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Light Pollution Is Throwing Off the Seasons

Researchers have discovered that the early bloom of some tree buds might be down to increasing amounts of light pollution.
Light pollution in the night sky. Image: Mike Lewinski/Flickr

We already know that light pollution has made the Milky Way invisible to one third of humanity. Now researchers have found that it might also be fast-forwarding the arrival of spring in the UK.

In a study published Tuesday in the journal Proceedings of the Royal Society B, researchers describe how night-time light pollution is causing early budburst—emergence of new leaves on a tree—in four common types of British tree: ash, oak, sycamore and beech. The researchers based their findings on data collected by citizen scientists and satellite imagery giving information on levels of light pollution in areas across the UK.

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"For the last 13 years, a bunch of citizen scientist have been noting the time at which four common tree species come into budburst,"Richard ffrench-Constant, paper co-author and an entomologist at the University of Exeter, told me. "We found that budburst correlates with the amount of artificial light in an area."

Ffrench-Constant said that well-lit urban areas tended to be warmer—a condition that also encourages budburst. However, as the natural phenomenon was up to a week early it could not, he said, be attributed to temperatures alone, and had to be down to levels of light pollution that were also present.

A budburst from an ash tree. Image: Judith Garforth

Early budbursts in trees can lead, said ffrench-Constant, to a "cascade effect" when one untimely natural phenomenon leads to a series of others that unbalance the ecosystem. Moth caterpillars, for example, try and time their eggs to hatch at the same time as budburst as this allows baby caterpillars to chomp away at the freshest juiciest leaves that promote optimal caterpillar growth. Yet the effects of light pollution on nature can throw everyone's timing off.

"If the moth eggs don't respond to the same stimuli, this means that the caterpillars will miss budburst and end up feeding on a bunch of tannin-enriched and horrible-tasting leaves, so they'll do badly," said ffrench-Constant.

"Birds also time their eggs to hatch when they'll be lots of caterpillars for their chick. Less caterpillars means less song birds—so this would have a knock on effect throughout the ecosystem," he said.

Ultimately, the researchers want to use their findings to deter the onslaught of early springs in the UK. Ffrench-Constant explained that the key would be to understand plant physiology and engineer LEDs that emit specific non-budburst encouraging light colors or wavelengths.

"It would be great to dial up specific frequencies of light that can allows us to drive around at night, but which don't promote budburst," said ffrench-Constant.