The plot that absorbed the most water (1.05 inches) had a small clump of bunchgrass 

 (Stipa sp.) under which the soil was wettable enough to allow penetration of the wet 

 front. Pinemat raanzanita (Aratostaphylos nevadensis) was growing on another plot and 

 water was able to penetrate along some of its roots but this plot absorbed only 0.75 

 inch of applied water. 



The other four plots were devoid of live vegetation. Three of these plots absorbed 

 0.30 to 0.55 inch of water because water penetrated the water-repellent layer at one 

 or two points. There was no soil wetting whatsoever on one plot, and only 0.15 inch of 

 water was absorbed by its litter. 



Shrvhs. — Average runoff from the shrub plots was much lower that that from pine 

 plots because soils on such sites were less repellent. Although patches of dry surface 

 soil (Pattern 4) were found on most of the shrub plots after the water application test, 

 they were never extensive enough to cause runoff in excess of 0.75 inch. 



Most shrub plots were close to pine trees and had varying amounts of pine needles 

 on them. The litter on squaw carpet (Ceanothus prostratus), pinemat manzanita, and 

 bitterbrush (Purshia tridentata) plots usually contained more pine needles than shrub 

 leaves; apparently these species produce relatively little litter, but efficiently 

 trap pine needles. Tobaccobrush (C. velutinus) and greenleaf manzanita (A. patuta) are 

 more prolific litter producers, and pine needles were usually a minor constituent of 

 litter on plots dominated by these species. Because of the admixture of pine needles, 

 it is uncertain how much of the water repellency was derived from shrub species. How- 

 ever, the results suggest that shrubs rarely cause serious water repellency; on the 

 contrary, they increase infiltration into soil rendered water repellent by pine residues. 

 The prostrate shrubs, squaw carpet and pinemat manzanita, seem to be especially 

 effective in disrupting water repellency because their roots penetrate the surface soil 

 at many points. 



Of the five shrub species tested, tobaccobrush produced the highest average runoff 

 and probably had the most water-repellent soil. Greenleaf manzanita had the lowest 

 average runoff and the least repellent soil. Since the amounts of pine litter were 

 approximately equal on plots of both species, it appears that greenleaf manzanita is 

 superior to tobaccobrush with respect to infiltration and soil wettability. Since plots 

 of the other three shrub species generally had more pine litter than tobaccobrush or 

 greenleaf manzanita, no judgment could be made as to their respective potentials to 

 induce water repellency. 



Bare ground. — There was at least one bare plot in the vicinity of each litter- 

 covered plot. These 22 plots were devoid of live vegetation. There were pine needles 

 on some of them but usually these had been cast within the past year and rarely covered 

 more than 10 percent of the plot surface. Without exception, the soil surface was 

 highly absorbent if no litter cover was present. However, there were varying amounts 

 of water-repellent soils below the surface of 11 plots. 



Runoff from the 11 plots that had no discernible water repellency (wetting Pattern 

 1) did not exceed 0.16 inch of water, and six of them produced no runoff at all. Seven 

 plots had patches or pockets of dry soil above the wet front (Pattern 3); total infil- 

 tration during the 30-minute test varied from 1.65 to 1.89 inches on these plots. Two 

 plots had discontinuous water-repellent layers about 2 inches below the soil surface 

 (Pattern 5) and absorbed 1.18 and 1.52 inches of water. Two plots had continuous water- 

 repellent layers 1 to 2 inches below the soil surface (Pattern 7) and absorbed only 0.65 

 and 0.80 inch of the applied water. 



11 



