A study funded by the National Science Foundation has discovered that urbanization delays the time that plants bloom in the spring, which has an effect on the seasonal timing in cities.
In cold climates, the study found, plants begin to bloom earlier. In warmer climates, their growth is delayed. The difference in timing is estimated to be between one and two weeks depending on the region.
Researchers took into account a 3.6-degree Fahrenheit temperature increase, as well as a fourfold increase in human population density. In combining these factors, scientists were able to estimate an average eight-day change in bloom time.
Pollution, changes in humidity, fertilizer runoff and the urban heat island effect could all have a hand in the delay. The urban heat island effect is a phenomenon in which cities have higher temperatures than surrounding areas.
The delayed growth means that plants grow spring leaves and flowers at different times than they would have historically, which can disrupt agriculture and other plant and animal species. For humans, these delays could also cause more severe and lengthy allergy seasons.
The study’s results have been published in Nature Ecology & Evolution. More information on the study is available here.