Variation in the development of woody vegetation of forested wetlands in the Connecticut River valley

Fitz, Philip
Peter Palmiotto, PhD
Department of Environmental Studies
The largest remaining forested wetlands in New England lie in oxbows of the Connecticut River valley in western Massachusetts. This study examines the long-term dynamics of the woody vegetation in three oxbows in the towns of Northampton, Hatfield and Whately in Massachusetts. Plots were re-established in 2004 from studies done there over a 30 year period by Drs. Marjorie M. Holland and C. John Burk. Forest canopy trees were identified and their basal area was measured in 10 x 10 m plots using the same locations and protocols as Drs. Holland and Burk in the 1970s, 1980s and 1990s. Throughout the 30 year period, the Northampton oxbow was dominated by silver maple in areas that were flat and low-lying, but the portion that was ridge and swale was dominated by shagbark hickory and black birch, more upland species. Throughout the Northampton oxbow, mature trees were thriving but there was little recruitment into the canopy of any species. The structure of the forest changed as saplings and young trees declined through the 30 year period. The Hatfield oxbow was dominated by silver maple and cottonwood, with cottonwood declining over the period. The Whately oxbow, higher in elevation that the other two oxbows, had more upland species throughout the period. The Whately oxbow was disturbed by substantial human activity over time. Variation across and within the oxbows was attributed to a combination of autogenic/allogenic and anthropogenic factors over time. Based on the dynamics observed a theory of episodic changes is proposed to explain the current forest structure. Autogenic/allogenic variation included elevational and topographic land features, high mortality of younger growth where regular flooding occurred, catastrophic flooding resulted in death of more mature trees, and replacement of species due to competition as conditions change. Changes due to both direct and indirect anthropogenic factors were documented, and shown to be at a much faster rate than autogenic/allogenic factors. Due to the limited acreage of these unique wetlands and their importance in both the adjoining riverine and terrestrial systems these wetlands should receive high priority for conservation.

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