Changes in plant form and function across altitudinal and wetness gradients in the wetlands of the Maloti-Drakensberg,South Africa |
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Authors: | Erwin J J Sieben Craig D Morris Donovan C Kotze A Muthama Muasya |
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Institution: | (1) Department of Plant Sciences, University of the Free State, Qwaqwa Campus, Private Bag X13, Phuthaditjhaba, 9866, South Africa;(2) Agricultural Research Council, Animal Production Institute (ARC-API), University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa;(3) Centre for Environment and Development, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg, 3209, South Africa;(4) Department of Botany, University of Cape Town, Private Bag X3, Rondebosch, 7701, South Africa |
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Abstract: | A survey of 93 wetlands in six catchments across the Maloti-Drakensberg is used to assess the distribution of plant functional
types across altitudinal and wetness gradients. Altitudes range from 1,000 to 3,200 m a.s.l. Within each catchment, the wetlands
were selected to cover the complete range in altitude and wetland types. In each of the selected wetlands, vegetation was
sampled in 3 by 3 m quadrats covering the entire range of wetness represented in the wetland, from temporarily wet to permanently
inundated soils. Plant species were allocated to one of 11 different functional types (examples are C3 grasses, C4 sedges, rosette plants, and shrubs), and the proportion of the vegetation in each sample occupied by each functional type
was calculated from the species’ abundances. Canonical Correspondence Analysis shows that “wetness” clearly has the highest
impact on the distribution of functional types, followed by altitude. The most important plant functional types in wetlands
are grasses and sedges, however, at higher altitudes, forbs (especially rosette plants) and bulbous plants become a more prominent
feature in the wetlands. The total amount of graminoids gradually decreases with altitude. The general trend is that sedges
tend to increase with increasing wetness and C3 plants (grasses and sedges) increase with increasing altitude, but these effects are not independent. The distributions of
C4 sedges and C4 grasses along an altitudinal gradient are quite different, and C4 grasses grow abundantly at much higher altitudes than C4 sedges. C4 sedges are very scarce at the altitudes represented in the Maloti-Drakensberg area, whereas C3 grasses occur in the permanently wet parts of the wetlands, especially at higher altitudes (normally mostly occupied by sedges).
Shrubs are rare in wetlands and tend to be an indication of disturbance. This study complements previous studies on the distribution
of grasses and sedges at the lower altitudes within KwaZulu-Natal, which found that at altitudes below 1,000 m a.s.l. C4 sedges were much more prominent, while forbs and rosette plants were largely absent. This confirms that C4 as an adaptation to hotter and warmer climates is sometimes a less favorable metabolism in wet high altitude areas. At high
altitudes, rosette plants and bulbous plants become more competitive in wetlands, probably because grasses and sedges present
at these altitudes generally grow smaller than they do in low altitude wetlands. |
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