Date of Award:
Master of Science (MS)
Arthur H. Holmgren
A study of the flora of Leslie Gulch Malheur County, Oregon was undertaken to elucidate the relationships of the flora and of the endemic species in the flora, and to determine if these endemic species are restricted to their present distribution by chemical factors of their substrate.
A checklist of native plants and a description of the major communities was made and floristic relationships were studied.
Chemical and mineralogical tests such as emission spectrography, x-ray diffraction and cation-exchange capacity as well as physical tests such as particle-size distribution and gravimetric water content were performed.
The results of the tests gave no indication of any chemical factor which may restrict the distribution of plants. A zeolite, heulandite, is present in 'the ash-tuff which is the substrate for the endemic species Mentzelia packardiae Glad and Senecio ertterae Barkely. However, this would not restrict plant growth.
It was concluded that the distribution of the endemics Senecio ertterae Barkley, Mentzelia packardia Glad, Ivesia rhypara Ertter & Reveal, Eriogonum novonudum Peck, and to some extent Astragalus sterilis Barneby and Trifolium owyheense Gilkey is determined primarily by physical factors of their substrates, and that they are pioneer species which may be competitively excluded from normal sites.
Artemisia packardiae Grimes & ertter ined. is a species which is restricted by a diminishing relic habitat.
The flora of Leslie Gulch has been complicated by interaction of a northern mesic association and a southern xeric association.
The endemic species Mentzelia packardiae and Senecio ertterae are recent species which evolved from a southern Great Basin flora which has moved north with the retreat of the last ice sheets.
Ivesisa rhypara and artemisia packardiae are recent species which evolved from a northern flora which followed the retreat of the ice sheets north.
Grimes, James W., "The flora of Leslie Gulch Malheur County, Oregon" (1979). All Graduate Theses and Dissertations. 4293.
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