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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.

Vegetation Assessment 2001 - Fragmentation of Australia's native vegetation: applications

Fragmentation of Australia's native vegetation: applications 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.

Dryland rural landscape between Gunning and Crookwell, NSW © Rosemary Purdie

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.

Table 26. Number of subregions in fragmentation classes.

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

Figure 30. Fragmentation classes in subregions.

Figure 31. Number of vegetation patches in fragmented vegetation in subregions.

Table 27. Subregions in fragmentation index class 1-1.

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

Table 28. Subregions in fragmentation index class 1-2.

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

Figure 32. Plant isolation index in subregions.

Figure 33. Fragmentation index classes in the Eyre Yorke Block bioregion.

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).

Table 29. Remnant native vegetation classes.

Percent native vegetation remaining (%)	Remnant Class
<30	1
70-30	2
>70	3

Table 30. Plant isolation index classes.

Percent of total area of native vegetation in fragments < 1000 ha	Plant Isolation Class
>60	1
30-60	2
10-30	3
<10	4

Table 31. Fragmentation index classes.

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 subregionsIntact vegetation very high fragmentation	3-2 subregionsintact vegetation high fragmentation	3-3 subregionsintact vegetation moderate fragmentation	3-4 subregionsintact 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.

Table 32. Remnant native vegetation in the Eyre Yorke Block bioregion subregions.

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.