Location and General Description
The Ethiopian Montane Moorlands ecoregion covers the higher parts of the Ethiopian Highlands Massif, from around 3,000 m to higher than 4,500 m. Below 3,500 m the ecoregion would have formerly graded into montane forests and grasslands. However, most of these areas are now farmed or used for grazing. The climate is presumed to be complex, but data are largely lacking. Annual rainfall is highest in the southwest (perhaps as high as 2,500 mm) where the dry season may only last for two months, and declines to as little as 1,000 mm in the north, where the dry season may last as long as 10 months. Estimates of the mean maximum temperature on the higher peaks are between 6° and 12°C while mean minimum temperature is between 3° and 10°C. Frosts are common throughout the year, especially in the winter months (November to March) (Rundel 1994). In Simien Mountains National Park, recorded temperatures range from a minimum of -2.5° to 4°C to a maximum of 11° to 18°C. On the Sanetti Plateau of the Bale Mountains diurnal ranges of 40°C (-15°C to + 26°C) have been recorded (Hedberg 1997).
Geologically, the area lies on Tertiary volcanic deposits, which are extremely thick in the Simien Mountains. The soils developed over these rocks are principally nitosols and in some areas lithosols. These highlands were formed over 75 million years ago, a large dome propelled upwards by volcanic action. Eventually the dome was split by the development of the Rift Valley which threads its way north-east between the southern and northern massifs. This volcanic period ended 4 to 5 million years ago, succeeded by severe climatic fluctuations in the Pliocene and Pleistocene. During the last Ice Age, the higher areas of the Ethiopian Plateau were glaciated and surrounding areas were covered with montane vegetation reminiscent of the Eurasian tundra. As the climate warmed the broad belts of sub-alpine vegetation contracted, and became restricted to higher altitudes. The ice cover on the peaks of these highlands retreated only a few thousand years ago; therefore, vegetation has only relatively recently colonized these areas (Kingdon 1989). Some areas remain barren, such as the central peaks area in the Bale Mountains that are covered with relatively recent lava flows.
Plant and animal colonists arrived at these remote highlands via several routes. The most consistent source is from the dry lowlands surrounding the highlands. Some tropical species arrived from the moist areas in the south and southwest, passing through the formidable barriers of the Kenyan deserts in the south and the White Nile floodplains in the west. Palaearctic invaders may have traveled through the jebels and escarpments that flank the Red Sea (Kingdon 1989). The low trench of the Rift Valley may have further isolated species by dividing the northern and southern massifs. The Ethiopian highlands are extremely varied and rugged, with the highest point at 4,620 m on Mt. Ras Dashan. Other high peaks are found on Mt. Zuquala, Galama Mountain, Mt. Damota, and in the Gughé Highlands. The highest point of the Simien Mountains National Park is 4,430 m, and the highest point of the Bale Mountains National Park is 4,377 m. The Bale Mountains are the largest continuous area above 3000 m in Africa. Numerous alpine lakes are found in this region, some of which persist year-round, providing valuable habitat for migratory Palaearctic water birds. These higher elevations are sparsely populated, although agricultural activities continue at considerable elevations wherever it is still possible to grow sufficient food to survive.
Phytogeographically the entire area is part of the Afromontane archipelago-like regional center of endemism (White 1983) and is mapped as ‘altimontane vegetation in tropical Africa’. Trees are absent at such high elevations, although some bushes and shrubs such as Hypericum revoltum do occur. The main vegetation types are moorland, grassland, and herb meadow. Much of the montane vegetation is a heathland scrub around 0.5-1.0 m high, dominated by Philippia, the tree-heather Erica arborea and other shrub species. Between the shrubs, the soil is bare and there are smaller plant species, such as Helichrysum, Alchemilla, Cerastium, and the grasses Koeleria spp. and Aira spp., which are also found in Europe. Steep rocky slopes and cliffs in the high-elevation regions support very little vegetation, while the sedge Carex monostachya dominates flat swampy areas. A distinctive feature of the vegetation in this zone is the giant Lobelia rynchopetalum, which reaches a height of 6 m when flowering. All of the plant species found in the Afroalpine zone show xeromorphic characteristics designed to reduce transpiration. As examples, Lobelias have thick leathery leaves, Ericaceae and Helichrysum have highly revolute leaf margins, and most of these species have a small leaf surface area (Hedberg and Hedberg 1979).
The Ethiopian Montane Moorlands are biologically distinctive and possess considerable endemism. They are, however, poorly developed when compared to the Kenya/Tanzania Highlands or those of the Albertine Rift, and they lack some plants typical of Afroalpine vegetation found farther south in the East African and Ruwenzori-Virunga Montane Moorlands. For example, there are no Dendrosenecio species and very few shrubby Alchemilla species. Moreover, species of Rosa and Primula are found, which gives the region an affinity to the Palaearctic montane areas farther north and in Europe (Hedberg and Hedberg 1979, Vuilleumier and Monasterio 1986).
Davis et al. (1994) estimate that there are about 950 vascular plant species, with at least 15 site endemics, in the Bale Mountains. However, it is difficult to ascertain the number of species found in this ecoregion compared to the other ecoregions found in the Bale Mountains. Although the total number of species for the Simien Mountains is unknown, Davis et al. (1994) estimate 5 to 10 site endemics. This level of endemism is probably repeated in other high mountains of the ecoregion.
There are several notable species of endemic--and highly threatened--mammals, including the Ethiopian wolf (Canis simensis) (CR), the rarest canid in the world. Also known as the Simien fox, the Ethiopian wolf lives in open moorlands higher than 3,000 m elevation. It is estimated that less than 400 individuals survive in the wild. Bale Mountains National Park contains the largest population of wolves, but that population has steadily decreased throughout the 1990s so that it now numbers only approximately 200 individuals (Sillero-Zubiri et al. 1997). The Ethiopian wolf may have evolved from a shared ancestor of the grey wolf (Lupus lupus) that made its way to northern Africa from Europe in the late Pleistocene. The northern population of Ethiopian wolf is considered a separate subspecies, C. s. simensis, distinct from the southeastern population found in Bale National Park and surrounding areas, C. s. citernii (Stuart and Stuart 1996). The Ethiopian wolf is unusual for a canid because it relies primarily on subterranean rodents for food. This strategy has allowed it to thrive in high altitude areas where rodent biomass is extremely high.
One large endemic rodent, the giant mole-rat (Tachyoryctes macrocephalus), has been estimated to approach densities of 2,600/km2 in the Sanetti Plateau in Bale N.P. (Kingdon 1989). Along with the diurnal grass rats (Lophuromys melanonyx, Arvicanthis blicki), the giant mole-rat and Starck’s hare (Lepus starcki) make up the vast majority of the Ethiopian wolf’s diet in Bale N.P. (Sillero-Zubiri et a. 1997). The giant mole-rat is found only in Bale N.P. and belongs to a family that is Eurasian in origin, having only recently colonized Afromontane regions. This ecoregion’s demanding high-altitude environment has fostered a high rate of speciation among rodents (Kingdon 1989). Mammals endemic to this ecoregion include the Ethiopian wolf and rodents including the giant climbing mouse or Nikolaus' mouse (Megadendromus nikolausi), the giant mole-rat, Ethiopian narrow-headed rat (Stenocephalemys albocaudata), gray-tailed narrow-headed rat (Stenocephalemys griseicauda), and black-clawed brush-furred rat (Lophuromys melanonyx) (Sillero-Zubiri et al. 1995, Yalden and Largen 1992). Near-endemic mammals include the critically endangered Walia ibex (Capra walie) (CR), the majority of which are found in the Simien Mountains National Park; the mountain nyala (Tragelaphus buxtoni), the gelada baboon (Theropithecus gelada), and a number of other rodents and shrews. Klipspringer (Oreotragus oreotragus) and rock hyrax (Procavia capensis) can also both be found in rocky habitats in this ecoregion.
The demanding high-altitude environment means that endemic species often display a number of unique behavioral, morphological and physiological adaptations. Gigantism is seen in several plant species (giant lobelias, tree heather and giant St. John’s wort), while the perenniel plants have evolved dry, paper-like flowers to withstand harsh winds. An endemic species of small toad, Altiphrynoides malcomi, has evolved so that fertilization occurs internally and eggs develop in moist soil (Sillero-Zubiri et al. 1997). Giant root rats have adapted to the severe winds and fluctuating temperatures by building extensive underground burrows and foraging above ground for short periods during the day (Sillero-Zubiri et al. 1995).
Other species, such as the endangered mountain nyala (Tragelaphus buxtoni), do not show any obvious adaptations. Lack of adaptations and the mountain nyala’s presence at lower altitudes suggests that this is a relict population and not a montane specialist (Kingdon 1989).
This ecoregion is also essential bird habitat, providing ample water in the form of alpine lakes and streams. Significant populations of Palaearctic birds winter here, with several thousand wigeon (Anas penelope) and shovelers (Anas clypeata) observed in the Bale Mountains, along with waders such as ruffs (Philomachus pugnax) and greenshanks (Tringa nebularia). Globally threatened species found in the Bale Mountains include the vulnerable greater spotted eagle (Aquila clanga), imperial eagle (Aquila heliaca), lesser kestrel (Falco naumanni) and wattled crane (Grus carunculatus) as well as the near threatened Rouget’s rail (Rougetius rougettii). Three Palaearctic species, golden eagle (Aquila chrysaetos), chough (Pyrrhocorax pyrrhocorax) and ruddy shelduck (Tadorna ferruginea) breed in the Bale Mountains, their only known breeding sites outside the north temperate zone. The near threatened pallid harrier (Circus macrourus) and Abyssinian longclaw (Macronyx flavicollis) are found in both the Bale and Simien Mountains (Sillero-Zubiri et al. 1997, Tilahun et al. 1996). The Abyssinian longclaw is considered near-endemic to this ecoregion, as are the moorland chat (Cercomela sordida), Abyssinian waxbill (Estrilda ochrogaster), moorland francolin (Francolinus psilolaemus), Rueppell's chat (Myrmecocichla melaena), ankober serin (Serinus ankoberensis), and spot-breasted lapwing (Vanellus melanocephalus).
Substantial blocks of habitat are protected in the Bale Mountains and Simien Mountains National Parks. People and their livestock are resident within both National Parks although there has been some forced relocation. While the Bale Mountains N.P. has been under management since 1970, it has never been formally gazetted. The Arsi controlled hunting area is also located in this ecoregion. While controlled hunting areas in Ethiopia tend to offer little protection (Kingdon 1989), sport hunting is currently banned in Ethiopia. The ecoregion is naturally very fragmented because it occurs only in the highest portions of the Ethiopian Highlands. Outside the protected areas, other habitat blocks are relatively intact when they are too high to be used by people for agriculture or grazing. Agriculture decreases above 3,200 m, where barley is the only crop that can be cultivated (Demissew 1996).
A formal survey of Simien Mountains National Park in 1996 found that human activities, especially overgrazing, are having a severe effect on the park. The majority of the Geech plateau was considered overgrazed or heavily grazed. One area of Erica arborea-Hypericum revolutum forest had deteriorated to the point where there was no undergrowth and no regeneration. In grassland areas, the number of Lobelia had increased because the species germinates readily on bare soil patches. However, even Lobelia will decrease as overgrazing intensifies (Nievergelt et al. 1998). The Simien Mountains National Park is currently designated a "World Heritage in Danger" site by UNESCO.
Types and Severity of Threats
Ethiopia's highlands are among the most densely populated agricultural areas in Africa. Increases in human population have substantially disrupted and eliminated habitat due to expansion of high-altitude agriculture, shifting cultivation, heather fires, and overgrazing by livestock. Delicate Afroalpine vegetation is not resilient; any tampering, especially fire, may have irreversible consequences (Demissew 1996). Heather fires also risk contaminating water quality. Both the Simien and Bale Mountains serve as important water catchment areas (Sillero-Zubiri et al. 1997). With the expansion of human habitation, many wildlife populations have become restricted to the national parks and are isolated due to extensive deforestation and grass burning in the surrounding regions.
Even within protected areas, the pressures are heavy. About 2,500 people currently live in the Bale Mountains National Park along with 10,500 livestock, and about 1,500 people inhabit the Simien Mountains National Park. In the latter, a recently constructed road has improved access and increased the levels of anthropogenic threats. A further overarching threat is global warming, which may reduce the overall area of this ecoregion or lead to its complete elimination. According to at least one researcher, the plateau in the Simien Mountains N.P. is much drier now than it was in the 1960s. It is not known if this is a local effect or the result of wider climatic changes (Tilahun et al. 1996).
Several distinctive endemics face global extinction. The Walia ibex, numbering fewer than 400 individuals (Nievergelt et al. 1998), is threatened through habitat loss and hybridization with free-ranging domestic goats. Ethiopian wolves are often struck by vehicles on the Sanetti Plateau road in Bale Mountains National Park and have suffered persecution due to an erroneous reputation as sheep-killers. Domestic dogs compete with Ethiopian wolves for food, transmit diseases such as rabies and canine distemper, and hybridize with them. The mountain nyala is primarily threatened by habitat loss. The lower reaches of its range are more suitable to the species than the upper less-vegetated areas, but in most parts of its range, this habitat has been taken over for cultivation and pastoralism. Populations of klipspringer have decreased in recent years in Simien N.P., possibly due to increased human activity (Nievergelt et al. 1998).
Justification of Ecoregion Delineation
This ecoregion forms part of the Afroalpine center of plant diversity across East and Northeast Africa (WWF and IUCN 1994). The lower boundaries are derived from White’s ‘altimontane’ vegetation unit, roughly following the 3,000 m contour. The Ethiopian Montane Moorlands are poorly developed compared to other East African moorland areas, lacking typical Afroalpine species like Dendrosenecio. However, they possess considerable endemism and contain affinities to the Palearctic realm, such as species of Rosa and Primula (Hedberg and Hedberg 1979, Vuilleumier and Monasterio 1986).
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Prepared by: Chris Magin
Reviewed by: In progress