Trees are essential for the proper functioning of all our natural environment systems—such as the water cycle, and food chain. They also improve the quality of life in our homes and neighborhoods.
This page highlights the benefits of tree canopy coverage for our community. Help us improve our tree canopy: learn how to plant and take care of trees.
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Trees and Air Quality
Trees and vegetation remove pollutants from the air in three ways:
- Absorbing gases
- Removing particulate matter from the air
- Reducing ambient temperatures through shade
Trees absorb gaseous air pollutants through the tiny pores on the leaf surface. Common pollutants that trees and vegetation can remove include nitrogen oxides, sulfur oxides, particulate matter, and ground-level ozone.
Trees can also remove particulate pollutants. These particles are removed from the air when they touch and settle on trees. This may only provide temporary relief, however, because rain or wind can dislodge particulate pollutants and return them to the environment.
Shade trees cool the air, helping reduce ground-level ozone pollution (ozone generation is dependent on air temperature). In addition, shade trees planted in parking lots reduce evaporative emissions (fuel evaporating from vehicle carburetors or fuel systems) of volatile organic compounds (VOCs). VOCs are ozone—precursors that react in sunlight and heat to form ground-level ozone—from parked cars.
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Trees and Energy/Climate Change
Trees provide many ecological services that support reduced energy use and benefit the environment.
Cooling the Air and Urban Surfaces
Trees and vegetation cool our homes, offices, streets, and cars by providing shade and through evapotranspiration (the evaporation of water from leaves).
Shaded walls may be 9 to 36°F (5° to 20°C) cooler than the peak surface temperatures of unshaded surfaces. Cooler walls decrease the quantity of heat transmitted to buildings, reducing the pressure on air conditioning systems. Cooler building surfaces reduce the urban heat island effect by decreasing heat re-transfer to the surrounding air, lowering overall ambient temperatures.
Trees and vegetation also cool the air by the process of evapotranspiration. Here, trees absorb water through their roots and transfer it up to the leaves, where it evaporates into the environment through leaf pore transpiration. This process uses heat from the air to convert water contained in the vegetation into water vapor, decreasing ambient air temperature. A mature tree with a 30-foot crown transpires approximately 40 gallons of water per day. Evapotranspiration alone can result in peak summer temperature reductions of 2 to 9°F (1° to 5°C). While this process reduces air temperatures, it does add moisture to the air. The positive cooling effect of vegetation usually outweighs any gains in humidity.
Reducing Energy Use in Buildings
Energy use inside buildings is lowered when the air temperature immediately around buildings is moderated by shade trees or by trees blocking wind. In the winter, evergreen trees around buildings help to break blustering winds, helping to reduce building energy consumption for heating. Lower energy consumption translates to reduced CO2 emissions from power generation (often coal- or fossil fuel-based).
Trees and vegetation remove atmospheric CO2 by sequestration. Trees sequester—or store—between 35 and 800 pounds of CO2 annually depending on their size and growth rate. The total quantity of carbon stored in mature trees may be 1,000 times more than the storage in small, young trees.
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Trees and Trash—And Recycling!
Extend the useful life of trees and tree products with the following practices:
Reuse the wood
Downed trees can be used for more than wood chip production. Depending on the tree size, species, and how it is removed, the wood might be re-used for a new purpose such as art or furniture. Think outside the chipper!
Need help finding someone to process a tree? Try looking for a portable sawmill owner or a participant in the Urban Wood Recovery Project like the Seneca Creek Joinery in Dickerson.
Dispose of Trees Correctly
Dumping leaves and yard waste is illegal. The Division of Solid Waste Services provides helpful tips on how to recycle and dispose of the following woody products:
You could also compost rather than dispose of leaves, grass clippings and woody debris. Learn how to set up composting in your yard. Grasscycling is another easy way to recycle your lawn clippings.
And finally, don't forget to replace your old tree by planting a new one!
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Trees and Watersheds
Trees provide many benefits to our watershed.
Reduce Stormwater Runoff
During rain events, impervious urban surfaces—such as buildings and parking lots—prevent rainfall from infiltrating (seeping into the soil). This excess rainfall turns into runoff, which flows untreated into local waterbodies carrying with it urban pollutants such as trash, oil, sediment, dirt, and debris. Trees and vegetation can help reduce the volume of runoff that enters storm drains. Researchers have found that evergreens, conifers, and deciduous trees in full leaf can intercept up to 36 percent of the rainfall that hits them.
Find out how you can get rewarded for planting trees to reduce stormwater from your property.
Improve Soil Stability
Tree roots help stabilize soil which, if loose and prone to erosion, might be carried away by stormwater runoff.
Tree roots also help to move water from the surface into deeper layers of the soil. This helps recharge the groundwater supply.
How Trees Benefit Our Homes
Trees mean green: Trees add as much as 20 percent to the value of your property. Studies also show that home values are higher on tree-lined streets. Trees have intrinsic value too. Whether it's fall color, spring flowers, or summer fruits, trees bring beauty to the landscape. By planting trees, you plant great places to live and relax.
Shade to save: Trees planted west or southwest of our homes and offices shade our rooftops, outside walls, and windows when the sunlight is brightest and hottest. This helps you save energy and lower your utility bills. Reduced home energy consumption also cleans our air through lower emissions from power plants.
Trees are great umbrellas: Trees help clean and cool water, and help control stormwater runoff—a major source of pollution in urban areas. Have a soggy spot in your yard? Plant a tree! Trees are a great landscaping solution to stormwater pollution.
Natural sounds, not neighborhood sounds: Your trees reduce the noise you perceive at home—so enjoy the sights and sounds of the trees near you.
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Trees and crime: Green neighborhoods with lots of trees have lower crime rates than barren, concrete environments. There are fewer acts of aggression by people, including drivers, and there are fewer cases of domestic abuse. Trees foster safer, more sociable neighborhoods.
Trees and children: Children who have parks and trees to play around concentrate better. Studies show that the effects of AD/HD are lessened. When there is a view of greenery out of their windows, studies also indicate that girls have better self-discipline. So plant trees for your children (and their children)!
Trees and UV-radiation: Trees provide shade from harmful ultraviolet radiation, particularly in playgrounds, schoolyards, and picnic areas.
Trees and neighborhoods: When neighborhoods are full of trees, residents spend more time outside mingling with neighbors—building personal ties, stronger communities, and a greater sense of well being.
Trees and stress: Trees, community gardens, and parks can help reduce physiological stress and aesthetically improve an area.
Trees and habitat: Trees provide an urban habitat for birds, animals, and insects.
Trees and local food sources Trees are an important economic resource for locally grown food (e.g., fruit trees).
For more information on the research mentioned above, visit the University of Illinois at Urbana-Champaign's Landscape and Human Health Laboratory Web page.
How Trees Benefit Businesses
Trees also provide many benefits for businesses:
- Shoppers are attracted to and linger longer on tree-lined streets—that means more sales and profits.
- Shoppers prefer and patronize shops with greener parking lots.
- Office and industrial space in wooded settings are more in-demand and more valuable to sell or rent.
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