Which of the following is classified as a type of fuel in wildland fire behavior?

Timber-Understory is classified as a type of fuel in wildland fire behavior because it consists of living and dead vegetation that can ignite and sustain a fire. This category includes tree canopy layers alongside shrubs and smaller plants that grow beneath them, all of which contribute to fire propagation. The moisture content, density, and arrangement of these fuels affect how a fire burns, its intensity, and its rate of spread.

In contrast, rock formations, wetlands, and sand dunes do not provide combustible material that would support the ignition or spread of fire. Rock formations are non-flammable, wetlands typically contain moisture that suppresses fire activity, and sand dunes primarily consist of soil and not organic material.