Last update: April 2, 2012 12:32:34 PM E-mail Print



Dr P.W. Roux

Director Karoo Region

The essence of physical science is usually distilled, finally formulated and presented as a law. In the biological sciences, or the science of living matter, such laws are difficult to come by, even more difficult to formulate and by nature not as irrefutable as those of the physical sciences. In fact, biological laws can better be described as laws of a loose or general nature and are subject to considerable latitude of interpretation.

In the case of the applied biological sciences such as pasture science or veld management, the formulation of strict laws is practically out of the question owing to the involved and complicated nature of these sciences which encompass both physical and biological fields. It would be more accurate to propound rules, guidelines and prescriptions inflexible laws rather than to formulate.

There are however situations in which it appears to be possible to formulate working laws on veld management. In this respect the following four laws of the veld are put forward for consideration and serious thought:


1. Law of the critical minimum

When the numbers of a formerly abundant and desirable plant species have diminished in the open veld to such an extent that the species is eventually sparsely scattered to rare, it is impossible to regenerate its population economically by the application of ordinary veld management practices.

Artificial and expensive methods will be required to regenerate the population. Such methods are, amongst a large number, cultivating the soil, reseeding or replanting, fertilizing, irrigating, applying special veld treatments, prolonged withdrawal from grazing and so on.

Usually perennial indigenous grass species, such as Themeda triandra (Rooigras), Tetrachne dregei (Stormbergplatblaar), Setaria neglecta (Stepgrass, Stiefgras or mannagras) and many more, fall under this law. A large variety of valuable low trees, shrubs and bushes also fall within this category.


2. Law of the critical maximum

When the numbers of an undesirable or invading plant species have increased to such an extent that the species has become abundant or practically dominant, it is impossible to decimate its numbers or eradicate it effectively by the application of economic veld management practices.

Artificial and expensive methods of control are required such as mechanical eradication or destruction, use of weedicides, prolonged withdrawal from grazing, radical veld improvement and so on. Fire can be used as a means of obtaining temporary relief from such plants but no permanent eradication or complete suppression. Examples of such plant species are Euryops spp. (Harpuisbos or resin bush), Elytropappus rhinocerotis (Renosterbos), Acacia karroo (thorn tree), Opuntia aurantiaca (jointed cactus), Stipa trichotoma (serrated tussock grass) and many more.


3. Law of the zone of critical control

In any heterogeneous plant population (veld cover) there usually exists an unstable balance between desirable and undesirable perennial plant species, each tending to become dominant. By critical control, such as judicious and correct veld management, the numbers of the desirable species can be increased and those of the undesirable species decreased. Through injudicious and incorrect grazing practices these two categories of plant species break away from the realm of the zone of critical control and the desirable species tend to fall under the law of the critical minimum and the undesirable species under the law of the critical maximum.

This law clearly intimates that sound veld management practices should constantly be applied in order to prevent the veld from becoming dominated or overrun by undesirable plant species which are extremely difficult to control.


4. Law of maximum-minimum grazing distance

When the fodder supply in the veld is at a maximum the walking distance of the grazing animal tends to a minimum, and, conversely, when the fodder supply is at a minimum the walking distance of the grazing animal tends to a maximum.

From this law it should be clear that, as veld improves, trampling by stock decreases and that stock as a consequence of their reduced activity require less food for maintenance and production.

On studying and considering these four laws it should become clear that each has bearing on every day veld situations which occur on a stock farm. The essence of these laws boils down to the fact that sound veld management practices are the most economic.



Karoo Agric 1 (5), 6