The influence of environment and livestock grazing on the mountain vegetation of Lesotho.
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Date
2011
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Abstract
The mountains of Lesotho form the catchments for the Lesotho Highlands Water
Project (LHWP), which is presently under construction, and their condition will
determine the longevity of the LHWP. The mountain rangelands also support an
extensive livestock system. However, there is concern that grazing is negatively
affecting the mountain vegetation to the detriment of both livestock production and
catchment function. Therefore, the impact of environment and grazing on the
vegetation was investigated to aid the development of management policy for the
conservation of the grazing, floristic and water resources of the mountains.
Vegetation surveys were conducted in the mountains in the east (Study Area 1: 2 625
- 3 350 m a.s.l.) and in the west (Study Area 2: 2 240 - 3 125 m a.s.l.). Indirect
gradient analysis (IGA) and classification were used to investigate the influence of
environment on vegetation pattern. Results of the IGA indicated that variation in
species composition in the mountains is related primarily to topographic variation, in
particular elevation and aspect. Five vegetation communities were identified in Study
Area 1 and seven in Study Area 2. These communities occurred consistently in
specific topographic positions in the landscape and were arranged along a
temperate/subtropical grass species continuum which was associated with a gradient
in elevation and aspect. In Study Area 1, the elevation boundary between the high-lying temperate grasslands and the lower subtropical grasslands corresponded with
the generally recognised boundary between the Alpine and Subalpine vegetation belts (viz. c. 2 950 m a.s.l. on northerly aspects and c. 2 750 m a.s.l. on southerly aspects). This boundary was lower in Study Area 2 (viz. c. 2 800 m a.s.l. on northerly aspects and c. 2 300 m a.s.l. on southerly aspects). Vegetation-insolation relationships were investigated in Study Area 1 using a model for
simulating solar radiation, temperature and potential evaporation patterns on sloping terrain (RADSLOPE). The spatial distribution of the identified vegetation communities
and the ratio of temperate (C₃) and subtropical (C₄) grasses in the sward were related to solar irradiance patterns, as influenced by topography. Results suggest that exposure, which increases with altitude, is probably also an important determinant of vegetation pattern in the mountains. The influence of grazing on the vegetation was studied by examining changes in species composition and cover that were associated with gradients in grazing intensity that exist around cattleposts in the mountains. There was little evidence of a shift in species composition and cover under grazing in the Alpine Belt but there was an identifiable grazing gradient in the Subalpine belt. There, short dense grasslands,
dominated by palatable species, degrade to a dwarf karroid shrubland with sparse
cover under prolonged, intense grazing. The optimum position along the grazing
gradient of the more abundant species was identified. It was proposed that the
relative positions, or scores, of these species along the grazing gradient can be used
in a weighted scoring procedure to provide an index for monitoring the response of the
mountain vegetation to grazing. However, the species’ scores still require verification.
The need for monitoring temporal changes in vegetation composition and cover in
order to assess the possible effects of the LHWP and other development initiatives
was noted. Such monitoring should be undertaken in conjunction with an overall
programme to assess the dynamics of the socio-economy in the mountains.
Therefore, interdisciplinary monitoring programmes are required to achieve this.
These programmes should be focused in a few key study locations rather than spread over a wide area.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg.
Keywords
Mountain plants--Effect of grazing on--Lesotho., Range management--Lesotho., Rangelands--Monitoring--Lesotho., Mountain ecology--Lesotho., Vegetation boundaries--Lesotho., Social ecology--Lesotho., Theses--Grassland science.