Ecology of Red Maple Swamps in the Glaciated Northeast: A ...

Fig. 6.1. Major changes in southern New England freshwater wetlands over a 20- to 33-year period (based on Larson
and Golet 1982 and Organ 1983). Progressive changes are indicahd by solid lines, retrogressive changes by
&-lted lines (classification according to Golet and Larson 1974).
following paragraphs, we review the major findings
of these three studies. We describe only
changes from one type of wetland to another; information
on wetland losses (i.e., conversion to upland)
is provided in a subsequent chapter.
Despite the relatively short periods examined in
these studies, the extent of wetland change was
dramatic. Overall, nearly 20% of the original wetland
area changed classification (Golet and Parkhurst
1981; Organ 1983). In both Rhode Island and
Massachusetts, more than 700h of the change was
progressive. Retrogressive changes were most
often caused by beavers or humans, chiefly
through the raising of water levels.
The model in Figure 6.1 summarizes the major
changes observed in these time-lapse studies. In
all cases, there was a predominantly progressive
flow from open water and emergent wetland toward
shrub and forested wetland. Certain classes,
such as forested swamp, open water, and deep
marsh, exhibited relatively little change (Table
6.1). About 95% of the forested wetland that
was present at the beginning of the study periods
was unchanged at the end. This is not surprising,
Table 6.1, hgrce of charge of southern New England freshwater wetland types during the recent past.
Values are the percentage of the original area of each type that changed to another type during the
nd bsses) are not included here.
15 tom-,
Magsachuse ts
(1951-77) d
7
34
Deep n~srvh 17 11
Shallow marsh 53 82
Wet meadow 32 59
Emergent wetland 76
32
66
ti0 37
Forested wetland
- -- - -- --- --- 5 4
--
"Wetland types are described by either Golet and I~rson (1974) or Cowardin et al. (1979).
'~tudy by Imon et at. (1980); forested wrtlnrlds wwe not inventoried.
Study by Colet and Parkhurst (1981).
d~tudy by Organ (1983).