Life form and species diversity on abandoned croplands, Roggeveld, South Africa

Abstract

The Roggeveld consists of an island of Mountain Renosterveld (Fynbos biome) surrounded by Succulent Karoo biome vegetation. Since management of abandoned croplands depends on a better understanding of their succession sequences, vegetation recovery on abandoned croplands in the Roggeveld was studied using species and life form diversity parameters. Abandoned croplands of different ages were compared with each other and to the natural vegetation. Therophytes and chamaephytes were the most abundant life forms. Chamaephytes made an overwhelming contribution to the relative cover. Species-area curves (exponential function) differed significantly between the abandoned croplands and natural vegetation. Species richness increased with time since abandonment but no similar increase in species evenness, Shannon or Simpson indices were found. A regression of species richness against age of abandoned cropland predicted that an abandoned cropland of approximately 33 years should be as species rich as the natural vegetation, but a principal cooordinate analysis of floristic data indicated that all the plots were floristically still extremely different from the natural vegetation. Across all nine survey plots only 15 species contributed to a high cover on the plots. Vegetation recovery on abandoned croplands in the Roggeveld occurs naturally, yet the rate of recovery varies among the life forms.

Keywords: diversity indices, Fynbos biome, old fields, species richness, Succulent Karoo biome

African Journal of Range & Forage Science 2011, 28(2): 99–110