The interactions of the flow regime and the terrestrial ecology of the Mana floodplains in the middle Zambezi river basin

The flow regime of a river is the main driver of the processes that make up a floodplain ecosystem. Changes in a flow regime will therefore result in changes in the floodplain. The Mana floodplains in the middle Zambezi river basin have been impacted by the construction of the Kariba dam as indicated by the decline in the population of mature, Faidherbia albida (F. albida) trees and the absence young trees. However, the relationship between the effects of the river impoundment, some 50years ago, and the current ecological state of the floodplain is not well understood. Hence, this study is aimed at describing the historic (pre-Kariba and post-Kariba dam) and the current terrestrial ecological state of the Mana floodplains. Data was gathered through review of literature, archival records and hydrological records. Furthermore, vegetation plots were set up to measure diameter at breast height (dbh) of F.albida trees and hence describe the current F.albida stand structure. Results from this study show that the Kariba dam altered the peak mean monthly flows by about 60%. The frequency distribution of the dbh sizes of the current F.albida trees depicted an even-aged stand structure (mean dbh of 103cm). There was no evidence of growth of young F.albida trees as there were no trees with smaller (less than 40cm) dbh sizes. The dry season densities of elephants, (Loxodonta africana) on the Mana floodplains have been increasing since the 1990s, and these also seem to have impacted on the F.albida stand structure. This perhaps partially has to do with the increased length of the dry season as a result of the changed river flows. Therefore, the influence of the altered flow regime and the impact of wildlife have acted interdependently in influencing the noted detectable changes to the ecology of the Mana floodplains.