It’s becoming common knowledge at this point that trees greatly benefit cities and the people that call them home. City trees and urban green areas regulate temperature, improve mental health and reduce loneliness for urbanites, clean the air and even reduce crime rates. Our tall, green friends do all of this for us, but did you ever think about what we do for them?
Is it possible that some trees are actually thriving in our cities?
Healthy city trees
A recent study from Boston University published in Nature Communications showed that urban trees can, in fact, get a special benefit from living and growing in a city.
The authors of the study set out to understand forest edges, which are groups of trees that, you guessed it, were on the edge of the forest. It has been commonly believed that these trees are more or less the same as their siblings on the forest interiors, breathing in just as much carbon dioxide and breathing out just as much oxygen. As a result, loner groups of forest edges, such as their sparser, city-dwelling cousins, were thought of as insignificant or at times disposable because they exist in smaller quantities.
The Boston University team looked at more than 48,000 forest plots in the US Northeast, examining trees in both forest interiors and forest edges, and comparing their growth rates. What they found was that trees in forest edges actually grow nearly twice as fast as those in forest interiors.
“This is likely because the trees on the edge don’t have competition with interior forest, so they get more light,” says Luca Morreale, a PhD candidate working in the study.
Do trees in the city trap more CO2?
What this means is that these urban trees do absorb slightly more carbon dioxide growing faster, but not at very significant levels. What was significant was how much less carbon they released from their soil. The soil around forest edges does release varying amounts of carbon dioxide depending on temperature. The soil around rural forest edges releases more because a general lack of shade heats the soil up, while the soil around urban forest edges releases less because there are more tall buildings to offer cooling shade.
This research has shown that forest edge trees in urban environments can actually store more carbon dioxide than previously believed, an important factor to consider as more cities around the world plant more trees.