Date of Award:

1985

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Advisor/Chair:

Neil E. West

Abstract

Mined-land reclamation practices in shrub-steppe ecosystems can be augmented by planting seedlings of locally dominant shrubs, e.g., mountain big sagebrush. Dispersion pattern could affect sagebrush performance by influencing amounts of windborne snow, soil and litter which accumulate around shrubs and by influencing water withdrawal by roots. Mountain big sagebrush seedlings were planted in plots on a reclaimed coal strip mine in two dispersion patterns: singly and in clumps of four at the same overall density. Performance of mountain big sagebrush was monitored during two growing seasons. Measures included plant survival, end-of-growing season aboveground biomass, leaf water potential components, soil water potential, twig and ephemeral leaf survival and reproductive allocation. Most measures of performance were similar for single and clumped plants. However, single plants had a greater twig elongation rate than clumped plants, and roots of plants in clumps removed less soil water to 50 cm than roots of single plants. In order for shrub dispersion pattern to affect plant performance via differential snow, soil or litter accumulation, the plants would have to respond to the added resources, probably water and nitrogen. An experiment was conducted to test if a small extra increment of water and nitrogen would affect mountain big sagebrush plants. The same plant performance indices listed above were monitored. The added water and nitrogen, either alone or in combination, had no effect except on reproduction. In 1983, there was a significant water* fertilizer interaction observed for some of the reproductive metrics, while in 1984 there was a significant water effect. While a significant main effect of nitrogen was expected under the prevailing wet conditions, the large reservoir of soil nitrogen evidently provided sufficient nitrogen. Reproduction was more sensitive to added water and nitrogen resources than was vegetative growth. The nearly equal performance of mountain big sagebrush in the two dispersion patterns may have resulted from several factors. Water availability to the experimental shrubs was very high throughout the study due to abnormally heavy precipitation and to removal of weeds from the plots. During drier years, dispersion pattern may have greater influence on the shrubs.

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