Germination response of seven east Australian Grevillea species (Proteaceae) to smoke, heat exposure and scarification

Seeds of plant species from fire-prone vegetation often show dormancy, and germinate in response to fire-related cues. Seeds of some east Australian G revillea species were known from earlier studies to germinate in response t o fires, but gave mixed results when heat shock was tested as a germination stimulus. In the current study, seeds of seven east Australian Grevillea s pecies were tested for their germination response to smoke, to short heat e xposure, and to scarification. Seeds were smoked in a chamber by using a mi xture of native woodland vegetation as fuel. The smoking and heating treatm ents were administered to seeds in bulk: this meant that subsequent germina tion data for these two treatments were not independent. Cumulative germina tion in the laboratory was scored for up to 60 days. All three germination treatments, when administered singly, increased germination: smoke increase d germination in all seven species, heat in four species, and scarification in a different four species. Pairwise combinations of the three treatments also increased germination in some species e.g. smoke and heat treatments combined led to the highest germination observed in four species, and to in creased germination compared with either treatment singly, in another speci es. Some treatment combinations appeared to interact: heat and scarificatio n combined led to decreased germination in three species. The role of heat exposure and scarification in increasing germination was not due to the bre aking of an impermeable seed coat: water uptake of both scarified and unsca rified seeds was rapid and equal (after 24 h) in all seven species. The res ults indicate that seeds of the Grevillea species investigated are responsi ve to one or more fire-related germination cues.