Intentional introductions of alien plants in Tanzania, particularly in East Usambara Mountains, can be traced back to the early 1890's, when a small botanical garden was opened at Amani. The botanical garden became the basis of the 'Biological-Agricultural Institute of Amani', which was formerly established in 1902 (Schulman et al. 1998; Frontier, 2001). During this period, many exotic trees and crops were introduced to Amani by Germans, who were interested in economic development; especially export of agricultural goods to Germany (Hamilton, 1989). The Royal Botanic Garden of Berlin provided 859 specimens of commercially important tropical plants to Amani Botanical Garden.
In 1902, 350 hectares of land were set aside at Amani as an area for the botanical Garden, running from the lowlands up to the plateau (Hamilton, 1989). Between 1902 and 1914 about 200 hectares of this area were developed as trial plantations including close to 1,000 different indigenous and exotic species from similar ecological zones in the tropics. Some were established in clear trial blocks and plantations, while others were planted in the residential and office areas of the research centre (Sandy et al., 1997). These plantations now constitute the Amani Botanical Garden, perhaps more appropriately termed an arboretum.
The Amani Botanic Garden and associated facilities are situated within Amani Nature Reserve in the East Usambara Mountains, a globally recognized centre of biodiversity and one of the most valuable conservation areas in Africa. In the 1930's, the Amani Botanical Gardens contained extensive collections of exotic economic and ornamental plants and represented the largest living plant collection in Sub-Saharan Africa (Maunder, 1999). It is likely that the Amani Botanical Garden still contains one of the largest collections of exotic plants in tropical Africa. It is estimated that about 600 different taxa were planted with about 460 still surviving (TAFORI, 1993; Iversen, 1991b). Whilst a botanic garden can play an important role in the conservation of biodiversity it should also be recognised that a collection of exotic species can represent a conservation liability. A number of plant species, introduced to the area through the Amani Botanical Garden, have become naturalised, and a small number of these have become invasive and potentially damaging to the local ecology (Maunder, 1999).
Amani Nature Reserve, in the East Usambara Mountains in northeast Tanzania was gazetted in 1997. It is the largest block of forest in the East Usambara Mountains. In terms of conservation, Amani is an important habitat for a large number of endemic and threatened species (Frontier, 2001), and therefore offers a unique opportunity for eco-tourism, training and study within the Eastern Arc Mountains. Despite this, the biodiversity of Amani Nature Reserve is threatened by the spreading of alien species, and some of these species, such as Maesopsis eminii, are reported to occupy very big areas of the Reserve (Binggeli, 1989; Mugasha, 1981). However, studies by Fowler & Nyambo (1996) and others indicate that Maesopsis may not prove a long term threat to the Reserve if disturbances are controlled. Therefore native trees may eventually replace the existing stands of Maesopsis. Recent studies by Maunder (1999) at Amani Nature Reserve have identified another 14 alien plant species that are locally important invasive species. These are Areca catechu, Arenga pinnata, Castilla elastica, Cedrela odorata, Cinnamomum camphora, Clidemia hirta, Cordia alliodora, Elaeis guineensis, Hevea brasiliensis, Lantana camara, Mimosa pudica, Phyllostachys henionis (now called P. nigra), Psidium cattleianum and Rubus rosifolius.
The content of the above text was based on part of John Richard's MSc research proposal, entitled: Status of the Panama rubber (Castilla elastica) in Amani Nature Reserve: Spread and Management options.
Environmental conditions at Amani (provided by Royal Botanic Gardens, Kew):
| Annual rainfall |
1945 mm |
| Max recorded annual rainfall |
3505 mm |
| Min recorded annual rainfall |
1377 mm |
| Humidity |
Very high |
| Annual mean temperature |
20.8 degrees Celsius |
| Mean daily max temperature |
24.6 degrees Celsius |
| Mean daily min temperature |
16.3 degrees Celsius |
| Soil type |
Red loam, texture light loam, sandy, readily permeable to water. |
| Soil pH |
4.6 to 5.2, sometimes higher in top few inches. |
