| Abstract: | Patches (1 m diameter) were cleared in a heavily grazed and a lightly grazed savanna in South Africa; half of them were covered once with grass litter. The greatest colonisation over three years occurred on heavily grazed patches with litter, the least on open, lightly grazed patches. Annual rainfall affected colonisation rate. Basal cover was lower on patches than in the surrounding vegetation. Patch composition was weakly affected by treatment, and was partly related to the composition of adjacent vegetation, but the proportional representation of species on patches differed from the surrounding vegetation. The stoloniferous Digitaria eriantha and the obligate seed reproducers Aristida bipartita and Heteropogon contortus were major components of patch communities but were uncommon in the surrounding vegetation and in the seed bank. Setaria incrassata and Themeda triandra were the predominant components of the surrounding vegetation and of the seed bank, but Setaria established very poorly and Themeda established well only on heavily grazed patches with litter. The pattern of seedling establishment was the same as that of colonisation. Most seedlings emerged atthe beginning of the wet season, with ca. 50% mortality soon thereafter. The colonising species can be partly predicted from the availability of propagules (vegetative or seed), emergence and establishment success, and subsequent growth. |
