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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.
BirdLife International (2020) Important Bird Areas factsheet: Lower Tana River Forests. Downloaded from http://www.birdlife.org on 25/10/2020.