Why is duff not a major influence on fire spread?

The assertion that duff is not a major influence on fire spread primarily hinges on its typical moisture content. Duff, which consists of partially decomposed organic matter found on the forest floor, can retain moisture from the surrounding environment. When duff is moist, it requires a greater amount of heat to ignite and sustain combustion. This moisture reduces the likelihood of duff becoming a significant fuel source in the spread of fire since a dry, easily ignitable fuel would be more effective in propagating flames.

The other factors contributing to fire dynamics, such as combustibility, heat production, and ignition resistance, are less relevant in this context. While duff can burn if sufficiently dried out, its moisture content plays a crucial role in limiting its ability to influence the rapid spread of fire. Therefore, the moisture factor is the most salient reason for duff's role in fire spread dynamics.