Trees are major capital assets in cities across the United States. Just as streets, sidewalks, public buildings and recreational facilities are a part of a community’s infrastructure, so are publicly owned trees. Trees — and, collectively, the urban forest — are important assets that require care and maintenance the same as other public property. Trees are on the job 24 hours every day working for all of us to improve our environment and quality of life.
Colorado’s urban forest provides many environmental benefits to our community. Aside from the obvious aesthetic benefits, trees within our urban forest improve our air, protect our water, save energy, and improve economic sustainability.
Unlike urban areas in the eastern U.S., canopy cover in Colorado decreases along an urban to rural gradient. In other words, since most trees have been planted much of the tree cover is in urban areas as opposed to “natural lands.” Therefore, estimated pollutant uptake rates are higher for residential compared to natural or unmanaged lands. Possible management implications of these estimates are that air pollutant uptake benefits from tree planting may be optimized by planting in areas where air pollutant concentrations are elevated and where relatively high planting densities can be achieved thereby enhancing the health of urban dwellers.
“In the first broad-scale estimate of air pollution removal by trees nationwide, U.S. Forest Service scientists and collaborators calculated that trees are saving more than 850 human lives a year and preventing 670,000 incidences of acute respiratory symptoms.
While trees’ pollution removal equated to an average air quality improvement of less than 1 percent, the impacts of that improvement are substantial. Researchers valued the human health effects of the reduced air pollution at nearly $7 billion every year in a study published recently in the journal Environmental Pollution. “Tree and Forest Effects on Air Quality and Human Health in the United States,” is available online at: http://www.nrs.fs.fed.us/pubs/46102
The study by Dave Nowak and Eric Greenfield of the U.S. Forest Service’s Northern Research Station and Satoshi Hirabayashi and Allison Bodine of the Davey Institute is unique in that it directly links the removal of air pollution with improved human health effects and associated health values. The scientists found that pollution removal is substantially higher in rural areas than urban areas, however the effects on human health are substantially greater in urban areas than rural areas.
“With more than 80 percent of Americans living in urban area, this research underscores how truly essential urban forests are to people across the nation,” said Michael T. Rains, Director of the Forest Service’s Northern Research Station and the Forest Products Laboratory. “Information and tools developed by Forest Service research are contributing to communities valuing and managing the 138 million acres of trees and forests that grace the nation’s cities, towns and communities.”
The study considered four pollutants for which the U.S. EPA has established air quality standards: nitrogen dioxide, ozone, sulfur dioxide, and particulate matter less than 2.5 microns (PM2.5) in aerodynamic diameter. Health effects related to air pollution include impacts on pulmonary, cardiac, vascular, and neurological systems. In the United States, approximately 130,000 PM2.5-related deaths and 4,700 ozone-related deaths in 2005 were attributed to air pollution.
Trees’ benefits vary with tree cover across the nation. Tree cover in the United States is estimated at 34.2 percent but varies from 2.6 percent in North Dakota to 88.9 percent in New Hampshire.
“In terms of impacts on human health, trees in urban areas are substantially more important than rural trees due to their proximity to people,” Nowak said. “We found that in general, the greater the tree cover, the greater the pollution removal, and the greater the removal and population density, the greater the value of human health benefits.”
Looking at trees helps us feel a sense of serenity. They seem to make life more pleasant. Trees have been shown to have an actual physical effect as well, enabling hospital patients to recover more quickly when their room offered a view of trees. Because of their potential for long life, trees are frequently planted as memorials, and friends and family members often become personally attached to the trees. It’s not unusual for a community to come together to save a large or historic tree, and residents are often resistant to removing trees when their cities plan to widen streets.
Trees improve air quality, conserve water, and harbor wildlife. They moderate the effects of sun, wind, and rain. During summer months, the shade trees provide keeps us cool and provides protection from direct sunlight. The downward fall of rain, sleet, and hail is initially absorbed or deflected by trees, which provides some protection for people, pets, and buildings. Trees intercept water, store some of it, and reduce storm runoff and the possibility of flooding. A windbreak can influence wind speed and direction.
Temperature in the vicinity of trees is cooler than that away from trees — the larger the tree, the greater the cooling. By using trees in cities, the heat-island effect caused by pavement and buildings can be moderated.
Air quality can be improved through the use of trees, shrubs, and turf. Leaves filter the air we breathe by removing dust and other particulates. Rain then washes the pollutants to the ground. Leaves absorb carbon dioxide from the air to form carbohydrates that are used in the plant’s structure and function. In this process, leaves also absorb other air pollutants—such as ozone, carbon monoxide, and sulfur dioxide—and give off oxygen.
By planting trees and shrubs, we return to a more natural, less artificial environment. Birds and other wildlife are attracted to the area. The natural cycles of plant growth, reproduction, and decomposition are again present, both above and below ground. Natural harmony is restored to the urban environment.
The economic benefits of trees can be both direct and indirect. Direct economic benefits are usually associated with energy costs: air-conditioning costs are lower in a tree-shaded home; heating costs are reduced when a home has a windbreak. The savings in energy costs and the increase in property value directly benefit each home owner. Trees increase in value from the time they are planted until they mature, and well-landscaped homes are more valuable than those that have no trees.
The indirect economic benefits of trees are even greater. Lowered electricity bills are paid by customers when power companies are able to use less water in their cooling towers, build fewer new facilities to meet peak demands, use reduced amounts of fossil fuel in their furnaces, and use fewer measures to control air pollution. Communities also can save money if fewer facilities must be built to control storm water in the region. To the individual, these savings are small, but to the community, reductions in these expenses are often in the thousands of dollars.
List of benefits adapted from Trees Are Good (http://www.treesaregood.org).
- Green Cities: Good Health
- Landscape and Human Health Laboratory
- Urban Natural Resources Institute
- Urban Ecosystems and Social Dynamics
- Vibrant Cities and Urban Forests
- Learn more about the Emerald Ash Borer with this Quick Guide
- Emerald Ash Borer First Responder Manual
- Emerald Ash Borer Decision Guide
- Emerald Ash Borer Control Options for Colorado
- Biological Control of EAB, Tetrastichus planipennisi, parasitic wasp released in Boulder, September 2014.
- Biological Control of EAB, Oobius agrili, parastic wasp released in Boulder, June 2015.
- NOW AVAILABLE: The Colorado Ash Tree Replacement Selection Tool. Download the tool here (Excel file, 1.2MB)
What should you plant instead?
Private Tree Landowners
- Do you have an Ash Tree? Identify the trees on your property with this handout or go to this video!
- How Colorado State University can help You with Your ash!
- Detection of emerald ash borer in urban environments using branch sampling
- Prevention and Response Plans to address Invasive Species Attacks on Urban Forest in Colorado
- Learn how to peel EAB infested branches with this video produced by Colorado State University Extension: http://youtu.be/caOw3Be0w_8
- EAB Survey Protocol
- For more information on the Emerald Ash Borer visit:
- Quarantine in Effect in Boulder County
The Colorado Tree Coalition and the Colorado State Forest Service are pleased to announce the release of CO-Tree View, Colorado’s Community Tree Map, at www.cotreeview.com!
CO-TreeView is a web-based tree inventory and mapping tool available for use by Colorado foresters, arborists, and other entities to record and map the location, species, and condition of the trees that make up Colorado’s urban forests. The tool enables proactive, data-driven urban forest management planning, grant solicitation and public outreach, and encourages inter-community collaboration.
Registered users can quickly and easily add tree inventory information and create customized, downloadable charts and maps. Request your CO-TreeView account today to begin using this free tool.
For more information on CO-TreeView, including detailed FAQs, click the “Overview/Intro” link from the CO-TreeView “Getting Started” window (from the CO-TreeView homepage). For help using CO-TreeView’s inventory and mapping tools, click the “Help and Tutorials” link. You can also view this CO-TreeView flier for more information.
When visiting, viewing and using the site it is highly recommended that you use a web browser other than Internet Explorer, such as Google Chrome or FireFox, as the application is much more stable in those browsers.
Colorado’s Forests: Challenges and Opportunities
- The following videos were created to help Colorado residents learn more about forest conditions, related threats and challenges, and solutions to forest health problems.
- The videos are intended to raise general awareness about major issues affecting Colorado’s forests. Please visit the Colorado State Forest Service webpage at http://csfs.colostate.edu/index.shtml for more information.
- The video was created in four parts, each about 7-11 minutes long for a total viewing time of 39 minutes
- Background and forest issues of concern (Segment 1): http://vimeo.com/87307649
- Forest management as a solution (Segment 2): http://vimeo.com/96730053
- The challenge of a growing Wildland Urban Interface (Segment 3): http://vimeo.com/97549777
- The importance of a wood products industry (Segment 4): http://vimeo.com/98376500
- Denver City Trees Report by Healthy Trees Healthy People
- Guide to Tree Care in Dry Climates
- Tree Pruning – late winter is a great time to prune
- Winterizing Trees!
- Caring for trees during drought – How much and Where to Water your trees