Quaking ground underfoot, cycles of flooding and drying – neither terrestrial nor aquatic, wetlands seem to occupy a category by themselves. In general terms, wetlands are defined by the presence of water within the rooting zone during the growing season such that it affects soil processes and plant growth. It follows that wetlands develop in the landscape where drainage is impeded, where water collects in topographic lows such as valleys or depressions, where the water table is high, or where there is significant flooding from rivers, lakes, or ocean tides. Forested wetlands occur in all these landscape settings.

Forested wetlands, more commonly known as swamps, flatwoods, mangals (mangroves), or inundated forests, have a wide distribution, occurring on every continent except Antarctica. They are extensive in equatorial areas, e.g., the Amazon, and the most abundant wetland type in temperate and boreal regions. Approximately 3% of the global land area is wetland and of this, it is estimated that 60% is forested (Matthews and Fung 1987). More exact areal estimates of forested wetland are unavailable because wetland statistics generally do not differentiate between forested and non-forested ecosystems, and forest statistics do not separate wetland from upland. Furthermore, compared with boreal and temperate upland forests, forested wetlands are a relatively understudied ecosystem world-wide (Lugo 1990). Descriptive literature on the most widely studied forested wetland ecosystem, mangrove swamps, can be traced back to 325 bc (Chapman 1976), yet research on ecosystem functions was not conducted until the 1930s (Walter and Steiner 1936). Studies in other forested wetland communities pale in contrast to the work on mangroves.