Afroalpine and Sub-Afroalpine Ecosystem

Description

1.1Description
The areas which on the average higher than 3200 meters above sea level (m.a.s.l) are generally referred to as the Afroalpine and Subafroalpine (Hedberg, 1957). The lower limit of the afroalpine belt falls at about 3500 m, while the upper limit of vascular plants lies around 5000 m (Hedberg, 1964), and subafroalpine areas ranges between 3200- 3500 m. These areas include chains of mountains, mountain slopes and tops of highest mountains in the country. The highest peak in Ethiopia is Ras Dashen (4533 m a.s.l), where an alpine climate near 0°C persists all year round, sometimes even with a snow cover lasting a couple of days (Hurni and Ludi, 1998). However, dry lowland savannas and deserts surround this moist highland area. Ethiopia has the largest extent of afroalpine habitats in Africa (Yalden, 1983).

The highlands of Ethiopia were formed between 40 and 25 million years from the present by lava outpouring of the trappian series in the Miocene and Oligocene (Mohr, 1971). The mountains are volcanic in origin dominantly overlie Precambrian basaltic and trachytic bedrocks. Moisture is not limiting, since most of these mountains attract much rain, and there is excessive internal drainage as the basaltic and trachytic bedrocks percolate water (Ensermu Kelbessa et al., 1992). However, at the upper alpine belt soil moisture could be limiting as water stays in form of heavy frost or ice and snow for prolonged time, and thus the amount of soil water available is the most important factor influencing the distribution of plant.

Due to the increasing population pressure there are frequent encroachments by man that result in widespread destruction of wildlife and their habitats. Friis and Sebsebe Demissew (2001), further noted that intensive human pressures on the mountains is probably one of the major reasons for the discrepancies between the maps, and different interpretations of the vegetation types by the different authors.

Comparatively there are more floristic and faunal studies from the afroalpine and subafroalpine ecosystems of Bale and Simien Mountains than from the same ecosystems of other regions such as Wello, Gemgofa, Arsi, etc.

In a series of publications Hedberg (1962, 1964, 1975, 1986 and 1992) made important analyses on the vegetation and ecology of afroalpine regions in Ethiopia. Weinert (1981); Weinert and Mazurek (1984), Uhlig (1988) and Uhlig (1991) also made ecological investigations on the vegetation of the Bale Mountains. Miehe and Miehe (1994) made a detailed study on ericaceous vegetation and plant communities within the ericaceous zones of the Bale Mountains. Yalden (1985 and 1988) made studies on the small mammals of the Bale Mountains. Sillero-Zubiri and Gottelli (1994); Sillero-Zubiri et al. (1997); Sillero-Zubiri and Tattersall (1995 a, b) have made extensive ecological investigations on an Endemic mammalian species, Ethiopian wolf. There is now a shift of interest from Bale and Simien Mountains to the high massifs of central highlands and Wello (Zelealem Tefera, 2001).

Blower (1966) proposed for the establishment of National Park in the Simien Mountains. Hurni and Messerli (1981); Hurni (1982, 1983, 1986, 1995), and Hurni and Ludi (1998) made series of studies in the Simien Mountains. Faunal studies mainly on rodents from the high mountains of Ethiopia were undertaken by Afework Bekele et al. (1993), Baskevich et al. (1993) and Afework Bekele (1995). An endemic and threatened species of mammal, Walia Ibex, which is restricted only to the Simien Mountains National Park was largely studied by Nievergelt (1970 a, b; 1971, 1981 and 1996).

Many other studies that are not included in the above citing are still focused on the Bale and Simien Mountains, and generally detailed and long-term researches are scant. Therefore, there is a huge gap of knowledge regarding the biodiversity compositions and status of many of the high mountains of Ethiopia.

The climate of Afroalpine ecosystem is governed by two fundamental geographical circumstances: the vicinity to the equator, and the high altitude above sea level (Hedberg 1964). Seasonal variations in climate are less important than the diurnal ones.

Soils of many of the Ethiopian alpine areas are little studied. Menassie Gashaw and Masresha Fetene (1996) made soil analysis from the alpine and subafroalpine belt of the Bale Mountains, Senettie Plateau. As of the various studies soils of alpine ecosystems are of volcanic origin, and the composition of the bedrocks are lavas of various kinds, basalts, agglomerates, and tuffs, etc. The soils of upper alpine belts are comparatively porous with low water-holding capacity, but offering good drainage. The soil conditions in the lower part of the alpine belt are different, where the closed vegetation has facilitated accumulation and retention of more fine-textured material. The extent of humus accumulation is largely depending upon the degree of moisture available, and upon temperature conditions. The more plant cover and moisture content, the more humus is accumulated in the soil (Hedberg, 1964). Within the alpine belt the extent of humus accumulation appears to decrease with increasing altitude (i.e. decreasing temperature and decreasing growth rate of plants). This evidenced in one of the Ethiopian high mountains at Senettie plateau (Menassie Gashaw and Masresha Fetene, 1996).

Distribution

1.2 Distribution
Land over 3000 m in Ethiopia is about 1589 thousand ha or about 1.3 % of the total area of Ethiopia (Daniel Gamachu, 1986). These high mountains are mainly distributed along the northern and southern sections of the country. Most of the high peak mountains are confined to the Amhara National Region (Gonder, Gojam, Wello and Shewa), to the Oromia National Region (Bale and Arsi), to the Southern People´s Nation National Region (Gamgofa and Sidamo), and to the Tigery National Region. The extensive high mountains of Ethiopia are scatteredly located, as once a BBC film producer commented, the mountains are “islands in the air”.

The great Rift system forms a distinct Rift Valley through the center of Ethiopia, averaging 80 km wide, which separates the two great plateaus with high volcanic mountains and deep river valleys, where the south-eastern plateau slopes south gently into Somalia, and the north-western one slopes west but is more abrupt due to faulting along the western border of Ethiopia (Beals, 1968).

Diversity

1.3 Diversity
Since the high massifs of Ethiopia are long separated from the rest of the lowland areas, they are rich in terms of species diversity and in endemics. Hedberg (1951) has made a taxonomic revision of the afroalpine flora of the East Africa, which contains only about 280 species. These species according to Hedberg (1986) by no means are restricted to the afroalpine belt but occur also lower down in the ericaceous belt or subafroalpine areas, and sometimes in the montane forest belt. Furthermore, species number gets lower with increasing altitude (Menassie Gashaw and Masresha Fetene, 1996). Hedberg (1986) considered the high level flora to be exceptionally interesting from phytogeograhical, ecological and evolutionary points of view. The percentage of endemics is much higher among those taxa, which are restricted to high levels than among those occurring at lower levels.

Hedberg (1986) further discussed that although the first afroalpines known to science came from Ethiopia, the afroalpine flora of Ethiopia has not yet been extensively explored. This is mainly because of the large-scale destruction of natural vegetation on most mountains, where it is difficult to have a clear delimitation of vegetation belts and transition zones.

The Ethiopian Afroalpine flora has gained some attention and being investigated since the start of the Ethiopian Flora Project in 1980, particularly the Bale Mountains on the southeastern plateau (Edwards, 1996). The Simien Mountains have been also investigated for their floral and faunal compositions as early as 1980. Nievergelt (1981) for instance has made a comprehensive listing of the flora of Simien Mountains, which consists of 165 taxa. Simien and Bale Mountains are endowed with a unique botanical and zoological combination of species, which have been able to resist human interference because of the extreme topography, altitudinal range of the landscape, and the extreme inhospitable climate. Therefore, except for these two high plateaus (Simien and Bale), the floral and faunal resources of the other afroalpine areas are poorly known.

Various floristic studies by large number of researchers listed out the following major or characteristic species from the Ethiopian afroalpine and subafroalpine areas: Lobelia rhynchopetalum, Rosularia semiensis, Knifofia floliosa, Euphorbia dumalis, Alchemilla haumannii, Alchemilla ellenbeckii, Hypericum revolutum, Hagenia abyssinica, Erica aroborea, Erica trimera, Philippia keniensis, Thymus schimperi, Hebenstreitia dentata, Cineraria abyssinica, Helichrysum citrispinum, H. splendidum, H. gofense, H. formosissimum, Festuca abyssinica, Haplocarpha ruppellii, Haplocarpha schimperi, Carex monostachya, Euryops prostratus, Aira caryophyllea, Anthemis tigreensis, Arabis alpina, Conyza stricta, Geranium arabicum, Erigeron affroalpinum, Euphorbia dumalis, Satureia biflora, Senecio schultzii, S. steudelii, S. unionis, S. vulgaris, Swertia volkensii, Trifolium burchellianum, Trifolium acaule, Romulea fischeri, Cerastium octandrum, Ranunculus multifidus, R. oreophytus, Stachys sidamoënsis, Veronica glandulosa, Sagina afroalpina, Silene burchellii, Anagallis serpens, Bartsia petitiana, Cotula abyssinica

Major faunal resources of the afroalpine and subafroalpine areas are: The Ethiopian wolf (Canis simensis), Gelada baboon (Theropithecus gelada), Walia ibex (Capra ibex walie), Mountain nyala (Tragelaphus buxtoni), Giant molerat (Tachyoryctes macrocephalus), Grass rat (Arvicanthis abyssinicus), Klipspriger (Oreotragus oreotragus), Golden jackal (Canis aureus), Serval cat (Leptailurus serval), Caracal (Felis caracal), Ratel (Mellivora capensis), Rock hyrax (Procavia capensis), Grey duiker (Sylvicapra grimmia), Anubis baboon (Papio anubis), Porcupine (Hystrix cristata) and Abyssinian hare (Lepus capensis).

Considerable portion of birds are also endemic to these ecosystems such as: Wattled ibis (Bostrychia carunculata), the White-collared pigeon (Columba albitorques), Thick-billed raven (Corvus crassirostris), Blue-winged goose (Cyanochen cyanopterus), and many other rare and common birds are also shared with the other East African alpines such as the Wattled crane (Grus carunculatus), Chough (Pyrrhocorax pyrrhocorax), Lammergeier (Gypaetus barbatus), Spot-breasted plover (Hoplopterus melanocephalus), Ruddy Shelduck (Tadorna ferruginea), Bearded vulture (Gypaetus barbatus), Augur buzzard (Buteo rufofuscus), Tawny eagle (Aquila rapax), Lanner falcon (Falco biarmicus), Chestnut-napped francolin (Francolinus castaneicollis), Alpine swift (Apus melba), Short-crested lark (Galerida malabarica), Tacazze sunbird (Nectarinia tacazze), and Malachite sunbird (Nectarinia famosa),

Although the floristic and faunal resources of the Ethiopian alpines are rich, it lacks some of the most conspicuous species occurring in East Africa (Hedberg, 1986), however, intensive exploration and comparative studies between the East African and the Ethiopian alpines; and between the northern and southern alpines of Ethiopia are lacking, and should obtain due attention to solve the taxonomic, evolutionary, phytogeographical and ecological problems (Hedberg, 1971).

Uses,Values

1.4 Use and values
The spectacular escarpments and gorges of most of these ecosystems provide extremely breathtaking scenery, and therefore, have great scenic values. Besides this, the rare and endemic wild fauna and flora of the afroalpine and subafroalpine ecosystems owe for tourist attractions, and generates foreign income.

Experiences have indicated that an estimated 80 % of people in the developing countries rely on traditional medicines for primary health care. People living in many of the high mountains of Ethiopia have enormous indigenous knowledge in herbal medicine. In the Bale Mountains for instance the use of wild plants as a traditional lore or healer is a common practice (Menassie Gashaw, 1991).

The afroalpine and subafroalpine vegetation are also extremely harvested for a number of purposes such as for food during drought period or as emergency food, forage for cattle, for roof thatching, fuel wood and for many other construction purposes.

Threats

1.5 Threats and rates of change
The afroalpine and subafroalpine environments are highly fragile due to the extreme climatic conditions (low temperature, harmful short wave radiations, etc). Survivals in these ecosystems are only possible with certain anatomical, physiological and morphological adaptations or modifications. Each of the most common five types of phanerogamic life forms such as Giant rosette plant, Tussock grass, Acaulescent rosette plant, Cushion plant and Sclerphyllous shrub representing the alpine belt (Hedberg, 1986) has its own form of adaptation.

But due to intensive human pressure most of the faunal and floral resources are now at risk. Degradation of natural resources, particularly vegetation and soils, is widespread and leads to a chronic food deficit. Demographic trends since the 1950’s show a doubling of the population every 25 years, resulting in scarcity of good land, shortening of fallow periods on shifting cultivation land, and deforestation even in the last remnants of natural forests. Soil degradation is widespread in the high mountains and a major threat to the ecosystem in general (Hurni and Ludi, 1998). The loss in vegetation and soils obviously implies great losses in valuable genetic material (Tewolde Berhan Gebre Egziabher, 1991).

The subafroalpine belt particularly, is suffering from encroaching cultivation and increased burning to produce pasture. Traditionally, these areas are used for grazing, harvesting of grass for roof thatching and barley cultivation. There is also a great danger of epidemic diseases transmitted from domestic animals, mainly from dogs to wild carnivores such as the Ethiopian wolf, Golden jackals; there is also a fear of hybridisation between Walia ibex and domestic goats. The intensified use of the flat highland plateau for livestock grazing, farming and the intensified use of both highland Erica forests and lowland broadleaf forests are major disturbances in the Simien mountains for instance, which lead to the restriction of Walia ibex to a narrow belt on the steepest cliffs (Hurni and Ludi, 1998).

Uncontrolled and deliberate fire set to gain agricultural land and fresh green fodder is also a major threat to wildlifes and plant resources. Heather burning is much common in most of the subafroalpine ecosystems; its effect on the biodiversity of the ecosystem is not yet investigated.

Population pressure has pushed the farmers onto steeper and steeper slopes, which can only give yields for a few years before the soil is washed away (Ensermu Kelbessa et al., 1992). On such harsh and inhospitable environment one could barely produce crops with the same amount and rate as below the tree line, since the growth rate is largely hampered or slow down by the inconvenient weather conditions. The woody vegetation belt, particularly giant heather, Erica arborea L., has been burnt and/or cleared from many areas further threatening the naturally fragile environment (Hedberg, 1971, Ensermu Kelbessa et al., 1992). Generally, the afroalpine ecosystems are less disturbed compared to the lower belt ecosystems (subafroalpine), this is mainly due to the climatic limit for crop cultivation and the capacity of the ecosystem to resilience to some of the disturbances.

The Erica-Hypericum woodland is being over utilized. The area covered by this type of woodland has diminished during the past 30 years. If the heavy utilization of wood resources continues at the same pace for the coming decades, the more easily accessible highland, Erica-Hypericum woodland might disappear. Moreover, due to a shortening of fallow periods and an increasing need to cultivate marginal and steeper land due to a shortage of available land, erosion rates will be considerably higher today than they were around 1950, when land use intensity must have been about one quarter of the present intensity. Hurni and Ludi (1998) further noted in the Simien Mountain, a soil loss of 123 t per hectare per year is estimated from a village named Argin, which is above 3000 m. However, it is only 3 t per hectare are compensated by soil formation every year. As land use intensified considerably, erosion rates increased and soil depths decreased, the retention capacity of the soil has drastically diminished. Reduced retention capacity leads to less infiltration of water and to higher runoff values, while increased erosion rates in the upper course of rivers will lead to higher sediment concentrations further downstream, and decreased water quality (Hurni and Ludi, 1998).

Until as recently as 10,000 years ago (Messerli et al., 1977), the highlands of Ethiopia were widely covered with Afroalpine moorlands and grasslands. But, man has altered large regions of the highlands for centuries, and the rate of change is very alarming and endangering the original species richness. Thus the original afroalpine and subafroalpine natural communities are now restricted almost entirely to scattered and not easily accessible areas, which are surrounded and isolated by agricultural areas. Sileshi Nemomissa and Puff (2001) observed in the Simien Mountains that the park is densely populated, and therefore, only patches of relatively undisturbed afromontane vegetation remain. The extinction of many original species in vast regions has to be seen in connection with this process of insularisation. Therefore, due to increasing human pressure into such fragile environments of the afroalpine and subafroalpine ecosystems, much more attention is needed to halt further threat and rate of destruction.

Status

1.6 Conservation status
Apart from the Simien and Bale Mountains, most of the highlands above 3000 m in Ethiopia are not as such protected or conservation measures are absent, to protect loss of species diversity, and to allow sustainable use of these ecosystems.

Simien Mountain for instance is blessed with outstanding wildlife in certain areas where some natural habitats remained. The Walia ibex in-migrated into Simien during the ice age (Nievergelt, 1981), only a few thousand years earlier than human land users. Because of this rare and endemic animal, Simien received the attention of the global community, which called for its protection and survival. This external interest led to a national initiative to create a National Park in 1969, thus forming a protection area where nature should survive (Hurni and Ludi, 1998). The long-term development goal should now be to preserve both the natural and cultural heritage of protected areas, by creating a protection zone for nature, a buffer zone to mitigate conflicts, and a development zone to provide better livelihood systems and sustainable use (Hurni and Ludi, 1998).

Similarly the Bale Mountains National Park was established in 1971 with the primary objective of conserving the wildlife and other valuable natural resources in the area. The Bale Mountains National Park lies in the south-eastern Ethiopia and encompasses 2,200 Km² of mountain and forest area. It was first proposed in the late 1960’s to protect the afroalpine habitat of the mountains, and the endemic animal species it contains such as Mountain Nyala, Menelik’s bushbuck and the Ethiopian wolf. Protection of the area has been carried out by the Ethiopian wildlife conservation organization (EWCO) since late 1970 with great success.

It was noted that while the term National Park has been used, settlement and human use of the area were considered incompatible with international concepts (Hillman 1986). It was decided that the term National Park gives great administrative advantages, indicates the intention to limit human interference but enables the conservation role to be maintained. It was agreed that gazettment is highly desirable for development and recognition, and that the gazettment process should be set in motion now since adequate knowledge is available.

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