Which type of fuel includes all combustible materials lying beneath the surface?

Ground fuels comprise all combustible materials that are found beneath the surface of the forest floor. This includes substances such as roots, decaying organic matter, and other materials that may be hidden from view but still contribute to the fire's spread and intensity. Understanding the characteristics of ground fuels is critical because they can smolder and burn for an extended period, often leading to deep soil heating and potential effects on soil and vegetation health long after the surface fire has been extinguished.

In contrast, aerial fuels refer to materials that are above ground, such as branches, leaves, and foliage that can influence the fire's behavior by promoting vertical fire spread. Surface fuels involve materials found on the ground that are readily ignitable and can easily combust, while ladder fuels are fuels that provide vertical continuity between surface fuels and aerial fuels. Each type of fuel plays a distinct role in how a wildfire behaves, but only ground fuels specifically capture all combustible materials beneath the surface.