July 29th, 2013 by

Stomata on a purple heart plant

Stomata on a purple heart plant. Credit: Yersinia pestis/Flickr

New research published in Atmospheric Chemistry and Physics has found that an estimated 460 lives in the U.K. could have been saved from premature death if only trees and plants had been less stressed by a heat wave-induced drought.

Trees clean our air: In addition to absorbing CO2 and producing oxygen, they also play an important role in filtering some of the most common pollutants. During a heat wave, however, a method that plants employ to conserve water also prevents them from filtering as much pollution. When the ground is dry, plants close their stomata — pore-like openings — to keep water in, but the stomata are also the mechanism through which they absorb all that air pollution, including ozone. While atmospheric ozone protects us from harmful cosmic rays, close to the earth, it’s the primary component of smog. So while water stays in when plants close their stomata, ozone and other pollutants stay out — out in the air we’re breathing.

London’s urban forest and skyline

View of London’s urban forest and skyline. Credit: scyrene/Flickr

So, as the summer heats up, at-risk populations, such as people with respiratory difficulties, are left vulnerable. The study found that of the ozone-related premature deaths that occurred in the U.K. during a 2006 heat wave, an estimated 460 would have been avoided had plants been absorbing pollutants at their normal rate.

As important as urban forests’ role in cleaning our air is, reading about this study brought to mind another important benefit of urban forests. They don’t just clean the air; they also cool it. This benefit of trees is especially significant in urban areas where what’s known as the heat island effect is in place. Because our buildings, streets and paved surfaces store the sun’s heat, temperatures in the city are higher than those in surrounding areas. Planting and caring for a healthy urban forest is one way to help cool cities.

That’s why we work to restore forests globally and why we’re starting our new project, Community ReLeaf, to help cities gain insight into their urban forests — insights that can inform management and planting strategies. Heat waves will continue to be a fact of life, but by doing what we can to mitigate the heat island effect, we may also be helping our forests clean the air.