Long Description of Figure 4:

Diagram showing heat flux to the mineral soil where duff burning is the heat source. The litter is on the top layer; underneath that is the duff layer and then below that is the mineral soil. At the left side of the diagram, the heat source has burned the litter layer and the left edge of the duff layer is exposed and is burning also, underneath the litter layer from left to right at a rate of about 3 cm/hour. This leaves the mineral soil exposed to the heat source and there is high heat flux. When duff does not burn, it is a barrier to heat flow. There is no heat flux in the mineral soil under the unburned duff.