Abstract
Houghton’s goldenrod (Solidago houghtonii, Asteraceae) is a rare Great Lakes endemic plant that is U.S. federally listed as threatened, state-listed in Michigan and New York as threatened and endangered, respectively, and a species of special concern in Canada. I partnered with the U.S. Fish and Wildlife Service (USFWS) to evaluate S. houghtonni’s resilience since there is limited analysis on its specific habitat needs and population dynamics. For this dissertation, I used greenhouse and field experiments to investigate the relationship between substrate moisture, substrate texture, and S. houghtonni germination; I established 288 field plots in a range-wide observational study that characterized S. houghtonni’s niche associations across key life stages and environmental gradients; and I evaluated the resilience of over half of the U.S. S. houghtonni occurrences using a portion of the USFWS Species Status Assessment (SSA) process. I also discussed conservation frameworks under the Endangered Species Act (ESA), rare plant conservation, and the challenges and opportunities within the theory-application gap. My results suggest that S. houghtonni germination is highest on smooth substrates with higher moisture content. I also found that S. houghtonni exhibits ontogenetic niche shifts throughout its life history, but most notably between germination and flowering. These shifts in niche requirements between two regeneration life stages add complexity to conservation prioritization. Finally, using a ranking process to evaluate S. houghtonni’s resilience, I found that less than 20 of its moderately or highly resilient populations occur on truly protected habitat. These results suggest that S. houghtonni should continue to be protected under the ESA. To address some of the challenges of rare plant conservation in the U.S., I propose a multispecies SSA process for ESA-listed species on Great Lakes coastlines. This work adds to the limited life history available for S. houghtonni, addresses the importance of understanding ontogenetic niche shifts in conservation planning, and suggests broad methods of amplifying rare plant conservation.