The Effects of Beaver Inhabitation and Anthropogenic Activity on Freshwater Plant Community Dynamics on Mount Desert Island, Maine, USA

Little, Amanda

'I defined hierarchical relationships between environmental gradients and wetland plant community structure in a system of small, isolated wetlands, and then investigated how beaver and humans influenced these gradients at multiple scales. At the wetland scale, the principle gradients that organized plant communities were 1) wetland size, 2) Sphagnum cover and water chemistry, and 3) quadrat-scale microtopography indicative of small-scale hydrology. Vegetation within large wetlands was more predictable based upon climactic and geologic factors than that of small wetlands, which was more affected by historical accidents and intervening levels of local control associated with microtopography. Wetland plant community structure reflected differences in time since beaver inhabitation; older wetlands had vegetation more typical of forested wetlands. Beaver impacts consisted of hydrologic modifications and disruption of antecedent plant communities, but did not extend to water chemistry or wetland size modification (which affected type of emergent wetland community) in the time frame of study. Because hydrologic alterations alone did not change emergent wetland type, wetlands that have in the past been considered part of a hydrosere may in fact be located along different successional trajectories associated with wetland size and water chemistry. The number of ponds, duration of flooding, and types of wetland vegetation were closely tied to beaver population levels. When populations were large, beaver colonized wetlands that they inhabited for only a few years, resulting in vegetation more typical of forested wetland plant communities. Both beaver and human activities disrupted forested wetland plant communities. By modifying wetland water chemistry and inhabiting Sphagnum colonization, human activity more extensively impacted the wetland environment that did beaver activity. The plant communities of human-impacted (degraded) wetlands were limited to either sedge meadow or marsh vegetation, whereas non-degraded wetlands tended to have fen communities. Two types of disturbance were necessary to shift wetland plant community trajectories into a degraded state: 1) water quality degradation due to humans and 2) vegetation disorganization due to intense human or beaver activity. The antecedent wetland plant community had to be sufficiently disorganized for water quality factors to move it into the degraded state of sedge meadow or marsh vegetation.' CD of disertation inside bound report. UTM's are provided for wetlands in Appendix B pg. 235; however, there were no coordinates for actual transect site location in regards to data collection. Also, there were no wetland specific species lists. Not all locations noted below were included as a study site, and very little information specific to wetlands inlcuded in the study was made available. /STUDY LOCATIONS:/ /MOUNT DESERT ISLAND/Great Meadow/NW of Witch Hole Pond/NE of Witch Hole Pond/Bear Brook Pond/Jackson Lab/Kentfield Marsh/ E of teh Bowl/Canon Brook/Cape Road/Bernard/S of 102/Seal Cove Road/Eagle Lake/Marshall Brook/N of 102/Duck Brook Road/Ripple Pond/Hio/Gilmore Meadow/Hull's Cove/Little Hunter's Brk Middle/SW Valley/Heath Brook/Duck Pond/Steward Brook/China Hill/SE of Sunken Heath/Hodgdon Brook/E of Fawn Pond/N of Eagle Lake/NW of New Mill Meadow/SW of Gilmore/E of Aunt Betty Pond/W of Eagle Lake/Little Hunter's Cedar/Long Pond Fire Road/