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. / Graduation date: 1992
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36321 |
| Date | 23 May 1991 |
| Creators | Karl, Michael G. |
| Contributors | Doescher, Paul S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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