Fall 2005

Fragmentation of U.S. Forests

The following findings about forest fragmentation are a synthesis of information from eight articles published by Kurt Riitters and his colleagues over the past 5 years.

• Considering first the overall distribution of forest area, there is at least some forestland cover nearly everywhere in the lower 48 States.
• Forest is the dominant landcover for one-third of all land area, and 70 percent of all forest area is found in forestdominated landscapes.
• Fifteen percent of forest is located in landscapes dominated by shrubs and grasses, and the remaining 15 percent occurs in landscapes dominated by agricultural and urban land uses.
• Considering the spatial arrangement of forestland, most forestland is near other forestland, over very large regions.
• The perimeter of a typical forest “patch” (clump of forest or forests touching one another at some point) is only about 300 feet from the perimeter of its nearest neighbor patch, except where there is not much forest, in which case that distance is 650 to 1,000 feet.
• At the same time, fragmentation is so common that one-half of all forest is within about 300 feet of forest edge, and less than 1 percent is more than 3,200 feet (0.6 mile) from forest edge.
• About half of all fragmentation is associated with the physical separation of distinct forest patches, and half is associated with small (less than 17 acres) perforations, or holes, in otherwise continuous forest cover.
• Overall, at least half of the fragmentation is associated with human land uses. Almost all fragmentation in the East is clearly due to human activities, whereas most fragmentation in the West is associated with semi-natural landcover types such as grassland and shrubland. Distinguishing natural from human factors is a problem in the West because landcover is a less accurate guide to actual land use.
• In both the East and the West, the largest reserves of intact forest are in public forests on land that is not suited for agriculture or urban development.
• In a global context, the Eastern United States contains the last major reserve of relatively intact temperate deciduous broadleaf forest, and this region is expected to experience significant urbanization—resulting in increasing fragmentation over the next 50 years.

Back to Sometimes a Great Notion: Visualizing Forest Fragmentation

For More Information:
Kurt Riitters at 919–549–4015 or kriitters@fs.fed.us