Patch grazing in the humid grasslands of KwaZulu-Natal.
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Date
1995
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Abstract
Patch grazing may be an important factor providing the focus from which wide-scale veld
degradation has occurred in the humid grasslands of KwaZulu-Natal. A number of discrete
studies were therefore initiated to examine the patch grazing patterns and selected factors
which may influence patch grazing at two sites in the humid grasslands of KwaZulu-Natal.
The sites were located at Ukulinga Research Farm, situated in the Southern Tall Grassveld,
and Kokstad Research Station in the Highland Sourveld.
An investigation into the frequency and intensity of gazing patches and non-patches at
Ukulinga Research Farm indicated that patch grazing was most evident and most extensive
during summer and autumn. As forage in the patches became limiting during winter animals
were forced to forage in areas not frequently grazed during the season. The patch grazing
pattern was further modified by the time of grazing commencement after a burn in early
spring. Early grazing significantly reduced the extent of patch grazing. With early stocking
animals were forced to graze less selectively while with increased delay in the
commencement of grazing, animals became increasingly patch-selective. Early grazing in
conjunction with an autumn rest and heavy grazing during winter could significantly reduce
patch grazing.
Urine and dung significantly influenced the patch grazing pattern. The sward surrounding
a urine deposit was preferentially grazed by both cattle and sheep for a period of at least six
months after deposition. Cattle rejected the sward surrounding cattle and sheep dung
immediately after deposition and for a period of up to six months. Sheep also rejected cattle
and sheep dung patches immediately after deposition. As dung deposits aged, sheep tended
to increase their grazing around both cattle and sheep dung pats, and after six months dung
did not seem to influence sheep grazing. Urine may be an important factor influencing patch
initiation and consequent patch development.
A study to examine the characteristics of patches and non-patches in the Highland Sourveld
revealed that patches were characterised by lower soil moisture, soil depth and hydraulic
conductivity, but by a higher soil nutrient status. Patches and non-patches could also be distinguished in terms of species composition and basal cover. Patches were characterised
by Increaser II species, especially Microchloa caffra and, non-patches by Increaser I species
such as Trachypogon spicatus, Alioteropsis semialata and Eulalia villosa.
Three seasons of patch grazing at Kokstad Research Station negatively influenced the vigour
of Themeda triandra in patches relative to the non-patches. The vigour of T. triandra in
patches was consistently low throughout a full season's rest. The vigour of T. triandra in
non-patches was initially significantly higher than the vigour in the patches and remained so
for c. 24 weeks. Vigour measurements at the start of the following season showed that
photosynthate accumulation had taken place and a full seasons rest proved to be sufficient in
restoring the vigour of T. triandra in patches to the same level as that in non-patches. A full
seasons rest did, however, not prevent animals from regrazing the same previously grazed
patches the following season. Growth in patches also started c. six weeks later than in nonpatches
and above-ground herbage production in patches was significantly lower than nonpatches
for at least 20 weeks after a bum. At the end of a full season's rest above-ground
herbage production in patches was still slightly lower than that in non-patches possibly due
to a difference in species composition between patches and non-patches.
Some implications of patch grazing are discussed together with an evaluation of some
management recommendations for the humid grasslands with the aim of reducing the
potential for patch degradation.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Grazing--KwaZulu-Natal., Range management--KwaZulu-Natal., Grasslands--KwaZulu-Natal., Theses--Grassland science.