Different kinds of plant canopies in wetlands enable great species diversity by providing a variety of microenvironments.

References

"Because there are usually a variety of vegetation types in wetlands, the presence of different kinds of plant canopies creates a complex mosaic of microenvironments. Plant canopies alter light regimes, water temperatures, oxygen concentrations, water chemistry, etc. The direct and indirect effects of plant canopies ultimately determine the spatial and temporal distributions of most organisms in wetlands. The environmental complexity created by plant canopies enables wetlands to support a much greater diversity of species than would be found in a hydrologically comparable situation, for examples [sic], the shallow area around a lake margin, without plants." (van der Valk 2006:13)

Book
The Biology of Freshwater Wetlands (Biology of Habitats)March 24, 2012
Arnold G. van der Valk