Analyzing Patterns of Forest Fragmentation
in Montgomery County, MD
and Fairfax County, VA

Montgomery County, Maryland and Fairfax County, Virginia are located adjacent to Washington, D.C. and have experienced rapid land use change during the past several decades. In 1950, both counties were essentially rural, agricultural counties, producing a variety of fruit and cereal crops, and dairy products. Fairfax County also had a productive timber industry. Today, both counties have become residential and commercial centers in the Washington Metropolitan Region. These land use changes are reflected in current land use patterns.

This land use map of Montgomery and Fairfax counties is part of the Region III (Mid-Atlantic) Multiresolution Land Characterization (MRLC) data set produced by the United States Geological Survey and illustrates the prominent role of residential development in the landscape of these two counties.

Despite rapid development, forests remain a dominant component of the landscape.

In urban and suburban areas, forests play an important role in flood and erosion control, water quality protection, and wildlife habitat. Forest ecosystem health must be maintained so that forests can continue to provide these ecological services in developed areas. "Forest health" is not well understood, but it is relatively well established that decreases in forest cover and increases in fragmentation will result in negative ecosystem effects. Forest loss results in the total loss of the ecological services performed by forests, while increased forest edge, created by forest fragmentation, can lead to decreased ecosystem functioning and degraded wildlife habitat. Measuring these aspects of forest fragmentation may provide insight into the relative forest health of Montgomery and Fairfax counties.

It was found that there are some interesting differences and similarities between the two counties in the amount and configuration of forests. Fairfax County has more forest, with 24% of the total county being forested. Montgomery County is only 19% forested. Fairfax County also has larger forest patches. The average patch size is 4.5 hectares compared to 2.7 hectares in Montgomery County. Forest core area, or the area of forest unaffected by edge, is significantly larger in Fairfax County. The average core area per patch is 1.1 hectares in Fairfax County compared to 0.6 hectares in Montgomery County. Despite the fact that Montgomery County has less forest cover and smaller forests patches, the level of connectivity between forest patches is similar between the two counties (average distance between neighboring forest patches is 40 meters in Montgomery County and 38 meters in Fairfax County). Connectivity between forest patches is important for the movement of wildlife.

These results lead to the issue of forest conservation. Both counties are under severe population pressure and are experiencing rapid rates of land conversion. In order to ascertain what the status of forest protection is at the county level, the amount of forest protected by the county parks systems was determined.

In Montgomery County, 19% of the total county area is forest, 9% is parkland, and 6% is forested parkland. In other words, 6% of the total county area is forestland that is protected by the county. In Fairfax County, on the other hand, 24% of the total county area is forest, 3% is parkland, and only 2% is forested parkland. Clearly, Montgomery County has a more comprehensive land acquisition program. In terms of the amount of forested land that is protected, Montgomery County is protecting 30% of the existing forests through the parks system and Fairfax County is protecting only 9%. This analysis indicates that while Fairfax County currently has more forestland, much of these forests may be threatened by development. Montgomery County has a more comprehensive protection program and may continue to conserve valuable forests. However, American Forests has suggested that developed areas should achieve 40% forest cover to assure proper ecosystem functioning. The results of this analysis show that both counties fall short of this goal.