This year the Okavango River is carrying more water than it has for many years. On a recent flight over the Delta I was struck by the impact the high water levels are having on trees. Much of the water in the Delta moves in big, shallow sheets, rather than in narrow, erosive channels. The water doesn’t cut the soil away from the roots, and topple them. Rather, shallow water covers the trees’ roots, and in time this will kill the trees.
When viewed from the air, one can get an idea of how much woodland has been inundated in this way. The dead trees can be easily seen from the air, by the grey colour of their exposed trunks and branches. Acacias, mopane and leadwood trees seem to be the species most affected. Not long after the water covers their roots they first lose their leaves, and then die. Of course, although it is unfortunate that these trees have been killed, it is all part of a great cycle. Over time the dead wood will be broken down, both by fungus, and by termites. If water levels drop rapidly, and stay low, the very tissue of the trees will become part of the topsoil. If the water stays high, then the trees will end up as part of the sediment load that the Okavango carries with it wherever it flows. The number of trees that have been swallowed up by the flood this way, in just a few months, made me think. Elephants generate much hostility amongst some people due to their habits of feeding on trees. Perhaps seeing the massive impact of a natural occurrence like this on trees might make people look at the impact elephants have in a different light.
In the bigger picture, the high water levels of 2010 are very good for the wetland and the surrounding area. Humans depend on fresh water just as much as wildlife does, so the increased flow reduces the risk of water being taken from the Delta itself. Right now, several rivers that run out of the Delta are flowing again, and supplying water to people living alongside them. The fast-growing town of Maun is also dependent on water from the Okavango River, and is benefitting from the abundance of water once again.
And of course, the Delta with its myriad lagoons, channels and floodplains is thriving with this recharge of water and nutrients.