Australian Natural Resources Atlas

Natural Resource Topics

The material below is an extract from the Australian Native Vegetation Assessment 2001 report. For ease of cross reference, figure, table and section references pertain to the chapter structure of this report. The Further Information section provides links to the Australian Native Vegetation Assessment 2001 report.

CASE STUDY: VEGETATION CHANGE AND INFORMATION TO SUPPORT REGIONAL VEGETATION MANAGEMENT

Role

This case study demonstrates the use of the National Vegetation Information System information on major vegetation groups and information hierarchy at Level IV to determine the changes in vegetation type and extent at a subregional level. Detail is also provided on the present land use and land tenure in the region as part of the information set necessary to underpin regional planning and management decisions.

Data sets

The Isaac - Comet Downs subregion has been selected as the subregion to demonstrate this application as it has a complete vegetation data set for both pre-European and present type and extent at 1:100,000 scale. The vegetation data sets are complemented by a complete coverage of land use in the subregion at 1:100,000 scale (Calvert et al. 2000). This congruence in scales of available data facilitates analysis.

Geology and vegetation

Isaac - Comet Downs is an extensive but diverse subregion in tropical western Queensland. It is an undulating subregion dominated by Tertiary and other Cainozoic deposits, with mid-Catena deposits being slightly more prominent. Tableland and dissected remnants of the upper Tertiary surface are widespread, supporting narrow-leaved Eucalyptus crebra woodlands on the earths of undulating plateaus, and bendee (Acacia catenulata) or lancewood (A. shirleyi) on the rocky hills and mesas. The lower parts of the Tertiary surface are dominated by brigalow (A. harpophylla) and Dawson gum (E. cambageana) communities on undulating clay or tenure contrast soils. These communities dominate the subregion. Alluvium is also prominent and the predominantly fine-textured soils of the alluvium carry brigalow or coolibah (E. coolabah) woodlands. Fine-grained Permian sediments are exposed due to long term weathering, giving rise to grasslands, open woodlands and areas of brigalow (Young et al. 1999).

Land use

The dominant land use in the subregion is livestock grazing with smaller areas of dryland agriculture and a large area of irrigated agriculture near Emerald (Figure 16). Two nature conservation areas are present in the subregion, Dipperu and Taunton National Parks (0.7% of the region). One large crown reserve, that is used for grazing and forestry, accounts for 2.8% of the region. The majority of the remnant vegetation is on freehold tenure. Overall the subregion, other than the Crown estate, is a mix in about equal proportions of freehold and leasehold tenure.

Native vegetation and change

Figures 17 and 18 show the pre-European and present vegetation types and extent of the vegetation mapped by major vegetation group. Table 9 presents the area of pre-European and present major vegetation groups.

The total area of the subregion is 27,011 km2 with 28% remaining vegetation of the pre-European extent. This diverse subregion had the fourth highest level of clearing between 1997 and 1999 (Sattler 2001).

The remaining native vegetation and areas cleared are presented in Table 10. The most impacted major vegetation groups, with less than 30% of the pre-European vegetation extent remaining, are:

All groups have restricted distributions in the subregion.

 
Figure 16. 1996/97 land use in the Isaac-Comet Downs subregion.

Figure 16. 1996/97 land use in the Isaac-Comet Downs subregion.
Figure 17. Pre-European vegetation Isaac-Comet Downs subregion.

Figure 17. Pre-European vegetation Isaac-Comet Downs subregion.
Figure 18. Major vegetation groups Isaac-Comet Downs subregion.
Figure 18. Major vegetation groups Isaac-Comet Downs subregion.

Fine scale detail on vegetation change

Because of the richness of the National Vegetation Information System database in this region, this analysis can be repeated at all levels of the hierarchy, providing the finer definition of vegetation types required for the development of management plans. This analysis is presented at Level IV (vegetation subformation) describing the floristic and structural characteristics for the upper- and mid-strata, and structure of the lower vegetation stratum.

Table 11 shows that 17 of the 51 (or 34%) of the subformations have less than 30% remaining native vegetation. These are primarily eucalypt and acacia woodlands with grassy understorey and eucalypt/acacia mixed open forests and low closed forests with shrubs and grassy understorey. Remnant management, connectivity between remnants and minimisation of any further clearing are key management responses for these vegetation types. As to how this is implemented in the subregion, which land areas, what interaction with tenure types is a task for the regional groups, armed with the knowledge that this assessment provides.

At the other end of the perspective, eleven (22%) of the subformations have more than 70% remaining vegetation. These are primarily eucalypt woodlands with acacia shrubs and grassy understorey, being the areas of lower site quality for agricultural and grazing development. Again, armed with this information, regional groups can develop vegetation management strategies.

Table 9. Pre-European and present major vegetation groups in the Isaac - Comet Downs subregion.

Major vegetation groups

Pre-European extent

Present extent

Area (ha)

Percent of total area

Area (ha)

Percent of total area

Cleared (primarily agricultural, grazing, urban and infrastructure)

-

-

1 955 790

72.41

Rainforest and vine thickets

34 386

1.27

4 860

0.18

Eucalypt open forests

1 731

0.06

397

0.01

Eucalypt woodlands

715 377

26.48

340 154

12.59

Acacia forests and woodlands

1 470 403

54.44

248 738

9.21

Callitris forests and woodlands

506

0.02

245

0.01

Casuarina forests and woodlands

23 429

0.87

8 651

0.32

Eucalypt open woodlands

380 877

14.10

125 895

4.66

Acacia open woodlands

1 704

0.06

0

0

Other shrublands

2 863

0.11

1 427

0.05

Tussock grasslands

68 541

2.54

12 629

0.47

Other grasslands, herblands, sedgelands and rushlands

1 162

0.04

774

0.03

Bare areas, claypans, sand, rock, salt lakes, lagoons, freshwater lakes
(increase in area includes the water storages, supplying water for the
high value irrigation development)

100

~ 0.00

1 518

0.06

Table 10. Changes to major vegetation groups in the Isaac - Comet Downs subregion since from pre-European settlement.

Major vegetation groups

Area cleared (ha)

Percent of pre-European
extent remaining

Rainforest and vine thickets

29 525

14.13

Eucalypt open forests

1 334

22.95

Eucalypt woodlands

375 223

47.54

Acacia forests and woodlands

1 221 665

16.91

Callitris forests and woodlands

260

48.51

Casuarina forests and woodlands

14 779

36.92

Eucalypt open woodlands

254 982

33.05

Acacia open woodlands

1 704

0

Other shrublands

1 436

49.83

Tussock grasslands

55 911

18.42

Other grasslands, herblands, sedgelands and rushlands

388

66.64

Table 11. Vegetation sub-formation in the Isaac - Comet Downs subregion.

Vegetation sub-formation (Level IV)

Pre-European
area (ha)

Present
area (ha)

Vegetation
cleared (ha)

Percent of
pre-European
extent remaining

Acacia low open woodlands/dichanthium tussock grassland

1 704

0

1 704

0

Eucalypt woodlands/coniferous woodlands/mixed unable to determine structural formation

468

0

468

0

Eucalypt woodlands/acacia tall sparse shrubland/grassy tussock grassland

16

1 916

-1 900

100

Coniferous woodlands/coniferous isolated shrubs/grassy tussock grassland

214

10

205

5

Acacia open forests/mixed open shrubland

467 518

45 973

421 545

10

Mixed low closed forests/mixed low woodlands

184

19

165

10

Acacia open forests/mixed tall open shrubland/grassy sparse tussock grassland

833 373

96 682

736 691

12

Mixed low closed forests/mixed tall open shrubland/grassy isolated tussock grasses

34 202

4 841

29 360

14

Eucalypt woodlands/mixed tall open shrubland/grassy open tussock grassland

10 559

1 561

8 998

15

Eucalypt woodlands/mixed tall open tussock grassland

16 611

2 457

14 154

15

Acacia open forests/mixed tall shrubland/grassy sparse tussock grassland

12 940

1 921

11 019

15

Acacia low isolated trees/astrebla and iseilema open tussock grassland

68 541

12 629

55 911

18

Eucalypt open forests/mixed tall open shrubland

1 616

353

1 263

22

Mixed woodlands

5 413

1 387

4 026

26

Eucalypt open woodlands/mixed sparse shrubland/spinifex sparse tussock grassland

147 066

38 275

108 791

26

Eucalypt woodlands/mixed tall isolated shrubs/grassy tussock grassland

14 757

3 876

10 881

26

Eucalypt woodlands/mixed open tussock grassland

7 422

2 067

5 355

28

Eucalypt open woodlands/mixed tall sparse shrublands

19 071

5 674

13 396

30

Eucalypt woodlands/mixed isolated shrubs/grassy open tussock grasslands

39 553

12 696

26 856

32

Eucalypt woodlands/mixed tall sparse shrublands

44 271

14 792

29 479

33

Eucalypt open woodlands/mixed tall sparse shrublands/grassy open tussock grasslands

78 362

28 517

49 845

36

Casuarina open woodlands

23 429

8 651

14 779

37

Eucalypt open woodlands/mixed low isolated shrubs/grassy open tussock grasslands

131 874

50 068

81 805

38

Eucalypt woodlands/mixed low tussock grasslands

123 629

47 204

76 425

38

Eucalypt mallee woodlands/spinifex woodlands

115

45

71

39

Eucalypt woodlands/mixed tall isolated shrubs/grassy open tussock grasslands

2 694

1 064

1 629

40

Melaleuca tall open shrublands

373

166

207

44

Eucalypt woodlands/grassy tussock grasslands

205 217

93 522

111 696

46

Eucalypt woodlands/acacia tall open shrublands/grassy open tussock grasslands

17 254

8 354

8 900

48

Eucalypt woodlands/acacia tall open shrublands

97 006

47 896

49 110

49

Eucalypt woodlands/melaleuca woodlands/mixed sparse rushlands

7 224

3 641

3 583

50

Mixed open shrublands

2 490

1 261

1 229

51

Eucalypt open woodlands

395

229

166

58

Acacia open forests/mixed low woodlands

36 245

21 627

14 618

60

Cyperaceae low open sedgelands

1 162

774

388

67

Eucalypt woodlands/dichanthium tussock grasslands

56

38

19

67

Acacia low woodlands/mixed sparse shrublands/grassy sparse tussock grasslands

30 893

20 943

9 950

68

Acacia woodlands/acacia tall sparse shrublands/grassy sparse tussock grasslands

88 919

61 235

27 684

69<

Acacia open forests/mixed tall open shrublands

514

357

157

69

Eucalypt woodlands

69 568

51 290

18 278

74

Eucalypt open woodlands/acacia open shrublands/grassy open tussock grasslands

4 110

3 132

978

76

Mixed woodlands/mixed tall open shrublands

901

708

193

79

Coniferous open forests/acacia sparse shrublands/grassy open tussock grasslands

291

235

56

81

Eucalypt woodlands/chenopod sparse shrublands/grassy open tussock grasslands

46 492

40 006

6 487

86

Eucalypt woodlands/grassy open tussock grasslands

1 635

1 423

212

87

Eucalypt woodlands/mixed shrublands/grassy sparse tussock grasslands

732

654

78

89

Eucalypt woodlands/mixed open cycadland

61

55

6

91

Eucalypt woodlands/acacia low sparse shrublands/grassy tussock grasslands

2 123

1 938

185

91

Eucalypt woodlands/acacia sparse shrublands/grassy open tussock grasslands

1 550

1 447

104

93

Eucalypt woodlands/acacia open shrublands/grassy open tussock grasslands

163

163

0

100

A negative value indicates an increase in extent of vegetation type

Key

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