Autecology, reproductive ecology, and demography of Astragalus australis var. olympicus (Fabaceae) Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rn301498r

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  • The goal of this study was to gather information on the autecology, reproductive ecology, and population dynamics of Astragalus australis var. olympicus as a baseline for conservation strategies and to help explain its restricted range. Approximately four thousand individuals occurred in four known population centers in the Olympic Mountains, Olympic National Park, Clallam County, Washington. The populations were restricted to plant communities on calcareous substrates largely on southeast to southwest slopes above 1450 m. A. australis var. olympicus was absent from surrounding non-calcareous soils. Several characteristics of the physical environment and competition with associated plants influenced its distribution within calcareous sites. The relative importance of the physical environment and competition differed between plant community-types. Most plants produced a large number of flowers and ovules, but relatively few of these formed fruits and seeds. In decreasing importance, ovules in fruits were lost to predation, seed abortion, and lack of fertilization. The absolute percentages of these fates differed from site to site and year to year. Excluding insects by bagging flowers significantly reduced fruit set, but seed set per fruit was unaffected. After seeds were scarified to relieve dormancy, germination was sensitive to temperature and moisture availability, but some seeds germinated at environmental extremes. About 11% of the seeds damaged by predispersal seed predators (weevil larvae) remained alive and were released from dormancy. Population sizes declined at three sites from 1985 to 1988, and a transition matrix model based on the 1987-88 transitions between seedling, vegetative, and reproductive life history stages projected this decline to continue. Therefore, further monitoring is warranted. Seedling survival was low and populations were dominated by reproductive individuals. Predispersal seed predation, damage by introduced mountain goats, and drought may have contributed to the observed decreases in population sizes. Historical reasons and an affinity for calcareous substrates seem to explain the rarity of the taxon, but minimal reproduction and slow or negative population growth may help maintain its restricted range and low numbers.
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