The influence of fire severity on recruitment of fynbos with particular emphasis on seed size : a field study in the Cape Peninsula

Fifty-two sites throughout the Cape Peninsula area burnt in the January 2000 fires were sampled to investigate the effects of fire severity on the recruitment of invasive and fynbos plants with particular emphasis on seed size. Four hundred fynbos species were divided into big- (>l0mg) and small-seeded (<10mg) species. Different measurements of burnt plant skeletons were examined to find the most appropriate indicator of the biological effects of a fire. It was found that the measurement of thinnest branch diameter of plant species with similar growth forms can be used as estimates of fire severity. Seedling density of fynbos species decline with an increase in fire severity, whereas recruitment of alien seedlings is not affected by fire severity. Big-seeded species and seedlings showed no significant correlation with fire severity, whereas the density of small-seeded species and seedlings correlated significantly with fire severity. It is likely that variations in fire severity that influences the depth to which seeds are killed will affect the ability of small seeds to emerge. High severity burns may thus have a different community composition by favouring the survival of big-seeded species