Light pollution is disrupting the seasonal rhythms of plants and trees


Urban plants' phenology is being severely disrupted by city lights that are on all night, changing when their buds develop in the spring and when their leaves change color and fall off in the fall. The growing season in cities is increasing, according to new research, and this can have an impact on anything from allergies to local economics.

Research team examined trees and bushes at over 3,000 locations in US cities as part of their study to see how they responded to various lighting conditions over a five-year period. Along with temperature, the natural cycle of day and night serves as a signal to plants of the changing seasons.

When compared to sites without evening lighting, they discovered that artificial light alone brought up the date when leaf buds first opened in the spring by an average of roughly nine days. Although the timing of the fall color shift in the leaves was more complicated, it was nevertheless delayed across the lower 48 states by an average of about six days. In general, scientists observed that the difference increased with light intensity.

Researchers further predicted the effects of evening lighting on five US cities—Minneapolis, Chicago, Washington, Atlanta, and Houston—based on various future global warming scenarios and up to an increase of 1% annually in the intensity of nighttime lighting. Although its impact on the date of the fall color change was more complicated, they discovered that rising evening light would probably continue to move the start of the season earlier.

Why it matters

The economic, climatic, health, and ecological benefits that urban plants provide might be significantly impacted by this type of change in the biological clocks of the plants.

On the plus side, extended growing seasons could make it possible for urban farms to operate continuously. As global temperatures rise, plants might potentially offer shade to cool areas earlier in spring and later in the fall.

However, adjustments to the growth season can also make plants more susceptible to harm from spring frost. Additionally, it may throw off the timing of other creatures, including pollinators, which certain urban plants depend on.

Urban light intensity varies among cities and among neighborhoods within cities.

An earlier and longer pollen season, which can aggravate asthma and other respiratory issues, is another possibility if urban plants have a longer active season. According to a research conducted in Maryland, the number of asthma hospitalizations rose by 17% during exceptionally early plant blooming years.

What still isn't known

It's unclear how the timing of fall colors will vary when nighttime lighting and temperatures rise in the future. Scientists predictions predicted that the intricate interaction between temperature and artificial light, which influences the autumn color, would cause the delay in coloring caused by climatic warming to end by the middle of the century and potentially even reverse. Further investigation is necessary.

We don't yet know how urban artificial lighting may alter in the future.

According to one study, from 2012 to 2016, the amount of urban light at night had grown globally by around 1.8% annually. The adoption of LED street lights, which consume less energy and have less of an impact on plants than conventional streetlights with longer wavelengths, and the requirement for shields to restrict where the light travels are two ways that several cities and states are attempting to limit light pollution.

The phenology of urban plants may also be impacted by other elements, such as soil moisture and carbon dioxide. Furthermore, various day-night temperature patterns may result from the quicker rise in temperature at night compared to during the day, which may have complicated effects on plant phenology.

Scientists can forecast changes in plant activities as a result of a changing environment by better understanding these interactions between plants and artificial light and temperature. Cities already act as living laboratories.