Graduate Thesis Or Dissertation
 

Recruitment predictors of an endangered prairie species : a case study of Erigeron decumbens

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0g354j883

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  • Preservation of rare plant species often requires establishment of new populations. Survivorship surveys are the most common method of post-introduction monitoring. However, they provide an incomplete picture of establishment success. This study is an attempt to develop a model for determining establishment success by determining the factors affecting recruitment in introduced populations of a rare species. Erigeron decumbens is an endangered forb endemic to the Willamette Valley of western Oregon. Several populations of E. decumbens have been introduced by governmental and non-profit agencies. While there has been some monitoring of the survival of introduced plants, no systematic surveys have measured recruitment in the new populations. We monitored recruitment in five introduced populations, and compared abiotic and biotic characteristics in these and five stable natural populations. Seventy percent of introduced populations produced fewer than one recruit for every three survivors. Thirty percent produced at least one and one half recruits for every one survivor. The factors that affected recruitment were site specific. Low recruitment (less than one recruit per three survivors) was associated with dominance by exotic species (Dactylis glomerata, Rosa eglanteria, Vicia tetrasperma, and Leucanthemum vulgare), high litter cover, high soil electrical conductivity, and low silt levels. Recruitment was highest at sites with higher native plant species richness and soil characteristics falling within the variation of large natural populations. Viable seed number per individual had the strongest linear relationship with recruitment, demonstrating that seed viability could be a strong limitation for this species (r² = 0.83). The results of this study suggest numerous guidelines for future reintroductions of E. decumbens. This research also demonstrates the utility of recruitment surveys to determine factors important in the success of introduced populations of rare plant species.
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