Rare wetland fires can help, hurt habitat

Severe wetland fires -- so rare they occur only a few times per century -- also can change vegetation and patterns of water movement, said Adam Watts, who led the study as a post-doctoral researcher in the UF/IFAS School of Forest Resources and Conservation.

During a smoldering fire, wetlands can become deeper if the fires burn muck or peat soils.

"In some cases, this could help improve habitat for endangered species, such as wood storks," said Watts, now a research assistant professor at the Desert Research Institute in Reno, Nevada. But wetland fires can also kill many trees and shrubs, causing changes to the vegetation that returns.

Fires in wetlands come from adjacent, higher, generally drier land. The blazes in the uplands can be a result of lightning strikes or human causes, such as stray cigarette butts.

While he worked at UF/IFAS, Watts examined the effects of smoldering wetland fires in the Big Cypress Preserve in South Florida. Unlike flaming combustion, smoldering fires remain in the ground and can last for days or even months.

Watts and his colleagues, all of whom were UF/IFAS researchers at the time of the study, hypothesized that wetland fires can change how water is stored and distributed in small wetlands and adjacent areas.

"Our work illustrates some of those changes," said Watts, who led the study, published in the journal Freshwater Science.

For example, fires in wetlands with deep organic soils can increase the amount of time that a spot in a wetland will remain under water. Organic soils are made up primarily of decayed plant matter.

"This concept is important because some plants can tolerate flooding for longer periods that others," Watts said. "And when a fire consumes some of the soil and make the soil surface lower in a spot, it can experience flooding for longer and change the type of vegetation that will grow there."

When drought strikes wetlands made up of largely organic soils, they sometimes dry out enough to burn during fires. Recent examples in Florida include the Okefenokee and Levy Prairie fires in North Florida in 2011, said Watts.

"Smoldering fires can burn away soil -- sometimes multiple feet of it -- and those fires could change the way that water is stored or moves through the landscape," Watts said.

In Florida, nearly all ecosystems -- even wetlands -- catch fire at some point. Depending the fire's severity, the fire's effect on wetlands can vary quite a bit, Watts said. When soils are moist and the amount of vegetation available as fuel is low, fires can remove dead plant matter and leave many plants alive, and they grow back. In a drought, fires can burn hot or long enough to kill trees and shrubs.

"This is not always bad, since some wildlife could benefit from the more open habitat that can result," Watts said. But land managers worry when wetland fires produce dense smoke, especially if roads or communities are nearby.