A Complex Adaptive Systems Analysis of Shaka Zulu and the Mfecane
and externally caused ( drought ) ( Maggs & Whitelaw , 1991 ). Deterioration of soil through exhaustion resulted from excessive planting without allowing fallow periods to permit natural regeneration by existing natural plant life and without application of lime and fertilizers to restore fertility ( Hall , 1981 ; Lea , 1977 ). The removal of restorative natural vegetation through slash and burn clearing exacerbated the problem ( Guy , 1985 ). The shift to cultivating maize accelerated the effects of soil exhaustion , which takes nutrients from the soil at a higher rate than native plants because maize needs more to grow ( Lea , 1977 ). Maize thus would quickly create a feedback effect of soil deterioration that in turn would decrease agricultural production ( Hall , 1981 ; Lea , 1977 ). Further , clearing land by use of fire would remove the ground cover necessary to protect the soil from rainfall and runoff and lead to substantial erosion of fertile topsoil ( Hall , 1981 ).
Exhaustion of pasture would also result from overuse , in this case overgrazing ( Lye & Murray , 1980 ). The more desirable and nutritious sweetveld was replaced by the hardier and more aggressive sourveld as herds increased ( Guy , 1985 ). More sourveld grazing meant a need to expand pasture , whether in search of sweetveld or to secure the larger amount of sourveld necessary to satisfy the herd ’ s nutritional requirements ( Guy , 1985 ). Herders also sped the decline of soil quality by clearing the ( to them ) useless forest and scrub forest by fire , removing the restorative native vegetation ( Guy , 1985 ). Such clearing led to heightened soil erosion as well as deterioration with the removal of the protective ground cover ( Guy , 1985 ; Hall , 1981 ).
In addition to changes in the quality of the soil (“ edaphic factors ”) changes in climate affected environmental quality . Drought was a problem early in the nineteenth century
( Cobbing , 1988 ). Drought was a part of the weather of Southern Africa , whether a short-term pattern of once every three years or a longer 20-year cycle ( Eldredge , 2001 ; Lye & Murray , 1980 ). Greater than normal rainfall preceded and heightened the effect of droughts in 1812 , 1816 – 1818 and 1821 – 1823 ( Eldredge , 2001 ; Nicholson , 1976 ; Peires , 1981 ). Increased rainfall would have accelerated soil deterioration by leaching more nutrients out of the soil , which would have lowered production of maize ( Hall , 1981 ; Lea , 1977 ). The impact of lowered production would have fallen on a population increased during the preceding wetter period ( Peires , 1981 ). An increased population making demands from a shrunken resource would have magnified pressures on the environment , as the productive capacity of resources available was unable to meet demand ( Gluckman , 1960 ).
The effect of environmental pressures of all sorts is representable by decline in productivity in the environment node . For each year in which there was an increase in Zulu population , population increases and food production caused a moderate decrease in environmental quality , i . e ., there was deterioration but not a catastrophic natural disaster . Using Sugeno and Yasukawa ’ s values assigned to linguistic hedges , a moderate deterioration would be equal to 0.08 of its predecessor ( McNeill & Freiberger , 1993 ). We arbitrarily assign a value of 100 for the initial year in order to illustrate the process .
The values of the interaction between the nodes of population , Great Man / amabutho , and environment are calculable through a series of iterations using Kiel ’ s Spreadsheet Method . If the interaction of the three nodes results in shortage and conflict , it is arguable that sufficient conditions for the Mfecane existed .
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