agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 9.9 1999
PASTORAL PRODUCTION SYSTEMS - AN OVERVIEW
M B Hardy
Western Cape Department of Agriculture
N M Tainton
Professor Emeritus, University of Natal
Sustainable
Livestock Production Systems
Management
of Livestock Production Systems in Stable (Humid) Environments
Managment
of Livestock Production Systems in Arid and Semi-Arid Environments
Two main categories of livestock owner can be identified in the pastoral production systems of KwaZulu-Natal - those whose main objective is purely commercial and who place great emphasis on the level of production achieved by the livestock, and those whose main objectives may be the provision of a variety of services (such as draught power, manure for fuel and milk for home consumption) to the owners and where the productive level achieved by the animals is of less immediate concern than in the commercial sector. Commercial producers typically operate on land held under individual land ownership, whereas the latter group operate mainly on communally owned veld. Among the former group also, both planted pastures and crop residues may often be used to support the veld in providing forage for livestock, while in the latter group pastures seldom if ever contribute forage to the feeding programme. Management objectives and management constraints will therefore differ greatly between the two groups and allowance needs to be made for this in the planning and execution of livestock and veld management programmes. Whereas both categories of owner strive to achieve their objectives they must operate within the constraints of a variable forage production environment to maintain the stability of the production system.
SUSTAINABLE LIVESTOCK PRODUCTION SYSTEMS
Humid grasslands
That livestock production systems have the potential to be sustainable is implicit in the concept of carrying capacity. Setting the carrying capacity of a system suggests that equilibria between herbage production and animal numbers may be identified for any vegetation type within which a defined level of sustained livestock production may be expected. What are these equilibria and how do they operate? To illustrate the interaction between vegetation and animals in grazing systems the following model was developed for a humid grassland (after Hardy and Mentis, 1986). The model was built on our understanding of how the vegetation responds to grazing management (in terms of veld condition) and how animal performance (in this case, cattle) is affected by veld condition. There are four main factors.Firstly, grazing intensity affects the floristic composition of the veld because of variable tolerance of plant species to grazing. Secondly, animal performance depends, at least to an extent, on the floristic composition of the veld because plant species vary in their productivity, palatability and nutritive value. Thirdly, heavy grazing will result in the dominance of grazing-tolerant, usually unpalatable plants (the Increaser II species). Light or no grazing will result in the dominance of grazing-intolerant plants (the Increaser I species). Fourthly, a single, bi-directional, pathway of change in proportional species composition (veld condition) develops in response to the intensity of grazing.
Vegetation response
If we depict the response of the vegetation to grazing intensity in graphical terms, veld condition score (S) could be shown on the y axis and grazing intensity (expressed as Animal Units per hectare - AU/ha) on the x axis (Figure 1). In Figure 1 veld composition score (S) is shown on a typical bi-directional successional pathway from low (very poor condition due to over grazing and dominated by pioneer species); to high (excellent condition, fire/grazing "climax" grassland); to scrub forest (which would develop in these humid environments if the vegetation was used at low grazing pressures and defoliation frequencies). Similarly, grazing intensity (AU/ha - an expression of the stocking rate being applied to the veld) is given from low (0 AU/ha) to very high (>2 AU/ha). The line shown as )S represents all points at which species composition (veld condition) will not change for a particular number of AU/ha (or stocking rate).For any veld condition score on the y axis, when animals are stocked to the left of )S (at a relatively low stocking rate) one would expect veld condition to improve (see the direction of arrow (a)). If, however, animals were stocked to the right of the )S line for a particular veld condition score, then one would expect veld condition to decline (see direction of arrow (b)).
Figure 1. The response of vegetation in terms of veld condition score (S) to stocking rate (H).
Figure 2. The stocking rate of cattle (H) that will be at maintenance (no gain or loss of weight) in relation to veld condition score (S).
The same x-y axes are used (Figure 2). In this case the plant species composition (veld condition) influences animals performance. The line shown as )H represents all points at which animal performance will be 0 (animals will not lose or gain mass, or there will be no gain or loss in animal numbers)for the range of veld condition scores given by the y axis. If animals were to be stocked at a point to the left of )H we would expect that the animals would show positive performance i.e. there would be a gain in weight or numbers (see direction of arrow (c)). If the animals were stocked to the right of )H, animals would lose mass or animal numbers would decline (see direction of arrow (d)).Cattle response
To reveal the interaction between veld condition and the grazing animal the two response curves ()S and )H) are superimposed (Figure 3). It should be remembered that the interactions shown here (Figure 3) are those expected for cattle production in humid, sour grasslands. Since )H is to the right of )S the implication is that veld in any condition could produce sufficient forage to maintain the stocking rates (with the animals at maintenance - no mass gain or loss) indicated by )H. If this situation is promoted then it is inevitable that veld condition will decline since stocking rates (AU/ha) will always tend to increase to a point to the right of )S, if animals are not removed from the system, as they gain in mass or they increase in numbers.
Figure 3. The interaction of vegetation, in terms of veld condition score (S), and stocking rate (H) in Highland Sourveld.
Therefore, if commercial livestock producers were to practice light stocking (low grazing intensity) by removing annual livemass gains, in which case the veld would be stocked to the left of )S in Figure 3, a high veld condition score could be maintained. In subsistence pastoral systems where numbers of livestock rather than individual animal performance is of primary concern, grazing intensity (stocking rate) will invariably be high (to the right of )S). Subsistence grazing systems are therefore likely to be maintained in an overgrazed state with veld condition generally at a low level.
The model shows close agreement with the perception that subsistence grazing systems in humid environments are heavily stocked, and have ‘poor’ animal performance and ‘poor’ veld condition. Indications are that ecological carrying capacity has been achieved in many area in that livestock numbers have been at current levels for decades. The nearly straight and vertical alignment of )H implies that, at these high stocking rates, veld condition is relatively unimportant. Any attempt to reduce stocking rate in the hope of improving veld condition in the long term is likely to meet with grazier's resistance, at least partly because of communal ownership of grazing lands. Of course, without reducing stocking rate the system will remain in the stable overgrazed state and veld condition will not improve. Particularly in the absence of controlling stocking rate, other means of ‘improving’ subsistence systems might be futile or counterproductive. Developing additional water-points, providing supplementary feed, improving the genetic potential of herds and flocks and controlling parasites and disease will probably result in accelerated soil loss and a further decline in veld condition, if that is possible (e.g. to a false karroid vegetation dominated by Felicia filifolia). Intervention in these subsistence systems may aggravate rather than relieve the position.
Arid and semi-arid regions
Large proportions of veld in KwaZulu-Natal are located in arid and semi-arid environments which have highly variable rainfall. In such regions, when compared to the humid grasslands discussed earlier, grazing systems are relatively unstable since environmental variability seldom allows the vegetation and animals to achieve an equilibrium state. Fodder production follows rainfall (distribution and amount) and animal production tracks fodder production patterns.In these arid and semi-arid environments, single- and multi-year periods of drought have major influences on forage availability and therefore, without outside interventions such as the removal of excess animals, on livestock populations. The effects of such external impacts on the dynamics of a vegetation -livestock system are illustrated in Figure 4 (after Ellis and Swift, 1988).
The X axis (H) in Figure 4 relates to the number of herbivores and the Y axis (P) relates to forage production. While Figure 4 has similar axes to those applied in Figure 3, the understanding of plant-herbivore dynamics is based on different assumptions. Firstly, the pastoralist activities in this system revolve about maintaining livestock numbers rather than in marketing livestock i.e. off take is in the form of products such as milk, draught power, dung and for use on ceremonial occasions. Livestock numbers are therefore regulated mainly by fecundity rates and the availability of forage. Secondly, forage production (P) responds sensitively to the variable rainfall, with low forage production in years of poor rainfall and high forage production (a rapid recovery) during years of good rainfall. Thirdly, livestock populations are never high enough during high rainfall seasons to use more than half the available forage. Under these conditions livestock are unlikely to exert a major impact on plants. Fourthly, livestock population size remains constant during short, year-long, periods of drought (individual animals will loose condition) but declines during multi-year (two years or longer) droughts. Fifthly, multi-year droughts are frequent enough and herd recovery is slow enough to prevent livestock numbers from approaching the theoretical ecological carrying capacity. Sixthly, droughts never last long enough to completely eliminate the livestock population. Populations of plants and livestock are unstable over time but are persistent.
Figure 4. The interaction of vegetation, in terms of dry matter production as influenced by rainfall (P), and livestock production (H) in arid and semi-arid environments.
The upper right-hand points in Figure 4 indicate high livestock population and high forage availability. In a single-year drought forage production declines whilst animal numbers will remain relatively constant. Individual animals will loose condition but would survive the relatively short period of low forage availability. Given a relatively high rainfall in the next season the animals will tend to regain lost condition and show a moderate increase in population size. However, should the period of low rainfall persist for a second year (or longer) then livestock numbers will decline.
MANAGEMENT OF LIVESTOCK PRODUCTION SYSTEMS IN STABLE (HUMID) ENVIRONMENTS
Here the aim of management, in many cases, is to reduce the heterogeneity of the system in order to facilitate management. Management actions aimed at dampening fluctuations in the system are effective because the manager has relatively strong control over the dynamics of the system via manipulation of management inputs such as fertiliser levels, stocking rates and burning schedules.
Considerable attention has been paid to grazing systems which either reduce the extent to which animals selectively graze (e.g. non-selective grazing (NSG)) or reduce the impact of selective grazing on the forage resource (e.g. controlled selective grazing (CSG), high performance grazing (HPG), short duration grazing (SDG) and deferred-rotation systems). Such systems usually involve land sub-division in order to reduce the variability of the forage resource available to the animals at any one time. Burning is also employed to remove accumulated low quality residual material and induce a uniformly palatable flush of new growth. Regular burning will also reduce the degree of heterogeneity caused by patch grazing.
In areas where rainfall is relatively high and reliable, multi-species veld is often replaced with mono-specific sown pastures to ensure a steady and reliable forage flow. Variability in the seasonality of available forage from veld can be reduced by planting pasture species with different seasonal growth patterns or by conserving material produced in one season for feeding at some other season, either as foggage (standing hay) or by harvesting it mechanically for longer term storage (as hay or silage).
MANAGEMENT OF LIVESTOCK PRODUCTION SYSTEMS IN ARID AND SEMI-ARID ENVIRONMENTS
Here, diversity and heterogeneity are an integral part of the system and the manager should not attempt to dampen these effects by, for example, importing fodder during times of drought. Such actions simply put greater pressure on the remaining resources which often has negative consequences for the stability and sustainability of the system.
Before major settlements were established in southern Africa, pastoralists recognised the variability of fodder production in arid and semi-arid environments and adapted their grazing strategies accordingly. Nomadic pastoralists employed a strategy involving migration of animals in small groups over large areas to ‘track’ pulses in forage production, manipulating herd structure and herd composition to meet subsistence requirements while minimising risk.
With the advent of commercial pastoral activities one of the main strategies was to use the arid and semi-arid areas only for winter grazing with animals being withdrawn to humid grasslands for the summer - the so-called "trek" farming system. Grazing impact was minimised with winter-only grazing and stocking rates could be set according to the amount of herbage produced during the rainy season. Alternatively, where the livestock production system was based solely on forage produced in these arid and semi-arid regions, the appropriate management strategy is to annually calculate the carrying capacity of the veld basing the calculation on the amount of forage available to the animals at the end of the growing season. Any herbage produced in the following season would be additional to the requirements of the production system.
Another strategy employed by both commercial and communal pastoralists is to include goats in their livestock production systems. In this way the fodder produced in these arid and semi- arid savanna regions is more efficiently used and livestock production is enhanced.
CONCLUSIONS
Extensive veld grazing forms the back-bone of the livestock economy of any region. It is therefore essential to understand what impacts livestock production systems are likely to have on the veld resource if the production systems are to be sustainable.
In humid regions management aimed at controlling fluctuations in fodder production are relatively effective because the manager has strong control over the dynamics of the system via manipulation of management inputs such are stocking rates and burning schedules. In arid and semi-arid regions the manager has little control over fluctuations in the fodder supply. Here the manager must adapt the livestock production system to suit the variability in fodder supply rather than attempt to manipulate the system to suit the graziers requirements
LITERATURE CONSULTED
ELLIS, J. E. and D. M. SWIFT. 1988. Stability of African pastoral systems: alternate paradigms and implications for development. J. Range Manage. 41:450-459.
HARDY, M. B. and M. T. MENTIS. 1986. Grazing dynamics in sour grassveld. S. A. J. Sci. 82:566-572.