Streetlights Make Summer Come Early — and That’s Not a Good Thing - Pacific Standard

Streetlights Make Summer Come Early — and That’s Not a Good Thing

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A study shows trees start budding up to a week early in the most brightly lit areas of the United Kingdom.

By Nathan Collins

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(Photo: Pix Spotting/Flickr)

Though carbon dioxide (deservedly) gets most of our attention when it comes to human impacts on the environment, scientists know there are plenty of other ways we damage the planet. A new study adds to that list of other effects: Streetlamps and other sources of light pollution are leading trees in the United Kingdom to start growing new leaves as much as a week earlier than they otherwise would.

“The results highlight, for the first time and at a national scale, a relationship between the amount of artificial night-time light and the date of bud burst [the first step in growing new leaves] in deciduous trees,” write Richard Ffrench-Constant and his colleagues in Proceedings of the Royal Society B. Such dramatic findings suggest a need to investigate the effect of artificial lighting effects on other trees and plants, too, they write.

Researchers have known for quite a long time that streetlamps and the like can have serious consequences for animals. Birds that migrate at night and baby sea turtles can become disoriented, and it can mess with nocturnal animals’ hunting and feeding schedules. But whether artificial light has a direct effect on plants has been less clear.

Streetlamps and other sources of light pollution are leading trees in the United Kingdom to start growing new leaves as much as a week earlier than they otherwise would.

To shed some light on that, Ffrench-Constant and his colleagues first looked to data on four tree species — European sycamore, European birch, pedunculate oak, and European ash — collected as part of the U.K.’s citizen-science project Nature’s Calendar, which tracks budburst and other seasonal events affected by climate change. Combining that with Defense Meteorological Satellite Program data on nighttime lighting, the team could then estimate how the degree of nighttime light pollution affected budburst. They also took account of local temperatures, since temperature is one of the key drivers of budburst.

Streetlamps and such had no impact on sycamores, the earliest-budding species, but substantial effects on the other three. In the worst case, ash in colder temperatures — four degrees Celsius, or around 39 degrees Fahrenheit — went through budburst about seven days earlier in the brightest areas than in the darkest parts of the U.K. Other tree species began budding two or three days earlier in the brightest places. Similar effects persisted, the researchers note, even outside of urban areas (that is, far from urban heat sources that could also affect budburst).

“This dramatic advance of budburst illustrates the need for further experimental investigation into the impact of artificial night-time lighting on plant phenology [seasonal effects] and subsequent species interactions” the researchers write. “As light pollution is a growing global phenomenon, the findings of this study are likely to be applicable to a wide range of species interactions across the world.”

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