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

of the year, the forest floor commonly consists of
deep hollows and convex mounds; in swamps that
lack surface water entirely or that are flooded only
temporarily, nnicrorelief is not as well developed
(Ehrenfeld and GuXick 1981). Lowry (1984) took
spot elevations at over 700 points in each of six red
maple swamps and six Atlantic white cedar
swamps in southern %ode Island and determined
that microrelief was more highly developed in the
cedar swamps, which had significantly higher
mean water levels as well. He dso confumed that
the extent of microrelief in the red maple swamps
was related to water level. Considering all points
more than 20 cm above the average level of the
depressions to be mounded, he calculated that
nearly 75% of the variation in the amount of
mounded ground among the six swamps could be
explained by differences in the 7-year mean water
levels among the sites. Figure 4.5 illustrates pronounced
microrelief in a seasonally flooded red
maple swamp.
How active a role vegetation plays in the development
of microrelief is unclear. Initially, the dis-
tribution of trees and shrubs in a swamp is determined
by the relative wetness of various possible
germination sites on the forest floor. Once they are
established, those trees that have the ability to
develop a compact, elevated root system clearly
stand a greater chance of surviving the effects of
prolonged high water levels. Root system development
thus may increase mound size. Significantly,
radial growth of red mqle trees in any given year
appears to be directly related to the deviation of
that year's average water level from the long-term
average. Lowry (1984) demonstrated that, in
Rhode Island swamps, growth was greatest in
years when water levels were closest to the 7-year
mean. This finding suggests that in each swamp
there may be an optimal distance, dependingupon
water regime and soil characteristics, between the
elevation of the average water level and the depth
of tree roots. Whether the role of vegetation in
microrelief development is active or passive, variation
in surface elevation within a swamp maximizes
the opportunity for any tree to achieve that
optimum position and to maximize its growth.
Fig. 4.5. Mound-and-pool microrelief in a seasonally flooded red maple swamp. Swamps with
particularly high water levels, such as this one, generally have high mounds and little vegetation
growing in the pools. The measuring stick is graduated in ZQ-cm incremenk; the water averages
15-25 cm in depth. The photograph was taken in mid-April.