Biology of Fire Ephemerals of the Sandplains of the Kwongan of South-Western Australia

Abstract

The growth, longevity, mineral relationships and reproductive biology of 18 species of fire ephemerals were examined in sclerophyllous shrubland, located mainly within the Jurien : Badgingarra region of the Northern Sandplains of the kwongan of SW. Australia. Ten of the species were monocarpic, completing their life cycle within the 6-8 month winter growing season after a summer or autumn fire. The remaining species were polycarpic, commencing reproduction in their second season and surviving and reproducing for a further two to eight seasons (depending on species). Detailed study was made of growth and dry matter allocation in the dioecious, sexually dimorphic, polycarpic species Tersonia brevipes (Gyrostemonaceae). Monocarpic species tended to produce smaller seeds, and exhibited greater seed output per unit biomass and higher harvest indices for dry matter and minerals than polycarpic species. Certain monocarpic species showed great plasticity in final dry weight, e.g. a 2700-fold difference between largest and smallest individuals in a sample of 250 plants of Stipa elegantissima (Poaceae), and a 180-fold range in a similarly sized sample of Macarthuria apetala (Aizoaceae). The fire ephemerals studied generally exhibited faster seedling growth rates, greater concentrations of P and N (but not of Ca, Mg and K) in seedling dry matter, but usually lesser concentrations of P and N (but not of Ca, Mg and K) in seed dry matter than in cohabiting obligate seeder or sprouter species with potential life spans exceeding 15 years. The above-mentioned features of fire ephemerals are suggested to be of special adaptive significance within the context of exploitation of transiently non-limiting habitat resources immediately following fire.