Date of Award:

1995

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Natural Resources

Department name when degree awarded

Rangeland Resources

Advisor/Chair:

David A. Pyke

Abstract

Biomass, tiller numbers, flowering, and genet survival were accessed for the rhizomatous Elymus lanceolatus ssp. lanceolatus and caespitose E. l. ssp. wawawaiensis growing in mixtures with a range of densities of each taxon. Models of aboveground biomass of each taxon as a function of mixed densities were used to calculate competition indices. Tiller numbers and biomass of ssp. lanceolatus were higher than those of the caespitose taxon in the first year, but declined in the second year, while biomass and tiller numbers of ssp. wawawaiensis changed little. All tillers of ssp. wawawaiensis emerged in autumn; tillers of ssp. lanceolatus emerged from autumn through late spring. The rhizomatous taxon better exploited open resources in the first year; ssp. wawawaiensishad slower growth, but its production of many tillers early in the season may allow it to quickly exploit seasonally variable conditions of semiarid environments. Decline in flowering at higher densities and in the second year was more pronounced than that of biomass and tiller numbers. Genet survival was high and similar for both taxa. Substitution rates indicated ssp. lanceolatus was the better competitor in both years. In the second year, the two taxa differed somewhat less in substitution rates. A greater overlap in resources used by the two taxa was indicated. Subspecies lanceolatus experienced greater intensity of competition. Substitution rates and relative efficiency index indicated ssp. lanceolatus was the greater competitor between early and late spring, when overlap in resource use was greater. Another experiment addressed advantages of clonal foraging of ssp. lanceolatus in exploiting soil nutrient patches. A foraging response was found in the rhizomatous taxon, with greater numbers of closely spaced tillers in high-nutrient patches adjacent to the main clone, but root biomass in these patches, and aboveground biomass of the clones, indicated that both taxa accessed nutrients in the patches, but ssp. wawawaiens is used only root growth. The taxa were similar in their tolerance of low levels of soil nutrients. No difference among genets in degree of foraging response, and no relationship between degree of foraging response and fitness when nutrients are patchy were found. Subspecies lanceolatus did not show such a foraging response to high neighbor densities in mixed-density plots. Instead, rhizome lengths were reduced by higher neighbor densities and in the second year, by reduced resources overall.

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