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The Tana Delta and Forests Complex

Date de soumission : 12/02/2010
Critères: (ix)(x)
Catégorie : Naturel
Soumis par :
Kenya Wildlife Service
Etat, province ou région :
Coast Province
Ref.: 5514
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Description

Coordinates:

Tana River Delta: S02 30 E40 20

Tana Forests: S02 30 E40 30

 

The Tana delta and the Tana forest which include the Boni, Dondori, Lunghi, Lower Tana forest, Lango ya Samba Witu forest and the Tana delta provide unique ecosystem that is the Northern limit of Eastern Arc Mountains and Coastal Forests biodiversity hotspot. This area represents a number of unique sites which may be nominated as serial sites. Further research is required to further expound on the values of this area. We proposed the two sites to be considered for serial nomination into the world heritage list.

The Tana Delta is the name loosely given to the floodplain ecosystem of the lower Tana River, a vast wetland complex on the Kenyan coast. Tana Forests are riparian forests along the meandering course of the lower Tana River, some 350km east of Nairobi and 240km north of Mombasa; both areas are described in details below.

Tana River Delta: The delta is roughly triangular in shape, with its apex at Lake Bilisa (north of Garsen) and its base a 50 km stretch of beach along Ungwana (or Formosa) Bay, stretching from Kipini in the north-east to Mto Kilifi in the south-west. This low-lying area is bounded by higher land to the east and west and to the south by a dune system bordering the Indian Ocean. It forms the interface between the river and the ocean, with fresh and brackish lakes and streams, freshwater and saline grasslands and wetlands, and succession stages of forest and woodland on the riverbanks and the dune ridges parallel to the shore (Robertson & Luke 1993).

The mouth of the river has shifted many times. Today, the main stream of the Tana follows an artificial course. More than a century ago, the flooded river cut through into a canal dug for navigation from Belazoni, on the main river, into the Ozi (itself possibly an old Tana course). As a result, the river now flows directly into an estuary at Kipini, rather than into the complex system of channels and distributaries leading to its old mouth at Mto Tana. Until recently, some fresh water still flowed into the 'old' delta through one of these channels, the Kalota Brook. However, since 1988 this has been blocked by a small dam built by Pokomo farmers, who use the tidal bore to push fresh water into their fields and irrigate their crops.

The entire floodplain in the lower parts is covered by alluvial sediments, transported and deposited during the annual flooding of the river. These lie over quaternary sediments that include marine sands, mud and coral breccia. Moving inland, the rainfall drops from around 1,000 mm per year at Kipini to less than 600 mm at Garsen. Flooding happens not as a result of local precipitation, but because of rain in the river's catchment on Mt Kenva and the Aberdare Mountains. Normally, the major floods occur in April-May with a smaller, short-rains flooding in October -November. The timing, extent and duration of the flooding vary greatly from year to year.

The Tana River Delta contains a very wide variety of habitats, including riverine forest, grassland, woodland, bushland, lakes, mangroves, dunes, beaches, estuaries and coastal waters. Small fragments of riverine forest, not nearly as extensive as the forests north of Garsen, occur along the present or former river courses. Diospyros and Sorindeia madagascariensis dominate the main canopy, with Cola clavata and Garcinia livingstonei beneath (Ecosystems Ltd. 1985). Phoenix reclinata and Barringtonia racemosa are also prominent (Survey of Kenya 1984). Some 67,000 ha of the delta are covered by floodplain grasslands, subject to seasonal flooding (Njuguna 1992). The extensive areas with heavy clay soils are covered by grasslands dominated by Echinocloa haploclada, along with E. staginina, Sporobolus helvolus, Panicum maximum and Cynodon dactylon. In areas that remain seasonally flooded for long periods, the sedge Cyperus rotundus dominates, with Ecinochloa colonum. Grasslands of Digitaria alscendens and Sporobolus confunis occur in more elevated, sandy areas, such as the levees along old river courses. Inland of the coastal sand dunes and mangroves, saline grasslands are dominated by the spiky Sporobolus spicatus the salt-bush Suaeda monoica West of the floodplain is bushland, with a diverse composition including species of Boscia, Combretum and Commiphora. Wooded bushland or grassland, with fire-resistant Doum Palms (Hyphaene coriacea), Terminalia spinosa and Thespesia danis, occupies a broad swathe east of the floodplain, merging (through intermediate woodland that includes Diospyros cornii and (Croton dichogamus) into the Boni Forest vegetation to the north.

Other bushland associations form a complex mosaic with the floodplain grasslands. Areas of bushed grassland on slightly raised ground are dominated by Acacia zanzibarica with the grass Sporobolus helvolus. Denser patches of wooded bushland thicket include the shrubs Dobera glabra, Grewia sp. and Commiphora schimperi, with Panicum sp., Leptothrium senegalense and Cenchrus ciliaria among the grasses. Parallel to the coast along Ungwana Bay run lines of high dunes; some as much as 37m above the sea. These are covered by their own distinctive vegetation, a dense thicket dominated by Dombeya sp. and Grewia similis. In the valleys the thicket mingles with taller trees, such as the palms (Hyphaene coriacea) and H. compressa, Garcinia livingstonei, Euphorbia candelabrum, and Afzelia quanzensis.

Palms are prominent in many places Borassus (Borassus aethiopum) and the Wild date Palm (Phoenix reclinata) as well as Doum Palm (Hyphaene coriacea). In places, especially those cleared and burned in the past, these form substantial palm-bushed grassland (Ecosystems Ltd.1985) mangrove forest, with all of Kenya's eight mangrove species represented, grows at Kipini in the Tana estuary and along the network of channels further south.

As well as seasonal wetlands in the oxbows and floodplain depressions, the delta contains a number of more-or-less permanent lakes and marshes. These include Lakes Bilisa, Dida Warede, Harakisa, Kongolola, Kitumbuini, Moa and Shakababo. Some of these may dry out in certain years but others, like Lake Shakababo and Bilisa, maintain true aquatic plants (including Nile Cabbage (Pistia stratiotes) and Water Lily (Nymphaea sp.) and good populations of several species of fish (Ecosystems Ltd. 1985, Njuguna 1992). Luo and Luhya immigrants to the area are responsible for an active and thriving fishery, while Orma pastoralists use these wetlands as dry-season grazing areas for their livestock.

Tana Forests: Along the last 65km of Tana River course, it has a broad flood plain, 1-6km wide, that is covered by alluvial sediment deposited during floods. Flooding takes place in response to heavy rains on the Aberdare Mountains and Mount Kenya watersheds rather than local rainfall in this hot, arid region. These lowland evergreen forests are patchy, of different succession stages, and are dependant on ground water supplied by the river. Characteristic trees include Ficus spp., Phoenix reclinata, Acacia robusta, Populus ilicifolia, Blighia unijugata, Sorideia madagascariensis, Diospyros mespiliformis and Mimusops obtsifolia (Robertson & Luke 1993). There are about 71 distinct forests, ranging in size from 1-1,100 ha and covering around 3,700 ha in total (Butynski & Mwangi 1995). They form part of a mosaic of habitats that includes grassland, wooded grassland, bushland and deciduous woodland. The forests lie on both banks of the Tana. Of the 71 patches, 16 (covering 1,000 ha) fall within the 17,100 ha Tana River Primate National reserve (which extends for about 36km along the river's present course), around 14 in the area managed by the Tana Delta Irrigation Project, and the remainder on Trust land (Seal et al. 1991).

Wildlife

Tana River Delta: The importance of the Tana River Delta lies in the expanse, intactness, variety and productivity of its habitats. The floodplain is grazed by a number of ungulates including the restricted East African coast sub-species of Topi, (Damaliscus lunatus topi), with some 30,000 or so in the area (Ecosystems Ltd. 1985). The rivers and channels support large numbers of Hippopotamus amphibius (estimated at 400-450: Ecosystems Ltd. 1985) while Nile crocodile (Crocodylus niloticus). Ungwana Bay is one of the few places Dugong (Dugong dugon), critically endangered in the region, has been recorded recently. The turtles (Chelonia mydas), Eretmochelys imbricata and Lepidochelys olivacea nest on the sandy beaches. Whitehead (1959) lists 22 freshwater fish species from the lower Tana, including three eels (Anguilla spp). and a distinct sub-species of Petrocephalus catastoma. The mangroves provide vitally important spawning and nursery grounds for many species of fish and crustaceans.

The extensive mangrove forests include the only significant stands in Kenya of Heriteria littoralis, and two other species that are considered threatened, Xylocarpus granatum and Bruguiera gymnorrhiza (Wass 1995). 280 plant taxa are recorded for the delta, and many more undoubtedly occur as there has been no thorough botanical survey; of these, 18 are considered rare in Kenya or globally (Robertson & Luke 1993). The Tana River Delta is a stronghold for two near threatened Bird species, Malindi Pipit and Basra Reed warbler, and 13 of Kenya's 30 East African Coast biome species occur. The wetlands, including the coastline and offshore islets, at times hold exceptional concentrations of waterbirds. Internationally-important populations have been no fewer than 22 species, during the flood season, the no-flood or both.

Tana Forests: At least two globally threatened bird species occur, along with at least two and possibly three of the species in the East African Coastal Forests Endemic Bird Area, and at least 19 of the 30 Kenyan species in the East African Coast biome. The threatened spotted ground thrush has been recorded in Kipini, near the river's mouth (Britton 1980). Birdlife is abundant in the variety of habitats at the site, and the ox-bow lakes and riverbanks harbour a variety of water birds. The fauna of these unique, remnant forests bears traces of ancient links to the Congo basin forests, during the Miocene period. They are the only home of two distinctive primates, the Tana River Red Colobus (Colobus badius rifomitratus) and Tana River Mangabey (Cercocebus galeritus galeritus). The populations of these species have decreased considerably in recent years and both are seriously threatened (Mendely et al. 1991, Butynski & Mwangi 1995). The critically endangered and restricted Hunter's antelope or (Hirola Beatragus hunteri) occurs in the bushland in the east bank. At least 61 plants are globally or nationally rare, and notable species include Anisocycla blepharosepala, undescribed Dichapetalum sp., Cynometra lukei, Cyphostemma ternatum, Synsepa msolo, Tylophora stenoloba, Pavetta sphaerobotrys ssp. tanaica and Uncaria africana (Robertson & Luke 1993). On sandy bars and banks in the river grows a popular tree, Populus ilicifolia, endemic to the Northern Ewaso Ng'iro, Tana and Athi/Sabaki rivers.

Justification de la Valeur Universelle Exceptionelle

(ix) and (x): The Tana Delta is an outstanding example representing significant on-going ecological processes of fresh water and coastal and marine ecosystems and has unique communities of plants and animals. It hosts the restricted East African coast sub-species of Topi, (Damaliscus) the turtles (Chelonia mydas), Eretmochelys imbricata and Lepidochelys olivacea nest on the sandy beaches; the fish species lunatus, including three eels (Anguilla spp) are found here including the distinct sub-species of Petrocephalus catastoma. The delta falls under the Northern limit of Eastern Arc Mountains and Coastal Forests biodiversity hotspot.

The Tana forests are outstanding examples representing significant on-going ecological processes in terrestrial ecosystems and have unique communities of plants and animals. The forests are the only home of two distinctive primates, the Tana River Red Colobus (Colobus badius rifomitratus) and Tana River Mangabey (Cercocebus galeritus galeritus). It is also home to the restricted Hunter's antelope or (Hirola Beatragus hunteri). The forest hosts at least 61 plants species that are globally or nationally rare.

Déclarations d’authenticité et/ou d’intégrité

The Tana Delta and Forest Complex include a large area with natural habitats for maintaining endemic and threatened biota. It has critical habitats essential for the survival of viable plant and animal populations.

Conservation issues

As there is no recognized management for the Tana delta disputes over the rights to water and land are at the heart of the complex conservation problems facing the Tana River Delta. The importance of the area for conservation is widely recognized, but there is little agreement on the appropriate steps forward and large parts of the area remains largely unprotected.

The numerous patches of riverine forest, woodland and bush lands in the delta are edaphic in origin, and their continued existence depends on critical minimum levels of flooding. The flood regime has already been disrupted by five large water impoundments (Seven Folks dams used for generation of hydroelectricity) upstream

A major sugar irrigation scheme is planned in the Tana Delta which is expected to increase sugar production and create employment. However environmentalist have raised concerns to large-scale sugar production schemes citing loss of important habitat, the impacts of fertilizers and pesticides, and the loss of grazing land for pastoralists.

The two major distributaries into the delta proper, the Furaha and Kalota Brooks, are now blocked by barrages constructed by the local people. The Furaha was cut off in the late 1970s and the Kalota in 1988, in both cases after a drought year. The Ozi rice scheme depends on natural irrigation from river water pushed back by the tidal bore at Kipini, and the lowered river volume in time of drought raised fears that the Tana might change its course again.

Environmental degradation in this recently pristine habitat continues apace. Destruction of woodland and mangroves, slash-and-burn agriculture, illegal hunting of wildlife and unregulated off-shore trawling are all diminishing the delta's resources. More disturbingly, there are reports of allocations of large chunks of land to individuals (Becha 1997).

The riverine forests are also home to the Pokomo people, who farm the river banks. They use mainly the ox-bows, growing rice next to the water and maize further back. The forest is exploited by them for fuel wood, timber and traditional medicines. High rates of population growth have increased pressure on resources, and large areas of forest have been felled to make way for cultivation. Generally, forests use is thought to be unsustainable, with fire, pole cutting and felling of large trees for canoes particular threats (Seal et al.1991, Robertson & Luke 1993). Insecurity on the eastern bank of the river has helped protect the forests there, which are generally in better condition. Many important forests, and an estimated 63% of the colobus and 44% of the Mangabey populations, occur outside the reserve. These patches are generally under more immediate pressure than those within it.

Comparaison avec d’autres biens similaires

The Tana Delta is similar to the Kakamega forest in Kenya as both are rich in biodiversity, have a high level of endemism making the areas important conservation sites for endemic and unique species that occur here.

Tana Delta is similar to the Discovery Coast Atlantic Forest Reserves in the rainforests of Brazil's Atlantic coast; are both rich in biodiversity. The sites contain a distinct range of species with a high level of endemism and reveal a pattern of evolution that is not only of great scientific interest but is also of importance for conservation. Both sites hold unique blend of both animals and plants, and although different, the sites provide a home to rare and endangered species.

As the Tana forests are the only home to the Tana River Red Colobus and Tana River Mangabey they are comparable to Kahuzi-Beiga national park in Democratic Republic of Congo, as this park not only also has a diverse and abundant fauna, it hosts one of the last groups of eastern lowland Gorillas. These properties are therefore unique and of great importance in ensuring the survival of these species.