Flowering, seed dispersal, seed predation and seedling recruitment in two pyrogenic flowering resprouters

Abstract

A few resprouting plants in fire-prone environments have no local seed bank (soil or canopy) when a fire occurs. These species rely on post-fire flowering and the production of non-dormant seeds to exploit favourable post-fire establishment and growth conditions. For two such pyrogenic flowering species (Doryanthes excelsa Correa and Telopea speciosissima (Smith) R.Br.), we examined the timing of seed release, patterns of fruit production, seed dispersal, seed predation and seedling establishment following a fire in the Sydney region of south-eastern Australia. Both species took some 19 months after the fire to flower and the first seeds were released 2 years after the fire. D. excelsa flowered and fruited only once after the fire. For T. speciosissima, plants also flowered at least once more in the subsequent 5 years, but produced seed in only the first three post-fire flowering years. Fruit production differed between species, with fruiting individuals of D. excelsa producing fewer infructescences, similar numbers of follicles, but many more seeds per follicle than fruiting individuals of T. speciosissima. Ultimately, D. excelsa produced approximately six times as many seeds per m² and four times as many seeds per adult in one flowering season than T. speciosissima did after four flowering (three successful fruiting) seasons.

Seeds were passively dispersed from fruits borne 3–4 m (D. excelsa) or 1–2 m (T. speciosissima) above the ground. Most seeds were found within 5 m (D. excelsa) or 3 m (T. speciosissima) of parent plants. The primary seed shadow of both species was a poor predictor of the distribution of seedlings, with more seedlings occurring further from the adults than expected from the distribution of seeds. Seed loss to predators was high in both species in exclusion experiments where mammals had access to clumps of seeds (77–88%). It was variable and generally lower (8–65%) in experiments where seeds were not locally clumped. However, for T. speciosissima, at one site, some 65% of seeds were lost to mammals and invertebrates in these latter experiments. At this site, these losses appeared to influence subsequent recruitment levels, as very low seedling densities were observed.

For both species, germination of seedlings first occurred some 2.5–3 years after the passage of the fire. The percentage of seeds produced to seedlings successfully established was low in D. excelsa (2–3%) and more variable across sites and years in T. speciosissima (0–18%). Resultant post-fire seedling densities of D. excelsa (two sites) and T. speciosissima at one site were similar, but they were much lower at the T. speciosissima site that had high levels of seed predation. Both D. excelsa and T. speciosissima are amongst the slowest woody resprouting species to recruit seedlings after fire in south-eastern Australia and lag years behind species with soil or canopy seed banks.