The effects of sheep grazing on the recovery of succulent Karoo vegetation.
Loading...
Date
1995
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Vegetation monitoring, recording the recovery or change in plant cover over time, for
several Karoo shrubs was undertaken to evaluate the Savory Grazing System on a farm in
the Succulent Karoo. This evaluation was quantified by establishing if the proposed 120-
day rest period between grazing events was sufficiently long enough for complete recovery
of the vegetation. Complete recovery was described as sufficient regrowth after a grazing
event so that continual cover loss would not result over time. Optimum resting periods
would ensure that cover loss, due to grazing, could be recovered so that plant size and
reproductive potential was not detrimentally affected.
The ellipse intercept method was used to sample piospheres (or zones of attenuating
animal impact) around water points in two vegetation types. From these results, 320 line
transects for vegetation monitoring were located between 140 and 180m from the water
points. One and a half year old piospheres of one farm were compared to seventeen year
old piospheres on another farm with similar vegetation composition. The piospheres on
the younger farm were expanding at an approximate linear rate of 80m per year, however,
this rate slows considerably, as was found on the farm with older piospheres. Stability or
equilibrium appears to be reached at approximately 320m from the water point in the older
system.
The line transects were used to record the change in cover of palatable and
unpalatable Karoo shrubs on a monthly basis over an 18 month period. In all instances
it was concluded that the proposed 120-day rest period was not sufficiently long enough
for complete recovery of the vegetation. The highly palatable species, especially
Osteospermum sinuatum and Tetragonia spp., were the most heavily utilized and
detrimentally affected. Larger individuals of the palatable shrubs O. sinuatum and
Tetragonia spp. were more severely grazed than smaller individuals as a result of smaller
individuals utilising spiny nurse plants under which to establish. If the present rest period
is continued the result could be overgrazing and local extinction of these important fodder
species.
The responses of two highly palatable species, O. sinuatum and Tetragonia spp.,
were monitored closely in relation to rainfall and grazing events. Grazed and ungrazed
(protected) individuals were monitored over one year to substantiate the results obtained from the line transects. The rest period was again found to be too short for full recovery
and was also found to be reducing the reproductive output of O. sinuatum and Tetragonia
spp..
The recruitment of O. sinuatum and Tetragonia spp. was also measured by
comparing seedling establishment in grazed, ungrazed (vegetation protected from sheep
grazing) and cleared vegetation. In an attempt to rehabilitate these rangelands, Pteronia
pallens, a dominant unpalatable shrub, was cleared and the resultant seedling recruitment
of O. sinuatum and Tetragonia spp. monitored and compared to grazed and ungrazed
vegetation. Juvenile recruitment of these species was found to be significantly lower in
the grazed than in the ungrazed vegetation. Recruitment of Tetragonia spp. was found to
be significantly higher in the cleared strip compared to the grazed and ungrazed vegetation.
The results obtained in this study suggest that the present grazing regime is having
a detrimental effect on the vegetation and that revised management procedures are needed
to ensure the conservation of these rangelands. The rest periods between grazing events
need to be lengthened as well as a reduction in stock numbers. Certain camps need to be
skipped on a seasonal basis during the flowering season in order to increase the
reproductive output of highly palatable species.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.
Keywords
Range management--Karoo., Grazing--South Africa--Management., Karoo vegetation--Management., Theses--Botany.