Graduate Thesis Or Dissertation
 

Effects of prescribed cattle grazing on reforestation in Oregon's southern Cascades

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  • Reforesting harvested lands in southwestern Oregon has been difficult because of low rainfall, high evaporative demand, and competitive understory vegetation. Herbicides have been a preferred method to control competing vegetation but herbicide use on federal lands was curtailed in 1984. As a result, interest in livestock grazing as a vegetation control method has increased. I used prescribed cattle grazing from 1986-1990 to assess effects on reforestation. Treatments were established on a low-elevation (670 m) site to evaluate seedling survival and growth of Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco.) and ponderosa pine (Pinus ponderosa Dougl.). Treatments were: a) seeding of palatable forage species (SU); b) seeding with grazing (SG); c) no seeding with grazing (NG); and d) no seeding or grazing, with paper mulch applied on Douglas-fir only (PM/C). Year 5 mortality among treatments ranged from 57 to 87% for Douglas-fir and 11 to 25% for ponderosa pine. Porcupine girdling and late-spring frost were major causal factors in ponderosa pine and Douglas-fir mortality, respectively. Competition from understory vegetation, browsing, and trampling were only minor causal factors in seedling mortality. Cumulative growth of both species was best in NG. Severe browsing by cattle in year 2 on SG resulted in reduced year 3 relative growth for ponderosa pine. However, year 2 browsing did not reduce long-term relative growth. By year 5, relative growth for ponderosa pine was greatest in SG and lowest in SU. During years 1-3, soil moisture availability was not enhanced on the grazed vs. ungrazed treatments. However, by year 4, xylem potentials and soil moisture indicated seedlings in SG were less water-stressed than those in SU. Reduced water stress probably resulted from reductions in roots of orchardgrass (Dactylis glomerate L.) because of defoliation. Sampling with a root periscope indicated roots were reduced for defoliated (SG) plants compared with undefoliated (SU) plants. Leaf area and root growth reductions were apparent mechanisms permitting increased soil moisture availability. These results suggested that prescribed cattle grazing can facilitate reforestation.
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file details KarlMichaelG1992.pdf 2017-11-01 Pubblico Scaricare