shade trees improve quality of life in urban settings
EcoGeek recently ran a post highlighting the correlation between income inequality and street tree inequality. The study in question was completed in 2007, and it’s certainly been true in my experience in cities that the fewer the street trees, the more marginal the neighborhood tends to be.
I’ve heard all sorts of things about the importance of trees in the life of the urban community, and I thought I’d take this opportunity to look for hard data to support them.
- Street Trees raise property values
In 2008, a study completed by the US Forest Service in Portland, Oregon, concluded that street trees have a substantial positive influence on home values. They studied several factors, and found that in order to boost property value, the tree had to have crown area within 100 feet of the house, and that though positive value was strongest for the house directly in front of the tree, neighboring houses with canopy within 100 feet also gained value.
Given that this study was done before the worst part of the economic recession hit, it would be interesting to see a follow up study looking at how these factors might change across geographic and economic variables. Would the same results still be found in Portland after the recession? How would the results vary in different cities across the country? Does the positive effect of street trees increase with the prevalence of hardscape? Or does it go up as the size of the lot gets smaller? Has the shift toward investor-purchased homes changed the value of street trees, and if so, is it a short-term shift?
With so many questions, I feel like I should call a professor and ask them to do a study.
It’s important to keep in mind, though, that it takes trees some time to get large enough to provide canopy cover. If a homeowner is planning to sell their house in three to five years and hopes to gain some value by planting street trees, they should do so now. Planting the largest tree one can afford, up to perhaps a six-inch caliper, is important to allow the tree to be large enough to visually register as a canopy. It’s possible to plant trees larger than six-inch caliper, but as they increase in size from there, it takes a seasoned expert to transplant them successfully, and the cost will rise dramatically. Of course, it all depends on the species of tree, so consulting a local expert is the best way to go.
- There’s a correlation between street trees and reduction in crime rate
Interestingly, a study was just released this month in the journal Landscape and Urban Planning showing that the presence of street trees does correlate to lower crime rates. The study focused on Baltimore and found that an increase in canopy of 10% was linked to a 12% reduction in crime. The theory is that the presence of street trees shows that the community is active and takes pride in itself, making it less attractive to would-be criminals.
- Street trees offer health benefits to the community
When I set out to research this category, I had in mind the ability of the trees to take up pollutants from the roadway, thus potentially lowering asthma rates, etc. According to a paper released by northlandnemo.org, this is true. Street trees absorb nine times more of the exhaust pollutants released by automobiles than do trees farther away from the road edge. But that’s not all they do for the health of the neighborhood. They also tend to lower blood pressure and improve psychological health.
- Street trees improve the bottom-line of adjacent businesses.
A study from the University of Washington came out a few years ago showing that street trees in business districts positively influence the behavior of patrons. The study even found that shoppers would be willing to pay up to 11% more for the same item in a treed business district than in one devoid of trees. Again, the theory is that the presence of street trees indicates that the community takes pride in it’s appearance, making it more attractive to shoppers. It probably doesn’t hurt that the shoppers feel so great with their blood pressure lowered and their psychological health boosted.
- Street trees help mitigate the heat island effect
This is one that the LEED rating system has been promoting for years now – plant trees to shade structures and hardscape, and the microclimate will stay cooler. According to the EPA, trees can keep surfaces 20-45 degrees cooler (F) than unshaded surfaces. Keep that in mind on hot sunny days!
Admittedly, this is not an exhaustive summary of the benefits of street trees, nor of the research available on these topics. Consider it a quick review of some complex issues that merit more attention.