This chapter reviews secondary information on geology and sociology, as well as original information on climate, soils wildlife, plant ecology and water resources for the central Borana Plateau. A 15 475-km² study area was selected because it represented an important region for the national livestock economy. Geology of the study area is dominated by quaternary deposits (40%), basement-complex formations (38%) and volcanics (20%). Except for a central mountain range and scattered volcanic cones and craters, the landscape is gently undulating across an elevation of 1000 to 1600 m. Vertisols occur more in valley bottoms while upland soils occur elsewhere. Valley bottoms are relatively scarce on the landscape and occupy about 12% of the study area. Vertisols appear higher in nutrient content and water storage capacity compared with upland soils.
The region is dominated by a semi-arid climate. Annual mean temperatures vary from 19 to 24°C with little seasonal variation and these decrease 1°C with each 200-m increase in elevation. Average annual rainfall for 10 sites during 1980-89 varied from 440 to 1100 mm (with an overall average of 700 mm) and this increased by 64 mm with each 100-m increase in elevation. The average of 700 mm is probably biased high because climate stations tend to be located at higher elevations. Rainfall delivery is bimodal; 59% of the annual precipitation occurs during March to May and 27% in September to November.
A "dry" year is defined as one in which annual rainfall is <75% of average and may occur one year in five. The probability that two consecutive years will have average or above-average rainfall, one dry year, or two dry years is thus 0.64,0.32 and 0.04, respectively. At least two consecutive dry years constitute a drought. In an average rainfall year the number of plant growing days ranges from 100 to 140 in the west and north of the study area, respectively, which corresponds to 1.5 to 2.0 t DM/ha/year of herbaceous forage production. Calculated throughout the study area, conservative calculations suggest that annual mean carrying capacity in an average rainfall year is 14 Tropical Livestock Units (TLUs)/km², or 217 000 head of cattle, but this can decrease to £ 10 TLUs/km² (or <155 000 head of cattle) in a dry year. Stocking rates for the near-average rainfall years of 1982-83 and 1988-90 suggest that mean animal density is commonly around 16 TLUs/km², or 250 000 head.
The region is dominated by savannah communities containing mixtures of perennial herbaceous and woody vegetation. Several native species of grasses and woody plants provide excellent forage. Forage nutritive value increases in rainy seasons compared to dry seasons and browse often retains higher nitrogen content in dry seasons compared to grasses. Elevation, with concomitant effects on temperature, precipitation and associated with shifts in soil parent materials, is the most important factor governing distribution of key plant species. In terms of fauna, the study area is home to at least 26 species of large wild mammals and 45 species of commonly observed birds.
The Borana Plateau is characterised by a general scarcity of surface water. There are over 540 hand-dug wells occurring in some 40 clusters largely to the west. These wells provide over 95% of the permanent water points and about 84% of the total accessible water in a typical dry season. The wells also provide about half of the annual water requirements for people and livestock, with the remainder provided by ephemeral and permanent ponds. Wells require large inputs of labour and are thus important in the social and economic life of Borana pastoralists. They also form the basis for traditional units of resource allocation called madda. There are about 35 madda with an average area of 500 km². Each madda, on average, may contain several well clusters serving some 100 encampments, 4000 people and 10 000 cattle.
The history of Borana society, its culture and resource allocation practices are reviewed. The Borana Plateau represents part of the remaining core area or cradleland of the southern highlands and rangelands from which the original Oromo culture expanded and conquered half of present-day Ethiopia during the 1500s. The core rangeland area contains historical Oromo shrines still worshipped by the population. The Borana territory has been reportedly shrinking since the early 1900s, largely because of induced habitat change and Somali encroachment from the east. The Borana social structure includes two moieties, five sub-moieties, 20 clans and some 60 lineages based primarily on patterns of male descent. Clans are widely distributed among madda and are the primary mechanism for wealth redistribution. Some 100 clan meetings are held each year in which the poor petition the wealthy for cattle. Political structure is related to the social structure. The Boran achieve consensus on important community issues through open, participatory assembly. Consensus and enforcement of social norms is achieved under the umbrella of the "Peace of the Boran", which refers to traditional values and laws. Two peer-group structures for males, the age-set system (Hariya) and generation system (Gada) are discussed with respect to distribution of social rights and responsibilities and/or regulation of human reproduction.
These two systems share many similar attributes, but ultimately are complementary in function. All males have a position in each. Hariya consists of 10 eight-year blocks of similarly aged individuals between the ages of 12 to 91 who share a collective identity that evolves with ascension into subsequent age sets. The Gada, in contrast, consists of seven grades and an increasing number of generation classes that are created every eight years. Gada grades can contain males of vastly different ages. Among other attributes, the Gada grades confer political and ceremonial duties and subject members to different rules regarding sexual behaviour. It has been hypothesised that the Gada was created during the 1600s to help the society cope with a population explosion. Computer models have suggested that Gada rules on reproduction served to reduce the population by 50% by the mid-1800s and the population may have slowly grown ever since. The human population in the study area may have been about 7 people/km² (or 108 000) in 1982 and may be growing at a rate of 2.5% per year. Hypotheses to explain this apparent surge in growth include (1) improved provision of food and medical inputs from outside agencies; (2) declining adherence of the population to traditional Gada norms; (3) external interference with the Gada system from national political interests; and/or (4) cyclic, functional aberrations in effects of Gada rules due to demographic shifts in the population.
The Gumi Gayu, or Assembly of the Multitudes, is chaired by the leadership and occurs once every eight years in the southern rangelands. It is a foundation of Borana life which attracts pilgrims from Ethiopia and Kenya. The assemblies of 1966 and 1988 are discussed in terms of key cultural and political proclamations. For 1988 the proclamations were indicative of a society under resource pressure. These included decrees to better maintain water points, restrict cultivation, establish calf fodder reserves, protect valuable indigenous trees, reclaim grazing reserves for cattle and prohibit water sales and alcohol abuse.
