"Fire changes the urban forest and considering fire when urban foresters make planning and management decisions will help to maintain the long-term stability of the urban forest," says Dr. Robert E. Loeb, a biologist and director of Academic Affairs at Penn State Dubois.
Something as simple as ensuring that off-road fire fighting equipment is available to urban forest firefighters can protect the forest and enhance the value of the forest for the public, Loeb reported in a recent issue of Arboricultural Journal.
Loeb compared the histories of undeveloped forests within parks in the New York City area with an old growth, well-studied urban forest in Cleveland, Ohio. The Cleveland forest has no history of forest fires and has changed little in tree density or composition since 1935 when records on the forest began. Fires in the New York City forests have contributed to an increased tree density of specific species.
"When a fire occurs in the thousands of forested acres in New York City's undeveloped parklands, the trees are beyond the reach of city water and road systems," says Loeb. "These fires are usually brought under control before buildings or mature trees are damaged but the fires destroy saplings, seedlings, herbs and the humus layer of the soil."
Using tree maps created under New York City Parks Commissioner Robert Moses during the 1930s, Loeb looked at Seton Falls Park and Mishow Marsh Watershed, Hunter Island, Pelham Bay Park both in The Bronx, N.Y.; and Turtle Pond Watershed, Alley Pond Park, Queens, N.Y. In Cleveland, he looked at records made by Arthur B. Williams in 1936 in North Chagrin Reservation, since renamed the A.B. Williams Woods.
Loeb compared the total tree composition in the forests finding that all New York forests studied had greater abundance of black cherry, white ash, black birch, sweet gum and oak than were found during the 1930s. Some New York forests had greater density of tulip, hickory, beech, red maple and black locust while others had decreased density of these species. Only flowering dogwood and hemlock decreased overall since the 1930s, however both these species are subject to recent insect and disease infestations. Notably absent were American chestnut and American elm, former dominant species that have been decimated by disease throughout the United States.
Thirty sample plots were counted for saplings and seedlings in each forest, of which five were burned in Seton Falls Park, 15 were burned in both Turtle Pond and Mishow Marsh watersheds and none were burned in A.B. Williams Woods. Loeb found that sassafras increased density in burned areas and that white ash, smooth sumac, sweet gum, red maples, flowering dogwood, tulip and black locust did not occur in areas that had burned. Sassafras increases in burned areas while black cherry, oaks and sassafras sprout from the roots of previous trees after a fire.
In the Cleveland forest, the only tree with a change in density was the sugar maple, however this increase may be explained by the report that there was a 1 to 250 ratio of beech saplings to maple saplings in 1935. Little saplings become large trees with the passage of more than 60 years and fire has not touched this forest.
"Williams contributed to the protection of the old growth forest by regularly explaining the value and importance of the Woods to the public through tours and the establishment of an environmental education center," says Loeb. "Pathways were well defined and signs of off-trail transit are rarely observed." Unlike the New York City forests, public interest and the lack of fire have helped preserve the stability of the A.B. Williams Woods.
"Reducing the frequency and severity of fire is critical if maintaining a diverse urban forest is important," says Loeb. "A first step would be to provide appropriate fire fighting equipment and training." The Penn State research also suggests involving the public in the forests through outreach programs about fire prevention and educational tours that teach the value of the forests. Other approaches are to remove campfire sites and hearths from the forests, provide fireproof erosion protection devices, create preferred pathways and block alternative paths and to employ fire-safe landscaping when replanting in inner-city forests.