THE DIRT

“We are trying to figure out precisely what types of nature provide the most health benefits,” said William Sullivan, ASLA, a landscape architecture professor at the University of Illinois at Urbana-Champaign, at the Environmental Design Research Assocation (EDRA) conference in New Orleans. The eventual goal is to be able to prescribe doses of nature, or specific activities in nature, to help with a range of illnesses. But we have a long way to go before we can get to this point. “We are just at the beginning of the research. We are moving in the direction of more specificity.” Sometime in the future, designers of all kinds will have guidelines that explain the best ways to reap the positive effects of nature. “But today — although we have good evidence that exposure to green landscapes is good for you — we can’t say if you design something this way, people will live four years longer.”

Sullivan brought together a unique group of researchers to explore the latest science and show the rest of us where all of this is going. A few graduate students at University of Illinois at Urbana-Champaign presented their data-based findings about the effects of nature on our own cognition and stress levels:

Dr. Bin Jiang said research shows “acute, chronic stress will lead to disease and death.” Stress has been directly linked with a number of the leading causes of death, including heart disease, diabetes, and suicide. In his study, Jiang examined how much stress recovery can be achieved through views of green streets. A group of people from the Midwest were alternatively stressed — by being asked to do complex math rapidly in front of a group or give a speech — and then shown images of nature. They were exposed to ten videos, with ten different levels of tree canopies, ranging from 2 percent up to 62 percent tree cover. These guinea pigs were surveyed to see how stressed they felt and then their physiological responses were also examined. Researchers took saliva samples to test for cortisol levels and tested their skin conductance, finger temperatures, blood volume pulse, and heart responses.

According to the surveys, increasingly green scenes improved stress recovery by 250 percent. But the actual physiological stress recovery rate — as measured by all the devices — was improved by just 55 percent. This shows that “we are prone to believing the narrative about nature.” Jiang concluded that “there is a positive, linear relationship between tree cover and self-reported stress recovery, and a curvilinear association between objective stress recovery and tree cover.” This means physiologically, there’s a peak tree canopy level and then it declines. According to Jiang, the optimal tree cover rate is 30-40 percent. But Sullivan interjected, “every tree matters. More of these kinds of studies need to be conducted on all types of nature: parks, bioswales, rain gardens, etc.”

Dongying Li presented an excellent study on high school landscapes and academic performance. There is an understanding that views of green spaces out of windows may benefit students. “Access to nature has been correlated with lower stress and higher attentional function.” But Li wanted to see if she could find a causal relationship between views of nature out a window and performance. Three sets of students were randomly assigned to be tested in a room with no windows, a room with a barren view of rooftops, and then a room with a green, leafy view. The results: green views significantly improved attention, while barren or no views had no impact. Li added that “the effect of the window view is greatest during the subjects’ rest period, not during their stress period. The window view also affects stress recovery. Students with views of green spaces recovered from the stress of classroom assignments considerably faster than their peers who had been assigned to classrooms without windows or those with views to built spaces.” She said the effect is not just from the green color but from the actual content of the landscape.

Sullivan said this makes the case for bringing trees closer to classrooms. “Somehow there’s a meme out there that if there are windows with some to look at, students will be distracted. This study shows that’s the farthest from the truth. We have spent hundreds of millions to boost academic performance in high schools and the results of programs like DARE are now clear: it has had zero impact. Simple interventions like putting in windows and designing campus landscapes to include many opportunities to have green views could significantly improve performance.” There’s a reason, it seems, those Ivy League schools are so leafy.

Finally, Chun-Yen Chang, Professor of Landscape Architecture at National Taiwan University, presented more amazing research, this time looking at the brain’s response to images of nature. In Taiwan, thirteen subjects suffered through being in an fMRI machine for hours at a time, exposed to urban scenes and then images of mountains, forest, and water. With images of the urban landscape, “all parts of the brain were active,” while fewer sections were active during the nature scenes. Here, we can introduce a novel word, at least for me: voxel, which is a measure of how busy a brain is. Chang said when we see a traffic jam spreading for miles with cars honking, our voxels are around 180,000. Meanwhile, a forest scene accounts for less than 100 voxels. And a beach scene even less: 28 voxels. Our brains respond to urban and natural scenes incredibly differently. If we have 180,000 voxels going, how many more can be used? What happens when we are at 180,000 voxels too long?

At one point, a participant asked, “If you know you have something to do later that’s stressful, can we immunize ourselves by going earlier into nature? Can we then recover from stress faster?” Chang said “attentional fatigue and stress are two different things. If we have something cognitively demanding to do, it’s good to spend time in green spaces. But there’s no evidence we can immunize ourselves from stress with nature.” Sullivan concurred, saying “there’s evidence that going to green spaces improves cognition for later. And if we have that evidence, we can then incorporate this into our discussion of the benefits of green infrastructure.” Instead of just focusing on the stormwater management benefits of green infrastructure, “what if we could prove green infrastructure can also boost innovation and creativity?”

And one more future area of inquiry: “Do the most ecologically-healthy landscapes result in the healthiest people?” Sullivan said this will be an important research area, as “we have to be smart about how we configure these natural places. An ecologically-healthy place could have snakes and spiders, which will end up scaring people away. We have a responsibility to create a healthy ecosystem but we can’t create stress and anxiety about being in nature.”

Explore all these research studies.