Woody vegetation–environment relations in a semi-arid savanna in the northern Transvaal

O’Connor, Timothy G.

doi:10.1016/s0254-6299(16)30846-8

Cited by 27 publications

(31 citation statements)

References 9 publications

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“…Floristic variation of southern African savanna woodlands shows a general correspondence to topo-edaphic variation (Joubert 1971;Leistner & Werger 1973;Coetzee et al 1976;Van der Meulen 1979;Van Rooyen, Theron & Grobbelaar 1981a, b, c;Coetzee 1983;Whateley & Porter 1983;Van Rooyen 1983;Le Roux et al 1988;O'Connor & Campbell 1986;O'Connor 1992), as was discerned in this study, yet the precise nature of this relationship remains elusive.…”

Section: Floristic Variationsupporting

confidence: 57%

“…Woodland communities of southern African savannas invariably differ in their physiognomy (Werger 1978;Van Rooyen et al 1981a, b, c;Coetzee 1983;Bredenkamp & Theron 1985;O'Connor 1992), as we have described for Klaserie. However, these previ- Table 4 for how well the ordinations performed.…”

Section: Woodland Physiognomic Structuresupporting

confidence: 54%

“…Colophospermum mopane woodlands are distinctive and widespread in southern Africa (Henning & White 1974;Werger & Coetzee 1978), but show significant floristic and physiognomic variation throughout their range (e.g. 's Louw 1970;Van Rooyen et al 1981c;O'Connor 1992). Hygrophilous communities within these semiarid savannas are invariably physiognomically and floristically distinct (e.g.…”

Section: Floristic Variationmentioning

confidence: 99%

“…Topo-edaphic conditions, woodland composition and structure, and the amount of browse are not independent of one another. Topo-edaphic conditions are an important determinant of the composition and physiognomic structure of African savannas, and structure often corresponds with composition (Leistner & Werger 1973;Coetzee et al 1976;Werger 1978; Van der Meulen 1979;Van Rooyen, Theron & Grobbelaar 1981a,b,c;Coetzee 1983;Van Rooyen 1983;Bredenkamp 1985;Bredenkamp & Theron 1985;Le Roux et al 1988;O'Connor 1992). However, these previous studies have not demonstrated a consistent finding about which topo-edaphic variables have the greatest influence on the vegetation properties of savanna woodlands.…”

Section: Introductionmentioning

confidence: 97%

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Topo-edaphic, floristic and physiognomic gradients of woody plants in a semi-arid African savanna woodland

Witkowski

O’Connor

1996

Vegetatio

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The variation in topo-edaphic conditions, woodland composition and physiognomic structure of a semi-arid savanna woodland, namely the 59 400 ha Klaserie Nature Reserve, was studied with multivariate techniques. Spatial variation in the texture and chemistry of both the A-and B-horizons was substantial. One gradient of the A-horizon was of increasing clay, silt, organic matter, pH and conductivity, while a second gradient was of increasing rockiness, slope and gravel content, associated in part with upper landscape positions. Physiognomic structure of the woodland also displayed substantial spatial variation. Variation in tree density had the greatest effect on total canopy volume, and the density of coppice and dead individuals were closely correlated. Topo-edaphic variation, after the effect of vegetation composition had been accounted for, had a direct effect on woodland structure, as clay content of soils or rockiness influenced shrub density, and catenal position together with silt-or gravel-content of soils influenced coppice density. Ordination analyses identified that the included topo-edaphic variables accounted for a significant amount of floristic variation, but also showed that important environmental variables were omitted. Floristic variation of woody elements was of the nature of a large number of relatively equivalent, independent gradients rather than of a few simple primary gradients. Ten woodland types were identified by TWlNSPAN which differed in their topo-edaphic and physiognomic character. Distinctive woodland assemblages were found on rocky outcrops or alluvial areas, on deep, sandy soils or on clay-or silt-rich soils, Colophospermum mopane formed the densest woodlands. Characteristics of the B-horizon were often dissimilar to those of the A-horizon, and seemed important for woodland composition.

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Section: Floristic Variationsupporting

confidence: 57%

Section: Woodland Physiognomic Structuresupporting

confidence: 54%

Section: Floristic Variationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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Topo-edaphic, floristic and physiognomic gradients of woody plants in a semi-arid African savanna woodland

Witkowski

O’Connor

1996

Vegetatio

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“…The geology, geomorphology and resultant substrate types of the area have been described, with a map, in O'Connor (1992), and are not recounted here.…”

Section: Study Areamentioning

confidence: 99%

Impact of sustained drought on a semi‐aridColophospermum mopanesavanna

O’Connor

1998

African Journal of Range & Forage Science

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Vegetation change on different substrate types was measured over 15 years in semi-arid Mopani Veld. Baseline data were collected in the terminal year (1982) of a decade of above-average rainfall, whilst the period of monitoring was characterised by below-average rainfall, with severe drought years occurring in 1988/1989 and 1991/1992. Grazing pressure was, on average, alleviated over the period of recording so that changes reflect primarily the effect of rainfall. Long-lived perennial grasses had declined markedly, annual and micro-perennial grasses had increased markedly, and the proportion of forbs had increased. Despite 7-17 years since the replacement of livestock grazing with wildlife at lower stocking rates, there was no evidence of an improvement in sward or soil condition, owing ostensibly to the effect of drought. The extent of change in botanical composition and in sward condition was influenced by substrate type. The rate of growth of the woody component had been slow: the average per annum increase in the radius of trees was 0.67 mm. For the dominant species, Colophospermum mopane, only individuals of less than 1 m in height consistently showed an increase in size. The basal area of dead standing trees had increased threefold.Complete mortality or substantial topkill of shrub species, in particular of Grewia spp., Ximenia americana, and Combretum apiculatum, and of adults of the latter, had occurred owing to drought. Shrub mortality was most pronounced on colluvial soils and sandveld. All species exhibited partial dieback of the crown. Overall, shrub recruitment has been limited except for that of H. mopane on colluvial soils but not on other substrate types, which is therefore likely to increase further its dominance on this substrate at the expense of species richness. Grazing pressure on desirable perennial grasses and browsing pressure on palatable woody plants has probably increased because of their decline, even if animal abundance has not increased, which will have a negative effect on their re-establishment. Acting in opposition, dieback of trees and shrubs has probably created a window of opportunity for the recovery of perennial grasses, but it would likely require an extended run of above-average years to reverse the changes in herbaceous vegetation, for which the availability of seed of perennial grasses is likely to be a major constraint.

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What shapes the range edge of a dominant African savanna tree, Colophospermum mopane? A demographic approach

Stevens

2021

Ecology and Evolution

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Woody vegetation–environment relations in a semi-arid savanna in the northern Transvaal

Cited by 27 publications

References 9 publications

Topo-edaphic, floristic and physiognomic gradients of woody plants in a semi-arid African savanna woodland

Topo-edaphic, floristic and physiognomic gradients of woody plants in a semi-arid African savanna woodland

Impact of sustained drought on a semi‐aridColophospermum mopanesavanna

What shapes the range edge of a dominant African savanna tree, Colophospermum mopane? A demographic approach

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