Are droughts good for wetlands?
BOSTON — When streams dry up, fish die. Turtles and frogs have nowhere to go. Birds and mammals can't drink cracked mud. Of all the things that make a wetland, water is the least dispensable.
The long dry spell plaguing the Northeast has not only stressed reservoirs, golf courses, and cornfields, but also marshes, swamps, bogs, and flood plains. These are the places that normally sponge up most of our rain. But this summer most of that water either stayed in the ocean or went somewhere else.
Are our wetlands in trouble, then? Will their wildlife die out, and will they fill up with crabgrass?
In a word, no. This isn't the Sahara. In the meantime, look around: For every dried-up field there's a cattail marsh or a blueberry swamp that's never been lusher. These spots are often too soggy for their own good. But the dearth of rain has exposed their soils, and their roots can breathe.
Go back to one of those cattail marshes in a month or so. Chances are you'll find a plucky little regiment of ankle-high maple sprouts all over it. Skilled opportunists, they're primed to make a forest where the marsh used to be. Don't bet on it, though - they'll probably all drown next May.
Most of our wetlands are thousands of years old and the products of climate and topography. They can stand a parched season or two.
Consider, for instance, the pond that dries up, killing all its fish. If the pond is natural, it has probably dried up before. But then how can it support fish? Revisit the pond in April, when there'll be a stream flowing out its low end. Follow that stream to the nearest river. Now you know how fish re-colonize the pond. Fish are great wanderers; if April is wet enough, you can see pickerels in parking lots and eels on front lawns.
Even in rainy summers, evaporation typically exceeds rainfall, and many isolated pools are dry by August. Some frogs and salamanders breed only in these ephemeral wetlands, presumably because their eggs and tadpoles are too tasty to survive in waters cruised by fish. The downside is that a whole year's reproduction can be lost if a pool dries up too soon, before the tadpoles lose their gills.
With the exception of creatures inhabiting sea floors or deep caves, few animals or plants depend on constant conditions. They ride shifting bands of variation, and are factory-tested for occasional extremes. Episodes like this summer's drought, so damaging to crops, are no threat to most wetlands and their inhabitants. They'll be hopping again when the rain comes back.
(c) Copyright 1999. The Christian Science Publishing Society