The Dead Forest of Chiefs Island: Soil Water Logging from Major Floods and Rainfalls Drive Rapid Vegetation Change in the Okavango Delta (Botswana)
Résumé
The flood-controlled Okavango Delta in Botswana is an endoreic alluvial fan system developing within the arid to semi-
arid Kalahari Desert. The Delta sustains a unique association of ecosystems, from rivers to floodplains, riverine forests to
savanna forests. This complex environment is nearly pristine from anthropic activity but its preservation, especially in the
face of global change, requires a detailed understanding of the functioning and evolution of its ecosystems. In this work we
describe extensive tree dieback in the savanna forest of southern Chiefs Island, the largest permanently emerged island of the
Delta. While tree dieback is generally linked to drought, extreme temperatures, fire or increased biotic attacks, we suggest
that the destruction in the years 2009–2012 of the Acacia sp. and Colophospernum mopane dominated forest unexpectedly
results from drowning through soil water logging associated to a series of successive exceptional floods and abundant rainfall
seasons. This result highlights the necessity of transdisciplinary studies in understanding the autogenic functioning of the
Delta as a prerequisite to describe the effects of global change.