Soil Heating Beneath Burn Piles: Effects On Soil Physical Properties and Water Chemistry in the Lake Tahoe Basin, CA.

Due to increased demands to reduce fuel loads, thinning followed by pile burning has become a popular treatment in the Tahoe Basin. However, concern has been voiced on burning within/or near stream environment zones. Our objective was to look at the effects of pile burning on soil physical and chemical properties in relation to overland surface water chemistry.  Six sites with a total of 24 burn piles were selected.  Burn piles were of varying size with sites divided between granitic and volcanic parent materials. Following the pile burns, we measured temperatures >450°C at the 5 cm soil depth that were maintained for ~12 hrs below 20 ft diameter piles.  Soil bulk density increased at all sites at the 0-5 cm depth.  Soil water repellency was high at the mineral soil surface and at 5 and 10 cm depths, but only when soil moisture was below 7 percent.  Repellency was substantially decreased at soil moisture contents of 7-10 percent.  Interestingly, we observed low infiltration rates on moist sites even though hydrophobic properties of the soil were greatly reduced.  This suggested that ash and fine material were clogging pores resulting in soil sealing.  Preliminary soil chemical analysis showed low to moderate changes in soil chemistry. There were slight increases in nitrate, phosphate, and sulphate in surface overland flows.  Additionally, water chemistry differed considerably between the volcanic and granitic sites.