9. Plant (ponderosa pine), 1.5 by 1.5-foot spacing 

 10. Plant Cponderosa pine), 2.5 by 2.5-£oot spacing 



The seeded grass plot was included to provide a comparison of results to those of 

 earlier studies. Seeded trees were used because initial treatment costs for tree 

 seeding were less than those for tree planting. Fertilizers have been shown to produce 

 dramatic increases in growth of ponderosa pine on forest soils elsewhere (Tarrent and 

 Silen 1963; Cochran 1973). Road fills, especially those constructed from granitic 

 materials, should show even greater response to fertilization. It was felt that spacing 

 should be tested for effects on both growth and erosion. The spacings tested are 

 closer than those normally used for reforestation; however, this was deemed necessary 

 to minimize surface erosion on lonmulched plots. 



Other researchers have shown the advantages of plant cover, litter, or both for 

 surface erosion control on granitic soils (Packer 1951; Bethlahmy 1967). Bethlahmy and 

 Kidd (1966) found that straw mulch and netting were necessary to effectively reduce 

 surface erosion on road fills seeded to grass during the early establishment period for 

 grass. Because of a needle life of 2 years for ponderosa pine, the initial small-top 

 size for planted or seeded trees, and the nature of the litter produced by such small 

 trees, little erosion control was expected from planted trees, especially during the 

 early years after planting. Thus, straw mulches were used on some planted tree plots. 

 Mulches were expected to provide some additional benefit to tree growth by reducing 

 soil temperatures, helping to reduce soil moisture evaporation, and discouraging com- 

 petition from other species. 



Erosion plots were 1/200 acre in size with dimensions of 7.25 by 30,0 feet. The 

 long axis of each plot was oriented up and down the slope. Plots were constructed from 

 1- by 12-inch boards on the top and sides. A plastic- lined trough, 6 inches deep by 

 8 inches wide was placed at the downhill side to catch sediment. Inverted V-shaped 

 deflector boards were installed on the uphill side of each plot to prevent rocks from 

 rolling across the plots. Retainer boards were installed in the access strip between 

 plots to prevent downslope soil movement during plot servicing. Straw mulch 1 to 

 2 inches thick was held in place by galvanized chicken wire (erosion net) stapled to 

 the ground. Fertilizer used for planted trees consisted of one Treefeed Pellet (28-5-0) 

 per tree placed at root level 2 inches uphill from the tree. This application am.ounted 

 to 108.9 pounds per acre of nitrogen and 19.4 pounds per acre of phosphorus for the 

 trees spaced 1.5 by 1.5 feet apart and 40.0 pounds per acre of nitrogen and 7.1 pounds 

 per acre of phosphorus for the trees spaced 2.5 by 2.5 feet apart. 



Plots were constructed in April 1968, as soon as snowmelt permitted. Following 

 construction, straw mulch and erosion net were applied on appropriate plots. Trees 

 were planted and fertilized the first week of May, in accordance with the experimental 

 design. Unfortunately, trees were planted about 1 month later than the optimum time for 

 planting at the site because of the time required for plot preparation. The 2-0 plant- 

 ing stock, which was obtained from the Lucky Peak Nursery near Boise, Idaho, was derived 

 from local seed sources. Appropriate plots were seeded to grass and trees in October 

 1968. Grass species mixed in equal proportions were seeded by a cyclone seeder at a 

 rate of 50 pounds per acre. Species used in the study were Topar pubescent wheatgrass; 

 Tualatin oatgrass, Manchar smooth bromegrass, crested wheatgrass, and intermediate 

 wheatgrass. The straw mulch was removed before applying seed and replaced immediately 

 after. This procedure helped assure consistency in erosion measurements over time 

 during preceding time periods, but would not be followed in production operations. Tree 

 seed, treated to reduce rodent losses, was applied at a rate of 2.5 pounds per acre, or 

 275 seeds per plot. Seeds were hand placed through the mulch on each plot to assure 

 contact with the soil surface and to provide proper spacing. 



6 



