Changing Fires Mean Changing Forests

Blog By: Grace McLeod Check out Contributing Bloggers for Bio

Figure 1: Early regeneration just two weeks after a wildfire. Photo: Grace McLeod

Standing under the towering pines, it's hard to believe there was a wildfire here just a couple weeks ago. The needles of the lower tree branches are scorched brown, and the smell of wet charcoal sits heavy in the humid air after last night's rain, but the black ground is scattered with tufts of bright green grass almost as tall as my ash-scuffed boots. It’s amazing how fast fire-dependent ecosystems start to recover!

The pine forests of the southeastern US have evolved with frequent fire (Figure 1). Many of the species of plants and animals depend on the regular disturbance, and without it, the open pine forests, which are highly endangered and host incredible biodiversity, will start to change to denser, more hardwood dominated systems. 

I talk to people all the time who have lived in Florida their whole lives and had no idea wildfires were part of the natural ecology. “Fires happen out west, not in Florida!” The reason so many people are unfamiliar with the flammability of Florida might be because fire regimes have changed a lot in recent decades. 

Fire regimes are a complicated combination of the timing of fires, the extent of the area burned, and the fire severity or how much of the vegetation is consumed. Different ecosystems have their own historical fire regime that they depend on to stay healthy. Out west, that might be a big, high severity fire that consumes the whole forest every 300 years. However, in the pine forests of the Florida Everglades, low-severity fire every three to six years burns off the underbrush only, leaving most of the trees unharmed.

All around the world, changes in fire management policies and practices have shifted fire regimes from their historical patterns, and climate change is going to alter them even more. We don’t know yet how ecosystems respond to those changes, but in the Malone Disturbance Ecology Lab, we are trying to figure it out, and we’re doing it from space!

Using satellite imagery from NASA’s Landsat mission, we can see changes in the wavelengths of light that get reflected back by Earth’s surface, and from this, we can determine things like the greenness of the plants. Using this change in greenness, we can measure how long it takes ecosystems to recover after fires, since satellite imagery has been collected for decades. By pairing the satellite imagery with over 70 years of fire history records from Everglades National Park, we can literally look back in time and see how changes in things like fire frequency or climate can affect the time it takes for vegetation to recover. 

We expect that areas that have burned more in the past, like pine forests (Figure 2), will recover more quickly than places that have not burned much, like hardwood dominated hammocks (Figure 3). We also think that post-fire extreme climate events like drought or intense rain, which are expected to increase with climate change, will also slow forest recovery time because they cause stress for the plants. If you have ever been in grad school, you know how hard it is to be stressed all the time.

Figure 2: In the endangered pine rockland ecosystem of Everglades National Park, regular frequent fire maintains an open canopy and biodiverse understory. 

Photo: Grace McLeod 

Figure 3: In hardwood dominated ecosystems called “hammocks”, the dense canopy and mesic microclimate prevent fire spread except under extremely dry conditions. Photo: Grace McLeod