Date of Award:

1999

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Natural Resources

Department name when degree awarded

Fisheries and Wildlife

Advisor/Chair:

John A. Bissonette

Abstract

The Ethiopian Wildlife Conservation Organization has little information on the lll extent and ecological determinants of plant species composition and distribution in Omo National Park. Elsewhere, the determinants of African savanna vegetation dynamics have been the focus of numerous investigations, yet our understanding of the hierarchical nature and relative importance of any relationships remains very general. As well, our ability to derive predictions about vegetation responses is limited to extreme generalizations. African savanna landscape ecotones have received even less attention than most landscapes. In this dissertation, I test hypotheses about plant species distribution-determinant relationships in Omo National Park, a park that occurs in a landscape ecotone. Determinants investigated include rainfall and topographic-related gradients in soil moisture and edaphic conditions, and availability of soil constituents. Rainfall pattern was determined from meteorological data and multiple linear regression. Topographic attributes were measured in the field. Availability of soil constituents was determined by evaluating and using spatial interpolation models using limited soils data, and construction of surface soil maps. Hypotheses were tested using the simple and partial Mantel tests of matrix association.

Results demonstrate that predictions using spatial interpolation models based on limited, coarse-scale soils data are accurate and reliable when compared with more data-intensive investigations. Results using spatial statistics indicate that the nature of the spatial pattern of perennial species associations is a monotonic spatial trend. The distribution of perennial species associations is influenced both directly or indirectly by rainfall. An indirect rainfall relationship occurs when there is variability in topography. The means of influence by the topographic-related attributes is unclear despite significant Mantel results. In the topographically invariant portion of the study area, however, exchangeable sodium and magnesium concentrations appear to indirectly influence the distribution of perennial species associations. Strength and ordering of the vegetation-determinant relationships varied depending on the type of perennial species association type being investigated. Differences in species range of tolerance and rate of change in species association, depending on association type, landforrn, and parent material differences, account for the nature of the vegetation-determinant relationships, the ordering of the determinants, and variability in responses.

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