The Influence of Urban Fringe Forests on the Development of Urban Communities (GR-2-97-009)

Forests, trees, developments, and tree conservation.

While forests are being converted to urban development, many fringe forests still surround metropolitan regions and remnant forest islands embedded within these regions as parks or scattered forests in residential developments. Though forests are prized for building sites, they lose biological integrity through the stresses imposed by the development process. Eventually, a forest is fragmented to the point it no longer functions as a forest and becomes more a collection of trees. This project documented the influence that forests have had on suburban and exurb expansion as well as investigated the influence urban development has on forest composition and structure. Forests are highly desired building locations, however, not all forests are equally preferred for development. Savanna-like stands — those with a basal area between 35 and 40 ft2/acre (8 and 9 m2/ha) — or approximately 65 trees per acre (26 trees per hectare) that are 10 inch (25.4 cm) diameter and 25 to 45 feet (7.6 to13.7 in) tall are the forests most preferred for development. This development activity has a significant impact, even when mature trees are conserved during the process. The conversion of the site from forests to urban results in soil changes including increases in pH, soluble salts, phosphorous, and potassium and a decrease in organic matter content. The remnant trees — those remaining after the stands were converted to housing — may appear healthy, however, due to the fragmentation of the stand, their vitality indicate a decline. Surprisingly, canopy cover, a common measure of urban forest health, may actually increase with development as many remnant trees though in decline survive for decades and natural forest disturbances such as fire are reduced allowing trees including exotics to become established. In addition, despite the cover, homeowners continue to plant trees in these forested developments. Efforts in tree conservation must focus on forest conservation and attempt to maintain intact forests islands at least 0.6 acres in size and with an area to perimeter ratio of 0.5 or greater.

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