Southern Rift montane forest-grassland mosaic
| Topics: | Ecoregions |
Nyika National Park, Malawi. (Photograph by Judy Oglethorpe)
Although it boasts fewer endemics than the Albertine Rift montane forests and Eastern Arc Forests to the north, the Southern Rift Montane Forest-Grassland Mosaic ecoregion is by no means impoverished nor lacking in unique species.
With the exception of the Nyika Plateau, the ecoregion is poorly conserved, and is increasingly threatened by cultivation and overexploitation of both forest and grassland resources, activities which have already transformed large areas of the ecoregion.
Location and General Description
The Southern Rift Montane Forest-Grassland Mosaic consists of a series of mountains and plateaus centered on the eastern and northern shores of Lake Malawi/Nyasa. Altitude and climate are the main factors separating this ecoregion from the surrounding miombo ecoregions (Central Zambezian and Eastern Woodlands). These woodlands occupy the plains and lower-lying areas surrounding the Rift Mountains and are characterized by the dominance of trees in the genera Brachystegia, Isoberlinia, and Julbernardia.
Source: WWF
Source: WWF
The major differences between this ecoregion and the adjacent and superficially similar Eastern Arc Forest ecoregion in Tanzania and Kenya relate to the differing climate regimes. The highland areas of the Southern Rift ecoregion receive rainfall from the surface convection off Lake Malawi/Nyasa, while precipitation in the Eastern Arc Mountains is derived from the Indian Ocean. This factor may have been responsible for the Eastern Arc mountain forests remaining stable during the Pleistocene droughts, during which time, evergreen forests were drastically reduced elsewhere in East Africa, resulting in floristic impoverishment. The Eastern Arc Mountains thus have a much higher degree of both generic and specific endemism than the Southern Rift montane areas. The Southern Rift Montane ecoregion is similarly separated from the [[Albertine Rift (Albertine Rift montane forests)] Mountains ecoregion] to the northwest on the basis of endemicity and overall biodiversity, as the latter is [[rich]er] in each category. Finally, this ecoregion is distinguishable from montane areas to the south because many northern plant taxa reach their southernmost distributions within the ecoregion, while Mount Mulanje in the South Malawi Montane Forest-Grassland Mosaic forms the northern limit for many species belonging to the southern flora.
The Southern Rift Montane Forest-Grassland Mosaic consists of several discontinuous mountain chains and plateaus that are centered on the Southern Highlands of Tanzania, where the East and West Rift escarpments meet. This ecoregion’s westernmost section lies on the Ufipa Plateau between Lakes Tanganyika and Rukwa, while the extensive north-central and north-eastern sections (collectively referred to as the Southern Highlands) are made up of several different ranges, including the Mbeya and Kipengere Ranges, the Umalila Highlands, the Poroto and Livingstone Mountains, and the Kitulo Plateau. The northernmost portion of the ecoregion in Malawi is found in the Misuku Hills, while the southernmost point of the ecoregion both within Malawi and Mozambique and overall lies in the Kirk Range. Between these two points are the extensive Nyika and North and South Viphya Plateaux, and a number of smaller mountains. Portions of the ecoregion within Malawi, including the Nyika Plateau and Kirk Range, overlap into either Zambia or Mozambique.
Nyika National Park, Malawi. (Photograph by Judy Oglethorpe) The general climate pattern around the Southern Rift Mountains is dictated by Lake Nyasa, from which winds carry moisture into the highlands. Average annual rainfall may be as low as 823 millimeters (mm) on the Ufipa Plateau in the northwest of the ecoregion, to as high as 2,850 mm in the wet Livingstone and Poroto mountains at the head of Lake Nyasa with a mean rainfall of approximately 1500 mm for the entire ecoregion. Precipitation is largely confined to the wet season months of November through April, although light rains or mist may occur at the higher altitudes during the dry season months of May through August. Mean annual temperatures in the ecoregion fall between 13?C to 19?C, with an average maximum of 22?C and an average minimum of 9.8?C. At the highest altitudes, temperatures as low as –5?C have been recorded, and frosts are common, with widespread, destructive frosts recurring every 25 years in the Southern Highlands of Tanzania.
The Southern Rift montane areas are composed primarily of Pre-Cambrian granites, gneisses, and schists formed 3,250 million years ago. Early uplifting and erosion of these original formations caused the addition of sedimentary rock, and additional granites were subsequently intruded in places. The Rift Valley faulting began during the late Cretaceous, creating the mountains and plateaux of this ecoregion adjacent to the great Rift Valleys, which are now inundated by Lakes Nyasa, Tanganyika, and Rukwa. During this time, localized volcanism deposited lavas and ash, chiefly in the Rungwe area north of Lake Nyasa. The ecoregion’s soils are primarily well-drained andosols and ferrisols, and its topography is characterized by large plateaux surrounding high peaks and ridges, bounded on all sides by escarpments or deeply dissected hill country. Plateau altitudes range from 1,400 to 2,400 meters (m), with the two highest peaks in Tanzania (Rungwe and Mtorwi) attaining 2,960 m.
The Southern Rift mountains and plateaus are important watersheds for Lake Tanganyika via the Kalambo River, Lake Rukwa via the Kafufu, Mtembwa, and Rukwa Songwe rivers, the Ruaha River via most north-flowing rivers, and Lake Nyasa via the Kiwira, Mbaka, Lufirio, Lumbila, Ruhuhu, Livulezi, Ketewaka and Nyasa Songwe rivers.
The Southern Rift Montane Forest Grassland-Mosaic ecoregion is composed of several structurally and compositionally distinct vegetation communities, the most dominant of which is grassland. The preponderance of this community is commonly attributed to the high frequency and extent of range fires, which have swept the ecoregion’s grasslands for centuries, continuously eroding the margins of the once abundant Afromontane forests. Dominant grass species in this vegetation type are Loudetia simplex, Exotheca abyssinica, Monocymbium ceresiiforme, Themeda triandra, Andropogon spp., Pennisetum spp., Setaria spp. A number of herbs, sedges, and geophytes also occur within the grassland community, as well as the occasional fire-resistant shrub, usually of the genus Protea. In areas of impeded drainage, permanent and seasonal bogs known as dambos may be found. These habitats, dominated by grasses and sedges, contain a remarkable abundance of species relative to their area, and are known for having rich orchid floras.
Several other vegetation types are set within the grassland matrix, the most prominent of which is Afromontane forest, although this constitutes less than 5 percent of the landscape, and is confined to fire-sheltered pockets, moist escarpments, valleys and watercourses. Afromontane forests can vary considerably in structure and composition, depending on available moisture, altitude, and disturbance regime. The most favorable circumstances produce tall, triple-canopied rain forest, in which the trees are festooned with epiphytes and lianes, while the patches found at higher altitudes and under poorer conditions are shorter and less developed in structure, and compositionally less diverse. Dominant tree and shrub species are Pouteria adolphi-friedericii, Apodytes dimidiata, Bersama abyssinica, Chrysophyllum gorungosanum, Cola greenwayii, Cylicomorpha parvifolia, Entandophragma excelsum, Ficalhoa laurifolia, Garcinia spp., Ilex mitis, Kiggelaria africana, Myrianthus holstii, Ocotea usambarensis, Parinari excelsa, Podocarpus latifolius, Polyscias fulva, Rapanea melanophloeos, and Syzygium guineense. The most common constituents of the herbaceous layer are species of the family Acanthaceae, and of the genera Impatiens, Begonia, Streptocarpus, Plectranthus and Peperomia. A fringe of smaller trees and shrubs, usually pioneer species, often surrounds forest patches, the width of which varies according to its exposure to fire. After some form of disturbance Afromontane forests are frequently found in states in which a single tree species dominates. Hagenia abyssinica and Juniperus procera are commonly associated with this condition, although the latter is now rare. Communities of the bamboo Arundinaria alpina are also found on slopes with high rainfall, primarily in the northern portion of the ecoregion, in stands of varying height and density. Certain forest tree species such asHagenia abyssinica, Juniperus procera, Podocarpus latifolius, Prunus africana, and Rapanea melanophloeos may be associated with bamboo. Bamboo patches are sometimes found within Afromontane forest, perhaps as a result of post-fire invasion.
The third distinguishing Afromontane vegetation type found within the ecoregion can be termed the "Ericaceous" zone, originally identified by Hedberg (1951). White (1983) divides this zone into two types, based on height, occasional variations in species dominance, and substrate. These communities, usually dominated by sclerophyllous shrubs of the family Ericaceae, occur on the higher mountains above the forest zone in a range of moisture and substrate conditions, although examples may be found at lower elevations in areas of shallow soil and frequent mists. Density of the shrub component varies according to environmental factors, and height ranges from 3 to 13 m.
Lastly, the lower reaches of the Southern Rift montane areas—the escarpments and broken hill country—are often occupied by vegetation associated with the miombo ecoregions. Most of the land between 1,200 to 1,800 m is clothed in woodlands dominated by Brachystegia, Julbernardia, and Isoberlinia, which ascend as high as 2,050 m on the xeric western escarpment of the Nyika Plateau. These woodlands may comprise a significant part of the ecoregion, as they constitute more than half of the Nyika Plateau National Park.
Biodiversity Features
Protea flower (Protea sp.) Nyika National Park, Malawi. (Photograph by Judy Oglethorpe) The Southern Rift Montane Ecoregion is both poorer in species richness and endemicity than the Eastern Arc Forest and [[Albertine Rift (Albertine Rift montane forests)] Montane Forest] ecoregions to the north. For instance, the Eastern Arc’s moist mountain forests alone contain 67 endemic trees, while all of Malawi’s evergreen forests contain only 10 unique species. One possible factor contributing to this ecoregion’s relative poverty may be its greater distance from the Equator. An inverse relationship between distance from the equator and species diversity (Biodiversity) is noticeable in Malawi’s Afromontane woody flora, where 232 species are recorded from northern Malawian forests, while southern forests have only 149 species. The forests of the Misuku Hills, the most northern portion of the ecoregion within Malawi, are the most diverse.
However, the ecoregion’s biota is by no means impoverished. The Kitulo Plateau in the Southern Highlands of Tanzania is considered botanically rich, boasting 350 plant species and several endemics. The highlands of Malawi are that country’s biologically wealthiest habitat type, particularly the Nyika Plateau, which has never been permanently settled and is now well protected by Malawi’s 3,134 km2 Nyika National Park and the 80 km2 Zambian Nyika National Park. The Nyika Plateau is undoubtedly one of the most significant areas of the ecoregion, as it is home to south-central Africa’s richest orchid flora, totaling 214 species, as well as 400 bird species and important populations of reedbuck (Redunca arundinum), roan antelope (Hippotragus equinus), zebra (Equus burchelli) and eland (Tragelaphus oryx). Lion (Panthera leo), elephant (Loxodonta africana), and buffalo (Syncerus caffer) inhabit the lower woodland areas of the park. Significant populations of large mammals are unlikely to be found elsewhere in the ecoregion. No large-scale migrations within the Southern Rift montane areas, with the exception of the seasonal migrations of zebra, roan, and eland between the Nyika Plateau and surrounding low-lying woodlands. Oribi (Ourebia oribi) are also found within the ecoregion. The top predator species include leopard (Panthera pardus), cheetah (Acinonyx jubatus), serval (Felis serval), and spotted hyena (Crocuta crocuta).
A number of restricted range species are found in this ecoregion, including 5 mammals, 18 birds, 6 amphibians, and 20 reptiles. The five near-endemic mammals include one small primate, the Mozambique galago (Galagoides granti), an insectivore, Crocidura desperata (CR), and three small rodents, Beamys major, Tanganyika mountain squirrel (Paraxerus lucifer), and Swynnerton’s squirrel (Paraxerus vexillarius, VU). Among the 18 birds considered endemic or near-endemic, only one is entirely restricted to this ecoregion, the Namuli apalis (Apalis lynesi, VU). Other near-endemic species include the churring cisticola (Cisticola njombe), the buff-shouldered widowbird (Euplectes psammocromius), Chapin’s apalis (Apalis chapini), black-lored cisticola (Cisticola nigriloris), olive-flanked robin-chat (Cossypha anomala), Fuelleborn’s boubou (Laniarius fuelleborni), uhehe fiscal (Lanius marwitzi), Iringa ground robin (Sheppardia lowei, VU), and the long-billed tailorbird (Orthotomus moreaui, CR).
Among the herpetofauna, there a number of strict endemics: Stewart’s river frog (Phrynobatrachus stewartae), Ngosi volcano chameleon (Chameleo fuelleborni), Poroto mountain chameleon (C. incornutus), Cordylus nyikae, Ukinga spinytail lizard (C. ukingensis), Eumecia johnstoni, Whyte’s water snake (Lycodonomorphus whytii), Braun’s mabuya (Mabuya brauni), and the Southern African stumptail chameleon (Rhampholeon nchisiensis).
Besides these species, there are numerous examples of plants unique to the ecoregion. Six protea species are limited to the ecoregion. Four orchid species and 2 sub-species are unique to the Nyika Plateau, and 4 more species are near-endemics, as they are also found on several of the highland areas adjacent to the Nyika Plateau. Besides these, the Nyika Plateau also holds 13 other endemic plant species, and 7 sub-species. Tanzania’s Kitulo Plateau hosts 3 strictly endemic plants, plus 15 others restricted to the Kitulo Plateau and other Southern Highlands mountain ranges. Examples of endemic invertebrates are the dragonfly Teinobasis malawiensis, which is known only from montane streams in northern Malawi, the Kitulo-endemic satyrid butterfly Neocoenyra petersi, and a further three butterflies confined to the Nyika Plateau. The ecoregion also contains a number of sub-specific endemics, particularly on the Nyika Plateau, where the red-winged francolin (Francolinus levaillanti crawshayi), the greater double-collared sunbird (Nectarina afra whytei), the Baglafecht weaver (Ploceus baglafecht nyikae), the rufous-naped lark (Mirafra africana nyikae), the chequered elephant-shrew (Rynchocyon cirnei hendersoni), 3 amphibian sub-species, two sub-species of skink, and four sub-species of butterfly are found.
A number of species of special concern occur in the ecoregion. The declining wattled crane (Bugeranus carunculatus) has an important breeding site in the Nyika National Park, and is also found in the Southern Highlands of Tanzania and on the Ufipa Plateau. The Nyika National Park also hosts the locally rare Denham’s bustard (Neotis denhami), the world’s largest breeding population of blue swallows (Hirundo atrocaerulea, VU), numbering 5000 pairs, and one of Malawi’s two important populations of cheetah. The southernmost populations of the globally threatened Abbott’s duiker (Cephalophus spadix, VU) occur in the Southern Highlands of Tanzania, where the threatened Iringa ground robin (Sheppardia lowei, VU) and 7 amphibian species of conservation concern are also found.
Current Status
The archipelago-like nature of the Southern Rift Highlands means that its component habitat blocks are naturally isolated from one another by topography. However, human intervention has caused further fragmentation and degradation within these habitat islands. Cultivation has been widespread throughout the ecoregion, and is rapidly increasing in places. Most of the Mbeya range below 2,200 m has been subjected to shifting cultivation, and the montane grasslands of southern Tanzania are considered to be in a state of rapid decline. In the Rungwe District of the Mbeya Region, remaining natural vegetation is largely confined to government proclaimed and traditional forest reserves, but even these conserved areas are subject to anthropogenic disturbances. An analysis of satellite images spanning twenty years up to 1989 has shown that at least 24 percent of the Kitulo Plateau has been transformed by cultivation and pasture improvement. The majority of grassland on Malawi’s second largest plateau, the South Viphya, has been planted over with exotic Pinus spp., and other areas of the ecoregion have been similarly afforested. In addition to the destruction caused by frequent wildfires, forests and woodlands have been further reduced by charcoal production, fuelwood harvesting, and cultivation. In Malawi, this deforestation is particularly pronounced, as all that remains of the once extensive mid-altitude montane forests are small relictual groves used as graveyards by local people.
The protected area network throughout most of the ecoregion is woefully inadequate with the exception of the Nyika Plateau area, the majority of which is protected inside Zambia and Malawi’s contiguous Nyika National Parks. None of the other portions of the ecoregion are protected in Zambia, and Mozambique applies no known conservation measures to its share of the ecoregion. Part of Chipata mountain is protected in Malawi’s Nkhotakhota Game Reserve, while Chirobwe mountain in the Dedza-Chirobwe Highlands has a forest reserve, although this is under pressure from wood collectors. The grasslands of the Southern Highlands of Tanzania, including the botanically important Kitulo Plateau, are almost entirely unprotected, as are those of the Ufipa Plateau. The Mbeya Region of Tanzania’s Southern Highlands contains 28 forest reserves of 1,350 square kilometers (km2) (although several of these fall outside of the ecoregion’s boundaries), but these have low levels of management and are often subject to illegal pitsawing, fuelwood collection, grazing, hunting, and uncontrolled burning. Many of these reserves are completely surrounded by and somewhat encroached upon by cultivation. Besides these official forest reserves, there are numerous smaller traditional forest reserves in the Southern Highlands, established by local communities for a variety of cultural reasons. At least 94 are known from the Rungwe district. Although many of these reserves are no longer maintained, and are under increasing pressure from cultivators, evidence suggests that they could play a valuable conservation role if appropriately supported by government.
Types and Severity of Threats
The most significant force of natural disturbance within this ecoregion is undoubtedly fire. Each year, large areas of the Southern Rift Highlands are swept by fires of primarily anthropogenic origin. The intensity of this burning regime, which has been practiced for centuries, if not millenia, is believed to have been the main cause of the replacement of previously extensive areas of Afromontane forests with grassland and scrub-grassland. Although it is unknown exactly how long fire has been a driving force in the ecoregion, and to what extent it has caused grassland to replace forest, fire has definitely reduced forests within the last century, and continues to do so. Of special concern are the few surviving pockets of the historically widespread Juniperus procera forests, particularly the patch on Nyika Plateau, as these have been reduced not only by fire but also by recent indiscriminate felling for charcoal production and other uses.
Cultivation poses the other severe threat to the integrity of the ecoregion, as land is increasingly being converted to crops such as tea, coffee, banana, finger millet, potatoes, and pyrethrum. Although shifting cultivation is practiced in places, allowing secondary succession to take place on previously worked fields, fallow lands are generally recolonized by widely distributed species which may preclude the regeneration of the unique elements of Afromontane]primary flora. In soil-disturbed areas of the Kitulo Plateau, grassland tends to be replaced by a "shrubby sward". Cultivation does not only change the composition of the ecoregion’s flora, but it can create serious erosion problems, as fields are often plowed on steep slopes. Overgrazing by large numbers of livestock also cause erosion problems in areas of high human population, such as parts of Malawi’s Kirk Range and Tanzania’s Mbeya and Rungwe districts, where densities reach 134 people/km2. The continuing destruction of Afromontane grassland habitat threatens the locally occurring churring cisticola (Cisticola njombe) and the blue swallow.
Alien organisms pose a threat to the ecoregion, chiefly in the form of exotic timber trees of the genera Pinus and Eucalyptus, which have been used in afforesting montane grasslands. Pinus is reported as being invasive in parts of the Southern Highlands. The bramble Rubus sp. has spread extensively throughout the Nyika National Park, where exotic rainbow trout were also introduced into dams and streams on the Plateau.
Justification of Ecoregion Delineation
The linework for this ecoregion follows the ‘undifferentiated montane vegetation’ unit within the Afromontane archipelago-like regional center of endemism, with one refinement of linework for the montane area to the northwest. Although White’s Afromontane areas are not distinguished into finer units, the montane areas of the Kipengere Range and the high elevation areas to the west of Lake Malawi share biological similarities. These montane areas form part of the Tanzania-Malawi Endemic Bird Area. However, the Eastern Arc forests, [[Albertine Rift (Albertine Rift montane forests)] forests], and Mount Mulanje are distinguished as separate ecoregions due to high levels of local endemism.
Additional Information on this Ecoregion
- For a shorter summary of this entry, see the WWFWildWorld profile of this ecoregion.
- To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
- World Wildlife Fund Homepage
Further Reading
- Beard, J.S. 1992. The Proteas of Tropical Africa. Kangaroo Press. Hong Kong.
- Carter, J. 1987. Malawi: Wildlife Parks and Reserves. Macmillan Ltd. London and Basingstoke.
- Chapman, J.D., and F. White. 1970. The Evergreen Forests of Malawi. Commonwealth Forestry Institute, University of Oxford, Oxford.
- Cribb, P.J., and G.P. Leedal. 1982. The Mountain Flowers of Southern Tanzania: A Field Guide to the Common Flowers. A.A. Balkema, Rotterdam.
- Dowsett-Lemaire, F. 1989. The flora and phytogeography of the evergreen forests of Malawi I: Afromontane and mid-altitude forests. Bull. Jard. Bot. Nat. Belg.: 3-131.
- East, R., 1998. African Antelope Database 1998. IUCN, Gland, Switzerland. .
- Hedberg, O. 1951. Vegetation belts of East African mountains. Svensk Botanisk Tidskrift 45: 140-202.
- Hilton-Taylor, C. 2000. The IUCN 2000 red list of threatened species. Gland, Switzerland and Cambridge, U.K. .
- Johnson, S.A. undated. A Visitor’s Guide to Nyika National Park, Malawi. Mbebzi Book Trust.
- Kerfoot, O. 1963-64a. A preliminary account of the vegetation of the Mbeya Range, Tanganyika. Kirkia 4: 191-206.
- Kerfoot, O. 1963-64b. The distribution and ecology of Juniperus procera Endl. in East Central Africa, and its relationship to the genus Widdringtonia Endl. Kirkia 4: 75-86.
- Kielland, J. 1990. Butterflies of Tanzania. Hill House, Melbourne and London.
- Kurzweil, H. 2000. Notes on the orchids of the Nyika Plateau, Malawi/Zambia. Orchids South Africa 31: 76-85.
- Lovett, J.C. 1993. Eastern Arc moist forest flora. Pages 35-55 in Lovett, J.C and S.K. Wasser, editors. Biogeography and Ecology of the Rain Forests of Eastern Africa. Cambridge University Press, Cambridge. .
- Lovett, J.C., and E. Prins. 1994. Estimation of land-use changes on Kitulo Plateau, Tanzania, using satellite imagery. Oryx 28: 173-182.
- McKone, D. 1995. A Brief Survey of the Traditional Forest Reserves of Rungwe District, Mbeya Region, Tanzania. Unpublished Draft Report. Government of Tanzania/EEC Agroforestry, Soil and Water Conservation Project, Mbeya and District Forestry Office, Rungwe District. Retrieved (2001) from: World Wildlife Fund.
- McKone, D. and V. Walzem. 1994. A brief survey of Mbeya Region catchment forest reserves. Government of Tanzania/EEC Agroforestry, Soil and Water Conservation Project/Regional Natural Resources Office, Mbeya. Retrieved (2001) from: World Wildlife Fund.
- Stattersfield, A. J., M. J. Crosby, A. J. Long, and D. C. Wege. 1998. Endemic Bird Areas of the World. Priorities for biodiversity conservation. BirdLife Conservation Series No. 7. BirdLife International, Cambridge, United Kingdom. .
- Stuart, S.N., R. Adams, and M. Jenkins, editors. 1990. Biodiversity in sub-saharan Africa and its islands: conservation, management and sustainable use. Occasional Papers of the IUCN Species Survival Commission. No. 6. IUCN, Gland, Switzerland. .
- Wasser, S.K., and J.C. Lovett, 1993. Introduction to the biogeography and ecology of the rain forests of eastern Africa. Pages 3-7 in Lovett, J.C and S.K. Wasser, editors. Biogeography and Ecology of the Rain Forests of Eastern Africa. Cambridge University Press, Cambridge. pp. 3-7. .
- Willis, C.K., J.E. Burrows, M. Koekemoer, and L. Fish. 2000. Plants of the Nyika, Vol. I: Preliminary Checklist. National Botanical Institute (SABONET), Pretoria. .
- White, F. 1983. The vegetation of Africa, a descriptive memoir to accompany the UNESCO/AETFAT/UNSO Vegetation Map of Africa (3 Plates, Northwestern Africa, Northeastern Africa, and Southern Africa, 1:5,000,000)UNESCO, Paris.
- Williamson, G., 1979. The orchid flora of the Nyika Plateau. Journal of South African Botany 45: 459-467.
- WWF. 1998. A conservation assessment of terrestrial ecoregions of Africa: Draft proceedings of a workshop, Cape Town, South Africa, August 1998. World Wildlife Fund, Washington, DC, USA.
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