Determinants of postfire flowering in the geophytic grass Ehrharta capensis

Abstract

Summary We conducted a fertilization–defoliation experiment to investigate postfire flowering in Ehrharta capensis, a cormous grass native to the Cape fynbos. Combined fertilization and defoliation produced a strong flowering response in E. capensis, suggesting that the strong postfire flowering pattern of this species can be explained largely by the effect of fire on soil nutrients and vegetation cover. Flowering was absent in control plants, and sparse in plants receiving single treatments. Comparable treatment dependence of flowering was not observed in two congeneric species that lack specialized storage structures and in which flowering is not apparently fire‐dependent. In E. capensis, flowering did not significantly reduce the dry mass of corms persisting from previous years, or the amounts of reserves these contained. We conclude that corm‐stored reserves do not contribute substantially to inflorescence production. Flowering E. capensis plants produced significantly larger replacement corms than did nonflowering plants, indicating that sexual reproduction does not occur at a cost to asexual persistence. The lack of a trade‐off between sexual and asexual reproduction may explain why E. capensis, and possibly other clonal geophytes, flower only when resource availability is high. Cost–benefit models, which predict a trade‐off, do not properly describe resource allocation in these species.