FEATURE
Bush encroachment in North
West province. Is it a threat?
Happy Msiza and Khuliso Ravhuhali
Current Address: Department of Animal Science, Pasture & Rangeland Science Component, Faculty of
Natural and Agricultural Sciences, North-West University
E-mail Address: [email protected]
L
ivestock production in the arid and
semi-arid rangelands of the North
West province faces challenges of in-
adequate forage supply due to the pre-
vailing rainfall unreliability. This limits the
productivity of livestock and the supply of
low quality and quantity of feeds during
the dry seasons. The rapid encroachment
and invasion of plant species in arid areas
have been widely reported as a common
form of rangeland deterioration.
croachment has dominated large areas of
the whole municipality. This makes live-
stock production no longer a profitable
agricultural activity.
As a result, it has the potential to compro-
mise rural livelihoods, as many depend
on this natural resource base. Animals
in these areas thus have to survive solely
on rangeland vegetation (or herbaceous
species) which is of low nutritive value
such as Aristida spp. and semi palatable
Eragrostis spp. throughout the dry sea-
son. Additionally, this lessens the sustain-
ability of animal production, and increas-
es the risk of food and feed scarcity.
Most Farmers across the Ratlou munici-
pality are battling with land degradation,
that is thought to be commonly charac-
terised by the invasion of Vachellia, and
Senegalia together with Dichrostahys
cinerea woody species (Figure 1 and 3),
which greatly suppresses the produc-
tion of herbaceous species as a result of
increased bush cover especially in the
Ratlou Municipality under Ngaka Modiri
Molema district. The extent of bush en-
Usefulness of the encroaching species
Through our observations in communal
areas within the municipality: (Makgobi-
stadt (25°46’41” S; 25°04’46” E, Lupor-
ung (25°47’34” S; 24°59’18” E), Makgori
(25°50’20” S; 24°49’06” E, and Logagane
(25°49’48” S; 24°53’20” E) villages, (Figure
2) Senegalia mellifera, Vachellia erioloba
and Dichrostachys cinerea woody species
were the most dominant in those areas.
We noticed that most of the woody spe-
cies available in the study areas were pre-
ferred by livestock especially goats and
cattle and their potential as the forage
provider for various livestock species in
communal areas have also been recog-
nized world-wide (Aganga et al., 2000;
Mlambo et al., 2015; Revermann et al.,
2018). From our wet chemistry proximate
analysis, these browse species (S. mellif-
era, V. erioloba and D. cinerea) have high-
er concentrations of crude protein (CP)
(above 10% DM) (Table 1). Failure to con-
trol this encroachment through disrupt-
ing the invasive woody plant community
structure can lead to alteration of the en-
vironment, which many grazing livestock
depend on.
Table 1. Average nutritional composition (g/kg DM, unless otherwise stated) values of three browse species found in the se-
lected communal areas under Ratlou Municipality
Tree species DM (g/kg) OM CP NDF ADF ADL
V. erioloba 929.5 868.1 124.3 501.3 359 210.6
S. mellifera 913.3 825.4 150,2 452.6 253.7 109.1
D. cinerea 915.8 856.8 143.0 461.8 311.4 185.5
DM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADL: acid detergent lignin and
ADF: acid detergent fibre. (Source: Ravhuhali 2018)
Soil as a factor
In addition to climatic conditions (rain-
fall of 350-400 mm and the temperatures
ranging from 2-39 °C (SAWS, 2019)),
which are harsh in these areas, soil fertility
is also known to contribute to the loss of
grass species. Given the relative geology
and prevailing semi-arid climatic condi-
tions, the soils, which are sandy loam or
continental red-brown shifting sand, tend
to be relatively shallow, leached, and are
highly weatherable. The soils in these
areas are hence prone to being infer-
tile (Frey, 2010). According to Ravhuhali
(2018), the topsoil in these villages have
lower concentrations of soil nutrients (Ta-
ble 2). This is assumed to have led to the
higher distribution of tree species density
as observed in those communal areas.
Depletion of soil nutrients can accelerate
land degradation by gradually reducing
the grass vegetation layer in many semi-
arid areas (Mainuri & Owino, 2014; Ai et
al., 2018). This provides an environment
where competition for resources is lim-
ited and hence facilitates the increased
germination of woody species seedlings
that access topsoil nutrients.
Table 2. Summary of nutrients concentration (mg/kg unless otherwise stated) of soil found in the selected communal areas
under Ratlou Municipality.
pH N (%) C (%) P K Ca Mg Na Fe Cu Zn Mn
5.02 0.011 0.27 2.5 65.3 1034.3 72.2 5.2 3.89 0.23 0.30 30.41
N: nitrogen; C: carbon; P: Phosphorus; K: potassium; Ca: calcium; Mg: magnesium; Na: sodium; Fe: iron; Cu: copper;
Zn: zinc; Mn: manganese (Ravhuhali 2018)
09
Grassroots
Vol 19
No 4
November 2019