Kaid Benfield

The case for more urban trees

Director, Sustainable Communities, NRDC, Jul 31, 12.

Tagged with urban planning, quality of life, environment, health, nature, trees, built environment, green space

I am lucky enough to live in a neighborhood with many large, mature trees. Our bit of urban forest is one of our community’s greatest assets, if you ask me. But, loved though they are, trees are getting to be a little controversial in and around D.C., and that worries me. I’ll get to that a bit later in the post, but first I want to share some of things I have learned about city trees in the last few days.

In particular, last week I spoke at a forum hosted by the California Center for Sustainable Energy, and after the program I was approached by someone from an initiative called San Diego County Trees. The initiative is the urban forestry project of the Energy Center, and they have all sorts of information extolling the benefits of urban trees along with a crowd-sourced inventory of street trees in San Diego.

I just spent time on the website, where the coolest feature is an interactive map of the whole county showing very specific tree locations and information, including quantified benefits to the region stemming (pun unintended but acknowledged) from its trees. As you can see in the image, these include carbon sequestration, water retention, energy saved, and air pollutants reduced.

You can even click on a specific tree and get detailed information on its species, size, and annual economic benefit to the community. San Diego County Trees invites its readers to add to the inventory with information on additional trees not presently counted.

If you’re interested in the subject of the community benefits of trees, you can get additional information from the websites of the National Arbor Day Foundation and the US Forest Service. Among the tidbits I learned on one or the other of those two sites are these:

- The net cooling effect of a young, healthy tree is equivalent to ten room-size air conditioners operating 20 hours a day.
- If you plant a tree today on the west side of your home, in 5 years your energy bills should be 3 percent less. In 15 years the savings will be nearly 12 percent.
- One acre of forest absorbs six tons of carbon dioxide and puts out four tons of oxygen.
- A number of studies have shown that real estate agents and home buyers assign between 10 and 23 percent of the value of a residence to the trees on the property.
- Surgery patients who could see a grove of deciduous trees recuperated faster and required less pain-killing medicine than matched patients who viewed only brick walls.
- In one study, stands of trees reduced particulates by 9 to 13 percent, and the amount of dust reaching the ground was 27 to 42 percent less under a stand of trees than in an open area.

...

Several years ago, walkability guru Dan Burden wrote a detailed monograph titled 22 Benefits of Urban Street Trees. Among other things, he calculated that “for a planting cost of $250-600 (includes first 3 years of maintenance) a single street tree returns over $90,000 of direct benefits (not including aesthetic, social and natural) in the lifetime of the tree.” Burden cites data finding that street trees create slower and more appropriate urban traffic speeds, increase customer traffic to businesses, and obviate increments of costly drainage infrastructure. In at least one recent study (reported after Burden’s analysis), trees were even found to be associated with reduced crime.

I think some of the most important benefits, though, are felt emotionally. Burden puts it this way:

Urban street trees provide a canopy, root structure and setting for important insect and bacterial life below the surface; at grade for pets and romantic people to pause for what pets and romantic people pause for; they act as essential lofty environments for song birds, seeds, nuts, squirrels and other urban life. Indeed, street trees so well establish natural and comfortable urban life it is unlikely we will ever see any advertisement for any marketed urban product, including cars, to be featured without street trees making the ultimate dominant, bold visual statement about place.

That is extremely well said.

...