Plant diversity of flowering displays on old fields in the arid Namaqua National Park, South Africa

Abstract

The main aim of this study was to classify the vegetation on the abandoned fields in the Namaqua National Park and to investigate whether the time since abandonment has impacted on the diversity and mass flowering displays. Sixty-two old field sample sites were surveyed using the Braun-Blanquet method. Floristic data were analysed to produce a hierarchical classification, while a principal coordinates analysis was used to establish whether the ordination supported the classification. Species richness (total number of taxa), as well as the Shannon-Wiener diversity index, was calculated per vegetation unit for the different life forms. Four old field communities were identified, each containing a unique complement of species, which differed in their potential to produce a mass flowering display. On the Skilpad section of the park, Ursinia cakilefolia dominated the spectacular mass floral displays for which the park has become well known. Old fields in other parts of the park did not produce the same spectacular displays. Although total and perennial species richness did not differ significantly with time since abandonment, the richness of annual species, in particular of the showy annual species, decreased with time since abandonment. The relative contribution of the perennial species to vegetation cover increased with time since abandonment, whereas the relative contribution made by showy annual species to vegetation cover declined with time since abandonment. Although species composition and the potential to produce mass flowering displays of the four communities differed, diversity parameters were similar. However, to maintain a flower display for tourists on the Skilpad section, a degree of disturbance is essential.

Conservation implication: Although deliberate disturbance is not desirable in a national park, we find that some disturbance is essential to maintain a spectacular flowering display. However, these intentionally disturbed old fields cover only a small proportion of the total area of the park. All other old fields in the park should not be disturbed, and should be allowed to recover naturally.