The high temperatures of urban environments causes trees to grow faster in the city than in rural areas. Researchers at Columbia’s Earth Institute have discovered this by planting seedlings of the American red oak in four sites from Central Park to the foot of the Catskill Mountains.
Cities are hotter because buildings, streets and other urban structures absorb more solar energy during the day, and radiate that energy at night. This causes a difference in temperature between the city and rural areas in the New York area, with an average difference of 2.4 degrees during the day and an average minimum of 4.6 degrees at night. Cities also have greater atmospheric nitrogen and CO2 concentrations, which are vital for plant growth.
By August, the city seedlings had developed a biomass eight times that of the non-urban trees. Besides their fast growth, the city grown trees also developed bigger leaves, giving them a greater photosynthetic area. Urban trees allocated proportionately less mass to roots, an important carbon sink, than did rural trees.
Since urbanization is happening everywhere at a rapid pace, this adaption of our trees and plants to city life may have an impact on urban forest management and climate change discussions.