Are City Plants Greener Than Country Cousins?
NASA — Trees and bushes in Central Park may have a big advantage over plants rooted in the country. A new NASA-funded study finds that concrete jungles, like New York City, create warmer conditions that cause plants to stay green longer each year compared to surrounding rural areas.
In fact, the study finds that growing seasons in 70 cities in eastern North America lasted about 15 days longer in urban areas compared to rural areas outside of a city’s influence.
Urban areas with high concentrations of buildings, roads and other artificial surfaces retain heat, creating urban heat islands. Satellites reveal that urban heat islands increase surface temperatures compared to rural surroundings.
These heat islands provide some early insight into how global warming might affect plant growing seasons and ecosystems. As temperatures warm due to climate change, growing seasons will likely change as well.
Xiaoyang Zhang, the study’s lead author and a researcher at Boston University, Boston, Mass., found that for every 1 degree Celsius (C) or 1.8 Fahrenheit (F) that temperatures rose on average during the early springtime, vegetation bloomed 3 days earlier.
Springtime land surface temperatures in eastern North American cities were on average 2.3°C (4.1°F) warmer than surrounding rural areas, according to the study. In late autumn to winter, the city temperatures were 1.5°C (2.7°F) higher than the surrounding areas.
Higher urban temperatures caused plants to start greening-up on average seven days earlier in spring. Similarly, in urban heat island areas, the growing season lasted eight days longer in the fall than the rural areas.
“If you live in a rural area and drive regularly into the city, and if you pay attention to vegetation, you will see a difference in the growing seasons in early spring and late autumn,” says Zhang.
Using information from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra satellite, Zhang and his Boston University colleagues discovered that city climates have a noticeable influence on plant growing seasons up to 10 kilometers (6 miles) away from a city’s edges. In other words, the impact of urban climates on ecosystems extended out 2.4 times the size of a city itself.
“Warming from global climate change will definitely impact ecosystems,” Zhang says. “Thus, urban areas provide us with some measures of how changes in temperature might affect vegetation.”
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Satellite image of Central Park, NYC
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