The Ethiopian highlands contribute to more than 50 % of the land area with Afromontane vegetation, of which dry montane forests form the largest part (Yalden, 1983; Tamrat Bekele, 1994). The evergreen scrubland vegetation occurs in the highlands of Ethiopia either as an intact scrub, i.e. in association with the dry evergreen montane forest or usually as secondary growth after deforestation of the dry evergreen montane forest. The Dry Evergreen Montane Forest and Evergreen Scrubland vegetations are the chjarachteristic vegetation types of this ecostem. These vegetation types were treated and discussed separately as follows:
3.1 Dry Evergreen Montane Forest
Typical dry evergreen montane forests in Ethiopia are situated on highlands and mountain chains with the following locations: the Chilimo forest (38° 10′ E and 9° 05′ N), 2400 ha; the Menagesha forest (38° 35′ E and 9° 00′ N), 2720 ha; and the Wof-Washa forest (39° 45′ E and 9° 35′ N), 3600 ha (Sebsebe Demissew, 1988; Tamrat Bekele 1994).
Dry Evergreen Montane Forest is a very complex vegetation type occurring in an altitudinal range of 1500-2700 m, with average annual temperature and rainfall of 14-25° C and 700-1100 mm, respectively (Friis, 1992). It is inhabited by the majority of the Ethiopian population and represents a zone of sedentary cereal-based mixed agriculture for centuries. This type of forest develops in areas of relatively high humidity, but not much rain, and where there is a prolonged dry season. The forests have diminished due to human interference and replaced by bushlands in most areas. Soils have become shallow as a result of soil erosion that has been taking place for centuries (Zerihun Woldu 1999; Anonymous, 1992).
The prominent features of tropical dry forests are their seasonality with respect to rainfall compared with the rain forests where the environment is stable throughout the year. Dry evergreen montane forests experience long dry seasons (4-8 months) and the rainy period is somewhat unreliable. During the dry season, not only moisture stress but also temperature increases and daytime humidity drops and watercourses either dry up or greatly diminish inflow (Demel Teketay, 1996).
The bulk of the plateau consists of volcanic rocks. There are, however, Pre-Cambrian outcrops in the south (Sidamo zone), west (Wellega), north (Tigray) and east (Harar). The Pre-Cambrian rocks form heterogeneous substrata for plant growth. Some, like the ultrabasics of Wellega, are so deficient in nutrients, especially phosphorus that they tend to be very poor in vegetation cover. Extensive parts of the Tekeze Valley have impoverished vegetation cover because the substratum consists of fossil laterite soils, which are deficient in cations and have been exposed as a result of geological erosion (Zerihun Woldu, 1999; Anonymous, 1992)
The Dry Evergreen Montane Forests are distributed in central (east, west and north Shoa, Arsi and Gurage zones), northern (east and west Gojam, north and south Gonder, south and north Wello, Oromia, Agew Awi, and south, east and west Tigray zones) eastern (east and west Hararghe, Afar and Dire Dawa zones) and southern (Bale, Borona, and South and north Omo zones) parts of Ethiopia. They are limited to five national regions in the country, namely, Amhara, Oromia, Tigray, South Nations, Nationalities and peoples, and Afar regions.
3.1.3. Species diversity
Dry Evergreen Montane Forest is multi-storeyed forest vegetation. The top storey consists of a non-uniform, non-compact layer of tall trees. These trees are known as “emergents” because they project above the vegetation mass. Below the layer of emergents is a mass of shorter trees of various heights. Still lower is a stratum of short trees and large shrubs, much less dense than the second stratum. Finally, there is the lowest stratum of shrubs, suffrutescents, and herbs. Epiphytes, lianas and parasites are common (Zerihun Woldu, 1999; Anonymous, 1992).
This vegetation is characterised by Olea europea subsp. africana, Juniperus procera, Celtis kraussiana, Euphorbia amplipylla, Dracaena spp. Carissa edulis, Rosa abyssinca, Mimusops kummel, Ekebergia capensis, etc. These incluses small to medium size trees, though some provenanaces of J. procerea can get very big and some others remain small. This vegetation type is associated with highland Bamboo (Arundinaria alpina) and extensive areas of grassland rich in species including many legumes. The most important genera are Hyparhenia, Eragrotis, Panicum, Sporoblus, and Pennisetum for the grasses and Triflium, Eriosema, Crotalaria for the legumes. These include a large number of endemics (Anonymous, 1992).
The bulk of the plateau was originally covered in evergreen forests. The eastern and higher altitude forests mostly consisted of Juniperus procera and/or Olea africana as the main trees with Acacia abyssinica or Acacia negrii predominating on valleys. Other large trees, including Afrocarpus falcatus, Olea capensis ssp. hochstetteri, Prunus africana, Apodytes dimidiata, etc. also occur. Smaller trees include Allophyllus abyssinicus, Euphorbia abovalifolia, Rapanea simensis, Olinia aequipetala, etc. Epiphytes including orchids, mosses and lichens (especially Usnea) are common. The shrub layer’s usual constituents are Discopodium penninervium, Myrsine africana, calpurina aurea, Dovyalis Abyssinica, etc.
Climbers including Smilax sp., Rubia cordifolia, Urera hypselodendron, Embelia schimperi, Jasminum floribundum and various species in the Cucurbitaceae, etc usually join the strata of vegetation. The ground is covered with grasses, various other herbs including ferns and mosses. Dead plant remains form a thick soil cover. On the drier and lower part of the north and east the complexity of the vegetation is greatly reduced, and it may only be three-layered. The upper altitudinal limits also consist of simpler forests of Hagenia abyssinica with associated small trees or shrubs of Hypericum revolutum, Rapanea simensis, etc. on deeper soils and Erica arborea scrub on the thinner soils of the slopes. Stretches of bamboo forest, Arundinaria alpina, also occur in places, its number of individuals of occurrence increasing towards the west (Zerihun Woldu, 1999; Anonymous, 1992).
Grasslands have come into existence or expanded owing to human interference and replaced most of the forest. This is especially true on the less well-drained flat areas, and invariably so on Vertisols. The grasses include various species of Hyparrhenia, Andropogon, Chloris, Pennisetum and many other genera. Many other herbs including geophytes also occur. Overgrazing, which is prevalent in most areas, tends to shift the grass flora from the more palatable grasses, e.g. Chloris gayana and Pennisetum cladistinum to less palatable highly silicified grasses, e.g. Pennisetum schimperi and P. glabrum.
Wildlife species diversity and distribution in the dry evergreen montane forest is not that much and low due to human interferances. However, this type of vegetation is an ideal environment for Elephant, Buffalo, and Lion. Today the following wildlife species are still managed to thrive hiding themselves in the dense remenant dry evergreen montane forest such as Leopard, Menelik’s Bushbuck, Warthog, Bohor reedbuck, Olive baboon, Grey duiker, and Hyaena. Various types of bird species occurring in this vegetation type include Wattled Ibis, Blue-winged Goose, Black-winged Plover, Yellow-fronted Parrot, Black-winged Lovebird, White-cheeked Turaco, Half-collared Kingfisher, Abyssinian Longclaw and Black-headed Siskin (EWNHS, 1996).
3.1.4 Uses and values
Similar to other forests, the Dry Evergreen Montane Forests provide fuelwood, construction material, farm implements, edible fruits, honey, medicinal plants, water and game for hunting. As one of the major activities of the local people is livestock production, it provides grazing areas. It also provides food, shelter and breeding areas for many wild animals. The forest prevents soil erosion and regulates the watershed in the surrounding and some of the forests are important water catchments for rivers. They are ideal places for naturalists and mountaineers, and areas of great pleasure for tourists. They are also outdoor laboratories for practical training of students and for researchers.
3.1.5 Threats and rate of change
The Dry Evergreen Montane Forests are under severe pressure of destruction caused by deforestation for wood products, fire, encroaching agriculture and overgrazing.
This forest is under severe pressure as a consequence of inhabitants’ need for agricultural and grazing land. There is a severe and increasing fuelwood gap in the country, which leads to depletion of standing stock and, hence, further degradation of the remaining forest stands. Since 85% of the population is concentrated in the highlands, the montane vegetation types, dry evergreen montane forests and moist evergreen forests, are most endangered. Another threat is the conversion of high forest sites to coffee and tea plantations. Reportedly, a number of investors have filed applications for forestland with the relevant regional authorities. In the process of decision making on these requests in most cases little consideration is given to ecological impacts in general and biodiversity conservation in particular.
3.1.6 Conservation status
Forests have virtually disappeared in northern Ethiopia exposing bare rocks and springs and streams are drying during the dry season. Southern and eastern parts of the country are following the same route. Many of the forests have been eliminated by human activities. As it is clearly mentioned earlier, the conservation status of many forests are in bad shape and not much is known for each forest. It is obvious that many forests have been disappearing at an alarming rate. At present, there are no significant measures to conserve the Dry Evergreen Montane Forests. However, some community based dryland forest and woodland conservation efforts have been observed in the northern parts of Ethiopia (Gonder, Tigray and Wello). Besides this communal conservation effort, the Menagesha state forest, which is one of the few remaining forests in cenrtral Ethiopia, has received long years of attention and protection, which goes back to the 1600s (Sebsebe Demissew, 1988).
3.2 Evergreen Scrub Vegetation
The evergreen scrub vegetation consists of both the montane evergreen thicket and the montane evergreen scrub. This vegetation occurs as a secondary re-growth on steep plateau slopes where there had been intense deforestation of large trees or montane forests. The montane evergreen thicket consists of dense growth of small evergreen shrubs, lianas and sparsely spaced small trees. Shrubs from the dominant part of the vegetation are 2-3 m high and some deciduous shrubs and trees could be found among the evergreens. Suffrutescents and perennial grasses are found tangled with shrubs. Whereas, the montane evergreen scrub consists of dense and dominant shrub stratum of evergreen plants, 3-5 m tall, and trees project out of this shrub layer. Below the shrub layer, lianas, suffrutescents, herbs and perennial grasses grow. These two types of vegetation usually form a mosaic on the plateau slopes. The scrub type usually occurs at lower altitudes and moister areas. The climate associated with this type of vegetation is largely influenced by surrounding high mountain massifs, and thus has a variable annual rainfall and temperature regimes.
The evergreen scrubs are expanding as a resutl of the deterioration of the areas that used to be forests. In the western volcanic ash areas of central Ethiopia, the gullies are becoming evergreen scrub (Zerihun Woldu, 1999).
Both the montane evergreen thicket and scrub vegetation types occur surrounding the scattered high mountains of Ethiopia, particularly in areas of high disturbance and deforestation at the montane line or immediately below the subafroalpine belt. These areas include rugged and highly degraded places in the northern parts of Ethiopia such as Tigray, Goder, Wello, Gojam; central Shewa and in the degraded parts of the Bale and Aris montane areas.
Characteristic species occurring in this vegetation include major shrubs such as Acokanthera schimperi, Carissa edulis, Scolopia theifoliaand, Euclea schimperi, Rhamnus staddo, Myrsine africana, Dodonaea angustifolia, Rhus spp., Calpurnia aurea, Jasminum abyssinicum, Osyris quadripartita, Ximenia americana, Protea gaguedi. Trees such as Teclea nobilis, Croton macrostachyus, Bersama abyssinica, Olea europaea, Juniperus procera, Ficus spp., Euphorbia abyssinica, Euphorbia candelabrum, and Dracaena spp. dominate this vegetation. The dominant liana in this type of vgetation is Pterolobium stellatum.
The faunal diversity of this type of vegetation is not that rich, where there are some remnant Leopards, Olive baboon, Grey duikers, Common Jackals and Klipspringer. Typical bird species in the evergreen scrub are Speckled Mousebird, Cinnamon Bracken Warbler, African Yellow Warbler, Winding Cisticola, Olive-bellied Sunbird and Green Twinspot (EWNHS, 1996).
3.2.4 Use and values
The evergreen scrublands are traditionally used for grazing, cereal cultivation and fuel wood collection. They are sources of traditional medicine and also serve as source of non-cultivated food plants. They also serve for construction materials. However, compared to the other vegetation types, evergreen shrub is not economically attractive, be it for grazing, agriculture or even wood.
3.2.5 Threats and rate of change
As a result of fuel wood extraction, intense grazing and farming the evergreen scrub areas are extremely threatened. Although the evergreen scrub vegetation types are fast colonizers of disturbed areas, and have been expanding at the expense of other vegetation types, they are disappearing at a very high rate due to high demand for fuel wood. Deliberate and unintentional fire is also a major threat to this type of vegetation, resulting in the elimination of fire sensitive plants particularly thin barked trees and tree seedlings.
Soil erosion is obviously very high particularly at the steep mountain slopes, resulting in the loss of many tons of soils every year. This has drastically reduced the species richness and diversity of the evergreen scrub vegetation.
3.2.6 Conservation status
No significant conservation efforts have been carried out in the evergreen scrublands, to tackle problems of severe deforestation, and land degradation. However, vegetation of this type is protected from severe human pressure in some National Parks, Reserves and Sanctuaries. In the northern parts of Ethiopia, particularly, in the Tigray national region (Zerihun Woldu and Feoli, 2001), there is a governmental attempt to mobilize the local community to tackle the problems of soil erosion and land degradation.