Trees in our woodlands, landscapes and communities pay us back in many ways, and we are getting better at understanding these benefits.
Tools for doing this range from i-Tree, a “series of free tools to quantify ecosystem services for individual trees or tree populations,” according to the itreetools.org website, to a wealth of new research on some harder to quantify social and health benefits of trees.
The i-Tree models allow us to project that a 20-inch diameter bur oak growing as a street tree in Kent provides annual benefits to the community of $165 per year, based on stormwater remediation, energy savings, air quality and other benefits.
Earlier this week, I was part of a conference, Partners in Community Forests, which highlighted recent developments in the ever-growing capacity of i-Tree, featuring Dave Nowack of the U.S. Forest Service and Scott Maco of the Davey Tree Expert Co.
Less obvious and more difficult to quantify, but becoming increasingly well-researched are direct human health benefits such as a study by G.H. Donavan of the U.S. Forest Service and co-authors in a 2011 paper in the journal Health and Place. In this research they conclude that “Tree canopy cover within 50 meters of a house reduced the number of underweight babies by 1.4 per 1,000 births.”
Quite a remarkable finding, but it tracks with numerous studies that show effects such as the improved recovery rates of hospital patients with views of trees and other natural settings.
The Donavan study compared tree cover around the homes of nearly 6,000 women who delivered babies in Portland, Ore., in 2006 and 2007. It notes that “to rule out other possible effects, the study controlled for over a hundred variables including the mother’s age, ethnic background, household income, education, prenatal care, and whether she already had children.”
The Health and Place article is titled Urban trees and the risk of poor birth outcomes. Find it using a search engine such as Google. (Oh, what a wonderful Web we weave.)
The Donavan study was one of many discussed at the conference by Kathy Wolf of the University of Washington and the U.S. Forest Service. Wolf and her colleagues are involved in a project to compile the research findings of the benefits of trees to our environment and communities. Check out the site at www.naturewithin.info and click on the link “Green Cities: Good Health.” There you can find research citations for everything from the effect of trees on local economies to effects of trees and green spaces on crime incidence in cities.
For example, economic studies cited include research that trees in yards and on streets can increase home values. The findings also say that high-quality landscapes can add to commercial property rental rates and shoppers say they will spend more for goods and services in business districts with a quality tree canopy.
With regard to crime and urban trees, Wolf said there is a point-counterpoint nature to the issue. Some suggest dense vegetation may provide cover for criminal activity, but other studies point to the opposite for certain types of plantings.
According to the findings:
• Graffiti, vandalism and littering is less in areas with natural landscapes than those without plants.
• Public housing residents who live near trees and natural landscapes reported 25 percent fewer acts of violence.
• Public housing buildings with greater amounts of vegetation had 52 percent fewer total crimes, 48 percent fewer property crimes and 56 percent fewer violent crimes than buildings with low amounts of vegetation.
Also, studies of neighborhoods report less property crime when there are trees in the right-of-way and more abundant vegetation around a house.
As with all studies and with everything involving trees, context is everything. For both social benefits and environmental benefits of trees, it matters which trees are selected, how plantings are designed, where trees are planted.
What is exciting is how we are progressing with these nuances. The i-Tree models now have a species function that is used to determine which species of trees provide the best profile for particular environmental services and where to plant these trees around structures and in landscape designs relative for example to sun exposure and other factors.
We are way beyond tree hugging, though that is cool, too.
Let’s close with the words of Rachel Carson: “Those who dwell with the beauties and mysteries of the earth are never alone or weary of life.”
Jim Chatfield is a horticultural educator with Ohio State University Extension. If you have questions about caring for your garden, write: Jim Chatfield, Plant Lovers’ Almanac, Ohio State University Extension, 1680 Madison Ave., Wooster, OH 44691. Send email to firstname.lastname@example.org or call 330-466-0270. Please include your phone number if you write.