Post by guest blogger Dr. Geoffrey Donovan. His two main research areas are the economics of wildfire and quantifying the benefits of urban trees. He has worked since 2001 as a research forester for the USDA Forest Service’s Pacific Northwest Research Station. He has a bachelor’s degree from Sheffield University in biochemistry and a doctorate in forest economics from Colorado State University.
In February, I wrote a guest blog post here summarizing my research into the relationship between trees and the sales or rental price of homes. I found that in my home town of Portland, Oregon, houses fronted by a street tree sold for over $7,000 more than a comparable house without a tree. Although the $7,000 figure might raise some eyebrows, the idea that trees could make a house more appealing to a prospective buyer is, I imagine, fairly intuitive to a lot of people. What is less intuitive is that trees may do something more fundamental: They may improve your health. In fact, the wellbeing of trees may be a matter of life and death for humans.
Let’s look at the life part of this relationship between human and tree health first. In 2011, I published a study looking at the relationship between trees and birth outcomes in Portland. Specifically, I focused on the probability of underweight and premature births. As with many of my studies, I had to be wary of the “nice-tree-nice-neighborhood effect”—that people who live in better neighborhoods tend to be wealthier and have better access to healthcare.
Therefore, I was careful to control for a wide range of demographics like income, education, and race. I also took into account the type of prenatal care a mother received and whether she had experienced any pregnancy complications in the past. Finally, I calculated tree canopy (the area of the tree when viewed from above) in 50, 100, and 200 meter buffers around each woman’s home. I found that women with more canopy cover within 50 meters of their homes were less likely to have underweight babies. Interestingly, a year after our paper was published, a study in Spain found that women in Barcelona who lived in greener neighborhoods were less likely to have underweight babies.
Now—scary as it might sound—let’s look at the death part of this relationship between human and tree health. In 2002, the emerald ash borer, an invasive bug, was discovered in Detroit. Since then, it has spread to 18 states in the Midwest and East and killed approximately 100 million ash trees. When I first heard about this pest, a thought occurred to me: If trees are good for your health, then killing 100 million of them would likely have a measurable impact on public health.
After some particularly painful data collection and analysis, I found that counties infested with the emerald ash borer had elevated levels of cardiovascular and lower-respiratory mortality. Specifically, from 2002 to 2007, these counties experienced an additional 15,000 deaths from cardiovascular disease and an additional 6,000 deaths from lower-respiratory disease. I don’t know how sick those people were before they died—I’m not suggesting that a healthy 20-year-old dies just because a tree loses a few leaves—but 21,000 deaths isn’t a trivial number.
These two studies suggest that there may be a fundamental connection between trees and human wellbeing. Planting a tree may not only help you sell your house for more money; it may also help keep you alive to enjoy spending that extra money. An investment with such a significant impact on the length and quality of our lives would certainly be one worth making.