Zambezian coastal flooded savanna

Untamed, the Zambezi River must have been a force to behold at the start of the rainy season. Spring floodwaters surged down the valleys through narrow river channels and gorges, and onto the vast floodplains at the mouth of the Zambezi, bringing nutrients and rich soils essential to the productivity and survival of the plants and animals of the delta. The closure of the Cahora Bassa and Kariba dams in the 1960’s and 1970’s, however, brought a halt to these annual cycles, and resulted in significant changes to the wetland ecosystems of the Zambezi. The civil war in Mozambique that continued for almost two decades decimated the large herds of buffalo and waterbuck that used to roam the plains of the delta and other smaller riverine coastal floodplains in the area. Despite these factors, the wetlands in the coastal regions of the Zambezi basin still contain some of the most diverse habitats in the region.

  • Scientific Code
  • Ecoregion Category
  • Size
    7,500 square miles
  • Status
  • Habitats

Location and General Description
The Zambezian Coastal Flooded Savanna is restricted to the coastal regions of Mozambique, and essentially comprises the floodplain deltas of the Zambezi, Pungwe, Buzi and Save Rivers that all drain the Zambezi Basin. The Zambezi delta forms the most extensive portion of the ecoregion, covering roughly 200 km along the coastline and penetrating up to 120 km inland (Timberlake 1998). The Buzi and Pungwe rivers flood around 4500 km2 of wetlands in their deltas (Hughes and Hughes 1992), while a number of small swamps at the mouth of the Save fall into this ecoregion. These flooded savannas are embedded within the southern Zanzibar-Inhambane Coastal Forest Mosaic, with the Eastern African Mangroves generally forming a thin barrier between this ecoregion and the ocean to the east.

The wetlands and floodplains of the Zambezian Coastal Flooded Savanna ecoregion are located along the lowland coast next to the Indian Ocean and are typically below 50 m in altitude. Relatively recently deposited alluvial and floodplain fluvisols predominate, overlaying sediments that were mainly deposited by the rivers during the Quaternary and Cretaceous periods.

Located in the sub-tropical climatic belt of Africa, the ecoregion is characterized by mild temperatures, with most of the rain falling in the warm austral summer months. A high-pressure system dominates over the southern African plateau for much of the year, and northeast and southeast airstreams from the Indian Ocean bring rain to the area during the months of October to March. The ecoregion experiences annual rainfall of 800-1400 mm per annum. Mean maximum temperatures range between 27 and 30oC, with mean minimum temperatures averaging 18oC.

Occurring in White’s (1983) Zanzibar-Inhambane Regional Mosaic, the vegetation of this wetland ecoregion contains both open grassland-dominated communities and mixed freshwater swamp forests. Dominant grass genera of seasonally flooded clayey depressions (‘tandos’) include Hyparhenia, Ischaemum and Setaria, while species such as Panicum curatellifolia, Uapaca nitida and Syzigium guineense are common woody species of the ecoregion. The swamp forest component, including Barringtonia racemosa, Ficus verruculosa and Phoenix reclinata, generally borders rivers, lakes, and lagoons. In more permanently waterlogged areas, reed swamps characterized by Phragmites australis and Typha capensis predominate, being replaced by mixed herbaceous and grass swamps under drier conditions. Associated vegetation types are numerous and include Borassus palm savanna, mangrove and dune forests as well as patches of mopane and miombo woodlands.

Until the 1970’s, much of the ecoregion was subject to seasonal flooding that spread out onto the floodplains at the onset of the rainy season. It was only with the construction of large dams such as the Cahora Bassa and the Kariba on the Zambezi River that these important inundation events were severely reduced.

Biodiversity Features
Deltas and coastal wetlands are generally rich in biota and habitats, since they are found at the interface between terrestrial, freshwater and marine environments. The wetlands and deltas of this ecoregion are no exception. The Zambezi delta has amongst the highest diversity of habitats in the Zambezi basin, which is reflected in a high species richness of mammals and birds.

Although a high diversity of mammals have been recorded in the wetlands of this ecoregion, the damming of the Zambezi River in combination with the lengthy civil war in Mozambique has resulted in the decimation of several populations. Species such as buffalo (Synerus caffer), waterbuck (Kobus ellipsiprymnus), Southern reedbuck (Redunca arundium), zebra (Equus buchellii) and hippo (Hippopotamus amphibius), which were found in high numbers at the onset of the Renamo-Frelimo war at the end of the 1970’s, had declined by as much as 90 percent by the early 1990’s (Goodman 1992).

Apart from the abovementioned ungulates, several other herbivores are found in this wetland ecoregion. These include eland (Taurotragus oryx), which migrates seasonally between the woodlands and more open grasslands; the early flushes of grass attract these large-bodied bovines into the open areas at the onset of the rainy season (Kingdon 1997). In contrast, Lichtenstein’s hartebeest (Alcelaphus lichtensteinii) and sable (Hippotragus niger) – whose centers of distribution are both in the miombo ecoregions of the Central African Plateau – move into the better watered drainage lines and grasslands during the dry winters, retreating to firmer ground and more wooded areas at the onset of flooding. Oribi (Ourebia ourebi) favor the less waterlogged areas on extensive floodplains such as the Zambezi delta, where termitaries, herbs and woody growth provide cover and supplement their diet. Nyala (Tragelaphus angasi), wildebeest (Connochaetes taurinus), steinbuck (Raphicerus campestris) and warthog (Phacochoerus africanus) are also common to the ecoregion. Elephant (Loxidonta africana) and black rhino (Diceros bicornis), once prolific in the area, are extremely scarce and may be locally extinct.

Large carnivores found in the ecoregion include lion (Panthera leo), leopard (P. pardus), cheetah (Acinonyx jubatus) and spotted hyaena (Crocuta crocuta). Side-striped jackal (Canis adustus) is also fairly common in savannas, swamps and moist floodplains throughout the ecoregion. While the African wild dog was historically found throughout sub-Saharan Africa in non-forested, non-desert regions, its current status in the ecoregion is unknown; it may in fact have become locally extinct. Smaller predators include the large spotted genet (Genetta tigrina), the African civet (Civettictis civetta) and serval (Felis serval). The African clawless otter (Aonyx capensis) is found along all waterways that provide adequate cover for concealment and shelter for breeding. The spot-necked otter (Lutra maculicollis) is also known from the wetlands of this ecoregion, as is the banded mongoose (Mungos mungo), white tailed mongoose (Ichneuma albicauda) and the bushy tailed mongoose (Bdeogale crassicauda).

The floodplains of the deltas in this ecoregion provide habitat for many species of overwintering and breeding waterbirds. For example, common waterbirds at the Marromeu Complex Game Management Area in the Zambezi delta include openbilled storks (Anastomus lamelligerus), saddlebilled storks (Ephippiorhynchus senegalensis) and white-backed pelicans (Pelecanus onocrotalus). Although no endemic bird species are found in the ecoregion, the Zambezi basin as a whole supports roughly 95 percent of the global population of the wattled crane (Bugeranus carunculatus) (Beilfuss 1995). About 20 percent (or 2,750 individuals) of the world population of this globally vulnerable species (WCMC 2000) is known to breed in the Zambezi delta (Beilfuss and Allan 1996, Goodman 1992, Singini 1996). Other birds of global concern include the great snipe (Gallinago media), which is a Palearctic migrant, the African skimmer (Rynchops flavirostris), an intra-African migrant breeder whose major population is found in the Zambezi basin, and the lesser flamingo (Phoenicopterus minor) (Timberlake 1998). The rare eastern African coastal forest bird species, East Coast akalat (Sheppardia gunningi, VU), is also recorded from the Marromeu reserve in the delta. (Hilton-Taylor 2000)

The Nile crocodile (Crocodylus niloticus), monitor lizard (Varanus niloticus) and python (Python sebae) are amongst the more common larger reptiles of the ecoregion,

The only strictly endemic vertebrate in this ecoregion is the Pungwe worm snake (Leptotyphlops pungwensis). There are three other snakes that are nearly endemic to the ecoregion, namely floodplain water snake (Lycodonomorphus obscuriventris), dwarf wolf snake (Lycophidion nanus) and eyebrow viper (Proatheris superciliaris). There is also one near-endemic amphibian, Afrixalus delicates, which occurs in the Zambezi delta area and then in the coastal area south of Maputo.

Amongst the invertebrates, there are some local endemics. Of the butterflies recorded only in the Zambezi Basin, four species are largely or totally confined to this ecoregion. They are: Ypthima granulosa, Acraea dammii, Euphaedra orientalis and Teniorhinus herilus (Pennington 1978).

The general absence of endemism in the fauna and flora may in part be due to the relatively recent development of most of these wetlands. There is some speculation regarding the palaeogeography of the Zambezi basin, but general consensus is that the Zambezi delta is relatively new and that there has therefore been insufficient time for distinctive biota to evolve (Timberlake 1998). The wetlands and deltas of the Pungwe and the Buzi may, however, be much older and it is here that restricted species and distinct biota may be found. It should be noted that the ecoregion’s fauna and flora is poorly known and greatly under-collected; this is particularly true for the Pungwe, Buzi and Save wetlands. The low rates of endemism may, therefore, at least partly be an artifact caused by insufficient research.

Current Status
Dam construction and two decades of armed conflict have had severe impact on the ecoregion’s biota, with up to 300-fold decreases seen in some large mammal populations. One consequence of the construction of the Kariba and Cahora Bassa dams along the Zambezi River has been to reduce the natural flooding of the Zambezi delta, making the area more accessible to hunters (Singini 1996). In addition, the military occupation of most of the protected areas and national parks during the armed conflict in Mozambique resulted in the massive extermination of many herd animals. For example, herds of up to 55,000 buffalo used to roam the floodplains of Marromeu and the Zambezi delta (Tello and Dutton 1979). At the beginning of the 1990s the numbers were estimated to be roughly 2,350 (Cumming et al. 1994); in 1995 less than 1,000 were counted in a survey of the Marromeu area (Singini 1996). Waterbuck were also seriously affected, declining from around 48,000 in 1978 (Tello and Dutton 1979) to 143 in 1994 (Cumming et al. 1994). Hippopotamus were similarly affected: a population of roughly 2,820 in 1977 had been reduced to 260 by 1990 (Anderson et al. 1990). However, in some cases, populations are beginning to recover.

The instability caused by the Mozambican civil war and the occupation of the military of the existing protected areas left the official conservation network in complete disarray. At present, the Marromeu Complex Game Management Area in the Zambezi delta is the only officially protected area within this ecoregion. Situated in the Zambezi delta, this protected area consists of a range of habitats including floodplains, rivers, mangrove swamps, muddy intertidal zones and sea grass beds. Historically famous for its massive herds of buffalo, Marromeu in the late 1980’s was still home to a range of animals such as zebra, Southern reedbuck, bushbuck (Tragelaphus scriptus), eland, oribi, suni (Neotragus mochatus), nyala, greater kudu (Tragelaphus strepsiceros), wildebeest, (Connochaetes taurinus), common duiker (Sylvicapra grimmia), blue duiker (Cephalophus monticola) and red duiker (C. natalensis) (IUCN 1987). Elephant and black rhino were also known to occur. Prominent waterbirds of the area include greater flamingo (Phoenicopterus ruber), wattled crane, and a large nesting colony of white-backed pelican (Pelecanus onocrotalus).

In addition to Marromeu, calls have been made to designate the Zambezi delta as a wetland of international significance under the Ramsar convention (Anderson et al.1990, Singini 1996). The delta is extremely important for numerous waterbirds, including the threatened wattled crane. Furthermore, it is probably the most diverse area in terms of habitats within the basin, and it provides expansive habitats to many large animals (Timberlake 1998).

While the animal populations of the ecoregion suffered severely as a result of the civil war, much of the habitat is still intact. Annual inundation has until recently been an integral part of the natural cycles of the wetlands and floodplains of this ecoregion. The combination of a myriad of permanent waterways with extensive areas that were seasonally exposed to flooding resulted in many of the wetland habitats historically being relatively inaccessible to humans. While building dams and restricting flooding made these areas more accessible, the armed conflict in Mozambique forced many people to migrate to urban centers or along major transport routes, which offered marginally safer living conditions. Many of the habitats of this ecoregion, therefore, remain in good condition, and wildlife restoration is a realistic possibility now that the war has ceased (East 1999). Furthermore, the comparative lack of development and settlement means that the area has one of the best conservation potentials in the region (Timberlake 1998).

Types and Severity of Threats
While the habitats of the ecoregion remain in relatively good condition, further dam construction, continued poaching, human resettlement and population growth along with agricultural development are just a few of the threats currently impacting these wetlands.

The impacts of dams are numerous. Although the Zambezi has already faced much of the damage caused by dam construction with the installation of Kariba and Cahora Bassa, two new projects are being proposed at Batoka Gorge below Victoria Falls and at Mepanda Uncua below Cahora Bassa. The Buzi, Pungwe and Save may face similar regulation of their flow regimes as more dams are constructed along their courses. Apart from making the wetlands more accessible to people, dams have a number of other deleterious effects. Swamp and floodplain habitat is lost as a result of reduced flows and inundation events, which in turn has significant consequences for wetland fauna and flora. For example, the Marromeu grasslands are clearly drying out and the changing hydrology of this area has given rise to growing concern with regards to the conservation status of the wattled crane (Timberlake 1998). Furthermore, a high proportion of important nutrients and sediments that are carried only by large floods may no longer reach the wetlands. The Zambezi used to flood extensively, and would occasionally cross over into the Pungwe Basin through Gorongosa National Park (Tinley 1977). With the cessation of flooding, productivity of the alluvial plain is now largely determined by rainfall. There are also reports of subsurface salt-water intrusion (Singini 1996) and of the invasion of the grasslands by woodland species (Timberlake 1998). Changes in flood regime are known to have large impacts on fish composition and productivity, which in turn affects pisciverous waterbirds.

With the decimation of several wildlife populations, any continued poaching poses significant threat to many species. In addition, the elimination of certain animals may have far-reaching consequences for the healthy functioning of these wetland ecosystems. For example, one consequence of drastically reduced hippo numbers has been the clogging of water channels by vegetative growth, often by alien species such as Eichornia crassipes. Not only does the growth of dense aquatic alien vegetation further impede flooding and outcompete natural vegetation, but it is also known to affect fish productivity and numbers.

Although human population density of the ecoregion is presently fairly low, the cessation of the armed conflict in combination with rapid population growth means that in all likelihood the ecoregion is going to face increasing exploitation over the next few decades. If the wetlands continue to dry out there is little doubt that subsistence farmers will increasingly encroach onto the floodplains in search of land for pastures or cultivation. In addition, large-scale wetland reclamation for sugarcane and coconut plantations may considerably reduce the ecoregion’s remaining intact habitat. Furthermore, although pollution is not presently a major problem in the ecoregion due to low levels of industry and development, wetlands are known to act as sinks for wastes and pollutants (Timberlake 1998). Use of chemical insecticides such as DDT for control of insects such as tsetse fly and mosquitoes, as well as increased human activity in the ecoregion may therefore also pose significant threat to the integrity of these wetland ecosystems. Finally, over-exploitation of coastal resources could lead to accelerated erosion and salination of these coastal wetlands, which are separated from the ocean by just a thin barrier of mangroves.

Justification of Ecoregion Delineation
The Zambezian Coastal Flooded Savanna ecoregion is included within White’s (1983) Zanzibar-Inhambane regional mosaic. As an interface between the marine, freshwater and terrestrial realm, it contains some of the highest habitat diversity within the Zambezi Basin. It is also distinguished from the inland Zambezian flooded grasslands in its important role for migrating and breeding waterbirds, including 95 percent of the global population of wattled crane. The largest area delineated is at the mouth of the Zambezi River, with other smaller patches of flooded savanna at the Pungue River, Buzi River and Save River in the south. In each case, the boundaries follow the maximum range of flooding from these rivers.

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Prepared by: Karen Goldberg
Reviewed by: In progress


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