Abstract 



Numerous studies suggest that ponderosa pine ( Pinus ponderosa Laws.) 

 should reduce mass erosion hazards on road fill slopes. A study, designed 

 with 3 replications of 10 treatments on 1/200-acre study plots, was con- 

 ducted to evaluate how well ponderosa pine survives, grows, and reduces 

 surface erosion on granitic road fills in the Idaho BathoUth. The study was 

 installed in 1968 and continued through 1972. Tree survival averaged about 

 97 percent after four growing seasons. Fertilizer increased planted tree 

 growth an average of 95 percent during the year of peak effect. Tree plant- 

 ing, coupled with straw mulch and erosion netting, reduced erosion an aver- 

 age of about 95 percent over 3 years. Planted trees alone provided surpris- 

 inglj^ large reductions in erosion, ranging from 32 to 51 percent. Planting 

 ponderosa pine at a spacing of 3 by 3 to 4 by 4 feet is recommended as an 

 erosion-control measure for granitic road fills in the Idaho BathoUth. 



