Germination ecology of six shrubs in fire-prone Cape fynbos

Abstract

To explain the recruitment and coexistence of species which establish after fire, this study predicted that each species would have different germination cues as a component of different regeneration niches. Furthermore, for species subject to natural fire frequencies of 10–20 years, fire-related cues, seed dormancy, extended longevity and fire-related germination cues might be predicted. However, results indicated broadly similar germination requirements. Seeds subjected to two heat treatments and a charcoal extract failed to show significantly enhanced germination. Instead, highest germination successes were achieved under alternating diurnal temperatures which implied an indirect fire cue, viz. the removal of insulating vegetation. Leachate solution inhibited germination in two species suggesting allelopathic effects during inter-fire periods. Only two species showed dormancy and three species did not have extended longevity but showed declining germinability after three years. Finally, in order to determine the potential germination from a soil-stored seed bank, data analysis simulated a seed bank comprising three years' accumulation of seeds. In each species the proportion of germinable seeds varied each year over the three years. Also, the germinability in response to ageing varied for each year's seed production. This would explain the variation in densities of the six species after different fire events, and hence offers a better explanation for species' coexistence.