The Transfer of Heat and Hydrophobic Substances During Burning

Abstract

Wet and dry sand was tested for water repellency, after burning pine litter (Pinus coulteri D. Don). Four conditions were studied: a burn of 25 min over dry or wet sand and a burn at 5 min over dry or wet sand. The thickest and most intense water‐repellent layer was produced by a 5‐min burn over dry sand. Although organic materials were translocated deeper in the dry sand during the 25‐min burn (down to 4 cm), some of the water repellency was destroyed in the upper 1‐cm layer. In wet sand, water repellency was concentrated in the upper 0‐ to 1.5‐cm layer. The translocation of hydrophobic substances and resulting water repellency depends on changes in their polarity and oxidation state. Relationships developed for fire over a dry soil may not adequately account for movement of organic substances in a moist soil. These results suggest prescribed burning should be done when the soil is moist on areas where water repellency is a problem.