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agricultural production guidelines  veld in kwazulu-natal

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Veld in KwaZulu-Natal 

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Co-ordinated Extension

KwaZulu-Natal Veld 2.4 1999

K G T Camp
KwaZulu-Natal Department of Agriculture

M B Hardy
Western Cape Department of Agriculture

Classification of Species
Veld Condition Assessment Procedure
The Significance of Veld Condition

 

INTRODUCTION

When planning a veld management system, the condition of the veld occurring in the Veld Type Units (VTU’s) of the farm is essential information. A veld condition score is used to estimate the productivity and grazing capacity of each VTU on the farm and the seasonal duration of the grazing. The veld condition assessment will also indicate whether special management techniques are necessary for the veld concerned.

Several factors play a role in determining veld condition. These include species composition, the vigour of the palatable species, basal cover and soil surface condition.

Only species composition can be objectively determined, and the veld condition assessment procedure is thus based on this factor. The condition of a sample of veld is assessed by comparing its species composition with the species composition of a benchmark site. The benchmark site is based on the species composition of the most productive sample of veld for the Bioresource Group concerned. Veld in the benchmark should be capable of providing the highest possible sustained animal production.

A farmer can determine his own benchmark for his farm or area. Benchmark values have, however, been documented for the most important Bioresource Groups and are in general use. Refer to Production Guidelines 4.2 to 4.10 for veld benchmark values for each of the Bioresource Groups of KwaZulu-Natal. Table 1 provides an example of benchmark values for Bioresource Group 8, the Moist Highland Sourveld.

 

CLASSIFICATION OF SPECIES

Ecological groupings
Most grass species have been classified and grouped according to their response to the intensity and frequency of defoliation (due to grazing and fire).

These groups are discussed below.

• 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 not abundant in veld which is in good condition. These species will replace Decreaser species where veld is too 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 an 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 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 that the avoided unpalatable Increaser III species gain a competitive advantage and increase in abundance.

The ecological grouping of grass species for all the Bioresource Groups of KwaZulu-Natal is given in Appendix Table 1. The ecological groupings are based on research findings as well as experience. Allocation of species within Bioresource Groups may therefore change as more information becomes available.

 

Table 1. Benchmark for Bioresource Group 8 (Moist Highland Sourveld).

Group	Species	Grazing Value	Benchmark
			%	Score
Increaser I	Alloteropsis semialata Eulalia villosa Trachypogon spicatus Tristachya leucothrix Forbs (legumes etc)	3 3 3 9 0	2 1 2 20	6 3 6 180 0
		Total	25
Decreaser	Monocymbium ceresiiforme Diheteropogon amplectens Brachiaria serrata Themeda triandra	6 8 3 10	2 1 1 45	12 8 3 450
		Total	49
Increaser IIa	Eragrostis capensis Heteropogon contortus Harpochloa falx	2 6 3	1 4 3	2 24 9
		Total	8
Increaser IIb	Hyparrhenia hirta Eragrostis curvula Eragrostis plana Eragrostis racemosa Sporobolus africanus	3 5 3 2 3	1 1 1 1 0	3 5 3 2 0
		Total	5
Increaser IIc	Microchloa caffra Paspalum scrobiculatum Forbs Sedges	1 3 0 0	1 0 5 1	1 0 0 0
Increaser III	Diheteropogon filifolius Elionurus muticus	0 0	2 5	0 0
		Total	14
		Grand Total	100	717

Score for the sample site = (site grand total/benchmark grand total) x 100

 

Classification of species according to their grazing value
Within the grass sward, the acceptability of species to the grazing animal varies considerably. Species which are highly palatable and digestible and, in addition, are highly productive, are regarded as species with a high grazing value. At the other extreme, the fibrous, unpalatable species, which may be highly productive but which remain unutilized throughout the year, or species which, while being palatable, produce very little herbage, are regarded as having little or no grazing value.

The grazing value of species is based on an assessment of relative palatability, potential production, digestibility and length of the season during which the herbage is acceptable to the animal. Species with high grazing value will have high production while species with low grazing value may have low or high production potential. In practice, therefore, the grazing value given to a species reflects the potential of that species to produce forage.

Veld in good condition will have a high percentage of high grazing value species which will maximise grass intake by the animal, resulting in a high level of animal production for that area of veld.

The grazing value of grass species is based on a scale of 0 to 10 as follows:

0 - 1 not utilised, fibrous with very low palatability,

2 - 3 unpalatable,

4 - 5 acceptable,

6 - 7 palatable,

8 - 9 highly palatable, and

10 highly palatable and utilised throughout the season.

The grazing value of veld species in different Bioresource Groups is also given in Appendix Table 1.

These values have been assessed subjectively, based on the experience of field workers and must be regarded as a guide. The grazing value of a species can vary according to Bioresource Group and to changes of VTU’s within a Bioresource Group. For example, Heteropogon contortus, in the moist Highland Sourveld (Bioresource Group 8), tends to have a high grazing value on doleritic soils whilst it is less palatable on poorly drained soils. Tristachya leucothrix can vary widely in grazing value in the Dry Tall Grassveld (Bioresource Group 13), due to a wide variation in the degree of hairiness the plants. A species such as Urochloa mosambicensis (which grows in Bioresource Groups 21, 22 and 23), while highly palatable, cannot be regarded as a reliable source of feed because it tends to whither away during hot, dry periods. Its grazing value is, as a result, intermediate.

The classification of Key Species
Key Species are defined as those species which have been found to respond most sensitively to defoliation by grazing (and fire). As the frequency and intensity of grazing changes their abundance in the veld changes more rapidly and dramatically than other species. A knowledge of how these Key Species vary in their abundance over time is therefore very useful for monitoring changes which may be occurring to species composition and, therefore, veld condition in a particular VTU. The Key Species are given weightings from 0 to 10. A weighting of 10 implies that the species is a Decreaser (see definition given above) while a low weighting (e.g. 2) implies that the species is an Increaser IIc or Invader species. Note that weightings provided for these Key Species are based on an ecological understanding of how these particular grass species respond to grazing. While the weightings of a species may be similar to its grazing value rating, the Key Species classification is used to monitor veld condition in an ecological sense rather than in terms of grazing value. Lists of the Key Species that have been identified for particular Bioresource Groups, and their weightings are given in Table 2.

 

Table 2. Key species and their weightings for two combinations of Bioresource Groups.

Key species	Bioresource Groups
	8&9	13, 14 & 16
Themeda triandra Tristachya leucothrix Heteropogon contortus Hyparrhenia hirta Eragrostis curvula Eragrostis plana Eragrostis chloromelas Sporobolus africanus Paspalum scrobiculatum Cynodon dactylon	9 10 6 3 4 3 - 2 1 -	9 10 6 2 - 4 3 - - 1

 

VELD CONDITION ASSESSMENT PROCEDURE

Assessing the condition of the grass layer
It is stressed here that, while the results of numerous research projects and vegetation surveys, as well as the knowledge of experienced field workers and farmers, have been used to develop the veld condition assessment technique presented here, the technique has not been thoroughly tested. However, this is the most practical technique presently available and, when applied together with observations on animal and veld production on a particular farm, the technique will prove an invaluable management tool to the farmer.

The veld condition survey must be carried out within the VTU’s which were identified during the farm planning stage. Should the camp to be assessed have more than one VTU, the largest or key VTU, should be assessed. Alternatively, all VTU’s in the camp could be assessed.

A transect should be sited across the VTU and permanently marked for future re-assessments. This transect should be at least 200 m long. To record the species composition, a spiked wheel with a marked spike is pushed along the transect, between the two transect markers. The plant nearest to the point where the marked spike strikes the ground, or the nearest living plant, is identified and recorded.

Another simple but accurate method is to use a sharpened spike approximately 1.2 m in length, instead of a wheel. The recorder walks along the transect and at every step thrusts the spike randomly into the ground ahead of him. The plant nearest to the spike point is identified and recorded.

Two hundred spike-point observations should be made per VTU. The vigour of each of the important indicator species should also be noted.

Two different objectives can be met by analysing the species composition recorded in the survey viz. current veld condition, and veld condition trend.

• Current veld condition is based on the complete species count and is used to measure the current grazing value of the veld, the current grazing capacity and to suggest management requirements. The method presented here is an adaptation of the Ecological Index and Weighted Palatability methods which are presented in more detail in Production Guideline 6.2 of this series.

• Veld condition trend is used to measure changes in veld condition which might have arisen as a result of veld management practices over a period of time. In this case only the grasses identified as Key Species for that Bioresource Group are used.

For both objectives high total scores relative to the total score for the benchmark indicate veld in good productive condition while low scores indicate veld in poor condition.

 

Table 3. Example of a veld condition assessment.

Bioresource Group 13 Dry Tall Grassveld                Farm:                                                 Owner: Date:                                                                                  Transect No:                                     Recorder:
Group	Species (& Vigour %)*	Grazing Value	Transect		Benchmark
			%	Score	%	Score
Increaser I	Cymbopogon excavatus Digitaria tricholaenoides Setaria nigrirostris Trachypogon spicatus Tristachya leucothrix (30)	1 6 5 3 9	1 1   1 3	1 6   3 27	0 0 0 0 11	0 0 0 0 99
		Total	6		11
Decreaser	Brachiaria serrata Cymbopogon plurinodis Digitaria eriantha Diheteropogon amplectens Themeda triandra (20)	3 0 7 7 10	2       8	6       80	1 0 0 0 67	3 0 0 0 670
		Total	10		68
Increaser IIa	Eragrostis capensis Heteropogon contortus (50)	2 6	9	54	2 2	4 12
		Total	19		4
Increaser IIb	Bothriochloa insculpta Digitaria monodactyla Eragrostis capensis Eragrostis chloromelas Eragoristis curvula Eragrostis plana Eragrostis racemosa Eragrostis superba Hyparrhenia hirta (50) Setaria flabellata Sporobolus africanus Sporobolus pyramidalis	3 1 2 2 4 2 2 4 7 2 3 2	6 1 2 6 10     5	24 2 4 24 70     10	1 1 2 2 0 0 2 1 2 0 0 0	3 1 4 4 0 0 4 4 14 0 0 0
		Total	20		9
Increaser IIc	Aristida congesta Brachiaria eruciformis Chloris virgata Cynodon dactylon Digitaria ternata Microchloa caffra (80) Melinis repens Sporobolus centrifugus Sedge Forbs, weeds	0 1 1 3 2 1 1 3 0 0	7     1   20     1 4	0     3   20     0 0	0 0 0 0 0 2 0 0 1 4	0 0 0 0 0 2 0 0 0 0
		Total	33		7
Increaser III	Elionurus muticus (90)	0	12	0	1	0
			100	334	100	820

Score for site = 334/820 x 100 = 40.7%
* Percentage vigour of some key species are given in parentheses

 

Analysis of the species composition

a) Assessing the current condition of a VTU in terms of grazing value and ecological status
The relative abundance (%) values of all species which occur in the benchmark site and which are recorded in the VTU being assessed, together with their grazing values, are entered into the "current grazing value" work sheet (see example in Table 3).

The % (relative abundance) of a species is calculated by dividing the number of observations recorded for that species by the total number of observations for the transect and then multiplying by 100.

The % of each species is then multiplied by the grazing value for the particular species and the answer is entered into the "score" column (Table 3). This is done for both the transect and the benchmark site. The values in the "score" column are then added and the grazing value for the transect (VTU) is calculated as a percentage of the total grazing value of the benchmark (see calculation at the bottom of Table 3).

If the grazing value for a particular species is not listed then the farmer should contact an experienced field worker (or use his own experience) to provide an estimate of what the grazing value of the species should be.

The veld condition assessment data (Table 3) are also used to assess the impact of past management of the veld concerned and used as a guide to determine management necessary for the VTU which was sampled. Referring to Table 3 it is apparent that this sample of veld has been poorly managed in the past because only 10% of the species composition consisted of Decreaser species compared with the optimum of 68% of the benchmark site. The Increaser I species have a total of 6% against the figure of 11% of the benchmark indicating that underutilization is not a problem. The Increaser IIa species show an increase compared to the benchmark, as do the Increaser IIb species. The Increaser IIc species however, show a large increase from the norm of 7% (in the benchmark) to 33% and this indicates that over-utilization has been a problem.

The recorder’s estimate of the percentage vigour of key species is the bracketed figure following the grass name. It can be seen that the vigour of the more desirable species is low.

From this evidence, it is apparent that a vigour rest of a full growing season is required. It would then be necessary to burn the veld before the start of the next grazing season and then to graze the sward in such a way so as to give the palatable species a chance to maintain their vigour and increase in abundance (see grazing management systems in Production Guidelines 3.3 to 3.6 and 9.8 of this series).

b) Assessing trend in veld condition
The same procedure used for calculating current veld condition is applied excepting that the % values of only the Key Species found during the survey are used. It is important that the same VTU as surveyed every 3 to 6 years and that records are kept of the grazing management system (e.g. number of AU grazing days per year) and of how often and when the VTU was burnt between surveys. This information will assist in understanding any changes in veld condition which may be monitored over time. Example calculations are given in Table 4.

It is not essential to score the veld condition trend against a benchmark value. By measuring results against the initial score, it is possible to ascertain whether the veld is improving or retrogressing. The example (Table 4) illustrates a situation where veld was initially deteriorating, under the management system being applied. Since 1981, however, a change in management appears to have stabilised the situation and veld condition may start to improve.

Assessing the browse potential of the bush component
In the thorn/grass communities, different methods are used to assess the woody and the grass components, respectively. Methods for assessing the grass component are outlined earlier in this document. Regarding the wood component, the assessment aims at measuring the number of plants by species, plant size and vertical distribution of live canopy. These parameters are used to determine the potential productivity of available, browseable material and the competitive influence of the woody plants on grass productivity.

The information collected in the survey is converted to tree equivalents (TE) and browse units (BU), to give a measure of total canopy volume and total browseable volume, respectively. For agricultural purposes, these units are used to predict the productivity of useful available forage. In strict, scientific terms, a tree equivalent (TE) is defined as an Acacia karroo tree of 1.5m in height. For practical purposes, however, any tree 1.5m in height is equated to a TE. Thus, a tree 4.5m tall approximates 3 TE and three trees, each 1.5m tall, also equal 3 TE.

Methods
Sampling of the woody component is carried out as follows: A chain, 100 m long, is laid out straight in the areas of the VTU representative of the whole VTU. The centre of a 2-m-long rod is then moved up to the chain, at 90E. Each woody plant falling within this 2m width along the length of the chain has the following recorded:

• plant species,

• plant height,

• height of canopy bottom from ground level,

• horizontal canopy radius, and

• whether the tree is palatable or not.

Note that the size of this sample plot is 2 m x 100 m = 200m² and the number of woody plants in the plot is recorded by species. Therefore, if one wants to calculate, for example, the number of woody plants per hectare, then the number of woody plants recorded in the 200m² plot is multiplied by 50. This would be for one sample site. Four to six such sites must be sampled in each camp, and, in some cases more sites, depending on camp size and the number of VTU’s in the camp.

The data collected during the survey must then be converted to tree equivalents (TE) and browse units (BU) in order to make a current assessment or comparison with previous measurements.

Tree equivalents
These are calculated from the estimates of the number of trees per hectare plus their average height. So, if the sampling procedure outlined above gives a value of 2000 trees per hectare which have an average height of 1.9m, then the number of tree equivalents per hectare is 1.9m divided by 1.5m multiplied by 2000 (i.e. 1.27 X 2000 = 2540 TE/ha).

While the calculation to determine the number of tree equivalents is relatively simple, the calculation for determining browse units (BU) is more complicated as only that portion of palatable browse that is accessible to the animal may be considered. The procedure for this is outlined below.

Browse units

• Mean canopy radius of each tree is calculated as (Figure 1):
  RAD=[{(Ht - H1)/2}+R]/2 (1)
  Where;
  RAD = average radius of canopy (m),
  Ht = plant height (m),
  H1 = height of canopy bottom from ground level (m), and
  R = average horizontal radius of canopy.

 

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