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.