Some important concepts and perspectives in rangeland ecosystem dynamics and their significance for rangeland science

MSc , North-West University, Potchefstroom Campus

Research was initiated to evaluate the influence of mismanagement on the range habitat and to study habitat and vegetation interactions during range succession and re t regression processes in the climatic climax grasslands of southern Africa. Simultaneously the impact of patch-overgrazing on range vegetation and habitat at tributes was assessed and patch-dynamics were monitored. In seriatim some of the main findings and contributions to range science are as follows: * Substantial habitat degradation occurs concomitant with. vegetation retrogression in overgrazed areas. Rainfall effectivity reductions of more than 50% are not uncommon in severely overgrazed areas. * Monitoring of vegetation attributes will give no timely warning of habitat retrogression due to a time-lag between habitat retrogression and vegetation retrogression. * A descriptive range ecosystem retrogression model, which illustrates the biotic and abiotic interactions and ecosystem degradation dynamics associated with rangeland retrogression processes, is presented. * Patches in poor condition expand at the expense degraded patches in years of below-average rainfall. of less * Patch-selective overgrazing has a detrimental effect on the stability of semi-arid rangelands. The resilience of range vegetation to unfavourable climatic conditions is adversely affected where patch-overgrazing occurs. * Results indicate that semi-arid rangelands which have retrogressed beyond a threshold of drought resilience can not rest-recover. * Urgent research is needed to devise management strategies to reduce patch-overgrazing in semi-arid and arid rangelands. If present levels of patch-overgrazing are not reduced substantially, the continued retrogression of these rangelands will not be halted. * Range vegetation succession towards a more desirable species composition, basal cover and phytomass production could be directed through habitat improvements. * Habitat condition governs rangeland vegetation trends. * The range habitat is more sensitive to mismanagement than the vegetation. Consequently habitat retrogression precedes vegetation retrogression. * Management strategies should be evaluated firstly according to their ability to preserve or-· improve the range habitat. * Habitat condition has to be assessed simultaneously with other relevant rangeland condition attributes to ensure that range condition assessments are a true reflection of the actual condition of the range. * A technique for objective habitat condition assessments in rangelands is presented . * The necessity of a much more habitat orientated approach in range science and management is illustrated. * A rainfall effectivity orientated environmental management philosophy is regarded as the key to successful natural resource management and preservation.

Masters