico.

This large forested area has a high density of natural gas wells, providing scientists with a unique setting that allowed them to study the effects of noise without some of the "confounding factors" often associated with noisy areas, such as roadways and artificial light.

Start Quote

Fewer pinon pine trees would mean less critical habitat for the hundreds of species that depend on them for survival”

End Quote Clinton Francis NESCent

In the first of two experiments, the team focused on birds, which, they explained, "are considered to be especially sensitive to noise pollution owing to their reliance on acoustic communication".

They placed patches of artificial hummingbird-pollinated flowers in noisy and quiet areas.

These convincing flower copies contained tubes of nectar, enabling the researchers to track exactly how much sugary fluid was consumed by visiting hummingbirds.

Industrial din, the scientists discovered, actually increased the activity of the birds. One species in particular - the black-chinned hummingbird (Archilochus alexandri) - made five times more visits to noisy sites than quiet ones.

Dr Francis explained that these hummingbirds might prefer noisy sites because another bird species that prey on their nestlings, such as western scrub jays, tend to avoid them.

Silent growth
Rattlesnake Canyon Habitat Management Area Natural gas wells in a forested area created the ideal setting to test the impact of noise on wildlife

In a second set of experiments, the team investigated the effect of noise on a species of tree that makes up much of the area's forest habitat - the Pinon pine (Pinus edulis).

The team scattered pine cones beneath 120 trees in noisy and quiet sites, and used a motion-triggered camera to record the animals that took the seeds.

Over three days, several animals visited the sites to take seeds, including mice, chipmunks, squirrels, birds and rabbits. Most significantly though, mice much preferred noisy sites, whereas western scrub jays avoided them altogether.

This, the researchers explained, could be very bad news for the trees.

Noisy world

Bat foraging near a motorway (Image: Stefan Greif/ Dietmar Nil)

The seeds that are eaten by mice, Dr Francis explained, don't survive the passage through the animal's gut. So an increase in mouse populations near noisy sites could mean that fewer seeds germinate in those areas.

In contrast, one western scrub jay can take hundreds or even thousands of seeds and hide them in the soil to eat later in the year. Some of these will eventually germinate.

The team went on to count the number of pine seedlings and found that they were four times as abundant in quiet sites compared with noisy ones.

"Fewer seedlings in noisy areas might eventually mean fewer mature trees, but because pinon pines are so slow-growing the shift could have gone undetected for years," Dr Francis explained.

"Fewer pinon pine trees would mean less critical habitat for the hundreds of species that depend on them for survival."

The researchers concluded: "Noise pollution is growing [and] this study emphasises that investigators should evaluate the ecological consequences of noise alongside other human-induced environmental changes that are reshaping human-altered landscapes worldwide."

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