Graduate Thesis Or Dissertation

 

Ecological relationships between cervid herbivory and understory vegetation in old-growth Sitka spruce-western hemlock forests in western Washington Public Deposited

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  • The relationships between black-tailed deer (Odocoileus hemionus columbianus) and Roosevelt elk (Cervus elaphus roosevelti) herbivory and understory vegetation in unmanaged forests in Olympic National Park were studied from 1985 - 1989. From 1985 to 1986 I studied the impact of cervid exclusion on shrub, fern, and forb forage quality, tannin content, tannin astringency, shrub morphology, and shrub standing crop biomass, in old-growth and seral forests. Long-term protection from cervid herbivory had little effect on forage quality, tannin content, or tannin astringency. However, herbivory reduced leaf area, leaf weight, and plant standing crop biomass. From March 1987 through March 1989 I measured the amount of cervid herbivory in the understory of old-growth forests, and the effects of that herbivory on herb, fern, and shrub biomass, production, and nutrient content. The amount, timing, and impacts of cervid herbivory varied among understory plant communities, plant species, and years. Forage biomass, production, herbivory, and the influence of herbivory, were greatest in areas with grass-dominated understories. In those sites, production was either stimulated or not affected by herbivory, and herbivory altered plant structure and nutrient content such that foraging efficiency was improved during both summer and late winter. In sites with a forb-moss herb layer, biomass, production, and herbivory were less. Although herbivory either stimulated or had no effect on production in forb sites, it had no effect on forage nutrient content or structure, and thus did not impact foraging efficiency. The effects of long-term exclusion of ungulates in the study area indicated that soon after exclusion, grass-dominated understories disappear. Thus, cervid herbivory was found to influence understories in old-growth forest on several spacial and temporal scales. In the short-term, cervid herbivory improved forage structure and nutrient concentration in grass dominated understories. In the long term, cervid herbivory maintained grass dominated patches within the system. On both temporal and spatial scales, the net result of cervid herbivory was the creation of a more favorable foraging environment for both deer and elk.
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