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 seaso n started early, several separate establishment opportunities occurred , but with late rains only one germination wave was observed. Small ra infall events of 10-12 mm were unable to trigger germination. The phen ology of emergence confirms the presence of a drought avoidance syndro me in this semi-arid climate. Seedling densities varied from a few in perennial Eragrostis rigidior grassland to 3000 m(-2) in annual Tragus berteronianus grassland influenced by runoff processes. Seedlings eme rged mainly from the top 1 cm of the soil. Vertical distribution of se eds showed a concentration in the top 1 cm of soil and the litter laye r. Grass seedling survival was positively correlated with seed size. T he importance of seedlings for the regeneration of grasslands is discu ssed. (C) 1996 Academic Press Limited