Species diversity in wetlands is determined
to a large extent by succession and
seasonal change, both of which allow a wide range of species assemblages to
coexist in close proximity. Some wetland types can be species-poor, good
examples being the large tracts of swamp dominated by a single species, such as
reed (Phragmites australis) or papyrus (Cyperus papyrus), lacking ground
vegetation because they are permanently inundated, and impeding submerged
vegetation through shading and the large volume of decomposing detritus. A
feature of wetland areas, however, is that so often several different habitat types,
each with its representative species, are mixed together in a small area. The
precise adaptations of different wetland plants to specific degrees of waterlogging
contribute to this high species diversity, with very small changes in topography
across a small area allowing different species assemblages to coexist. An
embanked river, for example, has an open water habitat, a fringing wetland, a
normally dry levee and a flood wetland, all within a few metres of each other.
Just as the water table produces spatial
patterns in wetland biota, so any
fluctuations will create temporal patterns in species diversify. In any one season.
diversity may be low, but when all seasons are considered together, diversity is
enhanced by seasonal turnover of species.
