The Kilombero river flows north-east through a 35-km-wide flood-plain between the Udzungwa mountains (TZ011, TZ066) and the Mahenge massif. The other major rivers are the Ruhudji and Ruaha, draining the Njombe Highlands to the south-west and the Kihansi and Ruipa, which fall from the Udzungwa mountains. The site is delimited by the TAZARA railway to the west and the Msenga–Malinyi road to the east. During the dry season (June–November) the main river is less than 100 m wide at Ifakara, the principal town in the valley. During the rains (December–May) virtually the whole flood-plain can be inundated, the river reaching some 6 km wide at Ifakara. There is a permanent swamp at Kibasira, south of the village of Mofu, and an unnamed swamp in the far south-west, on the Kihansi river, with a small stretch of gallery forest. The northern end of the valley is now largely given over to the cultivation of sugar-cane, including a commercial estate either side of the Great Ruaha river. Magombero Forest Reserve is an important forest that once would have been contiguous with the escarpment forest on the Udzungwa mountains. There is also a relatively large area of forest on the eastern bank of the Kilembero river, to the north of Kivukoni ferry, which is contiguous with forest in the Selous.
See Box and Table 3 for key species. Ploceus burnieri, first found in 1986, is known to occur from Kivukoni Ferry south along the river to Lake Mofu, while two new taxa of cisticoline warbler remain undescribed. Ardeola idae is described as quite common in the valley between June and November and, together with the adjacent Selous Game Reserve (TZ018), this is likely to be an important area for this species. A single record of Dendropicos stierlingi may indicate a larger population in the miombo woodland. The river is likely to be an important breeding location for Rynchops flavirostris, although no counts have been conducted during the breeding season. Numbers of Anastomus lamelligerus are thought likely to exceed the 1% threshold. There are extensive areas of riverine forest along the rivers that flow off the escarpments and these are known to hold populations of Alcedo emitorquata, Podica senegalensis and Anas sparsa. Gorsachius leuconotus and Scotopelia peli are found among the taller riverside trees. From preliminary ringing data, the valley may hold significant numbers of Palearctic warblers, particularly Acrocephalus schoenobaenus. The valley also holds the only lowland population in East Africa of Centropus cupreicaudus. Other species found along the valley in reasonable numbers include Vanellus senegallus and Pseudhirundo griseopyga. Magombero Forest Reserve is a vital cold-season wintering area for populations of montane birds and has avifaunal links with the threatened coastal forests. The valley holds very high densities of raptors. Seven species of the East African Coast biome have been recorded (see Table 3).
Non-bird biodiversity: The valley contains up to 75% of the remaining Kobus vardoni (LR/cd) population. The area is also an important dry-season refuge for approximately 5,000 Loxodonta africana (EN), and large herds of Syncerus caffer (LR/cd). There are nine known endemic plant species and one endemic amphibian, the toad Bufo reesi.
Pressure/threats to key biodiversity
The natural habitat at the northern end of the valley has already been destroyed and even the remnants of Magombero Forest occurring south of the railway are under tremendous pressure. During the last decade there has been increased immigration into the valley, to the extent that the foothills of the Udzungwa mountains between the road and the Forest Reserves have largely been given over to cultivation. Large tracts of land between the road and the river have also been parcelled up into smallholdings and in one area a 10,000-ha rice-scheme has been initiated. Overgrazing may be a severe problem, especially on the eastern side of the valley, as it affects the woodland–grassland boundary causing the wooded area to be degraded. Significant amounts of wood are cut for fuel.The Kilombero Valley Teak Company own and manage 28,229 ha of woodland in the valley. Of this, 4,628 ha is suitable for planting teak and 3,000 ha has been planted. Mitigation measures (such as thin miombo corridors between plantations) have been implemented, but their effectiveness has yet to be assessed. Perhaps the most concerning issue is the location of the plantations between the flood-plain and adjacent hills, interfering with the seasonal movement of mammals. It is important to protect the remaining riverine forest to maintain physical links with the escarpment forest on the Udzungwa mountains. There is existing legislation to protect riverside vegetation, but it is widely ignored.