Responses of Savannas to Stress and Disturbance: the Beginning of Desertification
Stress and disturbance may be natural or caused by man but usually from a combination of extreme values of environmental variables. Their prevalence in the Nigerian Savanna and effect on stability and resilience and, in a sense, desertification has been examined. The stress and disturbance identified include drought, wood cutting and land cultivation, herbivory, annual burning. It is concluded that annual burning does not constitute a destabilizing factor as such since it could be regarded as regular annual phenomenon to which the plant species are adapted, but mainly as a force that accentuates the effects of other destabilizing influences created through improper land use. Effort has been made to place different savanna systems into ranges of stability and resilience. Suggestions have been made for improving grazing system, controlling indiscriminate wood-cutting and ecologically sensitive farming systems. Drought control is distinctly impossible except through irrigation which is not yet extensively practised. Land use and vegetation mapping must be done on a local scale permitting the application of management tools to delineated land units. Parameters of description, evaluation and prediction vary according to land use; intensive or extensive, transformational or conservational. A scheme has been proposed for assessing the phenomena of stress, disturbance/perturbation and their relationship to stability and resilience in the savanna.