My dissertation research investigates the links between stream and riparian restoration and aquatic plant communities. Aquatic plants play important ecological roles in many stream ecosystems- they provide food and substrate for aquatic organisms and drive important physical and chemical processes. However, invasions of non-native aquatic plants or proliferation of weedy native aquatic plants can clog natural and human-made waterways, creating serious ecological and economic impacts. I am interested in how stream and riparian restoration affect these ecologically important but potentially nuisance-causing communities in terms of establishment success, survival, growth rates, and competition between species.
How does riparian canopy shading affect establishment and growth of native and non-native aquatic plants (stream invasibility)?
Many riparian restoration projects involve planting native vegetation along stream banks, often with an explicit goal of increasing shade over streams. However, riparian restoration can also involve removal of non-native shade-forming species (e.g., eucalyptus, tamarisk), which can reduce the amount of shade over streams. Because light is an important limiting resource for aquatic plants, changes in riparian cover are likely to affect aquatic plants, and to affect different species in different ways. Yet, the potential responses of aquatic plant communities to stream and riparian restoration are rarely considered.
In summer 2011, I conducted two experiments on establishment, survival, and growth of a common native aquatic plant (elodea) and an invasive non-native plant (Eurasian watermilfoil) under different shade levels. Because I wanted my results to be relevant to streams, I thought it was important to conduct my research in flowing water (most studies involving aquatic plants are conducted in non-flowing conditions in tanks). I was fortunate to be able to conduct my experiments in artificial stream channels at the Sierra Nevada Aquatic Research Laboratory (SNARL), a UC Reserve in the eastern Sierra Nevada Mountains, and to have artificial stream channels created specifically for my second experiment on UC Davis Putah Creek Riparian Reserve property. I found that while greater shade reduced growth rates of both species, establishment success was close to 100% in all shade levels, even >90% shade! This suggests that while increasing riparian shading over streams could reduce proliferation of aquatic weeds, it may not decrease establishment.
How do riparian canopy shading interact with priority effects to influence competition between native and non-native aquatic plants?
In summer 2012, I conducted another experiment on the effects of shade on aquatic plants- this time investigating how shade level affects competition between a native and a non-native species, and whether giving the native a five-week establishment advantage (priority effect) would affect competitive outcomes.
What drives patterns in aquatic plant community assembly after stream
In the fall of 2011, a mile-long section of Putah Creek, a perennial stream flowing eastward from the Coast Range through the California Central Valley, underwent channel and floodplain restoration: the wide, slow-moving channel was transformed into a narrower meandering channel, and gravel was added in many sections. In the process, water was diverted through large pipes, the channel dried out, and existing aquatic plants died back. I saw this project as a wonderful opportunity to research important theoretical and applied concepts in plant ecology in an understudied plant guild (aquatic plants). For two years following the restoration, I monitored the restored reach to examine patterns in establishment and succession of aquatic plants.
In particular, I am interested in how abiotic factors such as flow rates and light levels, and biotic factors such as competition and facilitation, influence the colonization and growth rates of different species, how these dynamics change over time, and what conditions favor native over invasive non-native species.