There is an increasing awareness that healthy urban forests improve the quality of life for people in urban settings. Consider what our urban trees do:
- Sequester carbon dioxide and release oxygen through the process of photosynthesis
- A single mature tree can absorb as much as 48 pounds of CO2¬/year and release enough oxygen to support two human beings.
- The Intergovernmental Panel on Climate Change has estimated that trees can sequester one ton of CO2¬/year at a cost of15/ton, an extraordinary value.
- Nationally, it is estimated that our urban forests store between 600 million and 990 million tons of carbon.
- Yield positive energy benefits, reducing heating and cooling costs by shading and sheltering buildings
- A well-placed mature tree can reduce annual air conditioning costs by 2 percent to 10 percent.
- It has been suggested that planting 100 million mature trees in U.S. cities would reduce annual energy use by 30 billion kWh, saving2 billion in energy costs. That amounts to20 per year per tree.
- Help reduce the urban heat-island effect. This is important because urban areas can be as much as 8°F to 10°F warmer than adjacent rural areas.
Trees are increasingly used as part of a green infrastructure program to reduce urban storm water runoff. Trees store rain water and then liberate the water vapor to the atmosphere through trans-evaporation. The root zone also absorbs water and enhances the penetration of water into the soil system. It has been estimated that an urban forest of 10,000 trees can retain approximately 10 million gallons of storm water a year.
In addition, trees in bio-retention areas can reduce urban storm water, mitigate flooding hazards and improve storm water quality. Studies have shown rain gardens can be effective in retaining and trapping up to 95 percent of urban-generated pollutants.
There are also strong economic benefits in creating and enhancing healthy urban forests. Urban forests and parks provide a significant return on our investment. A study conducted in Fort Collins, Colorado, suggested that every dollar invested in urban forests returns a benefit of $2.18. Think about the following:
• One large front-yard tree can increase the sale price of a house by 1 percent.
• The Center for Urban Forest Research has estimated that a property with trees is valued 5 percent to 15 percent higher than a comparable lot with no trees.
It is also suggested that planting urban trees is one of the least expensive ways to reduce urban air pollution and decrease health problems and related costs. A study conducted in New York City in 1994 estimated that the trees in New York City removed 2,007 tons of air pollutants with an estimated benefit to society of $9.5 million.
Trees are a cost-effective solution to improving urban air quality. The pores on the underside of a leaf surface are effective in removing nitrogen oxides, sulfur oxides and volatile organic carbon. The upper surfaces of the leaves intercept air-borne particulates (particulate matter having diameters of less than 2.5 microns and those with diameters of less than 10 microns), again contributing to a more healthful urban environment. In Chicago, it was estimated that trees remove approximately 234 tons of particulates having diameters of less than 10 microns.
It has been suggested that urban forests provide a restorative environment that allows people to relax and have greater life satisfaction. S. Kaplan, in 1995, developed the Attention Restoration Theory that proposes that natural environments can assist in developing greater attention and productivity. Urban forests have also been found to help children with Attention Deficit Disorder. The symptoms of ADD appear to be more manageable for a child in a green or natural setting.
It is clear that our quality of life is enhanced by our urban forests and that planting a single tree in an urban setting will yield a significant return on the investment. Greening our cities and expanding our urban forests will clearly improve our quality of life.