Author ORCID Identifier
https://orcid.org/0000-0002-6785-8381
Document Type
Dissertation
Date of Award
2026
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
First Advisor
Ranjeet Dr. John
Abstract
Understanding how environmental conditions and invasion dynamics shape native plant Communities is critical for conserving and managing the semi-arid grasslands of the Northern Great Plains (NGP). Invasive plant species are increasingly altering ecosystem structure and function across this region, yet knowledge gaps remain regarding the drivers of invasion, their spatiotemporal dynamics, and their associations with native plant communities. This dissertation investigates three questions: (1) what environmental conditions are associated with the distribution and abundance of the invasive legume Melilotus officinalis (yellow sweetclover; MEOF), (2) how does MEOF vary across space and time under climatic conditions, and (3) how are environmental gradients and non-native plant communities associated with native plant diversity across the NGP? Results showed that climatic variability, soil properties, topography, and ecosystem productivity were strongly associated with MEOF occurrence and abundance. Areas with favorable moisture conditions and higher productivity exhibited greater probabilities of invasion and higher MEOF cover. Spatiotemporal analyses revealed interannual variability in MEOF abundance, with bloom events occurring during years with favorable climatic conditions and prolonged moisture availability, highlighting the importance of climate in regulating invasion dynamics. At the community level, environmental gradients were more strongly associated with native biodiversity patterns than the direct presence of MEOF alone. Elevation, geographic gradients (latitude and longitude), and Palmer Drought Severity Index showed strong positive associations with native species richness (NSR) and diversity (ND) across more than 5,700 vegetation plots. Non-native species richness was positively associated with NSR and ND, whereas non-native plant cover was negatively associated with both NSR and ND, indicating contrasting relationships between invasion extent and invasion intensity. Legume presence was positively associated with native biodiversity metrics, suggesting that functional group composition may influence community responses beyond the effects of individual invasive species. Overall, this dissertation demonstrates that native biodiversity patterns in the NGP are associated with interacting environmental gradients and non-native plant community composition, with limited direct influence of MEOF at regional scale. By integrating field observations, remote sensing, predictive modeling, and Bayesian ecological analyses, this dissertation advances understanding of invasive species dynamics and provides a framework for monitoring and managing grassland ecosystems under environmental change.
Subject Categories
Biology
Keywords
Bayesian hierarchical modeling, Biological invasions, Grassland plant communities, Remote Sensing, Species distribution modeling, Yellow sweetclover
Number of Pages
225
Publisher
University of South Dakota
Recommended Citation
Saraf, Sakshi, "INVASION DYNAMICS, ENVIRONMENTAL CONDITIONS, AND COMMUNITY IMPACTS OF YELLOW SWEETCLOVER (MELILOTUS OFFICINALIS) ACROSS THE NORTHERN GREAT PLAINS" (2026). Dissertations and Theses. 448.
https://red.library.usd.edu/diss-thesis/448