Vascular plant community assembly in stormwater detention basins
Creators: name: Douthat, Kate Diana
Publisher: name: No Publisher Supplied
Year: 2022

description: In this dissertation, I explored stormwater detention basin plant communities in a regional scale observational study, basin-scale study of relationships between the community and abiotic factors, and a manipulative experiment comparing a range of predictors of species success. Stormwater detention basins are a form of artificial urban wetland. Stormwater detention basins are a rich study system for learning about wetland community assembly and the specific ecosystem functions of stormwater infrastructure. This dissertation contributes baseline knowledge of the detention basin ecosystem that can be used in future research and practice. Furthermore, this dissertation contributes to an understanding of the dynamics of an invasive species and the dynamics of dominant graminoids and grass-like species in marshes more generally. I found a large species pool of mostly wetland plants. The most abundant taxa by far were Typha spp. and Phragmites australis, followed by Juncus effusus, Lythrum salicaria, and Artemisia vulgaris. Typha spp. was also the most frequent taxon by site. Most of those top species were invasive, but most of the subordinate taxa were native. At the community level, soil moisture and marsh elevation were significant predictors of species distribution, though slope was not. According to models, Typha spp. almost 60–70% of Typha spp. occurrence and abundance was predicted by the soil moisture gradient alone. Occurrence of the other dominant species was not significantly correlated with elevation, and was only weakly correlated with soil moisture, which explained less than 10% of variation in occurrence. The final data chapter examined the biotic interactions between species and the balance of biotic and abiotic control on survival and growth. I tested a method proposed by Johnston and Zedler (2012) for initiating restoration plantings in areas invaded by Typha spp. using preferential associates from the regional species pool. Seedling survival was high for most species. It appears the method of selecting frequent species from the regional species pool was effective for achieving first-year seedling survival. I found that the neighbor identity of seedlings did not affect growth either positively or negatively, nor did neighbor identity affect Typha spp. growth. Altogether, this research identified trends in composition, diversity, and habitat quality in a novel urban ecosystem that has not been previously described. I created the first species list for stormwater detention basins that can serve as a baseline and basis for comparison with other wetland systems and planting guidance for practice. I identified the importance of soil moisture in predicting dominant species occurrence in a set of basins and created species response curves to describe the niche optimum and breadth of some dominant species in stormwater basins. Notably, I quantified the probability of occurrence of Typha spp. at a site under a range of soil moisture conditions. I contributed more evidence for the mechanisms behind species co-occurrence from a manipulated experiment.