Trees Can Save Your Life

Trees Can Save Your Life

A bold statement — and, if proof could be offered, an effective argument for allocating public resources to the protection and expansion of our urban forests.

Few will argue with E. O. Wilson that “nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction.”  However, many public agencies today have come to regard trees in the public realm as financial liabilities in the face of devastating cutbacks to their operating budgets.  Trees are good, but how can their care be justified when essential community services are in jeopardy?

What urban trees need is compelling evidence that they provide public health and environmental benefits that exceed the costs of their maintenance.  USDA Forest Service Research is sponsoring scientific studies and developing tools to do exactly that — effectively demonstrate to decision makers and community members that trees and forests are essential elements of healthy, well-balanced neighborhoods.

i-Tree, a state-of-the art, peer-reviewed computer software suite of urban forest inventory and analysis tools, is not new — but Version 5 (scheduled for release this spring) will have exciting new tools that can enrich your practice.

i-Tree Streets and i-Tree Eco are coming to your mobile device.  Version 5 will feature a new data collection web form.  Soon, any device that has an Internet browser — iPhones, Androids, or tablets — can be used to collect and enter field data.

i-Tree Canopy is an online service that can accurately estimate canopy cover without the need for GIS software.  With Version 5, you will be able to delimit a project area manually and then assess a range of conditions, from the amount of impervious surface to native habitat cover, with the option of analyzing canopy change over time using Google Earth historical images.


i-Tree Design estimates the economic and ecosystem benefits of individual and multiple trees — existing or planned — for a specific address.  Just enter a tree’s species, size, condition, and location into the online Tree Benefits Calculator to find out the dollar value of greenhouse gas mitigation, air quality improvements, and stormwater interception services the tree provides.  This year a mature redwood in my yard will intercept more than 1,400 gallons of stormwater, reduce consumption of heating fuel by 4 therms, and reduce atmospheric carbon dioxide by more than 1,000 pounds, saving me about $30.


Recent Tree Value Studies:  So, we have tools that can demonstrate that trees save us money and even help the environment, but what about saving lives? The work of Geoffrey Donovan, an economist with the Forest Service’s Pacific Northwest Research Station, has documented many surprising public health benefits associated with living in close proximity to trees.

Trees and Birth Outcomes:  Low birth weight is closely correlated to a higher rate of infant mortality.  Since this negative birth outcome is associated with prenatal maternal stress, researchers are examining environmental and other conditions known to reduce stress in pregnant women with the goal of improving infant health.  Dr. Donovan has applied the evidence that “greenness” improves the health of urban residents to a study of the relation of tree-canopy cover within 50 meters of the homes ofPortland,Oregon mothers-to-be to the birth weight of their children.  His study found that even a 10 percent increase in tree-canopy cover significantly reduced the number of low-birth weight infants, suggesting that the natural environment may affect pregnancy outcomes and should be evaluated in future research.

(G.H. Donovan, Y.L. Michael, D.T. Butry, A.D. Sullivan, and J.M. Chase.  2011.  Urban trees and the risk of poor birth outcomes.  Health & Place 17: 390–393)

Emerald Ash Borers Kill Trees—and People:  Trees have been demonstrated to improve air quality, but what happens when trees suddenly disappear?  Dr. Donovan is studying the effects of widespread Emerald Ash Borer (EAB) infestation on human health in 15 Eastern states.  Because EAB is killing many trees very quickly, it has been possible to measure negative changes in air quality and associated respiratory and cardiovascular problems in relation to the loss of trees.  By studying the effects of rapid tree removal, the research team has also been able to examine the positive benefits these trees provided before their deaths.  Their research indicates that EAB infestation has increased human mortality significantly, especially in more affluent areas (where it is presumed that people have more opportunity to take advantage of natural areas).

Trees and the natural environment are part of our public health infrastructure, especially in urban areas.  And equal access to their beauty and benefits is essential to achieving environmental justice.  These are powerful arguments for gaining public support and funding for our urban forests.

Notes:  treeScience: above, beneath, and inside the plan view — a regular column on tree-related issues of interest to landscape architects in the Bay Area — is compiled by Laurel Kelly, ASLA, landscape architect at H.T. Harvey & Associates.  Laurel is also an ISA-certified arborist and Registered Consulting Arborist® (email:

For more information about i-Tree and to download the i-Tree suite of tools at no cost, see

To find out more about research on the public health benefits of trees, visit Dr. Donovan’s website:

Dr. Donovan recently presented the studies highlighted in article at a webcast sponsored by the Urban Natural Resources Institute (UNRI), a science-based source for information and answers to questions on urban natural resources stewardship. A goal of the Institute is to strengthen public awareness of activities related to urban natural resources research and management. The Institute consists of Forest Service scientists, conducting science-based research on urban natural resource issues across the country.  For more information, please visit or via e-mail:

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