Introduction to Ethiopia

Geologically, Ethiopia is based on the Precambrian (more than 600 million years old) crystalline basement system underlying most of Africa. This basement is dominated by various schists, gneisses and granites which are exposed in areas where erosion has been intense, particularly along plateau fringes in the northern, western and southern parts of the country. Sedimentary limestone and sandstones several meters thick were deposited over this basement foundation when the sea engulfed the country from the south-east some 100-200 million years ago. Over nearly half of the country, these sediments were capped by successive flows of lava, composed mainly of basalts, which accumulated to a thickness of several thousand meters in some areas. The period of intense volcanic activity is still to be found in the form of a few live volcanoes and numerous hot springs (Constable, 1984).

Ethiopia is a country of great geographical diversity with high and rugged mountains, flat-topped plateau, deep gorges, river valleys and rolling plains. Over the ages, erosion, volcanic eruptions, tectonic movements and subsidence have continued to accentuate the unevenness of the surface.

Altitudes ranges from the highest peak at Ras Dejen, 4,620 meters above sea level, to the depression of the Kobra Sinka, about 110 meters below sea level. Most of the country consists of high plateau and mountain ranges with precipitous valleys dissected by numerous streams which are the tributaries of the major rivers, such as, the Abay (Blue Nile), Tekeze, Awash, Omo, Wabe Shebele, and Baro-Akobo.

The great Rift Valley separates the western highlands and the south-eastern highlands, and on each side these highlands give way to vast semi-arid lowland areas in the east and west, and especially in the south of the country (EMA, 1988).

Although the whole of Ethiopia lies within the tropical latitudes, the climate is cool in the highlands, although actual temperatures vary significantly with altitude. The annual range of temperature is relatively small because of the proximity of the equator, but the average daily range is wide because of the intense daily isolation at higher altitudes. The mean daily temperature during the highland growing season (from May to December) is 21.3° C, and it drops by 0.6° C for each 100 meters increase in altitude (Goebel and Odenyo, 1983)

Rainfall variability generally increases as rainfall total decreases, and is thus generally greatest in the lower rainfall areas of the north and north-east highlands. Rainfall intensity records are not generally available but it is widely accepted that rainfall intensities are high with most rain falling as heavy showers lasting a few ours at the most (FAO, 1984a).

Agroforestry :

For each proposed agroforestry intervention, the process of identifying of research needs should go through a logical sequence of steps. This starts with the description of the species specifications, both in terms of environmental and technology-specific requirements. It then proceeds into the review of potential species, whether already existing or from similar environments in different countries, using literature data-bases etc. The existing research in the country is then reviewed and gaps in terms of screening of species and management trials are identified.

Refer to the group of technologies where trees are closely spaced and interact with each other to form a closed canopy. The most complex type of agroforest is the mixed, dense, multilayer homegarden which includes a wide range of tree species of different sizes, as well as an undergrowth of annual plants. On the other extreme, are the single-species, single-strata tree blocks (for fodder, wood, or as enriched fallows). In between, lie the forest coffee and enriched bushlands which can be more or less complex according to the number and spatial arrangement of the trees being used.

Some of the species specificatioction which cut across all systems are fast growth and a deep-rooting pattern. Other specifications are then given according to the production purpose of the trees, either poles, timber, fuelwood or fodder. Since environmental protection and soil-fertility improvement are major service roles for all these technologies, there are some characteristics which apply regardless of the production purpose, like leafiness, nutrient-rich litter and high decomposition rate.

There are several species available, some of which are well known in the country, although they are mainly used as scattered trees in farm land or rare remnants from the natural vegetation. The notable exception is the coffee forest, a well-established system in the HPP zone, but which is obviously lacking dynamic management procedures.

Quite a number of species can also be proposed as potential trees for the agroforests, and a number of them are already adapted to different zones or are under screening trials. The key factor for the development of agroforests is the establishment stage of the trees, and this is why establishment trials are proposed for all the technologies. When the agroforest is of mixed nature, and/or multistory, as in the case of homegardens, these trials should e coupled with trials on planting sequence for the different species.

Once again, this is with the exception of the coffee forest where compatibility trials should also be carried out, as well as trials on the effect of management of the forest trees on coffee yield and quality. In all cases, trials on the effect of cutting/harvesting regimes on the desired yield and quality are recommended. Finally, monitoring of soil changes is a research topic of importance for the improved fallows.

Major agro-ecological zones of the Etiopian Highlands

Zone	Climate	Growig Period (No. of days)
High potential perennial zone (HPP)	Warmer and more humid	Mainly >240
High potential cereal zone(HPC)	Intermediate	Usually >180
Low potential cereal zone (LPC)	High ainfall variability Occasional drought	Mainly 90-150

Source: EHRS Project, UTF/ETH/037