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The Effects of Aboveground and Belowground Competition on Understory Species Composition in a Pinus ponderosa Forest

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The objective of this research was to test the hypothesis that water and nutrients, and not light, control understory plant species composition in a Pinus ponderosa forest in northeastern Oregon. The experiment was conducted as a split-plot experimental design with a 2 x 2 factorial analysis. To assess the effects of root competition of overstory trees on understory species composition, 20 plots (4 x 4 m) were trenched approximately 1.0 m in depth, and compared to 24 nontrenched plots. To increase light levels to understory vegetation, trees were thinned from 345 to 148 trees ha-1 in half of each block (2.5 ha) during the winter and early spring of 1986. Canonical discriminant analysis indicated that light accounted for the greatest environmental resource response among the treatments. The number of species (8) that increased in cover and density was 60% greater when tree root competition was reduced in the root-reduction treatment, versus 5 when tree canopy influences were reduced in the canopy-reduction treatment. Simple correlation showed that changes in species composition were significantly (P ≤ 0.05) related to both changes in aboveground attributes (light, midday air temperature, and soil temperature) and belowground attributes (soil water potential, pH, and nitrogen). Competition for limited resources, light, water, and nutrients, does affect understory species composition as evidenced by the response of individual species to increasing availability of these resources. For. Sci. 41(4):864-889.

Keywords: Competition; Pinus ponderosa; thinning; trenching; understory

Document Type: Journal Article

Affiliations: Department of Rangeland Resources, Oregon State University, Corvallis, OR 97331

Publication date: 1995-11-01

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Average time from submission to first decision: 62.5 days*
    June 1, 2016 to Feb. 28, 2017

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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