Woody plant communities of three urban wetlands and the success of an invasive shrub (Lonicera maackii) over natural and experimental flooding gradients.

invasive species;urban wetlands;honeysuckle;Lonicera maackii

Meghan Rhea Langley

University:University of Louisville

Department:Biology

关键词: invasive species;    urban wetlands;    honeysuckle;    Lonicera maackii;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=3551&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

Globally, wetlands are known for providing important ecosystem services that enhance the quality of human life and regulating global biogeochemical cycles. Despite the wide recognition of their value, temperate forested wetlands are the least protected type of ecosystem world-wide, and are threatened by human activities such as logging and development. The ecology of forested wetlands remaining in urbanized areas is impacted by a multitude of anthropogenic threats, including fragmentation (which decreases the amount of interior habitat and increases edge habitat), hydrologic modification (ditching and draining of wetlands) and the incursion of invasive species (which are frequently introduced by human activities). In the first study presented in this dissertation (Chapter 2), I examined how woody plant communities of three urban wetlands—the dominant biota of these ecosystems—changed along edge-to-interior and hydrologic gradients. Detailed measurements of elevation, surface water levels, and ground water levels were made to estimate the number of days each transect was flooded. The three study forests were surveyed in transects along edge-to-interior gradients (0-60 meters from the forest edge) and were found to exhibit a gradient of flooding (measured as the number of days flooded in sampled areas). Ordination with non-metric multidimensional scaling (NMS)—using Importance Values (IVs) of adult trees, saplings, tree seedlings, shrubs and vines in transects at 1, 5, 10, 30 and 60 m from the edge—was used to see if patterns in the woody plant community related to distance from edge, number of days flooded and other environmental variables. Distance from the forest edge and number of days flooded were the two variables shown to be most correlated with ordination axes generated from the species matrix (r2≥0.15), and each was associated with a different axis. The shrub community was most indicative of community differences along the hydrologic gradient (Axis 1); Lindera benzoin (a facultative shrub) and Cornus foemina (a facultative wetland shrub) were the species most associated with drier and wetter transects, respectively. The invasive shrub species, Lonicera maackii, was present at all sites, but more important at the two driest sites. Because the relative elevation (within a transect) of L. maackii plants increased with the number of days flooded, it appeared that higher elevation microsites may have provided refugia for the establishment and/or persistence of this invasive species in flooded areas. Fraxinus pennsylvanica (green ash) was a major component of the tree canopy species at all sites, and the imminent threat posed by the emerald