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

Globally, river ecosystems serve as significant sources for socio economic development through the goods and services they offer. Such services include tangible benefits like freshwater and non-material ones like aesthetic value. Underlying these services are functions that keep these ecosystems intact. Changes in these functions ultimately impacts on the capacity of the ecosystem to deliver its services. Human activities often lead to changes in ecosystem functions, which may have a negative impact on the potential to deliver ecosystem services. For example through river regulation activities like dam constructions, which modify the flow regime; the key process influencing river-floodplain ecosystems. Similarly, the Kariba dam is said to have led to the ecological changes of its downstream Mana floodplains. This was reported by research studies done in the 1980s which indicated a decline in Fardherbia albida (F. albida) tree species and increasing dry conditions on the Mana floodplains. These floodplains are a home to a number wildlife species and hence an important tourism site in Zimbabwe. This research was aimed at describing the historic (pre and post Kariba dam) and current terrestrial ecological state of the Mana floodplains. The study adopted the use of ecological indicators i.e. population dynamics of elephants (Loxodonta africana) and the current stand structure of F. albida. F. albida is native to the Mana floodplains and serves as a key source of foliage for wildlife in the dry season. Data was gathered through review of literature, archival records, analysis of satellite images and hydrological records. Furthermore, vegetation plots were set up to measure diameter at breast height (dbh) of F. albida trees. Semi structured interviews were also done with key informants to understand the history of the floodplain. Analysis of relationships between the flow regime, impact of elephants and stand structure of F. albida trees was also done. 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 40 cm) dbh sizes. Generally, the dry season densities of elephants on the Mana floodplains have been increasing since the 90s. Thus the alteration of the flow regime and elephant densities were identified as the direct drivers of change in the ecology of the Mana floodplains. These drivers have acted interdependently as indicated by the increased access and duration of elephants on the Mana floodplains due to the altered flooding events