A new study has shown that the bright lights in big cities can cause flowers to flower prematurely.
One academic discovered that trees blossom earlier in urban areas than they do in rural ones. It is probably due to artificial lighting from street lamps, advertisements boards, and other sources.
Although artificial light can significantly alter the day-night cycle of plants, it is often forgotten when lighting strategies are developed for cities streets.
Too soon bud can lead to trees that are not synchronized with other organisms (e.g., pollinators), which could threaten their survival.
The artificial light sources used after dark in Beijing are shown here. Even though artificial light can be a key to early blossoms, it is frequently overlooked by authorities when designing lighting strategies for cities streets.
The study was conducted by Lin Meng, a postdoctoral scholar at Lawrence Berkeley National Lab in Berkeley, California, who detailed her findings in the journal Science.
“Trees don’t have watches or calendars. But they seem to know when spring is coming sooner than we do,” she stated.
‘The timing of seasonal biological events – such as when trees leaf out, flowers open, and leaves turn yellow – is called phenology.
“We can use satellites for observing when spring plants become green around the world.
Meng used satellite data to compare spring green-up dates in urban and rural areas of the 85 most populous US cities between 2001 and 2014.
Because of the higher temperatures in cities, spring green up occurred six days sooner than normal in urban areas.
‘The six-day difference was mainly caused by warmer urban temperatures, which averaged 1.3°C [2.3°F] higher than surrounding rural temperatures,’ Meng said.
She also found that, while urban trees were greener than those in rural areas due to climate change, they responded slower than the rural ones.
According to a new study, artificial lighting can alter the timing of “spring green up” in urban areas compared with rural areas.
Meng stated that the urban trees weren’t sufficiently chilled in winter, and were therefore less sensitive to rising temperatures in spring.
“By contrast, some urban trees in warm southwestern and coastal regions (e.g. Texas, Louisiana, or Florida) responded better to temperature than rural counterparts. This could be a strategy for dealing with dry conditions.
It’s already known a warming climate has shifted the timing of global seasonal tree events like leaf budding and greening – also known as phenology.
Artificial lighting poses additional problems for urban trees.
These additional changes “have cascading ecosystem impacts” and could impact phenology more than just climate warming.
American cities have more tree leaves than rural areas. Artificial light can accelerate this phenomenon as the temperature rises. Image: Cherry blossoms, Beijing
The result is these locations can be up to 5.4°F (3°C) warmer than the countryside – a phenomenon known as the ‘urban heat island effect’.
‘We as ecologists know a lot about the impact of warming and increased carbon dioxide concentration on plants because these are the two most significant aspects of climate change,’ said Meng.
“But light doesn’t change in the natural world, so most people didn’t see it that way.”
Meng was inspired to become interested in this topic by his 2015 trip to Beijing, China to see the cherry blossoms.
She stated that she had seen the forecast and the peak-blossom period was already 10 days earlier at downtown Central Park.
“The night before, I had planned to go to Central Park to view the blooms. But, snow fell unexpectedly and I found that the flowers were almost gone the following day.
Meng hopes to study how different species of vegetation respond to the different light wavelengths in future research.
An example: LEDs with a wide-spectrum of light can have different impacts on the environment than those that emit mostly yellow-orange light.
A second area of interest involves identifying when trees become most sensitive to artificial lighting.
Meng stated that if answers to these questions are provided, it will help to make decisions about the types of lighting we require for each location to minimize ecological effects.