Germination and Seedling Survival Studies of Xanthorrhoea australis in the Warby Range State Park, North-Eastern Victoria, Australia

Abstract

Germination of Xanthorrhoea australis R.Br. was affected by temperature, stratification, the time of seed collecting, and light. Ninety eight percent of seeds germinated at the optimum temperature, 15-20°C, in the laboratory which matched field conditions during times of reliable rainfall. A varying temperature of 20-12°C brought seeds sown in soils out of dormancy 6 weeks earlier than those under a fixed temperature regime. The germination of seeds stratified at 4°C for 11 weeks was 90% compared with 40% for unstratified seeds. For spring- and autumn-picked seeds, germination in the dark was 98%; but for spring-picked seed, germination in light was 90% compared with 60% for autumn-picked seed, with both picked in the same year. After a simulated summer, when temperatures decreased, seeds in light (or on the soil surface) had 3% germination, while those in the dark (buried) had 40% germination. In field trials using five different substrates, germination of buried seed ranged from 30% to 55%, with a seedling survival in the first post-fire autumn of 28-43%, which was significantly greater (P < 0.001) than that of the surface-sown seed. However, in cabinet trials with the same substrates, there was no significant difference between germination in buried and surface-sown seeds (25-40% germination). The lower germination in the field of surface-sown seeds could be explained by loss due to seed predation, and lack of moisture, causing incomplete imbibition and water stress on seedling survival. These findings show that to establish X. australis in areas degraded by soil pathogens, fire or clearing, seeds should be sown in the late winter at a depth of 3 mm, with protection from grazing.