Artificial Street Lights Disrupt Urban Ecosystems: Study Reveals Impact on Tree Growth and Insect Populations

How was this research conducted?

The researchers wanted to investigate how artificial light affects the relationship between plants and insects. To do this, they focused on two street tree species that are common in Beijing: Japanese pagoda trees and green ash trees. Although the two trees are similar in many ways, the Japanese pagoda tree has smaller and softer leaves that are preferred by insects.

The researchers chose 30 sampling points on main roads that are usually lit by street lights at night. They then measured the illuminance (amount of light) at each location and collected about 5,500 leaves to assess the effect of light on traits such as size, hardness, water content, and levels of nutrients and chemical defense compounds.

If the leaves are larger, it means that the plant directs its resources (such as nutrients, water, and energy) to growth. If the leaves are stronger and have high levels of chemical defense compounds such as tannins, that means that these resources are allocated for protection.

What were the conclusions?

The researchers noticed that for both tree species, the higher the level of light, the harder the leaves. The harder the leaves, the less likely they are to be eaten by insects. The researchers did not find that insects were feeding on leaves in the brightest places at night.

They also noted that artificial light changed the levels of nutrients and chemical defense compounds in the leaves studied. For example, Japanese pagoda trees that are exposed to more artificial light have lower levels of nutrients such as phosphorus in their leaves. There is less evidence on the leaves that insects are eating them.

According to research, this could be a bad sign for the ecosystem. Shuang Zhang, one of the study’s authors, told the Guardian in an interview: “Herb reduction could lead to detrimental effects in ecology. Lower levels of herbivory mean a lower abundance of herbivorous insects, which may result in a lower abundance of predatory insects, insectivorous birds, and so on. The decline of insects is a global pattern that has been observed over the past few decades. We should pay more attention to this movement.”

Although the researchers say they don’t know exactly why trees react to street lights in this way, they suspect that exposing trees to artificial light at night could extend their photosynthetic cycles. . This can be very stressful for them because when a plant photosynthesizes, it absorbs energy, and if that happens all the time, the situation can be very serious and eventually off the plant.