Effect of a controlled burn on the thermophysical properties of a dry soil using a new model of soil heat flow and a new high temperature heat flux sensor

Abstract

Some fires can be beneficial to soils but, if a fire is sufficiently intense, soil can be irreversible altered. We measured soil temperatures and heat fluxes at several soil depths before, during, and after a controlled surface burn at Manitou Experimental Forest (southern Colorado, USA) to evaluate its effects on the soil’s thermophysical properties (thermal conductivity and volumetric specific heat capacity). During the burn the soil was heated to over 400°C at a depth of 0.02 m and to almost 100°C at 0.30 m. Relatively high temperatures persisted for several hours to days even over 1 m deep into the soil. At these intensities and durations significant changes in soil chemistry, structure, and nutrient cycling are likely. However, soil thermophysical properties, estimated before and after the fire with a new model of periodic heat flow in soils, were not significantly changed between the times shortly after sensor installation (October 2001) and 1 month after the fire (February 2002). Estimates of the soil thermophysical properties derived with the new model underestimate laboratory analyses performed on soil samples obtained after the fire. Also presented in this study are some of the first soil heat flux measurements made during a surface fire. Furthermore, data and analyses of the type discussed in this study should aid modeling studies of the soil thermal pulse associated with fire. The ultimate goal of this experiment was to provide tools to assist land managers in the use of prescribed fire to benefit ecosystems and to reduce the potential for harm by examining how the soil’s physical properties and different fuel amounts, geometries, and loading densities influence soil recovery and forest regeneration after fires.