Plant community composition, species coexistence, and community assembly in the riparian zones of small streams in New York State.

摘要

Many mechanisms may contribute to the diversity and composition of an ecological community. In riparian habitats, which are often described as both very diverse and very susceptible to biological invasions, flood disturbances may be a predominant structuring mechanism. In this dissertation I use several approaches to describe the mechanisms governing the diversity and composition of riparian plant communities along small streams. I performed a systematic literature review of the role of disturbances in facilitating plant invasions in general and in riparian plant communities in particular. General trends in the effects of disturbance on plant communities may be difficult to detect in part because of the breadth of events described by the term "disturbance". In field studies, I found that riparian plant communities and nearby upland areas did not differ in diversity or species composition at a local scale, but riparian communities harbored more species regionally, suggesting that the riparian zones of small streams may serve as a reservoir of regional species richness. Variation in the composition of riparian plant communities of small streams throughout the Upper Hudson watershed (NY) was correlated with annual mean temperature, soil texture, and the abundance of wetlands in the surrounding landscape, and community composition was spatially autocorrelated. In greenhouse experiments, plant growth and survival under flooding conditions were found to vary among species and among and various types of flood effects, suggesting that while floods may exclude some regional species from the riparian zone, it is likely not the only mechanism controlling riparian community composition. Finally, I used information on plant traits to investigate how introduced species might establish and succeed in riparian communities. I found that introduced and native species differ substantially in many plant traits, suggesting that introduced species might be able to succeed in these communities and coexist with native species by virtue of their dissimilarity and the associated potential for reduced competition with natives. The research presented in this dissertation taken together provides a deeper understanding of the factors controlling the diversity and composition of riparian plant communities along small streams.