agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 6.1 1999
VELD CONDITION
N M Tainton
Professor Emeritus, University of Natal
INTRODUCTION
Veld forms an important basis for animal production in KwaZulu-Natal. It is important, therefore, that the manager knows what state the veld is in, and how this state compares with productive veld. The concept of veld condition is used to achieve this. Veld condition can be simply defined as a measure of the state of health of a sample of veld. It will indicate to the manager the value of a sample of veld for any purpose for which it is to be used, and therefore also its monetary value. More specifically, it will indicate how many animals can be carried on the veld, and it will provide a guide as to how the veld should be grazed and how often it should be burnt.
Veld reacts to management in three important ways.
- Management will affect the vigour of individual plants, and therefore the total yield of forage produced.
- Management will affect the density of the sward. This will, in turn, affect yield, but will also influence the susceptibility of the area to soil erosion.
- Management will affect the species composition of the veld, which, in turn, affects yield (since some grasses grow more rapidly than others), and the forage value of veld (since not all species are palatable to animals).
Therefore, if one or more of these factors are measured, an indication of the state of health of any sample of veld should be obtained.
In practice, however, plant vigour and plant density are difficult to measure accurately. Therefore, we use the third factor, species composition, to provide us with an indication of veld condition.
Both stocking rate and grazing method influence species composition, because they influence the frequency (how often) and intensity (how severely) that individual plants of different species are grazed.Effect of management on species composition
Looking first at stocking rate, it is reasonable to assume that the higher this is, the more completely will each plant, on average, be grazed, and vice versa. Now plants vary in their ability to tolerate repeated severe grazing, and the palatable plants, in particular, will die when stocking rates are very high. When this happens, other species, more tolerant of severe grazing, will take their place. Many of these species are able to survive at high stocking rates because they are unpalatable and so are not themselves grazed intensively. On the other hand, many species are not able to tolerate long periods of lenient grazing in the absence of fire. They cannot tolerate shading for protracted periods. Hence they will die where veld is too leniently used, and other species capable of growing under such conditions will take over. These are normally also relatively poor forage-producing species.
The species which commonly occur in grassveld may therefore be divided into four categories, based on their reaction to grazing.
- Decreaser species are species which predominate in veld which is in good condition and decline in abundance when veld deteriorates in condition through over- or under-utilization. These species tend to die out (a) in veld which is too heavily grazed, (b) where grazing is extremely lenient and fire is excluded, or (c) where grazing is selective.
- Increaser I species are species which will increase in abundance where veld is leniently grazed and fire is excluded. Veld dominated by these species is uncommon in most grazing systems. This category of species may be divided into Increaser Ia: species which increase in relative abundance in veld which is moderately under-utilized and fire is infrequent; and Increaser Ib: species which increase in abundance where defoliation by grazing in minimal, or absent, and fire is excluded from the system.
- Increaser II species are not abundant in veld which is in good condition. These species replace Decreaser species where veld is overgrazed. This category may be divided into Increaser IIa: species which increase in relative abundance with moderate overutilization and indicate the initial stages of over-grazing; Increaser IIb: species which increase in relative abundance in veld which is heavily over-grazed (this subdivision includes a number of robust pioneer species); and Increaser IIc: these are pioneer and invader species which increase in relative abundance with severe over-grazing and usually when some degree of soil loss has occurred.
- Increaser III species are rare in veld which is in good condition but increase in abundance in veld which is selectively over-grazed. Here, selective grazing implies that the palatable species are grazed to the extent that they lose vigour such that the avoided, unpalatable Increaser III species gain a competitive advantage and increase in abundance.
In condition scoring a sample of veld, the relative proportion of Decreaser, Increaser I, Increaser II and Increaser III species is established, and this provides the following information.
- If Increaser II species dominate uniformly, the veld has been overgrazed.
- If Increaser I species dominate uniformly, the veld has been undergrazed or burnt too infrequently.
- If Increaser III species are abundant, grazing management has been such as to promote selective grazing.
- If the veld is a patchwork of Increaser I and Increaser II species, it suggests either past area-selective grazing, or a period of very lenient grazing following a period of very heavy grazing, or vice versa.
- The uniform dominance of Decreaser species suggests that appropriate management systems and stocking rates have been used.
- The above information can then be used to plan ahead. For example:
- where veld is dominated by Increaser II species, fire should be reduced and longer and more frequent rests should be given to encourage Decreaser species;
- where veld is dominated by Increaser I species, fire should initially be used more frequently to encourage the Decreaser species, and grazing pressure should be increased;
- where species selection is evident through the abundance of Increaser III species, management needs to be designed to reverse this trend; in most situations this would require the application of a controlled selective grazing programme to increase the competitive ability of the Decreaser species (refer to Production Guideline 9.2 in this series);
- where the veld is a patchwork of Increaser I and II species, fire may need to be introduced more frequently and management needs to aim at reducing patch selection using appropriate grazing systems; and
- where veld is dominated by Decreaser species, the grazing systems needs to aim at achieving maximum vigour and forage production in order to achieve maximum benefit from the potentially productive sward.
Also, where the forage value of the different species categories is known, a knowledge of their different proportions in the veld will provide an indication of the stocking rates which should be applied to achieve maximum animal production.
Veld condition therefore serves as a barometer on which decisions on veld management and stocking rate are based. Any measurement must, however, be set against a standard. In veld condition assessment, this standard is represented by samples of veld in each ecological zone which are judged to be in optimum condition from the points of view of both productivity and stability. Such sites are termed benchmarks, and all other assessments which are made of veld are then judged against such benchmarks. In essence, then, the benchmark is considered to have a condition score of 100%. The score for all other sites may then be presented as a percentage of this, depending on how much it diverges from the benchmark. By implication, all sites within an ecological zone are capable of achieving the status of the benchmark, provided appropriate management is applied.