City trees suffer from not getting enough sleep

Trees at night

CC BY 2.0 Max Pixel

Streetlights and other city circumstances lead to poor health and prevent urban trees from being all that they can be.

From the “Trees, They’re Just Like Us!” department, my favorite forester has weighed in on an issue I have long suspected: Urban trees, like much of the natural world, have a hard time when the lights are left on all night.

“They also have to sleep at night,” Peter Wohlleben told the audience at the Hay Festival of Literature in Wales. “Research shows that trees near street lights die earlier. Like burning a lamp in your bedroom at night, it is not good for you.”

And if anyone knows trees – and embraces anthropomorphising them – it’s Wohlleben. The German forester and best-selling author doesn’t shy away from talking about trees as if they were people. “I use a very human language,” he says. “Scientific language removes all the emotion, and people don’t understand it anymore. When I say, ‘Trees suckle their children,’ everyone knows immediately what I mean.”

Wohlleben has been studying and working in forests since 1987, so he comes to all of this with an admirable resume; and he points to research to back up his latest observations. In 2016 the European Commission funded a study into the impact of artificial light on trees and plants at night. According to The Times of London:

A paper published last year in the Journal of Ecology said there was evidence that artificial light affected the timing of “spring budburst”, leaf colouring and abscission (the shedding of dead leaves). This study concluded that changes in trees’ annual rhythm of producing leaves and blossom attributed to artificial light “may have significant effects on [their] health, survival and reproduction”.

Wohlleben states the obvious when he says that councils should turn off streetlights at night to help urban trees be healthier and live longer, as well as to save electricity. (The other benefits of reducing light pollution are legion, including the opportunity for us skygazing humans to enjoy the age-old pleasure of pondering the heavens … and seeing actual stars while we do so.)

Other challenges faced by city trees include the fact that they are like orphans, Wohlleben says, striving to grow but doing so without the support system of their neighbors – a recurring theme for Wohlleben who has shown how trees in the forest are social beings.

“Urban trees are the street kids of the forest,” he says, adding that their roots struggle in the harder soil under sidewalks. If that weren’t enough, they are also warmed at night by radiated heat from streets and buildings, unlike forests which cool down. They are deprived of the shared forest microorganisms that help them collect nutrients and water, and that they can be poorly attended to by city workers.

Meanwhile, these silently stalwart organisms of the streets do so much for us in return. As Mat McDermott wrote here earlier while singing the praises of trees:

• The net cooling effect of a single, young healthy tree is equivalent to 10 room-sized air conditioners, running for 20 hours a day. 10 air conditioners, a single tree!!

• A tree planted today on the west side of your house will result in a 3% energy savings in the five years time, 12% savings in fifteen years.

• A single stand of trees reduces particulate pollution 9-13%, with the amount of dust reaching the ground beneath those trees 27-42%, versus in an open area.

• If you have trees on your property near your home it accounts for 10-23% of your home value.

• In urban areas, assuming the cost of planting and maintaining a tree for three years at $250-600, it will return $90,000 in direct benefits over its lifetime (apart from beautification, etc.).

And there’s so much more; think crime reduction, increased wildlife habitat, improved mental health, and on and on. With all that trees do for us, the very least we can do, it would seem, is to turn off the lights before we put them to bed.

Read more on Wohlleben’s wonderful, forward-thinking thoughts on trees in his book, The Hidden Life of Trees: What They Feel, How They Communicate – Discoveries from a Secret World.