Landscape Health In Australia
A rapid assessment of the relative condition of Australia's bioregions and subregions
Gethin Morgan
Environment Australia, 2000
ISBN 0 642 37119 9
3. Synthesis: landscape stress
Deriving stress classes
The grouping of the 354 subregions into intensive and extensive use zones reflects continental scale difference in climate and land use potential. Any synthesis of the information collated for this project must assess the two zones separately. Subregions in the intensive use zone have a history of land use intensification, including clearing, pasture development, cropping and plantation establishment. Assessment of general landscape health in this zone must separate the cleared and developed areas from the undeveloped areas. The biodiversity component of landscape health in the intensive use zone relates largely to the extent, distribution and condition of the remaining native vegetation, and these reflect also in the health of the subregion as a whole. In the extensive use zone native vegetation is essentially continuous at the scale of this study. Biodiversity and landscape health are inextricably entwined across each subregion.
The particular condition and trend attributes used to provide a synthesis of landscape health were nominated by the project working group and the resulting measure called 'landscape stress'. The attributes used to derive these landscape stress ratings for the intensive use zone and the extensive use zone are shown in Table 3.
Where subregions crossed jurisdictional boundaries and value of the attribute differed between jurisdictions, a single class was derived for the subregion that reflected the relative extent of the subregion in each jurisdiction.
Intensive use zone
The decision table used to determine landscape stress is shown in Figure 81. The initial stress rating was based on the relative classes of vegetation extent, fragmentation, condition and percentage of subregional ecosystems threatened. These attributes were considered by the working group to be (within the attributes available) the primary determinants of remaining biodiversity. Other attributes were considered by the working group to reflect the major threatening processes on remaining biodiversity and were simplified to a high or low rating, which increased the stress rating by one in the case of the former, or had no impact, in the case of the latter. The different attributes were unweighted. Stress ratings for subregions of the intensive use zone are presented in Appendix 3.
| Intensive use zone | Extensive use zone |
|---|---|
| Current extent of native vegetation | Percent of subregion with least impact from total grazing pressures |
| Connectivity of native vegetation | |
| Percent of native vegetation in land tenures associated with conservative land use practices. | Percent of native vegetation in land tenures associated with conservative land use practices. |
| Percent of ecosystems threatened | No equivalent attribute |
| Percent of native vegetation with high dryland salinity | No equivalent attribute |
| Density of weeds | Density of weeds |
| Density of feral animals | Density of feral animals |
| Number of threatened species | Number of threatened species |
Figure 81. Decision tree table for determining an intensive use zone subregion landscape stress class. Attributes are hierarchical. Those used earlier in the assessment are considered more important and have a greater influence in determining the final landscape stress class.
Values recorded for condition attributes assessed, sequentially determine the interim stresss class of a subregion. Poor condition attribute scores move the interim stress class to a higher stress class and condition attribute scores indicative of good landscape health can reduce the interim landscape stress class.
| c1 extent of native vegetation class | Interim stress class 1 | c4 continuity in native vegetation class | Interim stress class 2 | c3b conservative land use class | Interim stress class 3 | c8a threatened ecosystems class | Interim stress class 4 |
|---|---|---|---|---|---|---|---|
| 1 | 3 | 1,2 | 3 | 1,2,3 | 3 | 1,2 | 2 |
| 3,4,5,6 | 3 | ||||||
| 2 | 4 | 1 | 3 | 1,2,3 | 3 | 1,2 | 2 |
| 3,4,5,6 | 3 | ||||||
| 2,3,4 | 4 | 1 | 3 | 1,2 | 2 | ||
| 3,4,5,6 | 3 | ||||||
| 2 | 4 | 1,2 | 3 | ||||
| 3,4 | 4 | ||||||
| 5,6 | 5 | ||||||
| 3,4,5,6 | 5 | 1,2 | 4 | ||||
| 3,4,5,6 | 5 | ||||||
| 3 | 5 | 2 | 4 | 1,2 | 4 | 1,2,3 | 4 |
| 4,5,6 | 5 | ||||||
| 3,4,5,6 | 5 | 1,2,3 | 4 | ||||
| 4,5,6 | 5 | ||||||
| 3,4 | 5 | 1 | 4 | 1,2,3 | 4 | ||
| 4,5,6 | 5 | ||||||
| 2,3 | 5 | 1,2,3 | 4 | ||||
| 4,5,6 | 5 | ||||||
| 4,5,6 | 6 | 1,2,3 | 5 | ||||
| 4,5,6 | 6 | ||||||
| 4,5,6 | 6 | 2 | 5 | 1 | 4 | 1,2,3 | 4 |
| 4,5,6 | 5 | ||||||
| 2,3 | 5 | 1,2,3 | 4 | ||||
| 4,5,6 | 5 | ||||||
| 4,5,6 | 6 | 1,2,3 | 5 | ||||
| 4,5,6 | 6 | ||||||
| 3,4,5 | 6 | 1,2 | 5 | 1,2 | 4 | ||
| 3,4 | 5 | ||||||
| 5,6 | 6 | ||||||
| 3,4,5,6 | 6 |
1,2,3 |
5 |
||||
4,5,6 |
6 |
| c7a weed density summary class | Interim stress class 5 | c5b salinity risk/hazard in native vegetation summary class | Interim stress class 6 | c7a feral vertebrate density summary class | Interim stress class 7 | c8bc number threatened species summary class | Intensive use zone landscape stress class |
|---|---|---|---|---|---|---|---|
| high density, increase interim stress class 4 by one | high risk or hazard, increase interim stress class 5 by one | high density, increase interim stress class 6 by one, interim stress class 7 by one | high number, increase interim stress class 7 by one | ||||
| low density, no change to interim stress class 4 | low risk or hazard, no change to interim stress class 5 | low density, no change to interim stress class 6 | low numbver, no change to interim stress class 7 | ||||
Extensive use zone
The decision table used to determine landscape stress in the extensive use zone is shown in Figure 82. Initial stress ratings were based on the relative classes of the percent of a subregion within grazing impact classes and the percent of a subregion's native vegetation in land tenures associated with conservative land uses. These attributes broadly indicate the relative grazing intensities and consequent likely impacts on biodiversity across subregions. They were considered by the working group to be primary determinants of remaining biodiversity. Other attributes including distribution and density of introduced weed species, distribution and density of introduced vertebrate species, threatened plants and threatened vertebrate animals were considered by the working group to reflect the major threatening processes on remaining biodiversity. They were simplified to a high or low rating, which increased the stress rating by one in the case of the former, or had no impact, in the case of the latter. The different attributes were unweighted. Extensive use zone stress ratings are shown in Appendix 3.
Figure 82. Decision tree table for determining an extensive use zone subregion landscape stress class. Attributes are hierarchical. Those used earlier in the assessment are considered more important and have a greater influence in determining the final landscape stress class.
Values recorded for condition attributes assessed, sequentially determine the interim stresss class of a subregion. Poor condition attribute scores move the interim stress class to a higher stress class and condition attribute scores indicative of good landscape health can reduce the interim landscape stress class.
| c3a least grazing impact class | Interim stress class 1 | c3b conservative land use | Interim stress class 2 | c7a weed density summary class | Interim stress class 3 | c7b feral vertebrate density summary class | Interim stress class 4 | c8bc number threatened species summary * class | Extensive use zone landscape stress class |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 1,2,3,4,5,6 | 2 | high density, increase stress class 2 by one | high density, increase interim stress class 3 by one | high numbers, increase interim stress class 4 by one | |||
| 2 | 3 | 1 | 2 | high density, increase stress class 2 by one | high density, increase interim stress class 3 by one | high numbers, increase interim stress class 4 by one | |||
| 2 | 3 | ||||||||
| 3,4,5,6 | 4 | ||||||||
| 3 | 4 | 1,2 | 3 | low denisty, no change to interim stress class 2 | low density, no change to interim stress class 3 | low numbers, no change to interim stress class 4 | |||
| 3,4,5,6 | 4 | ||||||||
| 4,5,6 | 5 | 1,2 | 4 | ||||||
| 3,4,5 | 5 |
Note: * Summary class data used in the description tables for landscape stress classification is listed in the Australian Natural Resource Data Library but is not presented in Appendix 3 due to coverage and scale limitations at the subregional level.
Continental landscape stress
As the landscape stress ratings were derived for intensive and extensive use zones using slightly different information, landscape stress ratings derived for one cannot be directly compared with those derived for the other. To create a single continental assessment of landscape stress across the two zones, approximate equivalence between the five stress classes used in the extensive use zone and the six used in the intensive use zone wa assumed. The zone equivalence of these six continental stress classes, are shown in Table 4.
The intensive use zone contains the most degraded landscapes37 subregions in the two highest landscape stress ratings having less than 30% of the original extent of their native vegetation remaining. This occurs mainly as small and discontinuous remnants, only a small proportion of which are managed conservatively. More than two-thirds of the ecosystems representative of these subregions have lost more than 70% of their original extent and are now at risk of collapse or total loss. There are no subregions in the extensive use zone that are in such poor health.
Subregions in the intensive use zone in the third highest landscape stress class usually have between 30% and 50% of the original extent of their native vegetation remaining, and although this is relatively fragmented, it has been cleared in such a way that moderate areas of most of the original ecosystems remain. The overall health of ecosystems in these subregions approximates that of the most heavily used subregions of the extensive use zone (those in the two highest extensive use zone stress classes), where although there has been little or no clearing, more than 70% of their area typically has a history of relatively high total grazing pressures. Decreasing grazing pressures in subregions in the remaining extensive use zone stress classes roughly correspond to decreasing land use pressures in the remaining intensive use zone stress classes.
The results of collating the intensive use zone and extensive use zone stress ratings into the continental stress rating are summarised in Figures 83 and 84.
| Continental stress classes | Intensive use zone stress classes | Extensive use zone stress classes |
|---|---|---|
| 1: most stressed | 1 | - |
| 2 | 2 | - |
| 3 | 3 | 1,2 |
| 4 | 4 | 3 |
| 5 | 5 | 4 |
| 6: least stressed | 6 | 5 |
- 37 subregions (10.5%) are in the two highest stress classes with 17 in the highest stress class. The most stressed subregions are concentrated in the south east, with south-eastern South Australia and most of Victoria falling into the highest class. The Avon Wheatbelt in south-west Western Australia also falls into this class, as do the Tasmanian Midlands and two subregions in southern Queensland, the West Balone Plains in the Mulga Lands bioregion within the Murray - Darling Basin and the Morton Basin within the South East Queensland bioregion. Two bioregions in tropical Queenslandthe Brigalow Belt and the Wet Tropicshave subregions within the second highest stress class. In New South Wales the Upper Slopes of the South Western Slopes bioregion, and the adjacent South Eastern Highlands also fall into the highest stress class. These are the subregions where little natural vegetation remains, and the vegetation that does remain is under increasing stress from a variety of threatening processes.
Within these subregions landscape scale responses are needed to prevent further decline and to maximise the protection of landscape health and remaining subregional biodiversity. Highest priority should be given to protecting and managing the remaining native vegetation and to revegetation strategies that concentrate on restoring or enhancing connectivity and increasing the area of the more significant remnants.
- 90 subregions (25.4%) fall into the third highest stress class, including the 61 most stressed subregions of the extensive use zone.
In the intensive use zone these subregions occur where natural vegetation remains to a slightly greater extent, but connectivity is marginal. Threatening processes already initiatedand in most cases continuingmean that these subregions are on the edge of major declines in biodiversity. In the extensive use zone these are the subregions that are relatively heavily grazed, usually over more than 90% of their area, and have high densities of weeds and/or feral animals. They include the western parts of the arid pastoral lands of Western Australia, the semi-arid parts of the Great Artesian Basin, the western semi-arid grazing areas of the Murray Darling Basin, the Barkley Tableland, the central-southern subregions of the Gulf Plains and north-western Cape York.
The landscape health decline in the subregions of this stress class can probably be reversed with concerted effort. Clearing should cease, and grazing pressures on native vegetation reduced through extended pasture spelling, strategic stocking and through the protection of viable areas in conservative tenures. Strategic weed and feral animal control is needed to maintain the areas of greatest biodiversity value.
- 75 subregions (21%) fall into the fourth stress class, equally shared between the intensive use zone and the extensive use zone.
In the intensive use zone subregions in this class are the 'intermediate' subregions where although moderate areas of native vegetation remain, including most of the subregional ecosystems, connectivity in native vegetation is typically low and relatively little of the native vegetation is conservatively managed.
In the extensive use zone these subregions are those where grazing pressures are moderate and only limited areas are in conservative tenures. A significant number of subregions are threatened by weeds.
Subregions in this stress class are those where it is likely that landscape processes and remaining biodiversity can be sustained through the general maintenance of the status quo, supported by strategic conservation initiatives including more detailed species level information gathering.
- 152 subregions (43%) are in the two lowest stress classes and are considered to be in relatively good health.
Generally speaking these subregions are of lower suitability for agriculture or pastoralism, and are distributed equally across the intensive use zone and the extensive use zone. Relative to the other subregions, weeds and feral animals are not yet a major threat to biodiversity and landscape health. In the intensive use zone continuing clearing of these subregions is the major cause of concern.
Before you download
Most publications are downloadable as PDF files. Adobe Acrobat Reader is required to view PDF files.
If you are unable to access a publication, please contact us to organise a suitable alternative format.
Key
Links to an another web site
Opens a pop-up window