The interactions of the flow regime and the terrestrial ecology of the Mana ﬂoodplains in the middle Zambezi river basin Sikhululekile Ncube, 1 Lindsay Beevers 2 * and Edwin M. A. Hes 1 1 Group of Aquatic Ecosystems, UNESCO-IHE Institute for Water Education, Delft, The Netherlands 2 School of the Built Environment, Heriot-Watt University, Riccarton, UK ABSTRACT 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 50 years 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 103 cm). There was no evidence of growth of young F. albida trees as there were no trees with smaller (less than 40 cm) 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. Copyright © 2012 John Wiley & Sons, Ltd. KEY WORDS dams; ecology; elephants; ﬂoodplain; Faidherbia albida; ﬂow regime Received 19 September 2011; Revised 22 September 2012; Accepted 23 September 2012 INTRODUCTION Globally, river ecosystems serve as signiﬁcant sources for socio-economic development through the goods and services they offer. Underlying these goods and services are functions that deﬁne the state of these ecosystems. Human activities often lead to changes in ecosystem processes, components and/or structure, which will change the functions of the ecosystem. Changed functions alter the potential of the ecosystem to deliver goods and services (Costanza et al., 1997; Daily, 2000; de Groot, 2005). Water resources development is one notable human intervention that is acknowledged to have resulted in the regulation of most large rivers in the world (Hughes, 2000; Beauchamp et al., 2007). Developments in the water environment for the supply of resources have included dam construction, water diversion (extraction), river channeliza- tion and construction of weirs and locks. The construction of dams in the 20th century on a signiﬁcant number of river basins has affected many large river systems worldwide (Patten, 1998; Williams and Cooper, 2005; Döll et al., 2009; Wen et al., 2011). Dams have been essential for water supply, irrigation, hydroelectric power generation, ﬂood control, navigation and ﬁsheries. Notwithstanding these associated socio-economic gains that dams have brought, they have also contributed toward the disruption of the ecological integrity of river–ﬂoodplain ecosystems (Junk et al., 1989; Petts, 1999; Thomas and Adams, 1999; Wen et al., 2009; Poff et al., 2010). Dams modify the ﬂow regime, the key process inﬂuencing river–ﬂoodplain ecosystems (Thomas and Adams, 1999; Bunn and Arthington, 2002; Brown and King, 2003; IUCN, 2003; Schoﬁeld et al., 2003; Magilligan and Nislow, 2005; Thoms et al., 2005). The river’s ﬂow regime is one of the major physical processes that controls biota in river– ﬂoodplain systems and hence the biodiversity of these ecosystems (Junk et al., 1989; Maingi and Marsh, 2002; Beauchamp et al., 2007; Rood et al., 2008; Stevaux et al., 2009). Alterations to the natural ﬂow regime in turn alter the magnitude, frequency and duration of ﬂoods, which impacts on the river–ﬂoodplain ecological processes (Brismar, 2004; Graf, 2006; O’Connor et al., 2007). It has been acknowledged that ﬂooding and the inundation of ﬂoodplains are a crucial process that enhances the exchange of moisture, sediments and nutrients between the river channel and the river–ﬂoodplain ecosystems and in the process maintains the connectivity between these river ecosystem components (Ward, 1998; Petts, 1999; Bunn and Arthington, 2002; Thoms et al., 2005). Furthermore, the *Correspondence to: Lindsay Beevers, School of the Built Environment, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK. E-mail: L.Beevers@hw.ac.uk ECOHYDROLOGY Ecohydrol. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/eco.1335 Copyright © 2012 John Wiley & Sons, Ltd.