What general characteristic defines ground fires?

Ground fires are characterized by their burning primarily in the organic materials situated below the surface layer of soil, such as peat, duff, and decomposed organic matter. This type of fire typically does not involve flames reaching high into the air; instead, the combustion occurs at or just beneath the surface, leading to smoldering conditions.

While options discussing surface burning or canopy involvement might seem relevant, they do not accurately capture the nature of ground fires. Ground fires primarily smolder and can remain undetected until they spread to the surface, distinguishing them from other types of wildfires like surface fires, which largely burn at ground level, or crown fires, which invade the canopy. By focusing on the characteristics of ground fires, the correct answer emphasizes their unique behavior and effects on soil and organic layers, which sets them apart from other fire types.