Physical Science and Research

Fire Behavior


Watch how quickly wildfire moves through this clip of the boreal forest burning near King's Creek, in Alaska. (No spoken audio).

Wildfires are a regular part of summer in Interior Alaska, and are part of a healthy boreal, or northern, forest ecosystem.

Lightning starts many fires, such as this one at King Creek in 2004. While you watch this intense, five-minute clip of the fire, think about:

Vegetation before and after – Fires in the boreal forest are stand replacing, meaning they burn with such intensity that most of the vegetation is consumed.

Wind – Watch how the wind speed increases and shifts as the fire approaches the camera. Wind is critical in the fire’s behavior. Wind increases the fire’s rate of spread, flame lengths and intensity. Most fires in Interior Alaska are wind-driven.

Firebrands – These are embers, flaming or glowing fuel particles that the wind carries into unburned areas. You'll see a fireband lofted by the wind from the fire’s flaming front and into unburned "fuels" in front of the fire. As the flaming front approaches, the firebrand grows in size due to the wind and heat from the main fire. Firebrands are one way fire moves quickly across the landscape.

Torching trees – Black spruce trees quickly burn upwards from the bottom. Black spruce is a tree which is “born to burn.” Their physical attributes make them more prone to burn than any other tree in the boreal forest. Branches cover the trunk from top to bottom and twigs and limbs angle down, giving fire an easy ladder from the forest floor to the canopy. Their needles are covered with a waxy substance that burns well. Their cones are semi-serotinous, meaning that they're partially sealed shut and need heat to fully open. Black spruce is a torch, with its limbs touching the volatile duff of the forest floor and its crown of cones tipped to the sky ready to offer fire to the wind.