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The Eastern Arc Mountains comprise a chain of separate mountain blocks running from southern Kenya through Tanzania in a crescent or arc shape. In Tanzania, the Eastern Arc consists of North and South Pare, East and West Usambaras, Nguru, Ukaguru, Rubeho, Uluguru, Udzungwa and Mahenge Mountains. The mountains and forests on them are very important to Tanzania and also globally. A large number of products and services are provided from the forests to the Tanzanian people, and globally important biodiversity values are found. In this paper, these important features are highlighted.
An understanding of forest area, fragmentation and loss is central to developing strategies to conserve biological diversity in the Eastern Arc Mountains. Using recent 1:250,000 land cover and use maps (Tanzanian Ministry of Natural Resources and Tourism, 1996) and 1:250,000 and 1:500,000 topographic maps, I examine natural forest area, fragmentation, and loss in the Eastern Arc Mountains. I estimate the maximum total area of natural forest, open as well as closed forest, in the Eastern Arc Mountains is 5,340 km2. The remaining natural forest in the Eastern Arc Mountains is highly fragmented. The median patch size is 10.2 km2, and the mean patch size is 58.0 km2. Based upon the estimates of various workers, approximately 1,447 km2 of closed forest remains in the Eastern Arc Mountains or 27 % of the remaining natural forest. Comparisons of the current to prehistoric forest cover suggest that 77 % of the original forest has been lost over the last approximately 2,000 years.
Published and unpublished data are used to assess the faunal (animal) values of the Eastern Arc Mountains in terms of the numbers of endemic species, and number of species shared with the adjacent lowland Coastal Forests and with the Tanganyika-Nyasa Mountain Forest Group. Emphasis is placed on vertebrates, although some data for invertebrate groups are also provided.
At least 74 vertebrate species are strictly endemic to the Eastern Arc Mountains, split as follows: birds 10 species, mammals 11 species, reptiles 23 species and amphibians 30 species. A further 40 species are near-endemics, but range slightly more widely than the strict definition of the Arc. Eastern Arc Mountain blocks that possess endemic vertebrates are the Taita Hills (two species), the East and West Usambaras (12 species), the Ngurus (one species), the Ulugurus (13 species) and eastern Udzungwas (13 species).
A minimum estimate of 265 invertebrate species confined to single Eastern Arc Mountain blocks was obtained, although insufficient collection and taxonomic work means that this figure is certainly an underestimate. Detailed work in the Uluguru Mountains provided an estimation of 169 invertebrate species endemic to that mountain alone.
Almost all endemic species are closed-forest specialists, although there are Eastern Arc endemic birds and butterflies confined to montane grasslands and heathlands. The most important locations for the conservation of biodiversity are the east-facing scarps directly influenced by the Indian Ocean in the largest highlands. The North and South Pare Mountains, Rubehos and Ukagurus seem genuinely poorer in endemics than other areas. The Eastern Arc Mountains possess species with both an ancient history and those of more recent evolution. Ancient affinities of the fauna are with West Africa, Madagascar and even SE Asia. An extremely long history of forest cover and environmental stability are the likely causes of these remarkable affinities.
The term ‘Eastern Arc’ was introduced in 1985 to describe an exceptionally rich area of restricted range plant species on the crystalline mountains of eastern Tanzania and south-east Kenya. About a third of the Eastern Arc flora is composed of restricted-range species. Qualitative and quantitative data are used to demonstrate that the endemics are spread throughout the elevation and moisture gradients of the Eastern Arc. Because of the high number of endemic plant species, all of the Eastern Arc forests are of importance to conservation. However, ridge-tops, heaths, limestone forests and dry forest types are vegetation formations occupying a small area and so are conservation priorities.
The Eastern Arc Mountains possess a bryoflora with high species diversity (about 700 species are known—more than in Uganda). The proportion of endemism (altogether 32 species, 4.57 %) is not high compared to phanerogams, but is high when compared with the bryoflora of similar areas. Monotypic endemic genera are Cladolejeunea and Neorutenbergia. Cladolejeunea aberrans (Steph.) Zwickel occurs in the Usambaras and Neorutenbergia usagarae (Dix.) Biz. et Pócs is distributed throughout the Eastern Arc. The latter is a representative of Rutenbergiaceae family with its other members living in Madagascar and on the Mascarene Islands. One notable feature of the bryoflora is the high number (45 species, 6.43 %) of Lemurian (Madagascan) species, which is most apparent in the Uluguru Mountains (40 species, 8.16 %). The bryoflora of the Usambara and Uluguru Mountains is well known. We know much less about the Pare, Nguru and Ukaguru Mountains and the bryoflora of Udzungwa Mountains is practically unexplored.
The floristic composition of forest on the East Usambara Mountains, Tanzania, changes steadily with increasing altitude. Conveniently, two altitudinal zones (lowland, submontane) can be recognised; the altitude between them lying at about 850 m, which is 550 m lower than the equivalent zonal boundary in central Africa. This depression is probably related to lower daytime temperatures, which are 4–5°C lower than in central Africa—attributed to the presence of persistent low-lying cloud at higher altitudes. There is a marked change in topsoil at about 850 m, with a sharp fall in pH and the presence of a thick mor-humus layer at higher altitudes. The vegetation/climate/soil system is dynamic. There is evidence of upward movement of vegetation zones and a warmer and less misty climate over the last 25 years. The mor-humus layer is lost in tree-fall clearings and under the invasive tree Maesopsis eminii; in the latter case (at least) topsoil pH acidity is over a pH point higher. This is a good site for further investigations of climatic, vegetation and soil changes. Forest persistence during the last ice age (assumed from the large number of endemic species) was probably facilitated by an even mistier (though probably otherwise drier) climate.
The Eastern Arc Mountains (EAM) contain some of the most biologically diverse and endemic-rich montane ecosystems in all of Africa. Because of the staggering degree of biodiversity, how little we know about the biota of the EAM and the rapid degradation of the remaining montane forests of these mountains, we are studying the natural history and biogeography of the small mammals (shrews and rodents) of this archipelago. We are also interested in specific questions such as the effects of forest fragmentation on and elevational distribution of EAM small mammals. To date we have surveyed the South Pare, East Usambara, West Usambara, Nguru, Uluguru and Udzungwa Mountains. We have documented a rodent fauna that is widespread across the archipelago, although restricted to montane and submontane habitats. Shrew species are much more patchy in distribution with each EAM or subset of mountains holding at least one seemingly endemic species, suggesting that speciation has contributed to the current pattern of species richness in insectivores. However, further analysis is required to discern how dispersal, extinctions and/or speciation have contributed to this pattern. Importantly, we have found very few introduced, exotic or savannah dwelling species in our surveys of undisturbed forests, even in forests in close proximity to disturbed areas or human habitation.
Previous biogeographical studies of forest avifaunal compositions of mountains in the Eastern Arc archipelago have focused primarily on patterns of species richness and die effects of montane area and isolation. This preliminary investigation examines species composition in terms of nestedness patterns for 12 mountains in this archipelago. Twenty-eight forest species (includes five species complexes), most of which are strictly confined to the Eastern Arc Mountains, were used to evaluate the hypothesis that species composition is random with respect to nestedness. Results show that the species ordering is significantly non-random. The discussion and conclusions focus on the nested subset patterns exhibited by 14 species and, to a lesser extent, ‘idiosyncratic’ species and islands. Factors that may have contributed to this pattern include selective extinction and colonisation; however, further work is necessary to elucidate which of these, or other factors, actually contributes to nestedness in Eastern Arc birds. Nestedness analyses serve as an important tool to predict what species may be at risk from extinction and which islands and species require greater conservation or research attention.
The history of the study of the terrestrial molluscs of the Eastern Arc Mountains is summarised and a checklist of species known from each range is presented. Current knowledge of the fauna is patchy but each of the ranges contains endemic species and collectively they support a major proportion of the Tanzanian land-snail fauna.
Recent research in the East and West Usambara, Uluguru and Nguru Mountains has revealed high levels of mollusc diversity in Bomole and Monga Forests (East Usambara Mountains) and in the limestone forest at Kimboza (Uluguru Mountains); these forests support the richest faunas reported so far from East Africa. In contrast, diversity and abundance is low in the forests of the Nguru Mountains. A similarity analysis is used to identify several clusters of sites that are related to geographical position and altitude. The significance of these findings for the conservation of East African land snails is discussed.
Geographically referenced biodiversity information is important for conservation management and zoning. Biodiversity surveys were initiated in the East Usambara Mountains in 1995 to provide baseline information on the biological values of the forests for management planning and monitoring, and to train field staff in the use of biological inventory techniques. They were conducted in ten-week field phases. Vegetation plots were laid along a grid of 450 m × 450/900 m. Forest disturbance was assessed using the grid transects. Selected groups of fauna were surveyed using standard methods. Inventories have been completed in ten forests covering 11,076 ha. New species have been discovered, and several range extensions have been documented. Data on local distribution of endemics and threatened species has been incorporated in management plans for Forest Reserves. About 35 foresters have been trained. During 1997 a database was developed for data entry, retrieval and mapping.
The establishment and use of computer databases to hold biological records is common in many countries. Such systems can accommodate a large volume of data with many potential uses, but many databases have failed due to poor design or programming, or to the lack of a proper user-need analysis. In all biological databases there are problems with the data being used. The most common problems are uneven collection effort, taxonomic confusion leading to unreliable records, difficulties with finding exact collection localities, differences in map projections leading to inaccurate record positions and more.
Data in databases, either the raw biological records, or interpreted/modelled range distributions, can be used for analyses of value to both conservationists and to academic biogeographers. However, all such analyses are highly influenced by the analytical scale, and results from one scale cannot be used at another. This is a fundamental problem with analyses using computerised data, especially for conservation planning. Data at different scales can be used to illustrate areas of high species richness, or areas where species of narrow distributional range congregate, although the results from one scale may not be applicable at another.
Computer programs can be used to select areas so that all species in the database are covered. The last method, using the principles of complementarity, is the most efficient way to select ‘ideal’ conservation areas. With such an analysis the theoretical minimum number of areas required to conserve all the species within a given database (e.g. all the birds in Sub-Saharan Africa) can be chosen. However, all such analyses are only indicative, as they do not take into consideration population viability, threats to the areas selected, or other ‘real-world’ variables that are important when conservation plans are being formulated.
For academics the patterns of species richness and range-restriction (i.e. endemism) can be used in large-scale models that can develop and test hypotheses to explain why species are distributed as they are and how evolution/extinction may have operated over time in order to produce the patterns observed. Such studies can have relevance to the development of conservation plans at the broad scale.
The structure and composition of the indigenous forest fragments of the Taita Hills of south-east Kenya were analysed. We collected data in all of the large forest fragments using Point Centred Quarter extensive surveys, supplementing these data with intensive surveys of 20 × 20 m plots. Our structural data on basal area per unit area, stem density, canopy cover, shrub density, stratification and extent of herbaceous ground cover clearly show that the largest fragment, Mbololo, is also the least disturbed. The next largest fragment, Ngangao, has suffered from intermediate levels of disturbance, and all other fragments have been very heavily impacted. Tree size class distributions show that nearly all of the large circumference trees have been lost from the smallest fragments, while the Chawia forest is selectively losing its small, easily-cut trees. Finally, we mapped the Importance Values (combined standard measures of abundance, biomass and dispersion) of each forest's tree species. The map indicates the forest biogeography of the region but also shows the extent to which all of the fragments except Mbololo and Ngangao are dominated by a very few secondary successional sub-canopy species. Only Mbololo and Ngangao may be viable forests in the long term.
The Taita Hills of south-east Kenya contain three endemic and threatened birds and many other endemic taxa. The area is combined with the Eastern Arc Mountains of Tanzania-Malawi in the latest analysis of centres of endemism in birds. Based on our recent fieldwork and historical records, we analyse the distribution and biogeographical affinities of forest birds within the Taita Hills. We find that the Taita Hills avifauna has been influenced as strongly by the Kenyan Highlands as by the Eastern Arc, especially in the high altitude moist forests. However, since the area is sufficiently differentiated to hold three endemic bird taxa, we feel that it merits consideration as a centre of endemism in its own right. Such recognition will hopefully foster the conservation of the Taita Hills forests and their unique species, before this biodiversity is lost.
An evaluation of biodiversity values of ten forest areas has been made in the Udzungwas, based on all data available on the distribution of restricted-range forest birds. The analysis shows that the evergreen forests in West Kilombero (Ndundulu and Nyumbanitu Mountains), Udzungwa Scarp north, Mwanihana and Udzungwa Scarp south contain all species of concern and have the highest conservation priority. The other forest areas: Kisinga-Rugaro, Dabaga, Kigogo, Image and Matundu are of lower importance for restricted-range birds; however, they still have high conservation value. For two areas, Nyanganje and Iyondo (forest at river Mngeta), no data were available. Mwanihana (3rd priority) is within the Udzungwa Mountains National Park. It is proposed that the 1st (West Kilombero), 2nd (Udzungwa Scarp North) and 4th (Udzungwa Scarp South) ranked sites should be conserved by supporting adjacent local communities and by giving one or more of these areas National Park status. Some management options are discussed.
The structure of an arthropod community in the forest floor vegetation was studied in a low altitude (about 700 m a.s.l.) forest valley in the Uluguru Mountains near Morogoro, Tanzania, by monthly sweep net sampling during one year (December 1996–November 1997). The community structure of arthropods changed relatively little during the study period. Eight groups (Araneae, Hymenoptera, Heteroptera, Homoptera, Diptera, Coleoptera, Orthoptera and Lepidoptera) made up over 95% of all the arthropod individuals caught. There were seasonal peaks in the abundances. The highest numbers of arthropods per sample were found during the late rainy season and early dry season (May–August). Arthropod groups generally follow the rainfall pattern; in particular the abundance of Diptera, Hymenoptera and Hemiptera increases with rains.
For the past 14 years hawk moths (Lepidoptera: Sphingidae) have been collected in a garden (580 m a.s.l.) in the ‘Forest Hills’ area of Morogoro, on the lower slopes of the Uluguru Mountains, Tanzania. Moths were attracted using two 160-watt mercury-vapour bulbs and a 15-watt ultraviolet tube-light. They were collected and counted on a white cotton sheet affixed to the wall of a house with the lights suspended in front of it, facing towards the western slopes of the lower Uluguru Mountains. Different species on the wing have been recorded on a nightly basis from June 1996 to December 1997. Altogether, during the whole study period, a total of 56 sphingid species have been encountered. Hawk moths are most abundantly on the wing from March to June peaking in May (late rainy season). The most common species are Agrius convolvuli, Daphnis nerii, Nephele aequivalens, Nephele comma, Euchloron megaera, Hippotion celerio and Hippotion eson. These can be caught throughout the year. The common species in Morogoro are almost identical to those in similar habitat in Freetown, Sierra Leone (West Africa).
The grasshopper fauna of the Uluguru Mountains and the East Usambara Mountains is compared. There is a marked relationship between habitat and similarity in species composition. The faunal similarity between sites rises with distance from the forest, evidently because the savannah species are widespread species that are recently colonising degraded areas, while forest faunas have a high level of endemism and flightlessness, indicating a long history of isolation and evolution. Flightlessness seems to be a result of a lower investment in wing and egg production and higher investment in prolonging life span, supported by a high persistence of the habitat and a high predation pressure.
Arthropod diversity and abundance at the order level was investigated along the Kihansi Gorge in the southern Udzungwa Mountains between June and August 1997 by using sweep netting, timed Lepidoptera counts, malaise-traps, solar powered light-traps, baited pitfall-traps, sticky-traps and baited butterfly traps. The study was undertaken to predict the possible effects of damming the Kihansi River above the fierce waterfall in the gorge. The gorge was divided into four micro-habitats, two of which are affected by waterfall spray (open spray, forest spray), and two of which were not affected directly by the waterfall (forest and riverine sites). The highest arthropod diversity was found in the forest spray, whereas the open spray contained the least. The forest spray area harboured the rarest arthropod orders. Arthropods are most abundant in the riverine site where 31 % of all sampled arthropods were recorded. The forest spray channel, forest site and open spray channel follow with 28 %, 23 % and 18 % of the sample respectively. It is suggested that the Mhalala Stream should be diverted to the gorge to replace the dammed Kihansi River. This would maintain at least partially the extraordinary micro-climate of the gorge and possibly retain the specialised arthropod community.
Threats of biodiversity loss, caused by the overexploitation of natural resources are serious local and global concerns. Available information on the components of biodiversity, especially in the natural-resource-dependent third world, indicates a gloomy trend. The situation for the forest biodiversity of the Eastern Arc Mountains is serious. Many deliberations on the urgency and possible conservation measures needed to limit or curb the pending catastrophes have not yielded the desired results. Growing human populations, adjacent to the biodiversity centres and without alternatives, continue seeking their forest-based material needs from the forests. Some of the most sought-after products come from endemic species. Thus, effective future biodiversity conservation strategies will not lie in the routine in situ, but through radical ex situ conservation. The present paper discusses these issues, including future needs for the identification of the species people want, their location in the forest ecosystem and the development of appropriate technologies for their acquisition, propagation and domestication.
There is a high diversity of natural ecosystems in the Eastern Arc Mountains, influenced by a long history of human colonisation. Natural products are an important part of the rural economy and people have a long tradition of utilising them, passed on orally from generation to generation. Urbanisation and migration in modern Tanzania have cut many of the traditional links with nature, and knowledge of nature and natural phenomena is no longer handed down from generation to generation as efficiently as in the past. Collecting the oral tradition in Tanzanian villages and saving it for the future is an urgent task. In this article the use of wild vegetables (Katariina Vainio-Mattila) and edible mushrooms (Marja Härkönen) are presented according to interviews and material collected during several visits to the Pare and the Usambara mountains.
A total of 920 traditionally protected forests have been found in sample areas in Handeni District (23 villages) and Mwanga District (Usangi and Ugweno Divisions). The size of the forests is between 0.125 and 200 ha. In earlier times sacred forests (one of the seven different types of traditionally protected forests in Handeni) were never abused, and as a result the biodiversity of whole forest ecosystems has been protected. In many parts they are the last remaining natural forests. About 40 % of the forests are severely degraded, partly because a rapid process of change in the villages. The abuse of the traditionally protected forests should be discussed publicly. The total area of forested land requiring protection could be over 4,000 ha in Handeni District and 400 ha in the North Pare Mountains. These forests are effective way to save locally the best areas for biodiversity.
An ethnobotanical survey was conducted between March and September 1997 in the northwestern and southern parts of the Uzungwa Scarp Forest Reserve using strip transects. Altogether 489 plant species from 107 families were recorded, most of them trees (37 %) and shrubs (27 %). Others were lianas, herbs, ferns and parasites. Endemic plants restricted to the Udzungwa Mountains and Eastern Arc endemic plants not restricted to the Udzungwas were present. It was established that local communities around the forest highly depend on the natural forests for forest products. Most human uses were for traditional medicine, fuelwood and building materials. Quality hardwoods Khaya anthotheca, Afzelia quanzensis, Milicia excelsa and Ocotea usambarensis were noted. To reduce the pressure on the natural forest, agroforestry is recommended in the area to meet some of the people's needs for forest products, thereby contributing to the conservation of biodiversity. It is also important to do more intensive surveys in the area and to document the valuable indigenous knowledge of useful plants.
Studies of human activities in the Uzungwa Scarp Forest Reserve, Udzungwa Mountains, were conducted in March–April and September 1997, in the western and southern parts of the forest. Different human activities, such as timber and pole cutting and withies harvesting, as well as the collection of non-timber forest products were recorded. Footpaths in the forest interior, past settlements and encroached areas were identified, as well as evidence of poaching. Due to the human activities, some timber species, for example Ocotea usambarensis, Milicia excelsa and AJzelia quanzensis are almost exhausted. It was established that the main cause of the pressure in the reserve is the lack of alternative sources of forest products and other income generating activities. It is suggested that the people living around the reserve should be allowed traditional forest product uses under agreed regulations. Agroforestry involving planting of some desirable indigenous trees and the domestication of wild fruit tree species is also recommended. Other income generating activities should be encouraged. This is likely to reduce the pressure on the natural forest, thus contributing to biodiversity conservation.
Stem cracks, decay and bark pattern in Newtonia buchananii trees were investigated and compared in a submontane rain forest in the Mazumbai Forest Reserve and adjacent human disturbed forest. One third of the trees growing in the reserve (32 %) and more than half of those in the disturbed forest (60 %) had stem cracks and/or decay—mainly as butt rot, often accompanied by brackets of wood-rotting fungi. One fifth (20 %) of the trees growing in the reserve and three quarters (76 %) in the disturbed forest showed rough and rugose bark. As N. buchananii is a main climax species in the area, the outcome of the death of the trees will be the formation of big gaps. Gap formation in the reserve seems to be accelerating and going beyond the ‘normal’ levels of a natural rain forest ecosystem, whereas in the disturbed areas it seems that N. buchananii will be extinct in the future.
The Uluguru Mountain forests of Eastern Tanzania are of high importance both for the conservation of biodiversity, and as a water catchment area for major urban centres. Only about 270 km2 of forest is thought to remain, mostly inside forest reserves. The most biologically valuable sub-montane forest has been badly affected by habitat destruction and only a small area in the north-east Ulugurus remains.
The main objective of the Uluguru Slopes Planning Project was to research the resource utilisation practices of villagers and their attitudes to forest conservation in the Ulugurus, through a socio-economic survey using participatory techniques. The findings demonstrated both that local communities are aware of the importance of forest conservation and that excellent examples of sustainable land management do exist. The results of the survey fed in to the planning of a follow-up project (funded by DANIDA), a key element of which will be the dissemination of this best practice more widely around the mountains.
The new Tanzanian forest policy was cleared in early 1998, and empowers community groups to own and manage forest resources. The Tanzania Forest Conservation Group (TFCG), a local NGO, is now in a position to rethink its role and move towards facilitating the balancing of local peoples' rights, responsibilities, returns from forest resources and relationship to forest maintenance. This article tracks changes in Lulanda Forest, in the Udzungwa, Eastern Arc Mountains, and analyses the evolution of local control over forest management.
Together with the Coastal Forests and Eastern Arc rainshadow, the Eastern Arc forests make up a botanical Centre of Endemism in Eastern Tropical Africa (CEETA), which covers a wide range of vegetation formations in four different phytochoria. The factors that gave rise to the concentration of restricted-range taxa in the different vegetation types appear to result from the same long-term geological and climatic processes. The endemic-rich vegetation types occur in three countries: Mozambique, Tanzania and Kenya and are managed under a wide range of land tenure arrangements from public land and private ownership, to Forest Reserve, Game Reserve and National Park. Much of the CEETA is recognised as a biodiversity ‘hotspot’ of global importance, but lacks a common management strategy. A possible common framework within which to develop an appropriate strategy is that of the World Heritage Convention. The case of the Australian Wet Tropics World Heritage Site is discussed as a comparative example.