Australian Native Vegetation Assessment 2001
Maria Cofinas, Colin Creighton
National Land and Water Resources Audit, 2001
ISBN 0 642 37128 8
Fragmentation of Australia's native vegetation: applications
Dryland rural landscape between Gunning and Crookwell, NSW
Photo: Rosemary Purdie
It is important to understand the nature of the patches or fragments of native vegetation remaining in cleared landscapes. This is a key element in the maintenance of ecosystem health, landscape function and the diversity of species within ecosystems.
Fragmented patches of vegetation may be the only remaining examples of particular vegetation groups or ecosystems in a region, contributing to the healthy functioning of that system and providing a source of material for any re-vegetation or restoration activities.
Key findings
The analysis highlights poorly functioning landscapes, where native vegetation is reduced to relic patches that are clearly under threat. The lack of viability of these small remnants provides a series of challenges for land managers. Fragments become increasingly more difficult to manage where the larger proportion of the total native vegetation is fragmented.
Table 26 and Figure 30 summarise the number of subregions found within each fragmentation index. Forty-two of Australia's subregions have less than 30% of native vegetation remaining and 22 are very highly or highly fragmented. Detailed information about these subregions is presented in Tables 27 and 28. These subregions occur in south-western Western Australia, south-eastern South Australia, central and western Victoria, the New England Tablelands bioregion in New South Wales and southern and central eastern Queensland.
Additional important information to consider in vegetation fragmentation is the number of patches of fragmented vegetation, their shape and size. An analysis of the number of fragmented patches in each subregion has been undertaken and presented in Tables 27 and 28 for the 22 most fragmented subregions. Figure 31 presents information on the number of fragmented native vegetation patches within a subregion.
The Avon Wheatbelt P2 subregion is an example of a stressed landscape. 8.5% of the native vegetation remains, 84.5% of this vegetation is fragmented and these fragments occur in 13 438 patches. Management of these remnants is likely to be costly and will require a high level of planning and priority setting.
| Remnant class | Plant isolation index class 1 >60% of total vegetation fragments |
Plant isolation index class 2 30-60% of total vegetation fragments |
Plant isolation index class 3 30-10% of total vegetation fragments |
Plant isolation index class 4 <10% of total vegetation fragments |
Number of subregions in each remnant class |
|---|---|---|---|---|---|
| 1 < 30% | 4 | 18 | 18 | 2 | 42 |
| 2 30-70% | 0 | 0 | 28 | 51 | 79 |
| 3 >70% | 0 | 0 | 0 | 233 | 233 |
| Number of subregions in each plant isolation index class | 4 | 18 | 46 | 286 |
| Subregion | Subregion area (ha) | Area of native vegetation | Percent native vegetation remaining | Remnant class | Area fragmented native vegetation < 1000 ha | Percent fragmented native vegetation in subregion | Plant isolation index class | Number of patches |
|---|---|---|---|---|---|---|---|---|
| Avon Wheatbelt P2 | 2,992,960 | 254,948 | 8.5 | 1 | 215,368 | 84.5 | 1 | 13,438 |
| Tara Downs | 449,396 | 28,388 | 6.3 | 1 | 18,608 | 65.5 | 1 | 775 |
| Fleurieu | 370,668 | 38,140 | 10.3 | 1 | 32,420 | 85.0 | 1 | 723 |
| Mount Gambier | 84,228 | 4,832 | 5.7 | 1 | 4,752 | 98.3 | 1 | 47 |
| Subregion | Subregion area (ha) | Area of native vegetation | Percent native vegetation remaining | Remnant class | Area fragmented native vegetation < 1000 ha | Percent fragmented native vegetation in subregion | Plant isolation index class | Number of patches |
|---|---|---|---|---|---|---|---|---|
| Avon Wheatbelt P1 | 6,524,180 | 1,129,720 | 17.3 | 1 | 409,228 | 36.2 | 2 | 18,633 |
| Victorian Riverina (VR) | 1,782,040 | 91,604 | 5.1 | 1 | 42,916 | 46.8 | 2 | 2,552 |
| Eastern Darling Downs | 1,639,340 | 253,884 | 15.5 | 1 | 104,032 | 41.0 | 2 | 2,200 |
| Wimmera (WI) | 1,699,344 | 130,636 | 7.7 | 1 | 49,192 | 37.7 | 2 | 1,617 |
| Moonie R. - Commoron Creek Floodout | 803,020 | 137,516 | 17.1 | 1 | 45,448 | 33.0 | 2 | 1,370 |
| Lucindale | 741,244 | 116,064 | 15.7 | 1 | 66,400 | 57.2 | 2 | 1,346 |
| Broughton | 1,032,948 | 123,148 | 11.9 | 1 | 37,812 | 30.7 | 2 | 1,235 |
| Southern Yorke | 436,436 | 74,916 | 17.2 | 1 | 23,528 | 31.4 | 2 | 1,053 |
| Taroom Downs | 644,068 | 52,880 | 8.2 | 1 | 30,196 | 57.1 | 2 | 900 |
| Warrnambool Plain (WP) | 234,380 | 31,084 | 13.3 | 1 | 13,544 | 43.6 | 2 | 785 |
| Mount Lofty Ranges | 300,352 | 47,132 | 15.7 | 1 | 15,940 | 33.8 | 2 | 548 |
| Glenn Innes-Guyra Basalts | 277,324 | 32,236 | 11.6 | 1 | 15,240 | 47.3 | 2 | 494 |
| Inverell Basalts | 230,992 | 35,068 | 15.2 | 1 | 17,596 | 50.2 | 2 | 303 |
| Callide Creek Downs | 298,160 | 33,000 | 11.1 | 1 | 12,028 | 36.4 | 2 | 268 |
| Deepwater Downs | 97,756 | 17,332 | 17.7 | 1 | 8,156 | 47.1 | 2 | 265 |
| Dulacca Downs | 162,288 | 30,612 | 18.9 | 1 | 10,812 | 35.3 | 2 | 241 |
| Yarrowyck-Kentucky Downs | 65,076 | 13,536 | 20.8 | 1 | 4,560 | 33.7 | 2 | 128 |
Methods
The analysis used one of many possible methods to highlight IBRA subregions:
- that have been heavily impacted by the broad clearing of native vegetation across the landscape; and
- where native vegetation only exists today as a series of small isolated remnants.
The contribution of native vegetation fragments in patch sizes smaller than 1000 ha as a proportion of the total area of native vegetation remaining in each IBRA subregion were analysed and categorised in classes. The 1000 ha figure was chosen as most appropriate for an Australia-wide overview. In highly fragmented environments at a regional level, a lower threshold would be appropriate.
The series of classes developed to simplify interpretation were based on:
- the percentage of remaining native vegetation in the subregion (Table 29, Figure 21);
- the percentage of the total area of native vegetation in fragments smaller than 1000 ha (plant isolation index) (Table 30 and Figure 32); and
- an amalgamation of these two classes, called the fragmentation index, which enables a comparison of the remaining vegetation in a region and how fragmented that vegetation is (Table 31, Figure 30).
| Percent native vegetation remaining (%) | Remnant Class |
|---|---|
| <30 | 1 |
| 70-30 | 2 |
| >70 | 3 |
| Percent of total area of native vegetation in fragments < 1000 ha | Plant Isolation Class |
|---|---|
| >60 | 1 |
| 30-60 | 2 |
| 10-30 | 3 |
| <10 | 4 |
| Remnant class | Plant isolation class 1 | Plant isolation class 2 | Plant isolation class 3 | Plant isolation class 4 |
|---|---|---|---|---|
| 1 | 1-1 subregions little intact vegetation very high fragmentation | 1-2 subregions little intact vegetation high fragmentation | 1-3 subregions little intact vegetation moderate fragmentation | 1-4 subregions little intact vegetation minor fragmentation |
| 2 | 2-1 subregions some intact vegetation very high fragmentation | 2-2 subregions some intact vegetation high fragmentation | 2-3 subregions some intact vegetation moderate fragmentation | 2-4 subregions some intact vegetation minor fragmentation |
| 3 | 3-1 subregions Intact vegetation very high fragmentation | 3-2 subregions intact vegetation high fragmentation | 3-3 subregions intact vegetation moderate fragmentation | 3-4 subregions intact vegetation minor fragmentation |
Applications
To demonstrate the application of such analysis for a bioregion and the variability in remaining native vegetation within a bioregion, information is presented on the Eyre Yorke Block bioregion in South Australia. At the bioregional level, 35% of native vegetation remains and the bioregion therefore falls into the third remnant class (30-70% remaining).
This bioregion contains five subregions, demonstrating considerable variation in fragmentation (e.g. two subregions have less than 30% of native vegetation remaining, are moderately to highly fragmented and contained more than 1000 patches of less than 1000 ha) (Table 32, Figure 33).
Management strategies for biodiversity conservation and the activities required to manage remnants in each subregion will vary according to this analysis and the threatening processes occurring in these regions.
| Subregion | Subregion area (ha) | Area of native vegetation(ha) | Percent native vegetation remaining | Remnant class | Area fragmented native vegetation <1000 ha | Percent fragmented native vegetation in subregion | Plant isolation index class | Subregional fragmentation index class | Number of patches |
|---|---|---|---|---|---|---|---|---|---|
| Southern Yorke | 436 436 | 74 916 | 17.2 | 1 | 23 528 | 31.4 | 2 | 1-2 | 1 053 |
| St Vincent | 1 085 804 | 99 016 | 9.1 | 1 | 23 520 | 23.8 | 3 | 1-3 | 1 219 |
| Eyre Hills | 1 171 684 | 369 572 | 31.5 | 2 | 67 984 | 18.4 | 3 | 2-3 | 2 676 |
| Talia | 1 089 072 | 689 876 | 63.3 | 2 | 36 108 | 5.2 | 4 | 2-4 | 1 167 |
| Eyre Mallee | 2 295 544 | 887 620 | 38.7 | 2 | 74 316 | 8.4 | 4 | 2-4 | 3 013 |
Limitations
This analysis presents one method to assess the level of fragmentation. There are a wide variety of methods available to estimate fragmentation, depending on the requirements of the user. Cut-offs for classes in this analysis can be modified to assess a range of scenarios. The interpretation of patch size is dependent on the scale of the mapping and the minimum mapping area.
In order to complete the information required by land managers, the results are best used in conjunction with the data on the extent of native vegetation for each subregion (e.g. in some subregions, the only significant areas of native vegetation remaining are found in either protected areas or crown reserves and the contribution of other fragments to the total area of vegetation remaining in such regions is relatively small).
Where possible, regional managers need to intersect this analysis of fragmentation with data on tenure and land use. This provides for a fuller understanding of management opportunities and allows for the development of practical priority management strategies.
Tailings dam at Weipa, Qld
Photo: Maria Cofinas
Disturbance of native vegetation
In addition to broad-scale clearing, native vegetation is affected by additional pressures, impacting on its internal integrity and long-term survival in the landscape.
Isolated vegetation fragments are even more susceptible to these pressures as their boundaries are exposed to disturbances (e.g. weed invasion) and land use practices (e.g. grazing of the understorey).
Information on these disturbances and impacts on the native vegetation:
- are valuable in assessing the status of these communities; and
- can help plan for and change land uses to minimise the impacts of disturbance and toensure these remnant vegetation patches are viable.
The mapping of some disturbances which can be distinguished through aerial photography has been undertaken in parts of south-west Western Australia as a pilot project. In addition to mapping the extent of remnant vegetation, it demonstrates the level of additional disturbances within vegetation fragments.
Additional information was collected on:
- mining and infrastructure disturbances;
- the potential risk to native vegetation from rising water tables and associated salinisation; and
- the potential risk to each vegetation type as a consequence of clearing at the broad landscape level.
Further information is available in the final project report (Beeston et al. 2001).
The mapping of disturbances within vegetation is not available across Australia. Information is only available for small areas and has not been consistently collected. The draft framework for the assessment and monitoring of native vegetation condition (Environment Australia 2001) attempts to provide a framework within which to collect information on an attribute basis which can then be aggregated into assessments of condition depending on the user requirements.
The landscape health assessment (NLWRA 2001c) has classified a range of disturbances into an assessment of health on a subregional basis, providing a region-wide context of landscape health.
Case Study: Vegetation Management, Recent Vegetation Change, Queensland
The extent of Australia's vegetation continues to change through selective species removal, planting, thinning, regrowth and clearing. In some States and Territories, rapid rates of vegetation clearing are affecting large areas of land that have already been highly cleared and fragmented or are in marginally productive areas. Information on native vegetation to support vegetation management in these jurisdictions requires more regular updating to ensure that:
- the rates of change and trends can be monitored;
- the types of vegetation being cleared are documented; and
- vegetation management plans are relevant.
This case study demonstrates the use of National Vegetation Information System data for Queensland with a baseline of pre-European and 1995 vegetation types and extent and information on areas cleared since 1995 to assess changes in vegetation extent over time. The information on the 1997 extent of vegetation was obtained from the Queensland Herbarium and has been derived from the Statewide Landcover and Tree Study (SLATS) data and the Queensland Herbarium remnant vegetation data for the State.
A record and analysis of these changes and trends in native vegetation type and extent are in themselves an indication of the condition of native vegetation in the landscape.
Approximately 627 000 ha of vegetation was cleared between 1995 and 1997 in the study area (Figure 34), equivalent to approximately 272 000 ha each year.
The majority of the vegetation cleared between 1995 and 1997 was eucalypt woodlands (47%, 293 810 ha), acacia forests and woodlands (25%, 156 987 ha) and eucalypt open woodlands (13%, 80 210 ha). The largest change relative to the 1995 extent was for casuarina forests and woodlands where 7559 ha was cleared from 240 274 ha in 1995, accounting for 3.2% of the major vegetation group.
An assessment of change within two subregions in the study area is presented.
Changes in vegetation extent in the Inglewood Sandstones subregion and Moonie River-Commoron Creek Floodout subregion
Information is presented on:
- the pre-European major vegetation groups and extent;
- the present major vegetation groups and extent; and
- land clearing between 1995 and 1997, vegetation types and extent affected.
This information highlights the changes and pressures on these subregions. Only the Queensland component of the Inglewood Sandstones subregion has been assessed as limited information is available on the New South Wales component.
Inglewood Sandstones subregion
Fifty-nine percent of the original vegetation cover remains in this subregion. The pre-European and 1995 major vegetation groups are shown in Figures 35 and 36; change from pre-European extent is shown in Table 33. Less than 30% of the acacia forests and woodlands, casuarina forests and woodlands and tussock grasslands remain in the subregion. Eucalypt woodlands and acacia forests and woodlands have had the greatest area of vegetation cleared since pre-European settlement even though 66% of the original extent of eucalypt woodlands remains.
| Pre-European | Present (1995) |
Cleared (pre-European to present 1995) |
||||
|---|---|---|---|---|---|---|
| Major vegetation group | Area (ha) | Percent total area of subregion | Area (ha) | Percent total area of subregion | Area (ha) | Percent remaining of pre-European area |
| Largely modified/cleared | n/a | n/a | 503,076 | 40.52 | n/a | n/a |
| Eucalypt open forests | 766 | 0.06 | 520 | 0.04 | 246 | 67.85 |
| Eucalypt woodlands | 943 485 | 75.99 | 620,478 | 49.98 | 323,007 | 65.76 |
| Acacia forests and woodlands | 118,250 | 9.52 | 9,305 | 0.75 | 108,945 | 7.87 |
| Casuarina forests and woodlands | 11,642 | 0.94 | 677 | 0.05 | 10,965 | 5.81 |
| Eucalypt open woodlands | 160,760 | 12.95 | 102,507 | 8.26 | 58,253 | 63.76 |
| Other shrublands | 27 | 0.00 | 27 | 0.00 | 0 | 100.00 |
| Heath | 4,724 | 0.38 | 4,192 | 0.34 | 532 | 88.74 |
| Tussock grasslands | 949 | 0.08 | 1 | 0.00 | 948 | 0.14 |
| Other grasslands group | 958 | 0.08 | 633 | 0.05 | 324 | 66.13 |
| Mangrove group | 0 | 0.00 | 144 | 0.01 | n/a | n/a |
The vegetation changes from 1995 to 1997 are presented in Table 34 and Figure 36 (where information was available).
Approximately 13 750 ha were cleared, mainly eucalypt woodlands (84%), eucalypt open woodlands, (11%) and acacia forests and woodlands, (4%). Minor types cleared included heath and casuarina forests and woodlands.
Large areas of eucalypt woodlands and the major vegetation groups with less than 30% remaining vegetation continue to be cleared.
Figure 34. Vegetation cleared between 1995 and 1997 in the Brigalow Belt region.
| Major vegetation group | Area cleared 1995-1997 (ha) |
|---|---|
| Eucalypt woodlands | 11,609 |
| Acacia forests and woodlands | 542 |
| Casuarina forests and woodlands | 11 |
| Eucalypt open woodlands | 1,547 |
| Heath | 37 |
| Other grasslands group | 2 |
Moonie River-Commoron Creek Floodout subregion
Eighteen percent of the original vegetation cover of this subregion remains. The pre-European and 1995 major vegetation groups are shown in Figures 35 and 36; change from pre-European extent is shown in Table 35. Less than 30% of the acacia forests and woodlands and casuarina forests and woodlands remain in the subregion. Acacia forests and woodlands and casuarina forests and woodlands have had the greatest area of vegetation cleared since pre-European settlement followed closely by eucalypt woodlands.
| Pre-European | Present (1995) | Cleared (pre-European to present 1995) | ||||
|---|---|---|---|---|---|---|
| Major vegetation group | Area (ha) | Percent total area of subregion | Area (ha) | Percent total area of subregion | Area (ha) | Percent remaining of pre-European area |
| Largely modified/cleared | n/a | n/a | 660 049 | 82.20 | n/a | n/a |
| Eucalypt woodlands | 212,812 | 26.50 | 72,765 | 9.06 | 140,048 | 34.19 |
| Acacia forests and woodlands | 263,788 | 32.85 | 14 342 | 1.79 | 249,447 | 5.44 |
| Casuarina forests and woodlands | 255,518 | 31.82 | 15,661 | 1.95 | 239,857 | 6.13 |
| Other forests and woodlands | 160 | 0.02 | 137 | 0.02 | 23 | 85.38 |
| Eucalypt open woodlands | 69,263 | 8.63 | 38,271 | 4.77 | 30,992 | 55.25 |
| Other shrublands | 1,381 | 0.17 | 1,381 | 0.17 | 0 | 99.99 |
| Other grasslands etc | 31 | 0.00 | 30 | 0.00 | 1 | 95.22 |
| Mangrove etc | 0 | 0.00 | 322 | 0.04 | n/a | n/a |
The vegetation changes from 1995 to 1997 are presented in Table 36 and Figure 36 (where information was available).
Approximately 880 ha were cleared, equivalent to approximately 380 ha each year. The majority of the vegetation cleared was eucalypt woodlands, (57% or 500 ha), acacia forests and woodlands (33% or 291 ha), casuarina forests and woodlands(6% or 51 ha) and eucalypt open woodlands (4% or 39 ha).
This subregion has smaller areas of vegetation being cleared but has only 18% of native vegetation remaining. Casuarina forests and woodlands have less than 30% of their original extent remaining with an additional 51 ha cleared between 1995 and 1997.
| Major vegetation group | Area cleared 1995-1997 (ha) |
|---|---|
| Eucalypt woodlands | 500 |
| Acacia forests and woodlands | 291 |
| Casuarina forests and woodlands | 51 |
| Eucalypt open woodlands | 39 |
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