Graduation date: 1982

Graduation date: 1989

Graduation date: 1982

Graduation date: 1987

Graduation date: 1983

Graduation date: 1987

Graduation date: 1984

Graduation date: 1967

The effect of defoliation intensity and season on Douglas-fir growth were studied in three replications in the Siuslaw National Forest during 1988-1990. Four intensities of defoliation were applied once in either spring or summer 1988. Stem diameter and canopy area were linearly inversely proportional to the level of defoliation. Defoliation intensity did not affect height growth (P > 0.05). Greater losses in height occurred when seedlings were defoliated in spring than in summer. No differences in predawn and mid-day xylem water potential were observed between trees defoliated in summer or spring 1988. However, in 1989, 25% defoliation reduced mid-day moisture stress whereas 50 and 75% defoliation increased mid-day moisture stress (P < 0.05). Effects of defoliation on length, width, and area of dominant and subdominant twigs as well as number of twigs were separated into different whorls. As indicated by the sharp slopes of the response surfaces, spring defoliation affected seedlings more (P < 0.5) than summer defoliation. No season or intensity effects (except second whorls) on area of dominant twigs were carried over to 1990. No effects (P > 0.5) of season or intensity on twig width were observed in 1990. Subdominant twigs were generally more sensitive to defoliation than dominant twigs. Greater losses (P < 0.5) in area of subdominant twigs occurred when seedlings were defoliated in spring than in summer. Similar to area, length of twigs continued to respond to defoliation intensity in 1990. Length and width of dominant and subdominant twigs were smaller for spring compared to summer defoliated trees. Number of twigs were linearly inversely proportional to the level of defoliation intensity in 1989. Intensity did not affect number of twigs in 1990 except second whorls. No effect of defoliation intensity and season on new whorls was detected. / Graduation date: 1992

Sod-seeding techniques offer graziers a convenient way to introduce superior grass cultivars into underproductive permanent pastures. Production loss and erosion are minimized. In conjunction with improved grazing management and fertilization, renovation can significantly improve yield and quality of pastures. Existent vegetation must be suppressed prior to introducing new cultivars. This study was conducted on two non-irrigated pastures near Corvallis, Oregon, one dominated by annual grass species and the other by perennial grasses and clover. A split-plot design with four replications on each site was used to compare three seeding methods and either (a) two herbicides following close mowing or (b) close mowing alone. The seeding methods were drilling with an Aerway Seedmatic chisel-type drill, drilling with a Tye double disc drill, or broadcasting seed followed by harrowing. Glyphosate and paraquat were the herbicides used for vegetation suppression. Effect of fertilization was compared to no fertilization. Sod-seeded perennial ryegrass had minimal establishment at the site dominated by annual grass species. An inadequate amount of time was allowed for germination of annual grass seeds before herbicides were applied. Annual grass seedlings suppressed the newly sod-seeded perennial ryegrass. Sod-seeded perennial ryegrass was successfully established at the site dominated by perennial species within one year after planting. Broadcasting followed by harrowing of seed resulted in a higher percentage of perennial ryegrass than either the Seedmatic chisel drill or Tye double disc drill. Sod-seeded perennial ryegrass did not contribute significantly to yield until one year after planting. Glyphosate gave better control of the species present before planting leading to a higher percentage of perennial ryegrass and improved yield compared to paraquat or close mowing alone when seed was broadcast and harrowed. Fertilization of unseeded plots increased yield but was not cost-effective. / Graduation date: 1994