Fire needs three things to burn. Oxygen, fuel and heat. They make up what's called "the fire triangle." Take any of the three elements away, and a fire can't burn. Which element is taken away when water is dropped on a fire? Which is removed when a line is scraped around a fire?
What's a fuel? It's anything that will burn.
What fuels do you find in a forest?
Forests have plants at different levels - canopy, understory, and forest floor. So, the fuels in the forest will be at different levels, too. "Aerial fuels" do not in touch the ground. They are at least 1 meter (39 inches) above the ground. Aerial fuels could be branches, leaves, and bark still on the tree or tall bushes. "Surface Fuels" are on the ground. Here you'd find bushes, logs, stumps and fallen leaves, needles, branches, and cones. "Ground fuel" is anything that will burn below the surface fuels. That could be roots or rotting branches, leaves and needles.
Ground fires burn the ground fuels. These fires usually don't have much flame, they smolder. Surface fires burn the surface fuels. And, crown fires burn the aerial fuels. Crown fires spread from tree to tree and are the most destructive.
Here's another way fires spread: fuel ladders. Fuel ladders form when fuels at different levels touch. Fuel ladders move fire up from the ground into the tree tops.
Very hot facts:
Fires need 3 things to burn: oxygen - air; heat - something to start the fire; fuel - things that burn.
Fire is a natural part of the forest.
Prescribed fires imitate the good that natural fires accomplish.
Wind speed, wind direction, air temperature, humidity, and the moisture in fuels are measured before lighting a prescribed fire.