Pacific Northwest Prairie Plant Responses to Warming Among Species, Across Space, and the Implications for Species Interactions and Coexistence

While plant species are adapted to, and in many cases rely on, temporal fluctuations, the rapid climate warming of the 21st century poses a substantial threat to species and community dynamics. Ecologists use shifting plant phenology, life cycle events such as flowering, as one of the key ways to track how species are being affected by warming. Plant species' responses, phenological and otherwise, often diverge among species and across space, suggesting reshuffled species interactions and uncertain changes in community composition. Modern Coexistence Theory (MCT) has proven a useful framework in recent decades for understanding species interactions and coexistence and investigating how certain environmental variables affect these dynamics. In this dissertation, I track plant responses to warming, particularly phenological and fecundity responses, to determine how variation in these responses among species and across local environmental gradients can restructure species interactions and coexistence. To do this, I implemented two large field projects using annual forbs native to Pacific Northwest prairies that are commonly used in restoration seed mixes for this ecosystem. The first was a common garden study with seven taxonomically and phenologically diverse species that I used to answer questions about the full phenological life cycle shifts and interspecific differences in species response to warming. In the second, I seeded two forbs in competition plots replicated at eight locations across abiotically variable sites to examine how warming effects vary across small spatial scales. Both studies used open-top chambers to passively create a warming treatment. In my first chapter, I observed the full life cycle of all seven species, from germination to fruit maturation. These observations provide unique information about early life development stages that are not typically studied and provide greater insight into what drives variation in phenological shifts. In my second chapter, I use five of the species from chapter one and ask how species -specific responses to warming impact their performance directly and indirectly through changes in species interactions. I use MCT to examine how these direct and indirect effects cascade to restructure species niche differences and fitness differences and ultimately predict how coexistence outcomes shift with warming. In my third chapter, I again use MCT to examine how warming affects species interactions and coexistence but focus on how small scale environmental variation has the potential to modify warming effects, leading to unique community -level outcomes across space. Overall, the results in this dissertation advance our knowledge of how the variation in species responses to warming leads to changes in community dynamics. Using species from Pacific Northwest prairies, a critically imperiled ecosystem, I aim to aid restoration of this system while also providing broad information about how warming impacts species coexistence.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Department of Biology

Grantor dc:publisher

University of Oregon

Year dc:date.issued

2026

Author dc:creator

• Erskine, Sarah

Advisor dc:contributor.advisor

• Diez, Jeff

Statement dc:rights

• All Rights Reserved.

Language dc:language.iso

en_US

Handle dc:identifier.uri

https://hdl.handle.net/1794/32702

OAI record oai:identifier

https://scholarsbank.uoregon.edu/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ascholarsbank.uoregon.edu%3A1794%2F32702