An experimental reintroduction of Pleuropogon oregonus, a rare wetland grass native to Oregon Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6108vf079

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  • Pleuropogon oregonus Chase is a rare wetland grass endemic to eastern Oregon. The species is composed of two widely separated populations, one in Lake County and one in Union County. In order to reduce the risk of extinction, the Oregon Department of Agriculture Native Plant Conservation Program initiated several reintroduction projects for the species in the early 2000s. Because there were some morphological distinctions (implying genetic differences) between the two population groups, plants from the different counties were considered to represent separate conservation units in reintroduction projects. The Union County ecotype established well at a site in Grant County (Logan Valley), but reintroduction attempts with the Lake County ecotype failed to produce self-perpetuating populations. This brings up the question of whether successful establishment is related to habitat quality at the reintroduction sites, the ecotype used, or some combination of both. In addition, the small natural patch sizes, mostly clonal growth, and low caryopsis production suggests that Oregon semaphore grass might suffer from low genetic diversity and inbreeding depression. Therefore, the question of whether separate ecotypes should be mixed in reintroduction projects merits consideration. On the one hand, planting allopatric ecotypes together runs the risk of disrupting co-adapted gene complexes. Yet if material used in reintroductions exhibits inbreeding depression, mixing disparate populations may be advantageous. Because environmental conditions often fluctuate in wetlands, vegetative community characteristics may be useful in measuring suitability. Ecotypes were reintroduced in separate areas and mixed in one area at the same reintroduction site, i.e., End Creek, in Union County. Although an effort was made to reintroduce ecotypes into areas that were similar, in terms of environmental conditions and vegetative communities, there were landscape-wide differences in the outplanting areas that were not measured in this study, such as changes in hydrology. Because the area in which the mixed ecotypes were reintroduced did not have any surviving plants, the question of whether mixing ecotypes promoted caryopsis production could not be answered. The areas with the most survival were in full sun, completely saturated soil and had vegetative communities similar to the source sites. Although more plants at End Creek survived in the Union County area than the Lake County area, this difference was attributed to the inadvertent selection of presumably better quality habitat in this area. High quality habitat appears to be the most significant factor affecting reintroduction success. Although reintroduction areas may appear to be suitable on a small scale, the effect of the surrounding landscape may affect establishment in ways that are not predictable on a small scale. This was most apparent in the mixed plot area which seemed appropriate on the small scale, but contained no surviving plants upon monitoring.
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