Eastern Afromontane

The montane regions of Africa have always presented a challenge for the evaluation of biogeography and of conservation priorities. The world’s mountain ranges, in general, are clumped —consider, for example, the Andes and the Himalaya. In contrast, Africa’s complex geological history has resulted in its mountains being widely scattered, especially through the eastern edge of the continent, but with highly distinctive floras surrounded by other vegetation types. So fragmented is this mountain system that White (1978, 1983) likened it to islands, calling it the “Afromontane archipelago-like regional center of endemism.”

Many of these “islands,” including some of the largest, are volcanic in origin. Most of the Ethiopian Highlands are formed of basalt, and the Kenyan Highlands of various volcanic deposits, including phonolite, nephelinite, and basalt. The highlands of the Albertine Rift are largely of Pre-Cambrian rocks, with islands of volcanic deposits, including those formed by the still active Virunga Volcanoes. Some of the more isolated mountains in the region are volcanic, including Mt. Elgon (4 315m), Mt. Meru (4 566 m) and Mt. Kilimanjaro (5 895 m) (White 1983). This volcanic and seismic activity was caused by the original separation of the African and Arabian tectonic plates, around 35 million years ago, and that resulted in the formation of the Great Rift Valley system that runs from Syria to Zimbabwe and Mozambique.

The flora of the Afromontane “archipelago” shows much uniformity and continuity, its composition changing with increasing altitude. The lower altitudinal limit is usually taken as between 1 500 and 2 000 m, although this is lower away from the equator, while the Knysna Forests in the Cape, which are considered to be the southernmost reaches of the Afromontane habitat, are at 300 m. The most widespread plant genus is Podocarpus (in the broad sense, including the recently segregated Afrocarpus), although Juniperus is found in drier forests of northeastern and eastern Africa. A zone of bamboo is often found between 2 400 and 3 000 m (Hubbard 1970), above which there is often a forest zone with Hagenia, extending as high as 3 600 m (Graham 1960). Many species common in montane forest, such as trees of the genera Podocarpus and Juniperus, have economic importance, while several crops including coffee (Coffea arabica) and tef (Eragrostis tef) were domesticated from the Ethiopian Highlands (Davis et al. 1994).

At the highest elevations, such as the Rwenzori Mountains, Aberdares, Mounts Kilimanjaro and Kenya, and Bale and Simien Mountains, Afroalpine vegetation occurs, typically from above 3 400 m. Afroalpine vegetation is characterized by the presence of giant senecios (Dendrosenecio spp.), giant lobelias (Lobelia spp.), and Helichrysum scrub. White (1983) referred to the Afroalpine vegetation as the “Afroalpine archipelago-like region of extreme impoverishment” because the flora is markedly poor in species. However, endemism is high, possibly due to extended periods of isolation.

The greatest biological importance of the Afromontane region derives from three ancient massifs. The largest of these, the Ethiopian Highlands, lies in the region’s northern portion, and covers much of Ethiopia with outliers in Eritrea, Djibouti, and Sudan. It is bisected by the northernmost extension of Africa’s Great Rift Valley system. To the southwest lies the Albertine Rift, straddled by the tiny mountain states of Rwanda and Burundi, and flanked by Uganda and Tanzania to the east and the Democratic Republic of Congo to the west. To the southeast and extending further south still, the Eastern Arc Mountains go from southeastern Kenya to south-central Tanzania, and then are extended south by the southern Rift mountains of southern Tanzania and Malawi, with distant outliers in the Chimanimani Highlands of eastern Zimbabwe, and Gorongosa of western Mozambique. The geological turmoil responsible for the uplift of these mountains has also resulted in the formation of some of the world’s most remarkable lakes, with Lakes Tanganyika and Malawi (Nyasa) abutting the Albertine Rift and Southern Rift mountains, respectively. To ensure that these three remarkable, yet highly threatened, mountain blocs are treated in sufficient detail, we present each separately here, but combine them for overall analysis and consideration as the Eastern Afromontane Hotspot.

Beyond these three main massifs, a number of outlying mountains are included in this hotspot. Perhaps most important are the Neogene Volcanics of the Kenyan and Tanzanian highlands, a geologically young formation that includes four of Africa’s five highest mountains, Mt. Kilimanjaro and Mt. Meru in Tanzania, and Mt. Kenya (5 199 m) and Mt. Elgon in Kenya. Possibly because of the relative youth of these mountains, their endemism is much less marked than that of the rest of the Eastern Afromontane Hotspot. Far to the north, the Asir Mountains of southwest Saudi Arabia and the highlands of Yemen have biological affinities with the Eastern Afromontane Hotspot, being as they were at one stage part of the large Ethiopian dome that began to arise some 75 million years ago (Kingdon 1989). In total, the Eastern Afromontane Hotspot covers an area of 1 017 806 km². The Drakensberg Range of South Africa and Lesotho (the high point being Thabana-Ntlenyana, 3 482 m), coupled with the Barberton, Wolkberg, Soutpansberg and perhaps Sekhukhuneland centers of endemism in southern Africa (Van Wyk and Smith 2001), form a similar high-altitude Afromontane outlier to the south, but are, for the moment, not included in the analysis.

White (1983) also included a number of other regions within his Afromontane archipelago-like regional center of endemism, namely the Angola Escarpment, the Jebel Marra in Sudan (an isolated volcanic massif near the border with Chad), and the Cameroon and Nimba highlands of West Africa, but noted that the inclusion at least of the Angola Scarp and the high-lying areas west of Mount Cameroon was problematical due to the presence of many lowland species. Indeed, we consider the Angola Scarp to be too poorly known, at present, for incorporation into the hotspot, while the Nimba Highlands are here considered within the Guinean Forests of West Africa Hotspot. The Cameroonian Highlands are the strongest contender for inclusion in this hotspot, but we retain them in the Guinean Forests Hotspot, restricting our definition of the Eastern Afromontane Hotspot to those high-lying regions of the Great Rift.

Overall, the Eastern Afromontane Hotspot holds impressive levels of biodiversity. Its plant diversity sums to a minimum of 7 598 species, of which at least 2 356 are endemic. For vertebrates, this hotspot holds 490 mammal species, 1 325 birds, 347 reptiles, and 285 amphibians, of which 104, 110, 93, and 79 species, respectively, are endemic. Including the Great Rift lakes into the hotspot also means that it is of phenomenal importance for freshwater fishes, with a minimum of 893 species occurring, of which at least 617 are endemic. Further details are given for biodiversity in each of the sections on the region’s major massifs.

Across the expanse of this complex hotspot, the threats are largely the same, with habitat loss due to conversion of land for agriculture, plantations and commercial estates, and logging for commercially valuable timber species, the primary threat. In addition, a host of no less insidious factors has led to the loss of much of the original vegetation in this hotspot, including the impact of fires, mining, infrastructure development, and collection of firewood and/or plants for medicinal use, while other threats, such as hunting and disease, have resulted in serious declines in the populations of many individual species. Overall, it is doubtful that much more than 10% of the original vegetation of this hotspot remains intact.

Rather surprisingly, around 15% of the hotspot is considered to have some level of official protection, but this figure is skewed by the inclusion of a number of protected areas that have limited real protection value, namely a number of areas in Ethiopia that can not even be termed “paper parks” because they have still not been officially gazetted. The true level of effective protection is likely much closer to the figure of 5.8%, which includes only those protected areas in IUCN categories I to IV.

Despite the complex nature of this hotspot, it is believed that the unification of these unique and floristically similar montane regions under a single banner will help to focus increased attention on these threatened habitats. Indeed, the fact that the Eastern Afromontane Hotspot is the only “archipelago-like” hotspot reflects its unique character amongst the list of global hotspots.

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