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Interannual Trends of Flowering Phenology and Native Species Richness in California Vernal Pools

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Nearly 90% of California’s vernal pool habitat has been destroyed by human activity in the past 100 years. The University of California, Merced manages one of the largest actively protected vernal pool habitats in the state, the UC Merced Vernal Pools and Grassland Reserve (MVPGR), aimed at conserving rare native species and landscapes through research, teaching, and outreach. Because the reserve was only recently established, little is known about the interannual patterns of vernal pool plants occupying the region. Consequently, the phenological and demographic responses of the native species inhabiting the MVPGR to reduced precipitation, biological invasions, and cattle grazing has not been quantified. The goal of this dissertation is to investigate the composition, flowering time, and invasion intensity of vernal pool plant communities across multiple climate years. Chapter 1 focuses on two wildflowers native to California, Limnanthes douglassi ssp. rosea (meadowfoam) and Trifolium variegatum (whitetip clover), and quantifies each species’ phenological response to variable precipitation and temperature across 7 years. Additionally, population size of both focal species in response to competition and eutrophication were assessed. I found that both meadowfoam and whitetip clover flower earlier in response to lower precipitation. Chapter 2 focuses on plant community responses to abiotic and biotic dynamics across zones within pools, which are established by soil texture and flooding gradients. Chapter 2 expands upon Chapter 1 by characterizing the community composition, invasion intensity, and interannual flowering trends of 42 plant species across three zones: pool bottom, edge and upland. I found a distinct plant community occupying each zone, and each zone responded uniquely to invasion and winter precipitation. The pool bottom plant community flowered earlier in response to lower winter precipitation, whereas native species in the upland plant community were negatively associated with non-native species richness. No correlations were found between precipitation and the floral phenology of upland species, and neither was there a correlation between non-native species richness and native biodiversity patterns in the pool bottom. The findings elucidate the sensitivities and ramifications of climate change, invasion, and eutrophication amongst ‘zones of vegetation’ on the UCMGVPR. Conserving the native species also requires community participation in the management and legislative process, and ideally the scientific process. Chapter 3 examines several recruitment and retention methods for a community science project involving UC Merced undergraduates and provides guidance on how to achieve a long lasting and high engagement project. I found that in-person presentations achieved a recruitment rate than email flyers. In addition, giving volunteers the freedom to decide the time and date they volunteer and providing periodic updates in the form of a newsletter can improve retention rate of volunteers at different stages.

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This item is under embargo until June 24, 2024.