Patch grazing in the humid grasslands of KwaZulu-Natal.

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.