Conservation of Rorippa columbiae : An Evaluation of Reintroduction Potential through the Study of Germination Ecology, Propagation Methods, and Habitat Requirements Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/df65vd38b

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  • Rare plant reintroductions are a critical conservation tool for the augmentation of diminishing populations, or re-establishment of extirpated populations. Analysis of reintroduction failures suggests that a sophisticated understanding of species biology, ecology, and habitat is essential for producing self-sustaining rare plant populations. This study sought to generate that background knowledge for the declining rare perennial Rorippa columbiae (Brassicaceae), to improve the likelihood of success for future reintroduction efforts. Specifically, this research aimed to develop germination and propagation protocols for the production of ex situ material, and to quantify in situ habitat attributes to inform appropriate reintroduction site selection. Laboratory experiments were conducted to evaluate the influence of light exposure, cold stratification duration, temperature regime, and source site on optimal R. columbiae germination. Results revealed that R. columbiae seeds require light and a higher temperature regime to germinate successfully, and do not require cold-moist stratification to break dormancy. Source sites produced significantly different germination responses. A factorial greenhouse experiment examined optimal propagation requirements by measuring the effect of propagule type, substrate type, and source site on R. columbiae emergence, and vegetative and reproductive growth characters. Models demonstrated that rhizome propagules and LA4 nursery grow mix consistently produced the highest emergence and growth measures. Genetic divergence between source sites was demonstrated in a common garden analysis, and a reciprocal transplant analysis showed no evidence of home-site advantage, indicating response variation cannot be attributed to adaptation. An observational field study assessed population health, landscape, soil, and biological community attributes associated with occupied patches of R. columbiae in southern Oregon. The population health assessment showed significantly different population sizes among extant populations, and a positive correlation between population size and vegetative and reproductive growth metrics. Though values of measured attributes varied considerably in R. columbiae habitat, when habitat associated with R. columbiae presence and absence were compared, the majority of variables exhibited no significant differences. Exceptions included an association between large, high performing R. columbiae populations and lower elevation, a lower percentage cover of bare ground, and lower calcium, magnesium, and potassium concentrations. Extant populations appeared associated with lower calcium concentrations, higher iron concentrations, and a higher percentage cover of bare ground and native forbs. These attribute associations signaled potential habitat preferences for future Rorippa columbiae modeling and reintroductions.
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