How Do Trees Benefit Me?


(Conservation Currents, Northern Virginia Soil and Water Conservation District, Summer 2011)

Quantifying Services Provided By Fairfax County’s Tree Canopy

by Jessica Strother, Urban Forester, Fairfax County Urban Forest Management Division

Admiring a Willow Oak, Quercus phellos. Credit: Lawrence Morris, University of Georgia, Bugwood.org                                       Trees... needed shade, a thing of beauty, a perch for a bird, and a challenge to deal with those leaves in the fall! This is what some people in our region think of when they think about trees, unless they slow down and take a closer look. In Fairfax County and in communities throughout the country, natural resource managers have been taking a closer look and calculating the benefits provided by trees and forests.

In 2009, the Fairfax County Urban Forest Management Division embarked on a project to measure and quantify the benefits derived from our trees on a countywide basis. State of the art forest analysis software from the U.S. Forest Service called "i-Tree" was used in this project. i-Tree software was used to provide a broad picture of the entire urban forest and uses local field data along with air pollution and meteorological statistics, to quantify forest structure, environmental effects and economic values provided by trees in various settings.

Tree Facts
DBH: Diameter at breast height
O3: Ozone, an air pollutant affecting human health
NO2: Nitrous dioxide, a greenhouse gas and air pollutant which can impact human health
SO2: Sulfur dioxide, an air pollutant which can impact human health and precursor to acid rain
PM10: Particulate matter of 10 micrometers or less, which can impact human health

Geographic Information System tools were used to randomly select areas where field data collection would occur and to ensure that adequate levels of data sampling occurred within 12 land use categories. These categories included residential, governmental, commercial, industrial and forested areas. County and Virginia state foresters collected data on tree species, trunk size, canopy coverage, ground covers and imperviousness of soils from 200, 1/10 acre plots scattered throughout the County landmass. Finally, all of this information was entered into the i-Tree software interface and sent off to the U.S. Forest Service for final data processing. In turn, the U.S. Forest Service produced a final report that included the following statistics:

i-Tree Report Results

  • Number of trees in Fairfax County: 20,900,00
  • Most common trees: Red Maple, American beech, Tulip poplar
  • Carbon stored: 3,879,000 tons/year = (value; $21.7 million/year)
  • Carbon sequestration: 218,000 tons/year (value; $4.51 million/year)
  • Building energy savings: value; $11.9 million/year
  • Avoided carbon emissions: value; $421 thousand/year
  • Structural values: value; $29.2 billion

Notes: 1. A ton is equal to a short ton (U.S. = 2,000 lbs) 2. Structural value is the value based on the physical resource itself (cost of having to replace a tree with a similar tree)

Other studies demonstrate that approximately 371 million cubic feet of storm water are intercepted and slowed by the County’s tree canopy during a typical storm event. National studies and research conducted by others are on-going to analyze and quantify the socio-economic and psychological benefits people gain from the trees and forests around them. Why is this of interest and a concern? Over the past 40 years Fairfax County has lost at least 48% of its tree canopy. This is due to a residential/commercial development, an increase in storms and their intensity, invasive alien plants taking over trees and their habitats, and the public’s need for more information about how to care for and protect trees and community forests. Fairfax County has approximately 41% tree canopy at present, which is somewhat better than other adjacent jurisdictions.

The Tree Nutrition Label was created using the i-Tree suite of software tools and developed by the USDA Forest Service, academia and the public to illustrate the ecosystem benefits provided by urban trees. For more information go to www.unri.org

Locally, to learn more about trees and services provided by Fairfax County go to Department of Urban Forestry

To take a closer look at some of the benefits and value of trees in your community, go to www.treebenefits.com

Your 24 inch Silver Maple will intercept 6,322 gallons of stormwater runoff this year.


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