I just spent a lovely weekend in the wilderness with some friends, carrying our equipment out to a cute cabin in the woods, cooking over a woodstove, cross country skiing, and generally enjoying the peace and quiet of a snowy forest. On our reluctant drive home, a friend and I discussed the striking clarity of mind we were both feeling after several days in the north woods. Maybe it was a few days away from the distraction of email or twitter, I certainly enjoyed turning my useless phone off. But maybe it was just being out among the trees.
In a crush of December deadlines, I read an article in Outside magazine by Florence Williams about the actual health benefits scientists can measure that result from spending time in nature that spoke to me. I left a job hiking through the southwest to come back to grad school and turn myself into an environmental journalist, and I’ve felt stressed and overwhelmed pretty much ever since. Sure, it’s largely a result of working really hard and learning lots of exciting things and trying to reinvent myself, but I believe that my “wilderness deprivation”, as I’m calling it, may be playing a significant role as well. And I felt so calm and clear-headed after this little trip that I’m taking that as supporting evidence.
However, I know that my personal experience does not exactly make a robust sample. But when I got back in to town I found some serious scientific evidence that might support my feeling that spending time out in the trees made me feel healthier and happier. A study published last week in the American Journal of Preventative Medicine entitled “A relationship between trees and human health,” found correlations between the loss of ash trees in midwestern communities to increased mortality from cardiovascular and lower respiratory diseases.
It’s certainly not the first study to link exposure to nature with better mental and physical health. The Williams piece reviews some of the research on stress hormone levels, which can affect both our mental and longterm physical health. Studies have shown that gazing out a window at a natural environment can improve recovery from gallbladder surgery and exposure to tree canopy has positive correlation with improved birth outcomes for pregnant women. But research with large sampled sizes and control over other variables have been rare.
This study takes advantage of the major destruction of ash trees by an invasive insect, the Emerald Ash Borer. Introduced in Michigan and discovered about a decade ago, EAB has spread out across the midwest as people moved infected nursery stock and infected fire wood, as well as it’s slow independent advance on forests. This resulted in a patchwork distribution of the dying trees. The midwest has lost more than 100 million trees lost so far, with no doubt more to come as the EAB continues to spread. Because of the patchy distribution of ash tree mortality, Donovan et al were able to compare data across 15 states and thousands of counties, controlling for other demographic variables, including income and race.
They found that across the entire infested area, the “borer was associated with an additional 6113 deaths related to illness of the lower respiratory system, and 15,080 cardiovascular-related deaths,” from 1990 to 2007. The relationship appears to be particularly strong in higher income areas- perhaps because there tends to be more tree cover in wealthier neighborhoods to begin with. As an observational study, there are certainly limitations to this research, but the finding seem to stand up to some basic scrutiny. To test their model, they also used the accidental death data for the same period, because there is no mechanism for the EAB to influence accidental death rates, and found no correlations.
But how would tree loss lead to increased mortality from heart and respiratory disease? This study only provides some ideas suggested by other researcher on the links between exposure to nature and human health.
Results do not provide any direct insight into how trees might improve mortality rates related to cardiovascular and lower-respiratory-tract illness. However, there are several plausible mechanisms including improving air quality, reducing stress, increasing physical activity, moderating temperature, and buffering stressful life events. Future research could fruitfully investigate the possible mechanisms linking the natural environment and health.
Further research needed. Not a surprising conclusion. But given the complexity of both human health and forest ecology, there’s a lot remaining to sort out here. It’s a really intriging paper, and I recommend checking it out, here’s the link again. Maybe we’ll never really understand how being around trees can make us healthier, or how we might suffer from losing them. But maybe increased evidence of health benefits could lead to increased value for natural landscapes- from shady street trees to wilderness adventures. I know I feel better after my time in the woods.