Vertical arrangement

Vertical arrangement refers to the location of fuels relative to the ground and the fact that fuels often exist in different layers.

• Ground fuels – combustible materials such as organic soils, duff, tree roots and buried logs beneath the surface litter.
• Surface fuels – loose materials lying on or immediately above the ground such as leaves, short grass, stubble, low shrubs and down dead wood ranging from twigs to logs.
• Aerial fuels – materials well above ground in the crowns of trees and larger shrubs.
• Ladder fuels – fuels that reach from one layer of fuels to another, such as midstory trees or shrubs, snags (especially those leaning against other trees) or broken limbs that are hanging from a tree into another fuel layer.

Where fuels occur in multiple layers, the complexity and unpredictability of fire behavior increases, and crews must give more thought to how it affects their actions. Tactics to prescribe burn a prairie will be much different than those for a restoration burn in a savannah with dry leaf litter, slash from thinning the stand, dead standing snags and dry conditions in the tree crowns.