Water depth and biotic insulation: Major determinants of back-swamp plant community composition

Based on phytosociological data, a polythetic divisive classification technique resulted in the delineation of eight broad vegetation types in the back-swamp areas of the Maunachira River System of the Okavango Delta, Botswana. A detrended correspondence analysis indicated that water depth was the major environmental factor influencing the distribution of submerged, floating-leaved and tall, emergent species dominated communities. The remaining communities, with relatively distinct boundaries between each of them, were of short emergent species assemblages rooted in peat deposits with a water depth of less than 0.7 m. Their species composition was not related to water depth, conductivity, pH, redox potential, water temperature or total nitrogen or phosphorus concentrations in the water. The relationship between the present day wetland plant community composition and its environment may be masked by long term, biotic, insulating processes such as the accumulation of resources during peat formation and clonal plant growth. This insulation process does not lead necessarily to long term community stability as has been previously suggested (Mitsch and Gosselink 1986).