Streetlights and other forms of artificial light brighten our cities at night, but they may be having unintended consequences on the environment.
A new study published in Frontiers in Plant Science reveals that artificial light at night can make tree leaves tougher and harder for insects to eat, which could disrupt the food chain in urban areas.
Artificial light has increased nighttime brightness around the world by nearly 10%.
While this light pollution is known to disrupt sleep patterns and ecosystems, its effects on plants, which rely on light for photosynthesis, have been less understood.
Now, scientists have found that this constant exposure to artificial light makes tree leaves tougher, which could have significant effects on the ecosystem.
“We noticed that tree leaves in cities often show very little insect damage compared to those in natural areas, and we wanted to find out why,” said Dr. Shuang Zhang from the Chinese Academy of Sciences, who led the study.
“Our research shows that in two common tree species in Beijing, artificial light at night made the leaves tougher and reduced the amount of damage caused by insects.”
To investigate, the researchers focused on two types of street trees: Japanese pagoda trees and green ash trees. Japanese pagoda trees have smaller, softer leaves that are usually more attractive to insects, while green ash trees have tougher leaves.
The team selected 30 sites along main roads in Beijing that are typically illuminated all night and measured the brightness at each location. They then collected nearly 5,500 leaves from these trees to study how artificial light affected their characteristics.
The scientists examined traits such as leaf size, toughness, water content, and levels of nutrients and chemical defenses. They found that the more artificial light a tree was exposed to, the tougher its leaves became. Tougher leaves had fewer signs of insect feeding, and in areas with the brightest lights, many leaves showed no insect damage at all.
“The exact reason why artificial light makes leaves tougher isn’t fully understood yet,” explained Zhang. “One possibility is that the extra light at night extends the time the tree can photosynthesize, leading it to allocate more resources to making its leaves tougher and less appealing to insects.”
The study’s findings suggest that this toughening of leaves could have a ripple effect throughout the food chain.
“If insects can’t eat the leaves, they might not survive or reproduce as well, leading to fewer herbivorous insects,” said Zhang. “This could then reduce the number of predatory insects, insect-eating birds, and other animals higher up the food chain.”
The researchers also noticed differences between the two tree species. Japanese pagoda trees exposed to more artificial light had lower levels of nutrients like phosphorus, while green ash trees had smaller leaves with more nitrogen but lower chemical defenses. This suggests that different tree species respond to artificial light in different ways, with some focusing more on defense and others on growth.
Zhang emphasized that this study was conducted in only one city and with just two types of trees, so more research is needed to understand how widespread these effects might be. “Our findings raise important questions about how urbanization and light pollution are affecting insect populations and the ecological processes they support,” she said. “We need to pay more attention to these trends, especially given the global decline in insect populations.”
As cities continue to grow and artificial light becomes more widespread, understanding its impact on the environment will be crucial for protecting the delicate balance of urban ecosystems.
