Contoocook River floodplain forest vegetation composition

Osgood, Jeff
Rick Van de Poll
Department of Environmental Studies
During the growing season of 1995, the east branch of the Contoocook River from Jaffrey to Concord, N.H., was examined for examples of mature floodplain forests with minimal human disturbance. Mature forest stands were targeted because the results of this study are intended to contribute to a state-wide survey of mature, natural floodplain forests. The three largest and best forests were surveyed and analyzed to determine the floristic composition of these sits. Base transects were established through the floodplain forest down the gradient from the high to the low floodplain. Lateral transects were established off the base transect when the dominant canopy vegetation changed. Plots were randomly placed along the base transects and lateral transects when canopy or dominant herbaceous vegetation changed. Analysis of the plot data resulted in the development of descriptions of typical floristic species compositions, species and percent coverages, for high, middle and low floodplain forests of the Contoocook River. Low and middle floodplain forests were dominated in the tree canopy by Acer saccharinum (Silver Maple). High floodplain forest was dominated by Acer rubrum (Red Maple), Quercus rubra (Red Oak), and Prunus serotina (Black Cherry). TWINSPAN analysis of the plot data corroborated these findings, and illuminated some of the fine-scale similarities and differences between plots and sites. Each type of floodplain had a distinct floristic omposition that correlated to unique environmental characteristics. The most important characteristic was the elevation and resulting variation in flood frequency of the site.

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