FEATURE
along a 50 m transect into the thicket
and 50 m into the transformed area.
The thicket patches were well utilized
and were more open than we expected
when viewing from the road. The
transformed patches were very open
and have been so for about forty years.
These areas have been exposed to
herbivory by Elephant (Loxodonta africana),
Kudu (Tragelaphus strepsiceros),
African Buffalo (Syncerus caffer) and
Red Hartebeest (Alcelaphus buselaphus
caama). Warthogs (Phacochoerus
africanus) are also common utilizers of
the transformed areas.
Results from soil samples
% Soil moisture
35
30
25
20
15
10
5
Thicket transformed
boundary
Our results were surprising, with the
highest soil moisture at the 40 m mark
from the thicket-transformed boundary,
in the transformed area.
This is probably due to a rainfall event
shortly before sampling. Work by Cowling
and Mills (2011) show that rainfall interception
by thicket canopy is some of
the highest in the literature, and where
rainfall events are small (<5 mm) there
is very little water reaching the soil.
The soil moisture response in this area
would explain the preference of the
animals for these transformed patches
as the higher soil moisture will produce
more green leaf as long as it lasts.
As expected, the soil in the transformed
area was more compacted than in the
thicket area, making it more difficult for
seeds to establish and for rainwater to
infiltrate (Sigwela et al. 2009).
Nitrogen in the soil was higher in the
thicket area, which is likely to be associated
with higher levels of protein in
the associated vegetation, or indicative
of the de-coupling of the nutrient cycle
in the transformed habitat leading to
steady-state of leakage.
0
Figure 4: Percentage of soil moisture in the transformed and thicket areas.
Penetromer Kg/m 2
4
3,5
3
2,5
2
1,5
1
0,5
0
Transformed 40m Transformed 20m Thicket 20m Thicket 40m
Vegetation type
Transformed 40m Transformed 20m Thicket 20m Thicket 40m
Vegetation type
Figure 5: Soil compaction measured with a penetrometer in kg/m 2 Red line indicates
the thicket-transformed boundary.
Thicket transformed boundary
There were also large differences in
the vegetation between the two areas.
The thicket areas had 17 woody species
with 462 individuals. The most common
woody species in these utilized thicket
areas were Azima tetracantha (Beesting
bush) with 73 individuals and Euclea
undulata (Common Guarri) with 61
individuals. Euclea is fairly unpalatable
(Haschick & Kerley 1997) and their unpalatability
may explain why they seem
to dominate the well-utilized xeric thickets.
Of the more palatable and typical
thicket species, there were only 19 individuals
of Portulacaria afra (Spekboom)
in the 1 500 m 2 surveyed in the thicket
and 47 individuals of Schotia affra (karroo
boerbean).
In the transformed area only nine woody
species were found with 104 individuals.
These were mainly Gymnosporia
(spikethorn) species which amounted
to a total 85 of the woody individuals
found in the 1 500 m 2 of the transformed
area.
The woody plants in the transformed
area seemed to be well utilized as the
average height of the vegetation in the
transformed area was only 10 cm compared
to the average height of 93 cm
in the utilized thicket. Individual woody
plants also covered a smaller area in the
transformed area with an average of
24 cm compared to 95 cm in the intact
thicket. During the survey in May there
were no grasses recorded, with the forb
layer dominated by a succulent vygie;
Drosanthemum.
What do these results contribute to
understanding the value of thicket
patches?
Patches in the thicket are often cleared
to provide forage to herbivores. These
transformed areas are frequently dominated
by grasses and provide highquality
forage with lots of valuable
young green leaf to domestic and wild
animals during the growth season. The
thicket, even when well utilized, covers
more nutrient-rich, less compacted soils
Grassroots Vol 20 No 3 September 2020
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