The effect of growing season length and water level fluctuations on growth and survival of two rare and at risk Atlantic Coastal Plain flora species, Coreopsis rosea and Hydrocotyle umbellata.

摘要

This study examined variables that may be limiting rare species of Nova Scotia's Coastal Plain flora to determine why they have not expanded to other lakeshores, including dam reservoirs with appropriate slope and substrate, and to determine how reservoir management could improve habitat quality. A transplant experiment was conducted to examine whether variables related to growing season (establishment time, position on shoreline, and water-level fluctuation) were limiting two at-risk species, Coreopsis rosea Nutt. (Pink Tickseed) and Hydrocotyle umbellata L. (Water-pennywort). Establishment time as well as timing and duration of flooding were found to limit both species. Unseasonable flooding and later establishment had similar effects in reducing biomass. The contribution of time spent above water to the final biomass was 2-3.4 times greater than time spent below water. At reservoirs, earlier spring draw down would reduce flood stress, while opening the dam during periods of high precipitation would avoid plant damage due to unseasonable flooding. Exposure of the lower shoreline for 49-71 d or greater would benefit H. umbellata, and exposure of the upper shoreline for 100-112 d or greater would benefit C. rosea. To conserve current habitat, we must also minimize disturbances to watersheds affecting natural fluctuations of occupied lakes..