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The East Usambara sub-montane rainforests in Tanzania are one of the most valuable conservation areas in Africa and constitute one of the greatest regions of plant diversity in the world (Sayer et al. 1992 in Viisteensaari, 2000). They are known for their exceptionally high levels of regional and local endemism; at least 100 species of plants are strictly endemic to the Usambaras, and the forests are noteworthy for several rare and near-endemic species of birds and reptiles (Rodgers & Homewood 1982; Sayer et al. 1992 in Viisteensaari, 2000).
The East Usambara forests also protect the water supply for more than 200 000 people in the nearby town of Tanga, and local people in the mountains depend on the forests for many of their daily needs (Viisteensaari, 2000). These forests have been under continuous exploitative human pressure for at least 2,000 years (Schmidit, 1989 in Frontier Tanzania, 2001). Until recently, especially before the past 50 years (Kikula, 1989 in Frontier Tanzania, 2001), this pressure was sustainable. However, the growing human population in the area is leading to increased pressure on the remaining natural forest, and represents the main threat to its survival (Frontier Tanzania, 2001). Biodiversity loss is a major problem and the cause of this loss as indicated by Bhatia and Ringia (1996) takes many forms:
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Fragmentation of forests. This reduces the effective area of habitats and divides plant and animal populations into smaller, isolated populations that become viable to local extinction. Fragmentation also creates gaps that become barriers to the dispersal and migration of animals and propagules of plants.
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Uncontrolled fires.
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Clearance for subsistence and cash crop cultivation.
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Collection of firewood and building materials.
Currently, biodiversity in these forests continues to be endangered by the rapid spread of invasive alien plants (IAP) (Hulme, 2005). To be classified as invasive, an introduced species must be capable of establishing self-sustaining populations in areas of natural or semi-natural vegetation (Macdonald et al. 1989 in Viisteensaari, 2000) and to produce a significant change in terms of composition, structure or ecosystem process (Hughes 1994; Cronk & Fuller, 1995 in Viisteensaari, 2000). Sheil (1994) in Maunder (1999) suggests that as many as 48 species may have become naturalised in the areas surrounding the Amani botanical garden plantations. A small number of these have become invasive and potentially damaging to the local ecology in the Reserve. But particular attention has been given to Maesopsis eminii (Binggeli, 1989; Sheil, 1994; Hall, 1995; Fowler & Nyambo, 1996) as a coloniser of canopy gaps.
This site contains species descriptions for 52 non-native plant species found in the Usambara forest.
The content of this page was based on part of Edward Ezekiel's MSc research proposal, entitled: Population status and spread of Cordia alliodora in Amani Nature Reserve, Tanzania.
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