More Trees for Fairfax County,  or
How Do We Achieve the County's New Tree Cover Goal of 45%?

The Advantages of Trees
The Downside to Trees
Trees Overall?
Trees in Fairfax County
Why Did We Lose Tree Canopy?
Fairfax County's Goal
The Problem With This Goal
Saving More Canopy Now
Where to Plant Trees:  Solutions and Non-Solutions

The Advantages of Trees

Doug, standing next to the trunk of an oak about 36 inches in diameter Doug in his yard with his biggest tree, an oak with a diameter of about 36 inches.

Trees take in carbon dioxide and give off oxygen. They also pull sulfur dioxide, ozone, and particulate matter from the air.

Trees help prevent erosion and flooding. Tree leaves slow raindrop velocity — the harder a raindrop hits the ground, especially bare ground, the more erosion it causes, and to the extent that tree canopy holds the rain, it delays runoff or, through evaporation, reduces it altogether. Fallen leaves protect the forest floor. Roots hold soil in place.

Trees along creeks and streams protect the stream banks and, by keeping the streams cooler, promote healthier streams for aquatic life.

Trees reduce summer temperatures. On a micro level, tree shading of a house reduces the air conditioning load. On the macro level of the city, tree canopy prevents asphalt and concrete surfaces from absorbing heat. If you look at temperatures on the late news, you'll see that suburbs (and even more so rural areas) are significantly cooler than cities, particularly after the sun goes down and concrete, brick, and asphalt release the absorbed heat.

Trees are aesthetically pleasing. Ask Joyce Kilmer.

Trees provide firewood when they reach the end of their natural lives.

The Downside to Trees

In the advantages above, tall mature trees are far better than smaller ornamentals, except possibly in aesthetic characteristics.

Trees need maintenance as they age, mostly in the form of pruning and topping (thinning of the canopy). Since few people like to work high above the ground with a chain saw, tree maintenance isn't inexpensive.

Trees block light (although deciduous trees only do so until they drop their leaves in the fall). Pruning can reduce this effect, however.

Tree roots can crack sidewalks, driveways, and foundations.

People worry that trees will fall on their houses. Power companies worry that trees will fall on power lines.


I'm going to take it for granted that, if you're reading this, you agree that maintenance and common sense placement of the right trees can negate the disadvantages. You agree that overall trees are a very good thing and we need more of them.

If you've done much reading, you probably agree with the conservation organization American Forests' guidelines that areas east of the Mississippi River should have 40% tree cover, and that in suburban residential zones this should increase to 50%.

Trees in Fairfax County

What follows is from the County's Tree Plan:

The abandonment of agricultural uses in the middle of the 20th century was accompanied by a rapid wave of natural reforestation. By the late 1960s, when the eastern portion of Fairfax County was described as suburban "bedroom community" to Washington D.C., agricultural uses were gradually abandoned in front of the wave of land development that generally traveled from east to west across the county. The sharp decrease in farming activities coupled with modest levels of land development allowed the county's canopy cover to rise to approximately 80 percent in the early 1970s.

Fairfax County's tree canopy is currently estimated to cover 104,000 acres or 41 percent of Fairfax County's landmass of 252,828 acres. Our overall tree canopy is comprised of 68 percent native forests (70,720 acres) that typically occur on public parklands, commonly owned open spaces, and on larger, privately owned parcels. . .

Change detection analyses demonstrate that Fairfax County has actually lost 48 percent of its tree canopy over the last 32 years. Along with the physical loss of trees, Fairfax County has lost significant levels of environmental services that were provided by those trees. For example, the 85,600 acres of canopy lost since 1973 had the capacity to remove approximately 2.4 million combined pounds of sulfur dioxide, carbon monoxide, ozone and particulate matter annually, at a value of approximately $6.8 million per year. In addition to air quality benefits, the county also lost significant levels of water quality, energy conservation and other socio-economic and environmental benefits with those trees.

Small diameter tall trees creating dense canopy. Smaller diameter tall trees have filled in to create a dense canopy in an older neighborhood.

Why Did We Lose Tree Canopy?

The simple answer is development. Town home communities with small yards provide little room for mature trees except in the common areas. Large houses on small parcels create similar limitations for the homeowner who wants large trees. Roads, shopping centers and office buildings limit the possibilities for trees. Future mixed use sites, including those built as transportation oriented development (high density around Metro stations), may have a few trees in the town square, but the sites will be mostly concrete.

Fairfax County's Goal

On June 18, 2007, Supervisor Gross (Mason District) moved and the Board of Supervisors formally adopted a 30-Year Tree Canopy Goal of 45%.

In support of this goal, Supervisor Gross stated that, even if the County continues to conserve trees at its present levels of effort, the tree canopy will decrease in size from 41% to around 37%. Supervisor Gross noted that the projected loss (10,200 acres) equates in area to seven Huntley Meadows Parks. To reverse this projection and increase the canopy goals over time, the proposal reviewed at the Environment Committee established 45% as the goal for 2037. This goal translates into approximately 20,400 acres of additional tree canopy. Although some of the gains are expected through natural processes, a large-scale planting program over a 30-year period also would be required. Total numbers of trees required to reach this goal is estimated at 2.6 million.

The Problem With This Goal

If this goal is to be more than empty feel-good environmentalism, there must be a plan to attain it. No one doubts that the County can afford to buy trees over this period of time, especially when some of the purchases will be made by homeowners and homeowner associations. The real problem is where these new trees will go.

To give this some perspective, the land area of the County is approximately 395 square miles. 20,400 acres is just under 32 square miles (at 640 acres to a square mile). That means that we have to cover 8% of the County with trees where currently no trees exist today. Where will this land come from? No one knows. But it's a safe bet that the County will not be tearing down neighborhoods or commercial development to plant trees — although it will certainly buy more empty land for parks, and that may offer some opportunity for increasing the canopy.

Saving More Canopy Now

If development can be made less destructive of trees and there is less tree loss for new development, the open area required for new planting can be reduced. Currently, the County has no authority to require developers to proffer tree-save as part of the development process; the way the Virginia Code reads, a locality may mandate tree cover on a site (up to specified levels), but a developer may meet that level with new plantings and/or saving existing trees.

We should:

Two dead trees this side of fence, one dead tree beyond fence. How not to save trees:  young trees dead in Clermont Park for lack of water. Newly planted trees require fertilizer and water for the first few years after planting and pruning throughout their life.

Where to Plant Trees:  Solutions and Non-Solutions

Here's a non-solution: prohibit homeowners from cutting down trees on their property without permission from the County.

Supervisor Gross said this: "It's not just developers who are taking trees down, it's sometimes homeowners new to the community. They don't want to rake leaves or don't see the value in a tree. There are other jurisdictions in the region who have rather strict rules on what you can take down, what you can replant. We'd like to have some of the same ability in Fairfax County." (DC Examiner, 6/23/2007)

No, we wouldn't. Imagine the outcry against this! And the worst risk of such restriction would be the loss of public support for all the County's tree programs. While we should educate homeowners about the value of trees, when it comes to preserving trees on private property, we should let a homeowner decide and trust to his or her good judgment.

Shall we plant trees on green roofs? At first blush, this sounds attractive, but it's another non-solution. A mature non-ornamental tree weighs multiple tons, and with the soil needed to support it, the weight would be well beyond the structural capabilities of a roof that anyone could afford to build. Let's consider small ornamentals on green roofs a bonus and have no illusions about using green roofs to vastly increase tree canopy.

Where can we plant more trees?

The bottom line, however, is that all of these measures combined, both tree save and new planting, will probably not get us to our goal. Maybe not even half way there. Working against this goal are plans for higher density development. To the extent that single family neighborhoods of detached houses are redeveloped, the effect on tree canopy will be catastrophic.

I'm afraid that I haven't come up with a plan to find all 32 square miles of land for new trees. To realize that goal, we're going to have to start thinking hard about it NOW and begin taking what action we can.

References and further reading:

American Forests
Fairfax County Tree Action Plan, December 2006
BoS Summary for June 18th (go to Item 44)
Virginia Code Section on Local Tree Canopy Ordinances
National Wildlife Federation Backyard Wildlife Habitat Program
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