John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Light pollution makes trees bud at least a week before normal, say researchers.
Here’s yet more info on how trees are so much more complex than we tend to think. In addition to warning each other about pests, and actually drooping as if tired when they’re “asleep,” there’s evidence they respond to light pollution by budding earlier in the year, in effect making for a premature spring.
At least that’s the case in the U.K., according to researchers at the University of Exeter in Cornwall. They took satellite images of the region’s nocturnal landscape and compared them to citizen-gathered data on when various tree species bud. The result: “We find that budburst occurs up to 7.5 days earlier in brighter areas, with the relationship being more pronounced for later-budding species,” they write in Proceedings of the Royal Society B.
Scientists have known for a while that artificial lights (especially in the red spectrum), while usually not enough to trigger photosynthesis, can alter a tree’s sense of “day,” leading to different budding/flowering times and extending its overall growth. The Exeter study proves it’s happening on a widespread scale and quantifies the abnormal growth effect from the U.K.’s legion of street lights and businesses.
Trees getting an early start to the year—why should anybody care? For one thing the survival of other organisms can be tied to trees’ schedules, the scientists say in a press release:
Researchers believe early bud bursting will have a cascade effect on other organisms whose life cycles work in synchronicity with the trees. The proliferation of the winter moth for example, which feeds on fresh emerging oak leaves is likely to be affected which may in turn have some effect on birds in the food chain that rely on it for food.
There’s evidence nighttime illumination lets trees cling to their leaves longer into the cold months. That means when the first winter storm arrives to cover them with snow or ice, the added weight on all the leaves is likely to break more boughs and branches. Longer periods of greening also allow leaves to potentially suck in more air pollution through the year, eventually harming the whole tree. The researchers suggest local governments use this new data to manage “light levels in our urban environment in a sustainable way."