Diversity of the herbaceous layer in mixed bushveld

Abstract

The diversity of the herbaceous layer in the Nylsvley Nature Reserve (Mixed Bushveld) was investigated to enhance the understanding of savanna ecosystems and to serve as a baseline for future monitoring to facilitate management. Species composition and density, dry weight contribution per species, and grass density was measured with a small-quadrat method. A total of 73 grass species were recorded. Plant communities were compared in terms of percentage composition and percentage dry weight per ecological group, species diversity and grass density with general linear modeling. The herbaceous layer of most plant communities consisted pre-dominantly of increaser I species (increasing in under-utilized areas), with increaser I and decreaser species (decreasing with under or over-utilization) producing the highest bio-mass. The dominance of increaser III species (becoming dominant in heavily over-grazed areas) in the Sporobolus ioclados-Acacia tortilis Savanna indicates previous over-utilization of this plant community. A generally high species diversity (Simpson’s index 1-D >0.72) in the reserve is influenced by environmental factors and is a reflection of previous low animal stocking densities and a rotational burning regime. Grass density varied from 53.07 to 219.13 grasses/m-2. A negative correlation (r = –0.6654) between grass density and species density supports the principle that species diversity is reduced in over-grazed areas. The high diversity of the herbaceous layer in the Nylsvley Nature Reserve may serve as a benchmark for comparing range diversity over time and space within this vegetation type.