44 



which had more small spots with broken soil surfaces, and more unstable 

 soil in drainage channels and slopes than the more lightly grazed pastures. 

 Yet in general this pasture showed no conspicuous evidences of accelerated 

 erosion. 



A supplementary study on nine 1/40-acre plots found no significant 

 surface runoff of precipitation or erosion from either close grazing, moder- 

 ate grazing, or nonuse (10) although unsatisfactory soil-surface conditions 

 with local movement of soil particles developed on the closely grazed 

 plots. The infiltration capacity of the soil was significantly reduced as 

 compared to the moderately grazed plots, and very significantly reduced 

 as compared to the ungrazed plots. Still, the infiltration capacity of the 

 soil on all plots remained high enough to absorb the rainfall that occurred 

 during the study. This finding helps explain the relative scarcity of 

 conspicuous soil erosion on rolling foothill lands closely similar to the 

 San Joaquin Experimental Range. 



The usual patterns of precipitation and plant growth in this locality 

 also helps the explanation. Characteristically, the first fall rains are 

 fairly gentle. Germinating and growing quickly, dense stands of annual 

 plants, particularly the flat rosettes of filaree, form a protective cover 

 over much of the soil surface. Winter rains are seldom torrential. Con- 

 sequently, under the usual rainfall pattern the porous soils of granitic 

 origin absorb most of the precipitation as it falls. Where soils are less 

 permeable or the annual-plant cover is scant, however, the hazards of 

 runoff and erosion are greater. 



A range unit with satisfactory soil-surface condition will have a layer 

 of old litter on most sites in all parts of the area. In general, the moist 

 ground in winter will feel soft and springy under foot. The thin layer 

 of decomposing herbaceous material and the relatively thick, even, and 

 vigorous growth of green plants will leave almost no bare soil apparent 

 to observers walking or riding over the range during the winter. These 

 conditions will be found in all but the rare winters when weather condi- 

 tions are so severe that plant growth is very sparse regardless of past 

 utilization. 



As explained previously, moderate grazing will maintain a satisfactory 

 layer of litter over most of a range unit. Under this degree of utilization 

 the litter may be thin on limited areas of livestock concentration, such as 

 wet swale bottoms, but the soil surface on these sites will be stable, 

 though somewhat compacted. On ranges with an unsatisfactory layer 

 of old litter, a lighter degree of grazing will often be needed. How long 

 this lighter grazing must be continued to build up the litter on ranges 

 that have been closely grazed for a number of years is not known. It 

 has been observed, however, that where the reduction in litter is limited, 

 satisfactory conditions may be restored by light grazing during a single 

 year of heavy forage growth. 



RATING USE OF EACH YEAR'S HERBAGE 



The degree of grazing of the current year is rated from the amount of 

 unused herbage of that year. On foothill ranges utilization is best rated 

 at the time of the first fall rains to determine how much plant material 

 is left to provide dry roughage and promote new green growth during 

 the fall and winter. 



