Olifants West Vegetation Survey 2011-2013

Transfrontier Africa

Patrick O’Connor; Research Technician: OWNR

1.1 Objectives

The objective of the survey was to establish the grazing capacity of the Olifants West region, Balule Nature Reserve.  The information gathered is critical for management of the reserve, as trends in vegetation quality and, consequently, the impact on animals, can be monitored to determine what adaptive measures need to be taken. However, the Olifants West region is an open system, where animals can move freely during difficult times. This means that management can overlook measures, such as culling or translocation of animals.

To accomplish this, transects were set up in the following regions: Rome 9 drainage line (S 24.17619, E 030.95689), Cambridge 6 (Billys Lodge) (S 24.12364, E 030.53.740), Cambridge 6 drainage (S 24.12.349, E030.53.564), Impalabos East (S 24 13.799, E030 56.933), Rome 9/ Olifants road junction (S 24 12.697, E030 58.173) and Rome 4/5 cutline respectively. These locations were chosen to represent the different vegetation structures, however, the overall vegetation cover, is predominantly a uniform mixed bush veld. Therefore, the grass and tree species recorded in each transect are similar, yet the frequency of each species differs.

2.1 Methodology

Within each region chosen, a random starting point was found by throwing an abiotic piece of material i.e. stone, over ones shoulder and where it landed was marked as the starting point. This was done to ensure that the transect was as unbiased as possible. The transectwas measured using a 100m tape measure, and a ‘line intercept’ or ‘drop point’ method was adopted to gather data on the vegetation within each transect. The species that occurred at each meter along the tape was recorded. The species name, whether that species is a tree, shrub, grass, herb, forb or sedge was documented. Next, the height class was measured, ranging from under 1m to above 4.5m, while the basal and canopy cover were also recorded (Table 1).

The data recorded will illustrate how dense the grass, tree/shrub, herb/forb and sedge cover is, along with the quality and quantity of vegetation for that particular region. Using this information, the grazing quality and frequency of all of Olifants West can be calculated.

Table 1. An example of the data sheet used in each transect. 

2.2 Statistical Methodology

After data capture, all recorded grass species were identified to grazing value, in terms of Decreaser, Increaser 1 and 2 (Van Wyk & Van Oudshoorn, 1999). Once established, the grazing value of the region can be calculated using the Dankwerts model (Equation 1).

Equation 1

The frequency of each species is worked out, thereby giving an indication as to how often that species occurs. This is calculated by dividing the number of each species, by the number of meters in the transect and then multiplying by 100 over 1, to give the answer as a percentage. The frequency is then used to calculate the Veld Condition Score (VCS).

The X2  value is substituted with the average rainfall of Olifants West, while the X1 value in the Dankwerts model is substituted with the VCS value. It is calculated by organizing each grass species into its associated class: Decreaser, Increaser 1, Increaser 2. Depending on the class of grass, the frequency is multiplied by a predetermined number (Equation 1 – 6).

Decreaser -      (Abundance/Frequency) x 10 = Total Value       Equation 2

Increaser 1 -     (Abundance/Frequency) x 7 = Total Value        Equation 3

Increaser 2a -  (Abundance/Frequency) x 5 = Total Value         Equation 4

Increaser 2b -  (Abundance/Frequency) x 4 = Total Value         Equation 5

Increaser 2c -   (Abundance/Frequency) x 1 = Total Value        Equation 6

The Total of all the above are then added together and the overall toatal is established. The overall total can then be applied to calculate the VCS (Equation 7).

                VCS = (Overall Total/ Constant (1000)) x (100/1)          Equation 7

3.1 Results & Discussion

The veldt condition score for 2013 was calculated to be 68.15. Figure 1 shows that this value is greater than those of the previous four years. When used in conjunction with the Danklwerts Model, it was shown that the reserve can support 0.25 animal units per hectare (AU/Ha), which has increased from last years value of 0.22 AU/Ha. As calculated using the Dankwerts model and with the knowledge that OWNR consists of 8800 Ha, the reserve can support approximately 2200.00 animal units.

Remember that this is based on an agricultural model and it is essential that the functioning of the ecosystem must be considered. A farmer might see the reserve as under-stocked, but an ecologist will remind the farmer that the health of the ecosystem relies on:

1.      Standing grass or above-ground biomass (for fire, soil erosion, water retention, competition with shrubs and undesirable invaders)

2.      Resilience against drought – maybe we get poor rain next year?

3.      This model is run and results show the best case scenario for the summer. Winter is a different story!

 

Figure 1. Veldt condition score per year

As illustrated by Table 2, OWNR is currently supporting 291.81 AU, according to the listed species. This value is lower than the previous 2011 recorded value of 553.86, and could explain the increase in decreaser grass species (Figure 3). With a lower overall animal unit per species as compared to 2011, the decreaser species are under less pressure from grazers and may explain this overall increase.

Table2. Game counts for 2012 and the corresponding total AU per species.

 

2012 Census

Animals per AU

Total AU per Species

Impala

978

6.03

162.19

Wildebeest

8

1.99

4.02

Zebra

57

1.51

37.75

Waterbuck

68

1.8

37.78

Warthog

44

4.71

9.34

Buffalo

13

0.9

14.44

Duiker

3

0.2

15.00

White Rhino

4

0.36

11.11

Steenbok

3

17.37

0.17

Total

 

 

291.81

 

Figure 2. Proportion of grazers and mixed feeders that comprise our primary consumers.

 

 

Figure 3. Grazing value of Increaser 2 and Decreaser grass species per year.

 

 

Figure 4 illustrates the frequency of decreaser or favourable grass species per region per year. Overall there is an increase in BillysPlain, Impalobos and Metsi drainage, when compared to previous years. 

 

 

Figure 4. Frequency of decreaser grass species per region per year

Things are looking up for our primary production in OWNR. We can attribute this to the two consecutive years of good rains.