Smoke and heat effects on soil seed bank germination for the re-establishment of a native forest community in New South Wales

The effects of plant-derived smoke and of heat on the emergence of seedling s from seeds were assessed. Seeds had been stored in forest topsoil used fo r mine site rehabilitation. The study was carried out in a dry sclerophyll, spotted gum (Corymbia maculata), forest community at the Mount Owen open-c ut coal mine in the Hunter Valley region of New South Wales. Samples of the surface 2.5 cm of topsoil were either exposed to cool smoke from eucalypt foliage for 60 min, heated to 80 degrees C, or left untreated. Seedling eme rgence from the seed bank in this soil was then monitored in a glasshouse. Within the first month, smoke alone promoted a 4.3-fold increase in the den sity of seedlings relative to control. There were 540 emergents per m(2) in the control and 2309 per m(2) in the smoke treated topsoil. Many annual an d perennial herbs emerged but grasses responded most strongly to smoke. Ger mination in seven of the 20 grass species was promoted by smoke. Smoke prom oted the germination of some introduced species as well as native species, and accelerated the rate at which seedlings emerged, although these differe nces sometimes declined with time. Heat also stimulated germination but smo ke and heat stimuli appeared to be complementary in their promotion of seed ling emergence from the topsoil seed bank. Each treatment increased the den sity of different species, enhanced the species richness of different compo nents of the seed bank, and had different effects on the rate of emergence. The results suggest that increased seed germination in the field immediate ly following a moderate intensity fire may sometimes be the result of smoke stimulation and sometimes the result of heat stimulation of the soil seed bank. These findings may have important implications for minesite revegetat ion programs where topsoils are replaced after mining and rapid germination of seeds stored in these soils is required during short periods when condi tions are favourable for germination.