Grass-on-grass competition along a catenal gradient in mesic grassland, South Africa

Interactions between mature grass plants and grass seedlings have been found to be both facilitative and competitive. To examine the effects of aboveground and belowground competition on seedling biomass and the effects of soil depth on competitive interactions, seedlings of three locally common grass species (Eragrostis racemosa, Themeda triandra and Panicum maximum) were planted into a natural grass sward on three different parts of the landscape varying in soil depth. Three aboveground treatments (full light competition, no light competition and clipping to simulate grazing), and two belowground treatments (full belowground competition and belowground competition excluded by a root tube), were used. On all soil depths the three grass species differed in mean mass, with E. racemosa having the least mass and T. triandra having the greatest mass. Simulated grazing by clipping the surrounding sward created niches for seedling establishment. This highlights the importance of maintaining stocking rates at a level that promotes seedling establishment.