Trees that are illuminated by streetlights tend to get harder and more bitter leaves that insects do not want to eat. And when the availability of edible leaves decreases, the number of insects, and subsequently birds, will also decrease according to the study, which is published in Frontiers in Plant Science.
The researchers studied around 5,500 leaves from 180 trees at 30 locations in Beijing. They then saw that leaves that were lit up at night not only became more bitter, they also formed more tannins, a substance that defends the leaves against various attacks. The more light the leaves were exposed to, the more bitter they became. The most bitter leaves did not even show any signs of insects having eaten them.
But more research is needed, the researchers add. It could also be that more light at night makes insects more visible to predators, which reduces their number, and thus their effect on the trees.
