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

since forested wetland is the endpoint of freshwater
wetland development in the Northeast. Open
water and deep marsh are also relatively stable
classes, at least over short periods, simply because
of their considerable water depth.
Shallow marsh, wet meadow, and shrub swamp
were highly dynamic. From 30 Lo 8@/0 of the original
acreage of these intermediate wetland types
changed classification during the 20- to 33-year
study periods (Table 6.1). The dynamic nature of
these wetlands can be explained, at least partially,
by their similar water regimes; typically, they are
seasonally flooded or seasonally saturated, as in the
case of forested wetlands. As a result, changes
among these classes (and from these classes to
forested wetland) may occur relatively quickly, especially
iffactors retarding change, such as mowing
or grazing, are discontinued.
Not only is there a high rate of change in the
intermediate wetland classes, but these classes are
also declining in abundance regionally (Larson
et al. 1980; Golet and Parkhurst 1981; Organ 1983).
Conversely, the more stable wetland types, particularly
open water and forested swamp, have increased
in abundance in most cases. Two major
factors responsible for the change in abundance of
the various wetland types are the decline of agriculture
in the Northeast and the construction of
impoundments for water supply, recreation, or irrigation.
Abandonment of agriculture has caused
formerly cleared wetlands to advance to shrub
swamp and forested swamp. That pattern of
change, which began in the mid-1800's, is still
significant more than 100 years later. The increase
in open water resulting from human activities is a
nationwide phenomenon (Frayer et al. 1983; Tiner
1984) that is augmented in some parts of the Northeast
by the increasing abundance of beaver ponds
(Organ 1983).
Dynamics of Red Maplie
Swamps
In southern New England, sigdicant areas of
emergent wetland and shrub wetland have developed
into forested wetland since 1940. Golet and
ParC\mt (1981) calculated a 7% increase in red
maple swamp over a period of 33 years in Rhode
Island. Organ (1983) estimated the increase in all
forested wetland types in Massachusetts to be 11%
over 20 years. By comparison, retrogressive
changes in forested wetlands have been relatively
minor. Beaver pond construction (Organ 1983), the
creation of ponds for irrigating cranberries (Tiner
and Zinni 1988), and impoundments for waterfowl
(Golet and Parkhurst 1981) have converted some
forested wetlands to open water, marsh, or shrub
swamp. Retrogression from forested swamp to
shrub swamp has also occurred as a result of the
cutting of trees for fuelwood and utility rights-ofway.
Even though data documenting forested wetland
dynamics in other parts of the Northeast are
not available, there is reason to believe the
changes found in southern New England hold elsewhere.
Based on U.S. Forest Service forest inventory
data, Abernethy and Turner (1987) estimated
that there was a 6% increase in forested wetland
in New York between 1940 and 1980. They attributed
the increase to abandonment of pastures.
Increases in forested wetland were noted for all
other northeastern states as well, except for
Maine, New Jersey, and Pennsylvania.
Accurate assessment of the effects of land use
on red maple swamps requires a thorough understanding
of both the processes of swamp development
and the conditions that cause these wetlands
to change to other wetland types. In the remainder
of this chapter, we describe the progressive and
retrogressive changes affecting red maple swamps
and the successional relationships between red
maple and other wetland forest trees.
Swamp Origins and Development
Some red maple swamps occupy deep, peat-filled
basins that were lakes during their early history
(Beetham and Niering 1961). Before red maple
trees could dominate such sites, a series of other
wetland types, including aquatic beds, emergent
wetlands, and shrub wetlands, would have developed
there. Because of the major change in water
regime required, the progression fmm deep, open
water to forested swamp would take thousands of
years under natural conditions. Other red maple
swamps are in shallow basins that originally may
have been only seasonally flooded, or on hillsides
that probably had a seasonally saturated water
regime throughout their postglacial history. In
these cases, the vegetated wetlands that first occupied
these sites were most likely emergent wetlands
(e.g., wet meadows) dominated by grasses,
rushes, or sedges. 'fie transition to shrub and
forested wetland in these locations codd have been
rapid, as long as the climate was conducive and