Which materials are classified as ground fire fuels?

Ground fire fuels typically consist of materials that lie on or close to the surface of the ground and are capable of sustaining a fire. Small twigs, leaves, and decomposing needles fit this definition well because they are fine, combustible materials that are usually found on the forest floor or in similar environments. Their small size allows them to ignite quickly and burn efficiently, contributing significantly to fire behavior, especially in the early stages of a fire.

In contrast, logs and branches, while also combustible, are generally considered more significant fuels that can contribute to larger fires rather than the surface-level ground fires. Heavy debris and soil typically don't support the propagation of fire as they contain too much soil or moisture. Freshly cut grass and sod can ignite, but their moisture content and compact nature make them less effective as ground fire fuels compared to the dry, fine materials mentioned in the correct answer.