America's Natural Wonders Photo Gallery

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There is one unyielding principle in nature: All is in flux. No living system remains static. The forest or prairie matures through spring and early summer, and dries out in late summer and fall, and may or may not ignite in flames. The rivers rise with spring rains and snowmelt, and may or may not sprawl across their floodplains; in late summer they flow weakly, awaiting the rains of fall.

Wetlands, as much as any natural community, are a beautiful demonstration of what some biologists term the “boom and bust” cycle. A wetland and its many inhabitants do not thrive on consistency; rather, they're adapted to cycles of good and bad times, prosperity and paucity, played out over the course of one year or many years. Most interesting of all, it is the period of demise that becomes essential for many wetlands to remain vital in the long term.

“Wetland” is a catch-all term; there are enough different types of wetlands to fill a small field guide. The archetypal wetland most of us think of is rimmed with a belt of cattails or bulrushes, with some amount of open water in the middle, and, as the summer progresses, “weeds” (aquatic vegetation) and algae spreading across the surface of that open water. Maybe there's a snag tree or two around the edges. These are the elements of the classic marsh, a very important type of wetland across much of the United States.

Marshes and their close relative, the swamp—which is a wetland that includes a good many standing trees or shrubs—are sometimes very large; the biggest are often allied with a river or lake system. Though this may sound like a “permanent” supply of water, it's usually not. In many areas, the swamp or marsh receives a big shot of water in spring, followed by a steady period of drying through the hot days of summer. In some areas, fall rains bring a new influx of water, while in other places the wetland may wait until the following spring to be recharged again.

As wetlands go, marshes and swamps rank among the largest and “wettest.” A great variety of smaller wetlands—tiny ponds and vernal pools nestled in forests across the country; the famous prairie potholes of the Northern Plains; the desert playas and other ephemeral pools of the Southwest—appear and quickly disappear. Their brief lifespan, in some cases a matter of weeks, is by no means an indication of their importance in the natural world.