Last update: March 30, 2012 11:06:14 AM E-mail Print



PW Roux


Over the past 300 years Karoo vegetation has undergone large-scale and often radical change, Dr Piet Roux, Director of the Karoo Region, said at the Grassland Society Congress.

This change, he said, has largely taken, the form of thinning out of the vegetation, decrease or total disappearance of perennial grass, and an increase and spreading of undesirable Karoo bush and woody shrubs. In many instances drier veld types have extended into areas which originally consisted of moister vegetation.

According to Dr Roux, the main cause of vegetation change in the Karoo is over-exploitation by sheep.

He explained that although seasonal fluctuations in climate increase the instability of the vegetation, there is no evidence that vegetational change is being brought about by an alteration in climate. In fact, thorough analysis of meteorological data has shown that a change in climate can hitherto not be statistically identified.

It is therefore evident, Dr Roux said, that changes in the veld over the last three centuries can be ascribed entirely to man and his agricultural pursuits.

It has been shown over and over again that a quick way to destroy vegetation and to downgrade the composition of veld is to mismanage it, especially when it is at its most vulnerable during droughts.

Another cause of change in vegetation is the migration of plant species. Although this is largely a natural process, Dr Roux made it clear that plant migration can, in fact, be considerably accelerated through the mismanagement of veld and the consequent easing of plant competition. He added that it was obvious that the less palatable and hardier plants would have the best chance to migrate.

He pointed out that changes in vegetation generally bring about detrimental effects. Higher rates of soil loss can be expected, he said, while the effectivity of the rainfall decreases. Farmers can also suffer severe stock losses as a result of the ingestion of toxic plants, or monotonous and one-sided diets. Degraded veld, furthermore, increases the outbreaks of veld predators like Karoo caterpillar, termites and locusts, which, in turn, cause expensive temporary fodder shortages.

According to Dr Roux most of the essential information to prevent veld deterioration has already been gathered. He said, moreover, that it is not impossible to reclaim already degraded veld and that much can be achieved by applying veld management principles and special techniques, establishing hardy fodder plants and revising crop production practices in sensitive zones.




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