Prescribed Burns

A climax ecosystem is one that has reached a stable, mature condition. When a forest is clear cut, for example, it takes decades for the competing saplings to grow back to mature height and shade out the sun-tolerant understory plants that sprang up after the cut. Upland pinelands, prairies, and other ecosystems are considered ‘fire-climax’ ecosystems. These are ecosystems in which periodic wildfires maintain that stable, mature condition. Fire-climax ecosystems have existed for thousands of years and the natural inhabitants are so well adapted to the effects of these fires that some cannot survive for long without them. This fire regime has created some surprisingly diverse ecosystems. Some references state that the longleaf pine forests of the southeastern United States are the most diverse ecosystems in the world after tropical rainforests and coral reefs.

As an alternative to wildfire, foresters write a ‘prescription’ for a controlled burn that designates the boundaries of the burn, evaluates the amount of flammable material in the area, and considers wind speed and direction and other site and weather conditions. They create fire breaks as needed and provide appropriate numbers of trained staff to keep the fire under control and prevent excessive smoke. Regular prescribed burns provide the benefits of natural wildfires but with much lower risk to people and property.

Prescribed burn in progress

The University of North Florida conducted controlled burns for most of the history of the campus. Burns stopped in the 1990’s and resumed in the pine forests shortly after the Sawmill Slough Preserve was designated in 2006. Prescribed burns have many benefits, including reducing the dense understory of saw palmetto, opening the tree canopy density, providing a better habitat for a resident population of threatened gopher tortoises, and encouraging the spread of native wildflowers. A few wildflowers, like the yellow crested orchid, flower for a few years after a prescribed burn, disappear, and return again with the next fire.

A prescribed burn is an interesting event to see. Animals flee the approaching flames or duck into a nearby gopher tortoise burrow. Most of the time, the flame is low as it runs over the pine needles. However, saw palmetto and Carolina jessamine contain volatile oils. When the flames reach them, they flare up like torches. While pines and old oaks tend to survive the burns, pineland ‘invaders’ like sweet gum and red maple are killed. Ashes from the fire release minerals that help fertilize the plants that are recovering. Shrubby plants like gallberry, running oak, and saw palmetto are burned back to the ground but sprout up again and recover rapidly. Ferns, wildflowers, and native grasses may resprout from the ashes within a week. Wildflowers may be found in bloom again a month after the fire.

When the flammable material is kept under control by regular prescribed burns, the burns produce less heat and smoke. It is less damaging to the ecosystem and less bothersome to human neighbors. When neglected, the flammable material builds up. A hotter, more the intense fire may kill mature pine trees and produce large amounts of smoke.

For more information please visit Burning the Sawmill Slough Preserve.