Since starting this blog in January 2019, I’ve written several posts describing the benefit of trees, focusing primarily on how trees absorb and reduce the amount of carbon dioxide released into the atmosphere (CO2) – a key contributor to global warming and climate change. (See, for example, Earth Day 2019, Let’s Plant More Trees, and Our Tree Farm). Recently I watched a PBS News segment describing a study underway in Louisville, Kentucky, which is investigating the public health benefits of planting more trees.
The genesis of this study, referred to as the “Green Heart Project”, may have occurred in 2002 when ash trees in Michigan were dying at an accelerating rate due the infestation of an Asian beetle known as the Emerald Ash Borer. Over the next 5 years, this beetle’s destruction spread into 15 states killing one million trees by 2007. During this same period of time and area, researchers observed that 21 million more deaths had occurred than would have otherwise been predicted. Assuming these additional deaths were not a result of trees falling on people killing them, the researchers speculated that the disappearance of trees may have been responsible for the increases in deaths – or said another way, the trees were saving lives.
The phenomena of environmental surroundings affecting health have been demonstrated before. A study of surgical patients in a Pennsylvania hospital between 1972 and 1981 showed that those with a window facing a nature setting had shorter stays and better results, as compared to patients whose window faced a brick wall. More recently, a study by Clemson University found similarly better hospital outcomes as a result of adding art depicting tranquil nature scenes.
But the degree in which trees actually effected people’s health, particularly stress, heart disease and diabetes, and might be responsible for saving lives, was unknown. Hence, the design of the Green Heart Project study. Specifically, the flip side of the ash tree loss, could planting trees in an area improve the health of the individuals. In 2017, The Nature Conservancy and its partners, including the University of Louisville, and the National Institute of Health (NIH), launched a 5-year study designed to address this question.
The city of Louisville is a good place for this study for several reasons. Louisville has experienced a decline in tree cover for years. In 2012, Louisville’s tree cover was 37%. And since then, the city has lost approximately 54,000 trees annually, largely due to cutbacks on maintenance and reduced replanting initiatives. A 45% tree cover is a typical considered a good planning goal. Louisville also has a significant air pollution problem, estimated to be the equivalent of smoking ½ cigarette per day. This may not sound like a lot, but experts say smoking as little as 1 cigarette per day elevates the risk of stroke or heart disease by about half as much as smoking 20 cigarettes per day. In other words, any smoking – even 1/2 a cigarette per day – is harmful to your health.
Within Louisville, a moderate-income neighborhood, covering approximately 3 square miles, in which there was a significant void in tree cover, was selected for the study. The neighborhood was parceled into 16 clusters, 8 of which would receive approximately 8,000 large, established trees. The other 8 clusters would not, thus creating the control group. Larger trees were selected to have a more immediate impact that planting smaller ones.
Residents within the neighborhood were interviewed for lifestyle and their health was evaluated and recorded for future comparisons. Also, within the neighborhood, monitors were installed on utility poles to record temperature, air pollution and noise pollution.
As illustrated in the diagram above, produced by the Nature Conservancy, many of the benefits of urban trees are generally well known. Besides capturing CO2 which is a significant contributor to climate change, trees clean the air by absorbing odors and pollutant gases (nitrogen oxides, ammonia, sulfur dioxide and ozone) and filtering particulates out of the air by trapping them on their leaves and bark. Additionally, trees cool the surrounding areas. It is estimated that one tree provides the equivalent coolant of 10 room-size air conditioners. The presence of trees encourages physical activity, e.g., taking walks which can reduce stress levels. Trees also give off airborne chemicals known as phytoncides. These chemicals help trees protect themselves from insects but our bodies respond to these chemicals by increasing the number and activity of white blood cells, thus boosting our immune system.
The goal of the Green Heart Project is to determine the specific and quantifiable health benefits of adding 8,000 trees into a defined area. For example, will the residents receiving the new trees realize lower blood pressure, less diabetes, less stress, and lower mortality rates. With these study findings, organizations such as governments and city planners, can assess the financial benefits associated with having healthier citizens as a result of planting trees. Similarly, employers that could reduce productivity losses (due to reduced missed days of work) as well as insurance companies that could lower health costs (due to reduced claims), can also evaluate the value of supporting new tree initiatives.
Heart disease is the leading cause of death in the United States. According to the Center for Disease Control (CDC) “Heart Disease and Stroke Cost America Nearly $1 Billion a Day in Medical Costs, Lost Productivity”. And that finding is based on 2015 data. I suspect the cost is much higher now. If adding trees in urban areas would reduce heart disease, stroke and diabetes, the payoff for that investment in trees, when compared to the healthcare cost savings, may be immense. And it wouldn’t hurt that more trees would also help save the planet.