oak re-sproutPhoto by: Kevin Main

Results of a Prescribed Fire

Author: Kevin Main

A thin haze of smoke hung over the scrub in the still of the morning. “That haze is all that is left of yesterday’s fire,” said Kevin Main, Archbold Land Manager, as he looked across a blackened area of scrub at Archbold Biological Station. Across the landscape a scattering of logs and stumps continued to smolder, each producing a miniature column of smoke. “The fire’s over,” said Main, “but the work is just beginning. Soon this area will be buzzing with researchers. They will be measuring plant regrowth, the effect of the fire on scrub-jays and much, much more. This area will be colored with flagging and stakes marking research plots. There will buzzing overhead too, as drones take post-fire imagery. We try to capture as much data as possible,” he finished with a grin “And don’t you just love the smell of wood smoke?”

“Fire in Florida was once as common as summer thunderstorms. It was something you grew up with and learned how to deal with for your own benefit.” Main continued, “Indigenous peoples and early settlers to Florida could not control lightning-ignited fires. Instead, they worked with fire. They burned around their dwellings to reduce the chance of a destructive wildfire. They burned to open up the woods to better browse for deer and other game. Historically, vast areas burned every 2-3 years, originally ignited by lightning, then later supplemented by indigenous peoples. Florida wildlife use fire to their benefit too. Native species have evolved with those frequent fire conditions. As a result, when fire is removed, those fire-loving species disappear with it.”

“A scrub-jay might need to move away from a burned area for a short period of time, but soon that area is prime habitat for jays,” said Main. “The post-fire recovery of an area includes things like increasing populations of insects, and greater flowering and fruiting of scrub oaks. Insects and acorns are key elements of a Florida Scrub-Jay’s diet. Plus, the fire changes the structure of the vegetation, making it more open, which makes it easier for jays to spot potential dangers such as snakes and hawks.”

“We study the effects of fire because it is so important to rare and endangered species,” said Main. “After each fire we map the fire severity. We fly drones over the area to capture pictures that are then combined into imagery we can upload to our Geographical Information System (GIS) so a digital map can be created that shows patches that burned hot, not as hot, or not at all. Different species respond differently to that post-fire patchiness. One way we know this is because we have fire severity maps going back for 50 years.”

post-fire aerial

Caption: (Left) Post-fire aerial drone imagery taken just days after the fire shows burned and unburned patches. This patchiness is typical of most burned areas. Different vegetation types often burn at different severities. (Right) Map of different fire severities created using Geographical Information Systems (GIS) mapping. Grey indicates areas that completely burned while shades of green indicate areas that didn’t burn or only partially burned.

Back in the office Main pulled out some old blue-line maps and laid them on a table. “The earliest maps were made just walking around the burned area and noting severity,” said Main, as he pointed to hand-drawn lines on the map. “Then we started flying over the areas and taking pictures from airplanes. Now drones do all the work. Mapping accuracy has increased throughout the years. With drone imagery we can accurately map patches as small as 25 square meters.”

Main continued, “We have been using color photography to determine patches of fire severity for decades, but that may change in the future. Newer technologies, such as multi-spectral imagery and Laser Light Detection and Ranging (LIDAR) may give us even better accuracy and new ways of looking at the effects of fire.

“Some of the newer technologies may require a drone flight before the burn and then right afterwards to compare the difference. Post-fire flights must be conducted within a couple of days of the fire due to the quick resprouting of some species, especially grasses.”

“The evidence of fire fades over time. The ash washes into the soil, the dead stems of woody species fall to the ground and decay, and the general openness is slowly filled back in with taller and denser vegetation. It’s important to capture fire data directly after the fire, but we also need to continue to follow trends in spatial structure of the vegetation and in species populations for years, and even decades after fires,” said Main.

“We may understand some of the effects of fire after studying it for so long, but our expanding knowledge just brings up more questions. There are still many gaps in the data. We know very little about effects of fire on soil organisms, for instance,” said Main. “The more we learn the better we will be able to manage habitat in a way that is beneficial for all species. All those stakes and flagging set out after a fire are more than markers for research activity. To me they also indicate we are doing our part to make sure no species gets left behind.”