Fire effects and short-term changes in soil water repellency - Mt. Carmel, Israel

The Mediterranean ecosystem of the Carmel Mountain ridge in Israel is subjected to an increasing number of forest fires of various extents and severities due to intense human activities in the region. On 8 April 2005, a low-moderate severity forest fire occurred at the northwestern part of the ridge and burned more than 150 ha of natural vegetation. Soil water repellency (WR) is a property usually modified by the litter and soil organic matter combustion as a consequence of fire, which has implications for the hydrological balance in the affected soils. A field study was conducted with the following objectives: 1) to investigate in situ WR changes at three soil depths as a consequence of the fire, 2) to evaluate the short-term evolution of WR under field conditions, and 3) to study the relationship between pre-fire vegetation type and slope aspect on the persistence of WR in the burned area. Soil WR was measured by the Water Drop Penetration Time (WDPT) test. Measurements were conducted monthly at 31 field sites within the burned area over a period of seven months (April 2005-November 2005), and compared to adjacent unburned areas. Soil WR measurements included more than 3400 WDPT tests at soil surface and at 5 and 10 cm depths. The results indicate that fire induced WR in previously wettable soils exhibited high levels of persistence at the soil surface during the first six weeks after the fire, while at 5 cm depth WR persistence was lower. At 10 cm depth soil was mostly wettable. After six weeks the frequency of WR occurrence diminished at the soil surface and at 5 cm depth. In addition, WR was found to be highly related with the pre-fire vegetation type and with slope aspect.