Does high-density stocking affect perennial forbs in mesic grassland?

Abstract

Livestock production is an appropriate land use for mainstreaming biodiversity conservation, but little is known about the impact of grazing strategies on forbs that contribute most species, in grasslands. This study compared the effects of high-density, short-duration stocking (HDG) with no grazing (control) on vegetation structure, composition and demography of selected perennial forbs in a South African mesic grassland in a three-year experiment in KwaZulu-Natal, South Africa. HDG resulted in four-fold more and deeper litter accumulation, which reduced irradiance. Cover of three forb species, including the alien Bidens pilosa, was promoted and cover of another three forb species was reduced under HDG. There were no short-term effects of HDG on diversity, evenness and species richness. Ninety percent of forb species were damaged by HDG; type of damage varied widely from leaves and stems grazed to tearing and shredding by the hooves of cattle. Study of demography revealed that HDG threatened future populations of the grazing-sensitive species Afroaster hispida, Agathisanthemum chlorophyllum and Gerbera ambigua through increased mortality or reduction in the recruitment of large from small individuals. This study has revealed that HDG potentially has negative direct and indirect effects on indigenous perennial forbs in a South African mesic grassland.

Keywords: biodiversity conservation, population dynamics, short-duration grazing