Current view: Text account
Site description (2001 baseline):
Site location and context
These are riparian forests along the meandering course of the lower Tana river, some 350-km east of Nairobi and 240 km north of Mombasa. Along the last 65 km of its course, the Tana has a broad flood-plain, 1–6 km wide, that is covered by alluvial sediment deposited during floods. Such flooding takes place in response to heavy rains on the Aberdare mountains (IBA KE001) and Mount Kenya (KE005) watersheds rather than local rainfall in this hot, arid region. The lowland evergreen forests are patchy, of different successional stages, and are dependent on groundwater supplied by the river. Characteristic trees include
Ficus spp.,
Phoenix reclinata, Acacia robusta,
Populus ilicifolia,
Blighia unijugata,
Sorindeia madagascariensis,
Diospyros mespiliformis and
Mimusops obtusifolia. There are about 71 distinct forests, ranging in size from 1–1,100 ha and covering c.3,700 ha in total. 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 36 km along the river’s present course), around 14 in the area managed by the Tana Delta Irrigation Project, and the remainder on Trust land.
See Box and Tables 2 and 3 for key species.
Circaetus fasciolatus,
Tauraco fischeri and
Anthreptes reichenowi are fairly common in this area.
This is the only known site for
Apalis chariessa chariessa, which however may now be extinct as the last record was in 1961. The status of
Sheppardia gunningi is unclear: recent surveys of eleven forest patches found this species only in the largest, Wenje East. The enigmatic
Cisticola restrictus is also poorly known, but may occur in bushland in the National Reserve.
Acrocephalus griseldis is a non-breeding visitor from November to April, and may be numerous on the lower Tana, in riverine thickets. The threatened
Zoothera guttata has been recorded from Kipini, near the river’s mouth, but it is not known if it occurs in forests upstream. The avifauna holds some unusual species for coastal forest (notably
Apalis chariessa, possibly extinct now, which is disjunct from the next known population in the Uluguru mountains of Tanzania). Birdlife is abundant in the variety of habitats at the site, and the oxbow lakes and riverbanks harbour a variety of waterbirds. The area is a stronghold for
Scotopelia peli, a species of regional concern. Other regionally threatened species include
Anhinga rufa;
Ephippiorhynchus senegalensis;
Hieraaetus ayresii (uncommon);
Stephanoaetus coronatus (uncommon);
Podica senegalensis;
Phoeniculus granti;
Turdoides squamulatus;
Erythrocercus holochlorus (moderately abundant in less disturbed fragments: recorded in 8 out of 11 recently surveyed); and
Anthreptes neglectus (recent records from Kitere forest).
Non-bird biodiversity: 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, Colobus badius rufomitratus (LR/nt) and Cercocebus galeritus galeritus (LR/nt). The populations of these species have decreased considerably in recent years and both are seriously threatened. The highly threatened and restricted ungulate Damaliscus (lunatus) hunteri occurs in the bushland nearby. At least 61 plants are globally or nationally rare, and notable species include Anisocycla blepharosepala, an undescribed Dichapetalum sp., Cynometra lukei, Cyphostemma ternatum, Synsepalum msolo, Tylophora stenoloba, Pavetta sphaerobotrys ssp. tanaica and Uncaria africana. On sandy bars and banks in the river grows a poplar tree, Populus ilicifolia, endemic to the Northern Ewaso Ngiro, Tana and Athi/Sabaki rivers.
Pressure/threats to key biodiversity
The riverine forests are also home to the Pokomo people, who farm the riverbanks. They use mainly the oxbows, growing rice next to the water and maize further back. They exploit the forest for fuelwood, 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, forest use is thought to be unsustainable, with fire, pole-cutting and felling of large trees for canoes particular threats. 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. A major GEF-funded project, which began in 1997, is addressing the issue of community use of the forests and their management for biodiversity conservation. It has, however, been plagued with implementation problems, mainly connected with the controversial issue of resettling people who are currently living in the National Reserve. The project will also not tackle the other major potential threat to the forests: dams on the upper reaches of the Tana river. Five major dams—Kindaruma, Gitaru, Kiambere, Kamburu and Masinga (IBA KE030)—already provide hydro-power and irrigation water. These impoundments substantially alter the natural flooding regime of the river, on which continued survival of the forests depends. Recent concern has focused on the planned Mutonga–Grand Falls Hydropower Project. An environmental impact assessment of the original proposal suggested that the new dams at Mutonga and Grand Falls would greatly reduce river discharge, silt deposition and the level of groundwater. This would lead directly to the loss of the riverine forest and the species that it holds. However, following further debate, the present design of the Low Grand Falls dam incorporates an artificial flood and sediment release facility. This is intended to release sediments and artificial floods twice a year, around April and November. Mutonga Dam will also have sand-flushing facilities. Although this increases the costs, these costs will be offset by the environmental value. Construction is to begin in 2003, for commissioning in 2008. Before detailed design and tendering begins, an additional environmental assessment will measure flood patterns for at least two rainy seasons. At least in theory, the new dams will have the potential to mitigate not only their own impact but that of the five existing dams as well. However, who decides whether, when and how the artificial floods are released remains a contentious issue.
Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Lower Tana River Forests (Kenya). Downloaded from
https://datazone.birdlife.org/site/factsheet/lower-tana-river-forests-iba-kenya on 23/11/2024.
