ECOLOGICAL ASPECTS OF SOIL SEED-BANKS IN RELATION TO BAUXITE MINING .2. 12-YEAR-OLD REHABILITATED MINES

Germinable seed stores were estimated for 12-13 year old rehabilitatio n sites in the jarrah forest over two seasons (autumn and spring). Col lected soils were subjected to combinations of smoking and heating tre atments before the germination procedure was commenced. The mean topso il seed reserve to a depth of 10 cm was 1938 seeds m(-2). Of this tota l reserve, more than 80% was found in the upper 5 cm of soil. The tops oil seed reserve of these rehabilitation areas was almost seven times that of the adjacent native jarrah forest (292 seeds m(-2); Ward et al . 1997). There was a seasonal effect with autumn-collected soils havin g significantly more germinable seeds (2723 seeds m(-2)) than soils co llected in spring (1153 seeds m(-2)). More than half (53%) of the tops oil seed reserve in rehabilitated areas was composed of annual weed sp ecies, dominated by Aira caryophyllea, Centaurium erythraea and the na tive Levenhookia pusilla. Of the total of 70 species identified, 13 sp ecies showed significantly higher germination in smoked trays while 11 species exhibited significantly higher germination in heated trays. S pecies responding to the smoking treatment tended to be annuals while those responding to the heating treatment were typically legume shrub species. Examination of the topsoil seed reserve and the vegetation pr esent in these areas showed that while the species composition was sim ilar between the seed store and the vegetation, there was a large diff erence in densities, with species occurring at much higher densities i n the topsoil than in the vegetation. However, the rankings of species were significantly correlated between the topsoil seed reserve and th e vegetation present at the site. The implications of these results to prescribed burning of these rehabilitated areas is discussed.