| Summary: | Since the late 1880's western juniper has expanded in range and
increased in density in sagebrush-bunchgrass, riparian, and forested plant
communities of the Pacific Northwest. Succession to western juniper
woodland has been shown to reduce the productivity and diversity of the
understory component, result in concentration of soil nutrients beneath juniper
canopies, and reduces soil moisture storage. This study assessed understory
plant succession, soil nitrogen (N) cycling, litter decomposition, and soil
moisture availability following cutting of a western juniper woodland on Steens
Mountain, Oregon.
Cutting of western juniper reduced below-ground competition for water
and N, increasing soil moisture storage and N availability for understory
species. Leaf water potentials were less negative, and N concentration and
biomass in understory plants were greater in the cut treatment. Understory
species responded to improved growth conditions with increased cover,
biomass, density, and diversity. In 1993, total understory biomass and
canopy cover were 870% and 300% greater, respectively, in the cut treatment
than the uncut woodland. Understory succession was dominated by plants
present on the site prior to cutting. Results indicated initial that bunchgrass
densities of 2 plants/m2 were sufficient for perennial grasses to dominate
following juniper cutting. Juniper cutting is an effective method for restoring
the understory component in sagebrush rangelands that are currently
dominated by western juniper woodland.
Nitrogen availability was greatest in cut-interspace locations the first
year following treatment and in cut-duff locations in the second year.
Nitrification was lowest in cut-slash and woodland-duff locations, areas
receiving fresh litter inputs and experiencing lower temperatures than
interspace (cut and woodland treatments) and cut-duff locations.
Decomposition of juniper litter was two times faster in the cut treatment,
however the release of litter N occurred earlier in the woodland. Large inputs
of N poor litter from cut juniper slash were hypothesized to have increased
microbial demand for N, resulting in immobilization of litter N. Immobilization
of litter N may be important in conserving N on sites following cutting. === Graduation date: 1997
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