ESTIMATING CLEARANCE OF ACACIA-DOMINATED ECOSYSTEMS IN CENTRAL QUEENSLAND USING LAND-SYSTEM MAPPING DATA

Preferential clearance of productive Acacia-dominated ecosystems was d etermined using digital land-system mapping and a 1994-1995 native veg etation remnant coverage from central Queensland. The previously mappe d land systems are composed of complexes of land units, covering a ran ge of productive potentials that are not individually mapped but defin ed according to their proportions within the land systems. Some land u nits were grouped into 11 'Acacia ecosystems' composed of unique combi nations of geology and vegetation dominated by brigalow (Acacia harpop hylla F.Muell. ex Benth.), gidgee (A. cambagei R.T.Baker) or blackwood (A. argyrodendron Domin). Calculation of the remnant area of these Ac acia ecosystems, assuming equal proportions of vegetation clearance of the land unit components within the land-system complexes (equal prop ortion calculation), was compared with a more accurate calculation bas ed on interpretation of aerial photography (aerial-photograph calculat ion) data. The aerial photograph calculation of remnant area was 44% o f the equal proportion calculation for brigalow on Tertiary clay and t he ratio between these calculations was greater than 100% for only one Acacia ecosystem of relatively low production potential. The proporti on of the remnant Acacia ecosystems relative to less productive ecosys tems on tenures assigned to production (leasehold and freehold) was co nsistently lower than on other tenures. The use of mapping consisting of-composite ecosystems with various production potentials for area-ba sed assessment of vegetation clearance will overestimate the remnant a reas of the relatively productive types unless a procedure such as tha t outlined here is used to correct for preferential clearance. This st udy provides near-complete and accurate data on the 1994-1995 status o f Acacia ecosystems in central Queensland. Relative to their original area, values ranged from 6.8% for brigalow on Tertiary clay to 37.6% f or gidgee-blackwood on alluvium.