Introduction
Nature offers a multitude of services to all walks of life, especially humans, and yet we often take it for granted. In Gretchen Daily’s 1997 book Nature’s services: Societal dependence on natural ecosystems, she defines the term ecosystem services. According to her book, “ecosystem services are the conditions and processes through which natural ecosystems, and the species that make them up, sustain and fulfill human life.” (Daily, 1997, pg. 3). Ecosystem services cover a broad range of things from maintaining biodiversity, to ecosystem goods (timber, food, medicine), to cleansing the environment, and much more. (Daily, 1997). Specifically in my own research, I wanted to look at the benefits provided by trees/forest environments to human health.
Image taken by a participant in the study in Bloomington, IN
Ability to Clean
Water Purification
Trees are vital when it comes to water purification. Water is an integral component of all living beings, and we as humans need clean water for drinking, cooking, cleaning, and many other daily tasks (American Forests, 2019). An article published by American Forests (2020), over half of the drinking water in the United States originates in a forest, mainly from the waterways that run through them. Full grown, mature trees can hold several thousand gallons of water which they in turn release back into the air as oxygen or water vapor. Trees also collect and filter rainfall using the canopy cover as a means of slow release into water sources and the soil. The slow release into the surrounding environment prevents major flooding which could cause massive soil erosion. Forests act like filters as well by preventing runoff of chemicals and soil into the water supply. With chemical pollution due to agricultural practices becoming a major concern, the value of trees to human health is highlighted. Another interesting aspect to note is that human health is not the only thing that benefits from the tree’s role in water purification; forests also play an important economic role in water treatment. In the same article from American Forests (2020), they found that for every ten percent addition in forest coverage, there is a twenty percent decrease in economic cost for water treatment.
Air Purification
Another important resource trees can help clean is the air. Leaves on trees have pores called stomata that allow them to take in compounds found in the air, and this physical property of trees makes them capable of filtering harmful components found in the air due to human activity. A background analytical study on forests and climate change published in March of 2019, found that forest might be able to hold as much as 30% of carbon emissions that are a result of human activities and infrastructure. However, CO2 is not the only compound trees filter. They can also take in nitrogen dioxide and particulate matter as well. (Bennett, Jan. 2020).
Many human activities today contribute to the presence of these harmful chemicals in our air. More people than ever are now driving cars, and the push towards urbanization has been profound. These shifts in human behavior have only contributed to poorer air quality in these urban landscapes, which are areas lacking in these natural resources that are capable of filtering the air (Fenger, 1999). The lack of trees/forest environment combined with the poor air quality can mean living in an urban environment, where there are far fewer trees, likely leads to a much greater chance of facing more serious health issues that are a result of air pollution. (Nowak, Hirabayashi, Bodine, & Greenfield 2014).
Image by Hannah Bruick, Bloomington, IN
Shinrin-Yoku
Time spent journaling outdoors periodically throughout the semester for this project proved valuable and became a very enjoyable aspect of my routine. Being in the midst of a pandemic has forced many people indoors, and one way that I have combated the boredom of being quarantined is through spending time in nature. While developing this project, I found that I had an interest in how nature can play a direct role in human health, both physically and mentally. With all of that in mind, I decided to focus the majority of my research on the benefits of trees and forest environments on human health, with the largest portion about a term that fit my interests: shinrin-yoku.
Most people have never heard this term before, especially in Western culture. Shinrin-yoku originates from Japanese culture and was used for the first time in 1982 by the Japanese Ministry of Agriculture, Forestry, and Fisheries. Shinrin-yoku essentially translates to “forest bathing” and is defined as immersing yourself in the forest atmosphere.(Ulrich, Frumkin, Blood, Buchanan, Goel, Iidaka, … Yamaguchi, 1991). There have been several studies done that were designed to identify and measure both the physical and mental impacts of practicing shinrin-yoku. There also seems to be a movement towards utilizing nature as therapy rather than conducting therapy in simply a clinical setting. Berger & McLeod (2006) present a framework for incorporating nature into current therapeutic practice, and is a topic that would benefit from further exploration and study.
Physiological Impact
Ulrich et al. (1991) conducted a study in Japan that explored some of the physiological effects of forest bathing through the use of field studies. Participants’ physiological changes were measured using salivary cortisol, blood pressure, pulse rate, and heart rate variability as indices. The study found that a forest landscape promoted “lower concentrations of cortisol, lower pulse rate, lower blood pressure, greater parasympathetic nerve activity, and lower sympathetic nerve activity” (Ulrich, Frumkin, Blood, Buchanan, Goel, Iidaka, … Yamaguchi, 1991). A study done by Tsunetsugu et al. (2007) measured blood pressure, pulse rate, heart rate variability, salivary cortisol concentrations, and immunoglobulin A concentration in saliva, all of which are related to stress response. The study found that time spent in a forest setting versus an urban setting had an impact on each one of these variables with the urban landscape eliciting a stronger stress response and a forest setting creating a more “relaxed” feeling (Tsunetsugu, Park, Ishii, Hirano, Kagawa, & Miyazaki, 2007). Craig, Logan and Prescott (2016) found that “natural environments might influence mood and stress physiology,” and that nature likely acts as a form of health promotion. Another study done specifically on diabetic patients found that spending time in and among a forest environment could effectively lower blood glucose levels (Ohtsuk, Yabunaka, Takayama, 1998).
Psychological Impact
Not only does shinrin-yoku present positive physiological benefits, but it also presents positive psychological benefits. Several studies have come to the conclusion that participating in shinrin-yoku has positive psychological health outcomes. Bratman et al. (2015) performed an experiment that measured rumination and neural activity in the subgenual prefrontal cortex, both of which are highly correlated with mental illness. The authors found that a 90-minute walk in a nature setting led to a decrease in self-reported rumination and a decrease in neural activity in the area of the brain being studied. The participants also engaged in a 90-minute walk through an urban landscape, but no such changes were seen (Bratman, Hamilton,Daily, & Gross, 2015). A study done in Europe, had similar findings and had evidence that living in an urban setting had a negative impact on mental health, specifically those living in urban areas were more likely to suffer from depressive disorders (Kovess-Masféty, Alonso, de Graaf, & Demyttenaere, 2005). A comparative study was done on working age adults both with and without depressive tendencies. This study found that while almost all of the participants showed improvements in the measurements taken, those with depressive tendencies tended to show greater improvements in mental health measures (Furuyashiki, Tabuchi, Norikoshi, Kobayashi, & Oriyama, 2019). Another study focused on how the environment might be manipulated to help someone who is struggling with chronic stress. This study found that living or spending time in a forest environment has advantageous mental health outcomes. The use of nature as a form of therapy or stress reduction was also highlighted. (Morita, Fukuda, Nagano, Hamajima, Yamamoto, Iwai, … & Shirakawa, 2007).
Image taken by a participant in the study. Bloomington, IN
The Experiment
The goal of my experiment was to showcase similar positive outcomes of time spent in nature. There are obvious limitations to my own data collection, many of which center on the fact that I could only collect data that I had the tools to do so with. My own experiment is a simplified example meant to highlight the direct health effects of time spent in nature versus time spent in a more urban setting.
The physiological aspect of this experiment focuses on the impact of using shinrin-yoku methods on heart rate. I collected heart rate readings from each participant in a variety of scenarios. The heart rate readings came from fitness apps and watches that track the heart rate of the wearer. I asked each participant to monitor their heart rate in three different scenarios. The first set of data collected was meant to establish a baseline heart rate in everyday life for each participant. Each person kept a record of their heart rate three times a day (morning, afternoon, evening) for a week. The second scenario was meant to record the effect of shinrin-yoku on heart rate. I had each participant record their heart rate while walking in a forest/nature setting and while sitting outside for at least half an hour. The final scenario was used to establish heart rate while in an urban setting. I had each participant record their heart rate while walking through an urban area and while sitting in traffic. I asked each participant to conduct these actions at least four times so that I could have multiple readings for each scenario for each individual. The heart rates from the multiple readings for each scenario were then averaged together.
I also wanted to include a portion on the psychological impacts of practicing shinrin-yoku. I conducted interviews with each participant regularly throughout the process and encouraged them to write down their feelings during or following each scenario. The participants then recounted how their mental health might have been affected by each environment.
Results
Ultimately I recruited 7 participants for my experiment, and each participant self-reported heart rate readings for the scenarios along with the baseline measurements and the interview on the state of their mental health. The baseline heart rate measurements were used as a method to establish each individual’s relative heart rate range. The measurements taken during each scenario were then related back to the individual’s baseline readings in order to establish whether or not heart rate was elevated or not and the heart rate readings from the forest setting and urban setting were also compared.
Overall, I saw a consistently lower heart rate in the forest settings compared to an urban landscape. The comparison between sitting in a natural setting and sitting in traffic yielded the greatest level of separation, or variability, in heart rate, with every participant reporting a lower heart rate while sitting in nature compared to sitting in traffic. The two heart rate readings taken while walking yielded similar results regardless of the environment with four of the participants reporting lower heart rates while walking through a natural environment, two participants with almost identical readings for the two landscapes, and one participant reporting slightly lower heart rate readings in the urban landscape.
Despite the lack of a clear cut answer from the heart rate readings, the mental health interviews yielded incredibly consistent results between all of the participants of the study. All of the participants of the study reported feeling as though the state of their mental health was better after spending time in the forest setting compared to the urban setting. I found that many of the respondents used words like “relaxed” or “calming” when describing their experiences in the natural setting and terms like “stressed” when describing time spent in an urban landscape. The scenario that seemed to have the most positive mental health response was sitting in nature, while sitting in traffic seemed to have the strongest negative mental health response.
Discussion
Generally, the results from my experiment seem to concur with the previous studies in that spending time out in nature can have positive health benefits. The results from the physiological portion of the experiment did not yield completely conclusive results, but the psychological effects seemed to support positive health outcomes from practicing shinrin-yoku, or forest bathing.
Unfortunately there were several limitations to my study. One limitation was the small sample size. I was only able to recruit seven participants that gave me enough readings, I had partial readings from four others, but I excluded them due to lack of consistent participation. Another thing to note is bias. I had each participant self-report both heart rate readings and the state of their mental health. There is always a chance of bias when utilizing self-reporting, but largely due to social distancing guidelines, taking measurements myself was not possible. Another key limitation to my study is that I only used one metric to measure physiological changes. I did not have salivary tests at my disposal, which was one of the more common metrics used in many of the studies done on shinrin-yoku.
Image by Hannah Bruick, Bloomington, IN
Conclusion
All in all, the literature along with my own experiment give reason to believe that practicing shinrin-yoku, or forest bathing, has beneficial health effects. Those health effects can be both physiological or psychological, and can promote a more healthy lifestyle. Given the current state in which a majority of our population lives in urban settings, this research could have a tremendous impact on improving human health. Introducing nature as a form of therapy, especially in Western culture, is a topic that could absolutely benefit from further exploration and implementation.
References
Bennett, Hayley K. T. (2020, January 02). How do trees clean our air? Retrieved from https://edu.rsc.org/feature/how-do-trees-clean-our-air/4010864.article
Berger, R., & McLeod, J. (2006). Incorporating nature into therapy: A framework for practice. Journal of Systemic Therapies, 25(2), 80-94.
Bratman, G. N., Hamilton, J. P., Hahn, K. S., Daily, G. C., & Gross, J. J. (2015). Nature experience reduces rumination and subgenual prefrontal cortex activation. Proceedings of the national academy of sciences, 112(28), 8567-8572.
Craig, J. M., Logan, A. C., & Prescott, S. L. (2016). Natural environments, nature relatedness and the ecological theater: connecting satellites and sequencing to shinrin-yoku. Journal of physiological anthropology, 35(1), 1-10.
Daily, G. C. (1997). Introduction: what are ecosystem services. Nature’s services: Societal dependence on natural ecosystems, 1(1).
Fenger, J. (1999). Urban air quality. Atmospheric environment, 33(29), 4877-4900.
Furuyashiki, A., Tabuchi, K., Norikoshi, K., Kobayashi, T., & Oriyama, S. (2019). A comparative study of the physiological and psychological effects of forest bathing (Shinrin-yoku) on working age people with and without depressive tendencies. Environmental health and preventive medicine, 24(1), 46.
Kovess-Masféty, V., Alonso, J., de Graaf, R., & Demyttenaere, K. (2005). A European approach to Rural—Urban differences in mental health: the ESEMeD 2000 comparative study. The Canadian Journal of Psychiatry, 50(14), 926-936.
Morita, E., Fukuda, S., Nagano, J., Hamajima, N., Yamamoto, H., Iwai, Y., … & Shirakawa, T. J. P. H. (2007). Psychological effects of forest environments on healthy adults: Shinrin-yoku (forest-air bathing, walking) as a possible method of stress reduction. Public health, 121(1), 54-63.
Nowak, D. J., Hirabayashi, S., Bodine, A., & Greenfield, E. (2014). Tree and forest effects on air quality and human health in the United States. Environmental pollution, 193, 119-129.
Ohtsuka, Y., Yabunaka, N., & Takayama, S. (1998). Shinrin-yoku (forest-air bathing and walking) effectively decreases blood glucose levels in diabetic patients. International Journal of Biometeorology, 41(3), 125-127. doi:10.1007/s004840050064
The Important Relationship between Forests and Water. (2019, October 03). Retrieved from https://www.americanforests.org/blog/the-important-relationship-between-forests-and-water/
Tsunetsugu, Y., Park, B. J., Ishii, H., Hirano, H., Kagawa, T., & Miyazaki, Y. (2007). Physiological effects of Shinrin-yoku (taking in the atmosphere of the forest) in an old-growth broadleaf forest in Yamagata Prefecture, Japan. Journal of physiological anthropology, 26(2), 135-142.
Ulrich, R. S., Frumkin, H., AJ. Blood, R. Z., TW. Buchanan, K. L., V. Goel, R. D., T. Iidaka, M. O., . . . M. Yamaguchi, M. D. (1991, January 01). The physiological effects of Shinrin-yoku (taking in the forest atmosphere or forest bathing): Evidence from field experiments in 24 forests across Japan. Retrieved from https://link.springer.com/article/10.1007%2Fs12199-009-0086-9
Why it Matters: Water. (2020, September 02). Retrieved from https://www.americanforests.org/why-it-matters/water/?gclid=CjwKCAjw_Y_8BRBiEiwA5MCBJhBXPfzNHRfZdFBQ71ND7zbT3GjETQL2u5rsyr8eC2XcW1L8m8EYNhoCPhwQAvD_BwE
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