Comparative seed germination ecology of Austrostipa compressa and Ehrhartacalycina (Poaceae) in a Western Australian Banksia woodland

Austrostipa compressa, a native ephemeral of southwest Western Australia wa s stimulated to germinate under a range of temperatures, in the presence of light, and exposure to smoke-water. This combination of environmental cues results in winter-maximum germination in immediate postfire and disturbed- soil environments of this Mediterranean-type climate. In contrast, Ehrharta calycina, an introduced perennial grass from southern Africa that has inva ded Banksia woodlands, germinated under a wide range of temperature and lig ht conditions, but showed no promotive response to smoke-water. Although A. compressa seeds tolerated heat shock better than E. calycina, the self-bur ial mechanism of A. compressa seeds ensures protection from fire. High-inte nsity fire could have a greater impact on E. calycina, as the seeds of this species tend to accumulate in the top of the soil profile where they are m ore susceptible to high temperatures. Although seeds off. calycina are more susceptible to high temperatures, survival of mature individuals by postfi re resprouting ensures continued survival in native woodlands. Estimates of soil seed bank densities showed extreme variability, but some recently bur nt areas of the Yule Brook Botany Reserve contained up to 8000 seed m(-2) o f A. compressa and nearly 75 000 seeds m(-2) off. calycina. Viable soil see d bank densities of A. compressa are reduced with time-since-last fire, but areas of greater than 45 years since the last fire, still contained up to 119 seeds m(-2). In both species, only about half their soil seed bank germ inates following fire, thus ensuring the potential for later recruitment. M assive soil seed populations of E. calycina in native Banksia woodlands pos e a major problem to management of this plant community type.