|Abstract or Summary
- 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.