Everybody knows trees are nice. They are green, shady, they smell nice and they provide fruit and flowers to keep us happy. But new studies by the US Forestry Service and others have discovered that trees can help you live longer too. By Jeremy Torr & Phil Stamper.
Shalersville, Ohio, US, 21 August 2013. A recent study by urban forestry guru David Nowak and other researchers at U.S. Forest Service together with tree experts The Davey Institute (which has been nurturing and studying trees since 1880) found that urban trees can save at least one life per year in most major cities and up to 8 people per year in large metropolises like New York City.
As many studies have shown – and images from Beijing reinforce - urban particulate air pollution is a serious health issue. Growing trees in cities can help remove fine particles (particulate matter or PM) from the atmosphere and consequently improve air quality and human health. In the study, the researchers analysed the effect of trees on PM2.5 concentrations and human health for 10 U.S. cities.
The results were astonishing; the total amount of PM2.5 removed annually by trees varied from 4.7 tonnes in Syracuse, NY, to a massive 64.5 tonnes in Atlanta. The study went further and estimated the monetary value of the tree’s presence was some US$1.1 million in Syracuse to US$60.1 million in New York City – mainly from reduced human health complaints and people dying.
Most of these tree values were from the effects of reducing deaths. “Particulate matter can cause significant health effects that include premature mortality, pulmonary inflammation, accelerated atherosclerosis, and altered cardiac functions,” note the study’s authors.
Typically just having more trees can save around 1 person per year per city, but this can go as high as 7.6 people being saved from dying through not having to inhale large amounts of particulate matter in New York City, the study estimated.
The researchers point out that larger particles between particulates 2.5 to 10 micrometers in diameter—also called coarse dust particles or PM10—are removed by trees at a higher rate by acting as a kind of collector sieve for water to wash off later, but the health benefits of PM2.5 removal is 30 to 350 times more valuable. Some estimates say PM2.5 can kill up to 2.5 million people each year. Overall, the Nowak study claims that “the average health benefits value per hectare of tree cover was about $1,600, but varied [from city to city].”
It’s not just city dwellers that benefit from trees. A study published in the American Journal of Preventive Medicine recently noted there was an increase in mortality related to cardiovascular and lower-respiratory-tract illness in areas infested with the emerald ash borer. This effect was greater as infestation progressed and in total the lack of healthy trees could be linked to 6113 deaths related to lower respiratory system illness, and 15,080 cardiovascular-related deaths. That’s a huge number in just 15 US counties – extrapolated across a nation it could mean millions of people dying due to there being too few healthy trees nearby.
The study further noted that “this adds to the growing evidence that the natural environment provides major public health benefits.” Which also indicates that if developers cut down lots of trees and build apartments instead, then more people will die.
The value of trees goes beyond their ability to clean up air quality. According to a recent U.S. Forest Service study, “urban forests are responsible for storing 708 million tons of carbon—a service valued at $50 billion.” And the overall average annual percent air quality improvement (not just PM concentrations) ranged between 0.05% in San Francisco and 0.24% in Atlanta.
The study concludes that “trees can produce substantial health improvements and values in cities.” Although more research is needed to improve these estimates, this study also leaves room for new research that explores the local effects of tree-filled landscapes in cities. As Finnish researcher Eeva Karjalainen noted in a 2010 scientific review, “Forests provide enormous possibilities to improve human health conditions.”
So as well as giving us better air to breathe, trees apparently make us calmer. “People with less access to nature are more prone to stress and anxiety,” notes Frances Kuo, director of the Landscape and Human Health Laboratory at the University of Illinois. “This reflected not only [in] individuals’ self-report but also measures of pulse rate, blood pressure, and stress-related patterns of nervous system and endocrine system anxiety.”
With a list of positives like that, it makes you wonder why we are cutting so many trees down to make dwellings and car parks.
As Bill Laurence, Laureate at Cook University in Australia says, “Our parks are the last vestiges of Australian nature – a final refuge for our irreplaceable biodiversity and ecosystems. A return to the outdated views of the 19th century – when parks were little more than playgrounds for city dwellers to escape the urban malaise – would run counter to everything that Australians have learnt about environmental conservation.” He is right. We need trees!
For more info on the Nowak study go to: http://www.fs.fed.us/nrs/pubs/jrnl/2013/nrs_2013_nowak_002.pdf
For more info on Laurance views go to: