THE DISAPPEARING GRASSY BALDS OF THE BUNYA MOUNTAINS, SOUTH-EASTERN QUEENSLAND

The physical setting of 61 grassy balds on the Bunya Mountains in sout h-eastern Queensland was surveyed during 1995, and a further 73 balds were assessed from aerial photographs taken in 1951 and 1991. Balds we re analysed to search for consistent environmental patterns that may a ccount for their existence. There was little association between measu red environmental variables (including altitude, surface rock cover, s lope, landscape position, surrounding vegetation, bald area) and the o ccurrence of balds, although large balds have a weak association with steep slopes and relatively low rock cover. Grassland was on shallower soil than forest. Some, but not all balds were surrounded by rainfore st. No consistent relationship was evident for all measured balds surr ounded by eucalypt forest. About 26% of the area of balds existing in 1951 had been invaded by forest by 1991. The extent of the invasion wa s generally higher for balds surrounded by eucalypt forest than balds surrounded by eucalypt and rainforest or rainforest only, but showed l ittle relationship with other environmental variables. The invading tr ee species groups could not be associated with environmental variables . The lack of environmental correlation of bald location and size, and the rapid change in bald area is not supportive of hypotheses relatin g bald maintenance to intrinsic physical conditions. There is relative ly poor species diversity of Eucalyptus on the Bunya Mountains and thi s narrow ecological range of species may be a limitation on the coloni sation of the grasslands. Indirect evidence for the role of grazing an d fire as agents of bald maintenance are discussed, and it is conclude d, that fire, and not grazing, is likely to be a major influence.