THE ROLE OF BIOTA IN THE INITIATION AND GROWTH OF ISLANDS ON THE FLOODPLAIN OF THE OKAVANGO ALLUVIAL-FAN, BOTSWANA

A group of islands of varying size on the floodplain of the Okavango a lluvial fan, were studied to establish the processes which lead to the initiation and growth of islands. It was found that islands are initi ated by the mound-building activities of the termite Macrotermes micha elseni. These termites import fine grained materials to use as a morta r for the construction of epigeal mounds. Their activities create a to pographic feature, raised above the level of seasonal flooding, and al so change the physical properties and nutrient status of the mound soi l. Shrubs and trees are able to colonize these mounds, which results i n increased transpiration. As a result, precipitation of calcite and s ilica from the shallow ground water occurs preferentially beneath the mounds, resulting in vertical and especially lateral growth, causing i sland expansion. (C) 1998 John Wiley & Sons, Ltd.