The shortfall of tree cover in most of our cities is contributing to increased mortality from air pollution.
Lack of adequate canopy and its healing, pollutant-absorbing properties takes on added significance with release of a recent international scientific assessment. This study’s conclusion: even at modest levels, lethal tiny particulates dispersed primarily through vehicle exhaust, are responsible for some 100,000 respiratory-related premature deaths annually. Moreover, the fatalities occur largely in metropolitan areas.
The magnitude of city-situated mortality is no surprise. Consider that the American Lung Association reports 43 percent or 140 million Americans live in counties - many of them urban - that violate federal air quality standards.
Trees, especially ones with small hairy leaves such as birch, yew, and elder, excel at absorbing particulates. These species are capable of cleansing as much as 70 per cent of nearby street-level particulates.
Alas, few of our cities have achieved their full “canopy potential” within their alloted boundaries. The average canopy is 27 percent, well short of the 40 percent recommended as an acceptable minimum cover by the American Forest Association.
In fact, all too many cities are experiencing shrinkage of whatever tree cover they have, largely due to development, insects, disease, and drought. The loss is all the more distressing because of the rich potential for many of our cities to extend their green urban canopies. Note that urban planners contend that in many instances, it costs only four dollars per resident to expand a city’s tree cover.
In the nation’s capital, (known as the City of Trees) authorities are aiming by 2032 to increase its 35 percent arboreal blanket to 40 percent. Sounds ambitious, yet, estimates are that metropolitan Washington’s surface area can support 67 percent cover.
New York City’s green canopy amounts to approximately 21 percent, but its potential is pegged at 45 percent, skyscrapers notwithstanding.
At the expense of lung health, too much land in our cities has been allocated to non-porous pavement. To broaden the canopy, city planners advocate planting trees in grassy spots, in locations adjacent to thoroughfares and parking lots, and even on porous cement.
Trees provide mental as well as physical health benefits curtesy of their aesthetic calming effects. And there are other ancillary dividends — flood control, cooling shade that moderates the urban “heat island” effect, lower electricity bills, rising property values, and added wildlife habitat.
We will all breathe easier when flyovers of our cities provide views in which buildings seem interspersed between foliage rather than the other way around.