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<br />Dymess, C.T., 1976, Effect of soil wettability in the high Cascades of Oregon: PacifIc <br />Northwest Forest and Range Experiment Station, Portland, Oregon, U.S.D.A. <br />Forest Service Research Paper PNW-202, 18 p. <br />Researchers studied fire-related in:1pacts over the course of six years following a wildfire in <br />the Willamette National Forest in Oregon. Vegetative cover consisted of lodgepole pine <br />stands, and soil textures ranged from loamy-sands to sandy-Ioams. Results showed a <br />considerable variation in water repellency with depth in burned area soils compared to <br />unburned controls. Similar to other studies, the surface inch of soil was usually wettable <br />after the fire, but deeper layers (1-6 inches) exhibited signifIcant water repellency. This <br />condition persisted up to fIve years after the fire, and was negligible by the sixth. Wettability <br />of lightly burned soils recovered faster than in heavily burned areas during the third and <br />fourth years. Results also indicated that infiltration rates in burned soils decreased three- <br />fold. The author notes that contact angle measurements of water repellency tended to be <br />more reliable and consistent than water drop tests. The use of a wetting agent (Aqua-Gro) <br />did little to alleviate water repellent conditions. <br /> <br />Emerson, W.W., and Bond, R.D., 1963, The rate of water entry into dry sand and <br />calculation of the advancing contact angle: Australian Journal of Soil <br />Research, v. 1, no. 1, p. 9-16. <br />This study used the rate of capillary rise of a wetting front in a vertical column of sand to <br />calculate the advancing contact angle. The method differs from a similar study by Letey, <br />Osborn, and Pelishek (1962), where the contact angle was calculated by measuring the <br />downward rate of wetting front infiltration. <br /> <br />Everett, R.L.,Java-Sharpe, B.J., Scherer, G.R, Martin, W.F., and Ottmar, R.D., 1995, <br />Co-occurrence of hydrophobicity and allelopathy in sand pits under burned <br />slash: Soil Science Society of America Journal, v. 59, no. 4, p. 1176-1183. <br />Researchers examined the development of allelopathic and water-repellent layers with <br />respect to fire under broadcast and piled slash. The paper cites research describing some <br />environmental conditions under which allelopathic substances form. These conditions are <br />similar to those which result in natural water repellency. Experimental plots consisted of <br />sand pits under slash. Following fire, water-repellent layers developed between zero and <br />eight-centimeter depths, and were up to eight centimeters thick. Moderate water repellency <br />was found to extend to greater depths and thicknesses than severe repellency. In addition to <br />water-repellent layers, slash burning produced underlying allelopathic layers. Researchers <br />observed a higher occurrence of water repellency and allelopathy under burned slash piles <br />than under broadcast slash. With respect to vegetation, alleiopathic effects appeared to be <br />limited to unsaturated soil conditions. Water-repellent layers were also found to decrease <br />seed emergence and development. The authors conclude that the experimental results imply <br />the potential for severe erosion following fires, due to the combined difficulty of vegetative <br />reestablishment, and complications with water repellency. <br /> <br />15 <br />