Graduate Thesis Or Dissertation
 

Conservation biology of Plagiobothrys hirtus (Boraginaceae) : evaluation of life history and population enhancement

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  • Plagiobothrys hirtus (Boraginaceae) is a state and federally listed endangered plant found only in Douglas County, Oregon. This vernal pool endemic has historically been threatened by agricultural conversion of seasonal wetlands in the Sutherlin area, and is currently being eradicated as habitat is lost due to the rapid urban development occurring in southern Oregon. To promote the conservation of Plagiobothrys hirtus, plants were produced in the greenhouse and transplanted into field sites to augment the size of two diminishing natural populations. This work also resulted in propagation, cultivation, and transplantation protocols which are expected to be used in future reintroductions. Greenhouse-grown plants were installed in six plots within three soil moisture zones at each of the two sites, and were randomly assigned one of four treatments: weeded, fertilized, both weeded and fertilized, or left untreated as controls. Success of the transplants was evaluated by monitoring survival and fecundity. Transplants were most successful in the wettest zones; fertilization before transplanting, and above-ground removal of competing vegetation increased transplant success, although the effect of these treatments varied with soil moisture. Transplant success was correlated with plant community composition; as the proportion of vegetation comprised of wetland species increased in plots, the proportion of transplants surviving also increased. Knowledge regarding successful cultivation and transplantation of P. hirtus will be useful for future reintroduction projects, as will the ability to identify sites likely to support created populations of this rare species. We also investigated the life history and ecology of P. hirtus, by comparing this rare species with P. figuratus, a common, closely related congener. Although the two species are similar in morphology, breeding system, pollination ecology, and seed germination, they differed in life history strategy, as P. hirtus was determined to be facultatively perennial, while P. figuratus is strictly annual. When grown together in the greenhouse, plants of P. hirtus continued to grow and flower as long as resources were abundant, and could propagate vegetatively, while those of P. figuratus died after flowering ceased. When compared with its common relative, flowers of P. hirtus occurring in natural populations received similar numbers of pollinator visits and set comparable amounts of seed. The breeding system and seed germination biology of the two species were also similar. Based on these investigations, P. hirtus would appear to have more options from a reproductive strategy standpoint, yet the species is naturally much rare and more narrowly distributed.
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