and 1972, respectively; reductions were significant at the 95 percent level in 1970 and 

 1972 and at the 90 percent level in 1971. Mulches caused a highly significant reduc- 

 tion in erosion that averaged about 95 percent of that occurring on the control plots 

 for the 3 years of data. 



Mulch effects would be expected to lessen over time as the mulch material deter- 

 iorates. Slight time trends did appear on most plots; overall average reductions in 

 erosion of 98, 94, and 92 percent were recorded for the 1970, 1971, and 1972 water 

 years, respectively. Similarly, the growth of trees on the unmulched plots would be 

 expected to provide greater erosion protection over time; however, no consistent time 

 trends were detected nor were block effects with respect to erosion, even though growth 

 averaged about 40 percent higher in the block located near the top of the road fill. 



14 



