EFFECTS OF BAUXITE MINE RESTORATION OPERATIONS ON TOPSOIL SEED RESERVES IN THE JARRAH FOREST OF WESTERN-AUSTRALIA

We studied the effects of soil handling operations during bauxite mini ng and restoration on the numbers and depth distribution of seed store d in the surface soil of the jarrah forest. Germinable seed stores wer e determined in four sites of undisturbed forest, these same sites aft er clearing and burning of forest residues, in the soil immediately fo llowing the construction of topsoil stockpiles, in the respread topsoi l and then after deep ripping of the respread topsoil. Average density of germinable seed at four sites prior to disturbance was 352 m(-2). After clearing and burning, the seed store had decreased to a mean 74% of the original forest soil seed store density. When the topsoil was stockpiled prior to respreading, the seed content was further reduced to 31% in freshly constructed stockpiles and had declined to 13% after 10 months in the stockpiles. After ripping of the respread topsoil th e seed content was 16% of the original forest seed store density. In o ne site where the topsoil was directly stripped and respread with no p eriod of stockpiling but with a period of fallow, the seed store was 3 2% after respreading and then increased to 53% of the original forest store after ripping. This increase may have been caused by an underest imate of the reserves due to insufficient heating of the samples to br eak dormancy in fire-requiring species. In the forest topsoils seed wa s concentrated in the upper few centimeters of the soil profile, where as after the mining and restoration operations seed was evenly distrib uted throughout the returned soil profile to a depth of 20 cm. Small-s eeded annual species, which were common in the forest seed store, were more sensitive to the soil handing operations and declined to very lo w numbers, whereas hard-seeded plant species such as Acacia spp. were less affected by the soil handling operations. Implications for bauxit e mine revegetation operations include the recommendation that direct return of topsoil should be carried out wherever possible with a minim um delay between clearing, stripping, respreading, and ripping.