Water levels of Malheur Lake in southeastern Oregon fluctuate widely with seasonal and cyclic climatic changes. Seven years of severe flooding from 1978 to 1984 produced the highest water levels in recorded history and covered almost all marsh vegetation. Seven years of drought followed the flooding, and by 1992 the water level had dropped to the lowest point in nearly 60 years. A survey of vegetation colonizing the lakeshore as flood water receded was conducted from 1989 to 1992 to describe the reestablishment of marsh vegetation. Six transects were placed in three different ecological units of the lake. Frequency and cover data for each plant species were recorded. Recruitment from seed banks produced germination the first year of annual, mud flat species followed the second year by perennial emergent seedlings. The emergent seedlings generally did not survive the drought as water levels continued to recede. The seeds of introduced Eurasian species were distributed by wind, became lodged in the cracks of drying mud flats and then germinated following winter rains. The central ecological unit, fed by both the Blitzen and Silvies Rivers, did not show severe effects of drought and species of emergent vegetation grew without apparent signs of drought stress.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5857 |
| Date | 10 February 1994 |
| Creators | Spencer, Sherry Vlasta |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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