Dry woodland and savanna vegetation dynamics in the Eastern Okavango Delta, Botswana.
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Date
2012
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Abstract
The Okavango Delta is an extremely dynamic system with variable vegetation comprised of permanent
swamps, seasonal swamps, dry islands, floodplains and dry grassland, savanna and woodland. The system
is largely driven by the interaction between fire and the annual flood, which filters down from the
Okavango River catchments in Angola. While extensive research has been conducted on the flood-driven
vegetation little is known about the dry woodland and savanna regions bordering these flood-driven
habitats. A taxonomic classification of woody species composition resulted in eleven vegetation types.
These data were then reanalyzed in terms of woody species morphology allowing these eleven vegetation
types to be grouped into four functional response groups in order to provide a platform for improving the
understanding of how dry woodland and savannas interact with the environment. These four groups were
the savanna group mixed thornveld and the three woodland groups; mixed broadleaf woodland, shrub
mopane woodland and tall mopane woodland. Burning in mixed thornveld and mixed broadleaf woodland
was found to decrease woody species density and grass fuel loads and could be used for grazing
management to remove unpalatable growth and improve grass species composition, while burning in
shrub mopane woodland and mixed mopane woodland merely decreased the woody understory and is not
recommended. Utilization dominated by grazing livestock resulted in overutilization of the grass sward
leading to bush encroachment in both mixed thornveld and shrub mopane woodland, while utilization by
goats alone resulted in underutilization of the grass sward and a dominance of herbaceous annuals.
Livestock utilization had no effect on the occurrence of Pecheul-loeschea leubnitziae, a shrubby pioneer
previously thought to be an indicator of overgrazing, however extensive P. leubnitziae cover was
associated with a sward dominated by shade-tolerant grasses with low forage quality. Shrub mopane
woodland and tall mopane woodland appear to be more stable vegetation states than mixed broadleaf
woodland and mixed thornveld being less vulnerable to colonization by pioneer species and alteration as a
result of utilization or environmental factors. For this reason management and monitoring of mixed
thornveld and mixed broadleaf woodland is essential to prevent vegetation degradation and to ensure
optimal forage availability for both livestock and wildlife.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
Keywords
Vegetation classification--Botswana--Okavango River Delta., Woody plants--Effect of fires on--KwaZulu-Natal--Ithala Game Reserve., Range management--Botswana--Okavango River Delta., Vegetation management--Botswana--Okavango River Delta., Grasses--Botswana--Okavango River Delta., Rangelands--Monitoring--Botswana--Okavango River Delta., Theses--Grassland science.