SURVIVAL OF SEROTINOUS SEEDBANKS DURING BUSHFIRES - COMPARATIVE-STUDIES OF HAKEA SPECIES FROM SOUTHEASTERN AUSTRALIA

The study assessed the survival, during bushfires, of seedbanks of six serotinous Hakea species found in the Sydney region of southeastern A ustralia. The survival of seeds was examined when fruits were heated i n a muffle furnace at ambient temperatures ranging from 200-800 degree s C for 1 min. For each species, fruit weight and dimensions of fruit walls were measured to characterize insulation. A field experiment was performed to examine the survival of the serotinous seedbank of Hakea dactyloides in a bushfire. Ambient and internal fruit temperatures we re recorded during the fire. The viability of seeds from fruits expose d to the fire was tested and compared with an unburnt sample. Viabilit y of seeds within fruits exposed in the furnace varied according to sp ecies. Seeds of large fruited species such as Hakea constablei and Hak ea propinqua survived, whereas those oi the small fruited species Hake a teretifolia and H. dactyloides suffered significant mortality. The t hreshold temperature for death in four species was linearly related to the thickness of lower and lateral fruit walls, and to dry weight of fruits. Internal and external temperatures of fruits decreased with in creasing height on experimental H. dactyloides plants in the field. Hi gh levels of mortality (relative to the unburnt control) corresponded with fire temperature maxima greater than 400 degrees C (external) and greater than 60 degrees C (internal). In general, these temperatures occur when shrub crowns burn. A high risk of death for H. dactyloides, H. teretifolia and H. sericea seeds will result because fruits of the se species have thin walls.