Effect of seasonal rainfall pattern on seedling emergence and establishment of grasses in a savanna in south-eastern Botswana

The emergence and spatial distribution of grass seedlings were studied in a degraded savanna in south-eastern Botswana. When the rainy season started early, several separate establishment opportunities occurred, but with late rains only one germination wave was observed. Small rainfall events of 10–12 mm were unable to trigger germination. The phenology of emergence confirms the presence of a drought avoidance syndrome in this semi-arid climate. Seedling densities varied from a few in perennialEragrostis rigidiorgrassland to 3000 m−2in annualTragus berteronianusgrassland influenced by runoff processes. Seedlings emerged mainly from the top 1 cm of the soil. Vertical distribution of seeds showed a concentration in the top 1 cm of soil and the litter layer. Grass seedling survival was positively correlated with seed size. The importance of seedlings for the regeneration of grasslands is discussed