Trees, Dirt and Streams

Raw Dirt, Construction Site, George Mason University

Fairfax, VA, August 2010

©EOP

Yesterday afternoon, with the car thermometer registering 101 degrees F, I drove to the Vienna-Fairfax Metro station to pick up my wife. The area just south of the station looked radically different from its visage on my last trip to that station a few weeks earlier. A wooded area of several hectares had been stripped of all vegetation and was bare dirt being worked over by large construction machinery. It is the second property near the intersection of Route 29 and Nutley Street recently stripped of vegetation for new construction. In close proximity to the Metro Station, high density land uses are certainly justified, but was it necessary to clear away every last tree?

Fairfax County claims to be concerned about its tree cover, and has an ordinance to that end which, according to a news release from the County:

The Fairfax County Board of Supervisors adopted a tree preservation ordinance at its Oct. 15 (2007) meeting, protecting four types of trees. Under the new law, individual specimen, heritage, memorial or street trees can be protected from being cut down.

The new measure is not intended to protect large wooded tracts. Instead, the law only affects individual trees that property owners voluntarily agree to safeguard.

The board approved the law because even a single tree can benefit the environment. One mature tree with a 26-foot canopy can absorb the emissions of a vehicle driven 11,500 miles every year.

Homeowners, residents or groups can recommend individual trees for protection. After a public hearing, the board will approve the preservation of specific trees. Easements also may be required to protect a tree’s roots. If needed, property owners will donate the easements to the county.

As defined by the law, specimen trees are those that are notable in their size and quality for their species. Heritage trees have a historical or cultural interest. Memorial trees, as the name suggests, commemorate a memorial. Street trees are those that have been planted by the county on public rights of way.

There is a $2,500 fine for removing a protected tree without permission from the county. The ordinance takes effect immediately, and it has been added to the county code as chapter 120.

The preservation ordinance supports the county’s 30-Year Tree Canopy Goal adopted by the board in July. The county aims to blanket 45 percent of the county with tree cover by 2037. It is important to preserve existing trees because the county expects to lose 4 percent of its canopy during the next 30 years. To reach the goal, the county and the public also will have to plant an additional 2.6 million new trees.

Once achieved, the canopy goal is expected to save taxpayers money. The trees when matured should produce savings equivalent to $5.3 million for air pollution removal and $4.7 million in energy conservation every year. The additional canopy also will have the capacity to absorb more than 10 million pounds of carbon dioxide annually, which could eliminate the need for $1 million in greenhouse gas reduction services each year.

For more information about the new ordinance or 30-Year Tree Canopy Goal, call 703-324-1770, TTY 711, or visit www.fairfaxcounty.gov/dpwes/environmental/trees.htm.

It is interesting to note that the ordinance applies only to specific trees, not to forested areas. Since much of the woodland in the county is second growth, frequently a product of the reforestation of exhausted tobacco and other farm lands since the early and middle parts of the 20th century, that forest growing on nutrient poor land contains very few "specimen" trees notable for their age, girth, historical importance or beauty. Moreover, the ordinance only applies if land owners agree.

Fairfax City (under Virginia's peculiar local government system not a part of Fairfax County even though it is completely surrounded by it) calls itself a "Tree City USA." The City does indeed have many grand old trees and small woodlands, one of the strongest reasons attracting us to live here. Fairfax City has a stringent ordinance requiring City permission for tree removal. Despite that ordinance, a large parcel on the eastern edge of the City adjacent to Main Street (Route 236) was stripped of all vegetation for construction of residences just as the Cheney-Bush recession began in 2008, and the land has remained bare dirt since. As of a few weeks ago activity at the site has suggested that building will commence soon, but for about two years, through the melting snow of intense winter blizzards and torrential summer rainfall, dirt has eroded from that parcel into storm sewers flowing into nearby streams.

There has been a construction boom on the Fairfax campus of George Mason University over the past several years, and while some of that building used sites that previously had been parking lots, a major project at the north west corner of the campus, adjacent to Fairfax City, has also stripped several hectares of all vegetation. At the height of land, the site is the headwaters for a small stream which flows across the campus into a  holding pond. Despite some serious efforts to minimize erosion during construction, recent heavy rain has turned that pond a muddy brown, filling it with silt from the construction site a few hundred meters to its north. Eventually some of that silt will wash into the Occoquan, a primary source of water for the Virginia slurbs of Washington, DC.

Mason Pond, muddy after summer thunderstorms

George Mason University Campus, Fairfax

©EOP

Discussion of deforestation frequently focuses on the widespread cutting of trees in the Amazon Basin, in Brasil's Atlantic rain-forest, in Borneo or elsewhere in the tropics. In fact deforestation is a matter of consequence in many other areas. A recent Scientific American posting suggested that urban dwellers are driving deforestation. It was focusing on conditions in poorer countries where urban demand for food and fuel is leading to forest clearance, but the argument could well be extended to the United States where the demand for new slurban construction sites is causing large areas to be stripped of trees and other vegetation.

Fairfax City and County together have a large set of small-scale clearances which, in total, have a substantial impact on climate and water flow.The cooling effect of wooded land on nearby areas is well-known and easily demonstrated. On a hot and sunny summer day, walk from a copse of trees, even a small one, onto a patch of bare ground and the difference is instantly apparent. In a heat wave like the ones that have blighted the summer of 2010, a wooded area can be as much as 5 degrees C cooler than nearby open areas.

The effects of wooded land on water flow are a little more complicated. Forests even out the flow of streams, holding back some of it during and just after heavy rain and then releasing water in drier periods. The geology and soil of the Fairfax area and the torrential rains common with summer thunderstorms provide perfect conditions for filling streams with silt when the soil is bare.Wooded areas slow and filter the rapidly flowing rainwater draining after a storm, and they retain much of the material that could become silt. Water authorities in the county and nearby are well aware of the problems deforestation, and impermeable surfaces like paving  (a subject for another posting), create. Heavy rains in deforested areas lead to rapid runoff of silt loaded water into streams and reservoirs, while in a longish drought like the one in the first part of summer 2010, those streams and impoundments diminish or even dry up (their storage capacity getting smaller each storm as silt accumulates). When needed for water supply, that shrinkage can lead to sleepless nights for water managers after a long dry spell!