Rj. Fensham et al., ESTIMATING CLEARANCE OF ACACIA-DOMINATED ECOSYSTEMS IN CENTRAL QUEENSLAND USING LAND-SYSTEM MAPPING DATA, Australian Journal of Botany, 46(2), 1998, pp. 305-319
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.