Life form spectra in the Hantam-Tanqua-Roggeveld, South Africa

Abstract

The Hantam-Tanqua-Roggeveld subregion is situated in an area where the Fynbos, Succulent Karoo and Nama Karoo biomes meet. Life form spectra were compiled at a species richness and vegetation cover level in order to determine the affinities of the vegetation of the subregion with respect to its Succulent Karoo, Fynbos and Nama Karoo Biome status. A percentage succulence was also calculated for both species richness and cover. Comparisons of life form spectra and succulence were made across the eight vegetation associations found in the area and across three broad vegetation groups, i.e., Mountain Renosterveld, Winter Rainfall Karoo and Tanqua Karoo. Mountain Renosterveld vegetation was characterised by high chamaephyte, cryptophyte and therophyte species contributions. Compared to the other broad vegetation groups, the Mountain Renosterveld group showed phanerophyte contributions at the vegetation cover level to be highest, but the degree of succulence was low. Winter Rainfall Karoo vegetation was co-dominated by high levels of chamaephyte, cryptophyte and therophyte species with chamaephytes dominating the vegetation cover. Succulent contributions to species richness and cover values were higher than for Mountain Renosterveld vegetation. Tanqua Karoo vegetation was dominated by chamaephyte species or co-dominated by chamaephyte and cryptophyte species with therophyte species contributions lowest of all vegetation groups. Contributions by succulent species to richness and vegetation cover were high in the Tanqua Karoo. Life form spectra of the Mountain Renosterveld associations compared poorly to other sites in the Fynbos Biome. However, the low level of succulence in the Mountain Renosterveld associations also precludes its inclusion into the Succulent Karoo Biome. The large contribution of succulent species at a species and vegetation cover level in Winter Rainfall Karoo and Tanqua Karoo associations confirms that these two groups belong to the Succulent Karoo Biome. Affinities to the Nama Karoo Biome were indicated by the low level of succulence at a vegetation cover level in one of the Winter Rainfall Karoo associations (Roggeveld Karoo).