Fire leaves a vivid record of U.S. forest management practices on tree trunks
Aug. 17, 2005
By Kelee Riesbeck
When forest fires rage in the western United States during the summer's driest months, U.S. forest service administrators can blame it on the management practices of the past, says researcher Ryan McEwan.
"The fire suppression campaign of the past allowed a build-up of fuel (brush) in the dry western U.S., which is why fires get out of control so easily," he says.
McEwan and his colleagues are working on ways to prevent such disasters by reconstructing the history of forest fires in the eastern U.S. deciduous forests. By starting as early as when Native Americans inhabited these forests, McEwan aims to compare the historical fire record with today's forest conditions to help inform the way forests should be managed.
Native Americans used fire as a tool to flush out game, clear plots for agriculture and home sites, and to encourage new growth on the forest floor. Indigenous North American populations declined because of diseases introduced by Europeans, however, and fewer fires were set. This created a "fire history gap," McEwan says. After this gap, more Europeans arrived and began clearing much more land than the North Americans had cleared, resulting in the "almost total denudation of states like Ohio by the 1920s-1930s," says McEwan, a doctoral candidate in environmental and plant biology who is advised by Professor of Forest Ecology Brian McCarthy.
McEwan uses dendroecology, or the study of the tree rings, in combination with the study of fire scars from fallen eastern deciduous tree samples to recreate the eastern deciduous forest's fire history record. Fire scars show up as a black mark within a specific tree ring on a cross-section of a downed tree. Tree samples are like calendars, he says. By looking at a cross section of a fire-resistant mature tree like the Bur Oaks found in the Central Kentucky Bluegrass region, McEwan can determine not only a tree's age but in which years the tree experienced a large amount of growth (indicated by a wide tree-ring), a small amount of growth (indicated by a tightly packed tree-ring record), and when it survived a forest fire.
McEwan's research shows that eastern deciduous forests not only survived fires but were structured by them. These fires destroyed brush and less fire-resistant maples, which produce less nutritious seeds for the wildlife. This provided more sunlight for oaks, the seeds of which are highly nutritious and better able to sustain animals in the forest. It's now well known that historical fires in the west helped to prevent wildfires by burning fire fuel like brush, says McEwan, whose research has been funded by several entities, including Ohio University, Sigma Xi and the Ohio Biological Survey.
Today forest managers are beginning to take another look at using fires to sustain some of the remaining oak forests of the east, the student notes. As oak acorns are more nutritious for wildlife and because oak is a desirable homebuilding product, setting fires in some areas of the landscape could allow mature, fire-resistant oaks to flourish, he says.
But forest managers in the dry, western region must act soon, McEwan warns.
"Watch the news this summer and you will see helicopters dumping fire retardant into forest surrounding small western towns," he says. "If managers had used fire as a tool, in accordance with an understanding of historical fire regimes, in many cases this situation could have been avoided entirely."
Kelee Riesbeck is a freelance writer for the Office of Research Communications.