IMPLICATIONS OF SEEDLING EMERGENCE TO SITE RESTORATION FOLLOWING BAUXITE MILLING IN WESTERN-AUSTRALIA

Seedling emergence of 12 selected northern jarrah (Eucalyptus marginat a Donn ex Smith) forest species were investigated to assist Alcoa of A ustralia Ltd. in maximizing the establishment of topsoil species in re -habilitated bauxite mining sites. The species, which encompassed a ra nge of seed weights (0.024 mg to 87 mg), plant families, seed-storage types, life forms, and germination requirements, were placed on the so il surface and at depths of 1, 2, 5, 10, and 25 cm under controlled co nditions in a glasshouse. Ability to emerge from deep burial was found to depend on feed size for species that annually release their seed t o the topsoil but not for species that store their seed on the plant. All selected species were capable of emerging from 2 cm depth of buria l, but eight of the 12 species were either unable to emerge from 5 cm or showed a significant reduction in emergence from 5 cm depth of buri al compared to optimally buried seed. This group included two small-se eded species, Stylidium calcaratum and Chamaescilla corymbosa; the maj or forest dominant, Eucalyptus marginata; the serotinous canopy-borne seed of Hakea amplexicaulis; and the wind-dispersed seed of Xanthorrho ea gracilis. A few seeds of the legume species Kennedia coccinea, Acac ia pulchella, and Bossiaea aquifolium established seedlings from depth s of 15 cm, Currently, Alcoa removes the upper 15 cm of topsoil separa tely from the underlying soil prior to the commencement of mining. Thi s topsoil is respread at a similar depth following mining as part of t he rehabilitation procedure. It is recommended that Alcoa continue to strip topsoil to a depth of 15 cm but investigate the option of respre ading topsoil onto rehabilitated pits at a shallower depth to maximize establishment via the sail seed bank.