UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Plant community resistance, resilience, and recruitment in tidal freshwater marshes of the Salish Sea Lane, Stefanie L.


Tidal freshwater marshes (TFMs) are found within estuaries where freshwater from outflowing rivers becomes mixed with saltwater from inflowing tides. These habitats are relatively rare owing to their limited spatial extent within estuaries, yet are of critical importance for ecosystem services to humans and habitat value to numerous species. Land use changes in the Pacific Northwest of North America have negatively impacted TFMs through persistent stressors such as altered hydrologic regimes which change habitat conditions, and introductions of non-native plant species which displace native plant species. In light of extant degradation and projected impacts under climate change, it is important to understand how the plant communities comprising TFM habitat respond to stressors in order to prevent or remediate habitat loss. This dissertation pairs observational studies of vegetation changes with experimental tests of seed recruitment to understand plant community resilience. In Chapter 2, I used three datasets spanning 40 years to assess plant community resistance to compositional changes, and found that species homogenization of distinct assemblages may be threatening biodiversity. In Chapter 3, I used historical restoration sites to assess plant community resilience following grazing disturbance, and found that non-native, invasive species competitively exclude native species recovery. In Chapter 4, I used a novel experimental mesocosm to estimate recruitment rate of five plant species in relation to tidal elevation/gradient. I found that successful germination is low overall, and each species’ germination rates are restricted to very specific tidal elevations. Together, these insights serve to inform conservation practice by providing case examples of plant community changes under different disturbance contexts. Additionally, understanding the species composition and abundance in seed banks is useful for generating new questions to test plant community response to disturbance. The prevalent conservation practice of setting aside land is often assumed to be sufficient to maintain native or ‘natural’ habitat. However, this research shows the potential for negative habitat changes occurring in TFM plant communities in the absence of management intervention. Practical interpretation of this dissertation highlights the urgency for active management of protected and restored habitats to improve plant community resilience, in the face of multiple stressors.

Item Media

Item Citations and Data


Attribution-NonCommercial-NoDerivatives 4.0 International