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

Abstract

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.