These pages have been extracted from the full document which is available at: http://www.environment.gov.au/biodiversity/publications/terrestrial-assessment/index.html
This work is copyright. It may be reproduced for study, research or training purposes subject to the inclusion of an acknowledgement of the source and no commercial usage or sale. Reproduction for purposes other than those above requires written permission from the Commonwealth. Requests concerning reproduction and rights should be addressed to the:
Disclaimer The then National Land and Water Resources Audit’s Biodiversity Working Group had a major role in providing information and oversighting the preparation of this report. The views it contains are not necessarily those of the Commonwealth or of state and territory governments. The Commonwealth does not accept responsibility in respect of any information or advice given in relation to or as a consequence of anything contained herein.
Cover photographs: Perth sunset, aquatic ecologists Bendora Reservoir ACT, kangaroo paw: Andrew Tatnell. Ecologist at New Well SA: Mike Jensen
Editor: Biotext Pty Ltd and Department of the Environment, Water, Heritage and the Arts
15
Chapter 2
Terrestrial ecosystems
16
For the purposes of this Assessment of Australia’s Terrestrial Biodiversity 2008
(hereafter referred to as the ‘Assessment’), terrestrial ecosystems are defined as all
ecosystems that are not aquatic or marine. This chapter presents findings in relation to
native vegetation as the key surrogate of terrestrial ecosystems. While the extent and
condition of native vegetation is not necessarily a good proxy for fauna, the retention,
natural regrowth and restoration of native vegetation remains a crucial biodiversity
conservation issue for Australia.
2.1 Key findings
Native vegetation is a key surrogate for biodiversity.
Native vegetation is a cost-effective and powerful surrogate for biodiversity. The distribution of threatened species and communities is closely aligned with areas where native vegetation has been extensively cleared.
The extent of native vegetation is known.
National mapping of native vegetation has advanced significantly since 2002 with improvements in data and in mapping technologies (e.g. through the Native Vegetation Information System). Although important gaps remain (in scale, and in defining some major vegetation groups such as derived native grasslands), we now know the extent of most major vegetation types in the landscape.
From the national vegetation data sets, we know that about 87 per cent of the Australian continent still has native vegetation cover.
National Forest Inventory data, which compiles state and territory forest mapping information, estimate total forest cover to be 149 million hectares (using Australia’s State of the Forests Report 2008 definition of forest).
Native vegetation has been modified or cleared.
Native vegetation has been modified and cleared since European settlement, especially from intensive agricultural and urban areas (particularly in southern and eastern Australia and in south-western Australia). The losses have been greatest in eucalypt woodlands and have also been significant in eucalypt open forest and mallee woodlands and shrublands. The loss of biota in the cleared and modified areas has been dramatic and continues today (e.g. in woodland birds).
Native vegetation is being lost faster than it is replaced.
Broad-scale clearing has been reducing since 2002, however nationally, native vegetation is still being cleared and modified faster than it is replaced. A net loss of forest (including native and non-native vegetation) of around 260,000 hectares per year occurred between 2000 and 2004 and was primarily attributed to clearing for agriculture and urban development.
We are making progress towards assessing native vegetation condition.
Since 2002, there has been progress in the collaboration between national, state and territory jurisdictions in improving Australia’s vegetation information. This includes approaches to modelling, monitoring and mapping vegetation condition, on both national and more localised scales. Reference-based methodologies are being used in most states for target setting, investment and planning decisions, and reporting.
17
2.2 Indicators
Indicators reported on in this chapter are listed in Table 2.1.
Table 2.1 Indicators
Indicator Current reporting capacity rating
The extent and distribution of native vegetation
Good nationally for extent
Moderate nationally for type
Change in the extent and distribution of native vegetation
Poor nationally overall
Good nationally for forest (Kyoto definition)
Good in Queensland for woody vegetation
Good in Victoria for native vegetation cover
Status and trends in native vegetation condition
Poor nationally
Good in Victoria
2.3 Native vegetation extent and condition
Many lines of evidence show the association between native vegetation and biodiversity.
Chapter 4 demonstrates that the distribution of threatened species and communities is
closely aligned with areas where native vegetation has been extensively cleared and
fragmented, and provides several data-rich examples of the direct linkages between this
disturbance and loss of biodiversity. Broad-scale land clearing was listed nationally
under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act)
in 2001 as a key threatening process for biodiversity. Chapter 5 examines trends in land
clearing, and Chapter 6 describes how the threat of broad-scale clearing has been
addressed and assesses the likely outcomes for biodiversity. Native vegetation is a
particularly powerful surrogate for biodiversity because of the extent of coverage and the
applicability or correlation to other biodiversity attributes such as habitat, ecosystem
services, and landscape processes.
Apart from their value as surrogates, national native vegetation datasets have many other
uses. They can be used to model the distributions of mammals and other biota; as a basis
for setting priorities for reservation, conservation and restoration/recovery; and in
overlays with other national datasets such as land use to inform and target national
programs.
Native vegetation is a critical element in biodiversity conservation and in building
resilience to established and emerging threats (for example, native vegetation will be
crucial in species adaptation to climate change). How well we manage native vegetation
in the landscape will be the key in determining ultimate outcomes for biodiversity. It is
essential that we understand the linkages between native vegetation and biodiversity in
order to manage it well.
While it is important to consider the extent of native vegetation, of equal importance is
native vegetation condition. Although we can be confident that biodiversity will be
depleted if there is no native vegetation, it can still be reduced in areas of extensive
18
native vegetation in poor condition, for example, native forests and woodlands that are
heavily grazed, have little understorey structure and have very limited recruitment.
Similarly, the extensive native grasslands of the rangelands have been modified by
grazing and other pressures. The evolving national approaches to assessing vegetation
condition, such as the Victorian Habitat Hectares method (Parkes et al 2003), include
measures of both extent and condition.
2.3.1 Native vegetation type and extent
The extent of native vegetation remaining in the Australian landscape by major
vegetation type is shown in Figure 2.1. This map is derived from the National Vegetation
Information System (NVIS), which collates data from a variety of sources and spatial
scales.
Figure 2.1 Extent of native vegetation by major vegetation groups
Source: NVIS version 3 2005
NVIS, Australia’s national vegetation mapping system, was developed by all Australian
governments under the first phase of the NLWRA. The Department of the Environment,
Water, Heritage and the Arts (DEWHA) is responsible for compiling the native
vegetation component of NVIS from state and territory mapping data.
The mapping and extent statistics produced for this Assessment incorporate a recent
NVIS update from the states and territories (NVIS 2005). They are based on 23 major
vegetation groups and 67 major vegetation subgroups, derived from more than 9000
distinct vegetation types now represented in NVIS.
19
Because of the considerable progress towards a consistent mapping protocol for native
vegetation through NVIS, and substantial updating of mapping in the last decade, gaps in
state and territory mapping are now relatively rare. However, many areas are still
mapped at a broader scale than the NVIS target scales of 1:100 000 for the intensive land
use zone and 1:250 000 for the extensive land use zone (NLWRA 2001, NLWRA 2007).
Figure 2.2 shows that native vegetation is present across most of the Australian
landscape. (Note: In NSW, as an interim step in the review of native vegetation extent,
the classification of native vegetation has included any vegetation with a likelihood of
being native. For example, grazed lands with the potential of having greater than 50 per
cent native ground cover at some point during its seasonal lifecycle has been classified as
“native”. Similarly, vegetation of unknown origin has also been classified as native).
Figure 2.2 Extent of native vegetation in 2004, overlaid by Interim Biogeographic Regionalisation for Australia (IBRA) 6.1 subregional boundaries
Source: Bureau of Rural Sciences 2009
2.3.2 Trends in native vegetation cover
Jurisdiction-wide temporal monitoring of woody vegetation cover is carried out in
Queensland and mapping of native vegetation cover in Victoria. The National Carbon
Accounting System (NCAS) can be used as a surrogate for assessing national trends in
native woody vegetation of >20 per cent canopy cover (see Figure 2.6).
20
Change since 1750
Reconstructed mapping of pre-1750 native vegetation provides a historic baseline for
examining gross change in the extent and type of native vegetation since European
settlement (Figure 2.3).
Figure 2.3 Estimated extent of pre-1750 native vegetation by major vegetation group
Source: NVIS Version 3 2005
Comparing this map with the present-day map of native vegetation (Figure 2.1) provides
an indication of broad-scale changes in the extent of major vegetation groups over the
past 200 years. These changes are particularly apparent in southern and eastern Australia
and in south-western Australia. Some major vegetation groups have undergone
substantial modification. Eucalypt woodlands, eucalypt open forest, and mallee
woodlands and shrublands, in particular, have been extensively cleared and in some
regions are retained as remnants in relatively small patches (e.g. eucalypt woodlands at
Figure 2.4). In southern Australia, clearing has reduced these groups to fragmented,
minor portions of their original extent.
21
Figure 2.4 Current distribution of eucalypt woodlands and estimated change in extent since 1750
Source: NVIS Version 3 2005
Over 50 per cent of pre-1750 vegetation has been lost from several Interim
Biogeographic Regionalisation for Australia (IBRA) subregions along the east coast of
Queensland and northern New South Wales, south-west Western Australia, and southern
Victoria and South Australia. Less than 10 per cent of the pre-1750 native vegetation
remains in some IBRA subregions in southern Australia and south-east Queensland, but
more than 70 per cent remains in the majority of IBRA subregions of central and
northern Australia.
Although these changes mainly occurred decades ago, they continue to impact on
biodiversity today. The ongoing decline in woodland birds, for example (see Chapter 4),
is a legacy of past clearing and subsequent incremental habitat decline in eucalypt
woodlands. It is important to recognise the long lags in the biodiversity responses to
pressures. These responses reveal some resilience and provide opportunities for
conservation efforts, but can also mask very serious long-term trends.
22
Trends in national forest cover
Australia’s capacity to report on forest extent is improving with advances in high-
resolution remote sensing technology (Montreal Process Implementation Group for
Australia 2008). The definition of forest used by Australia’s State of the Forests Report
2008 is described as a landscape dominated by trees that includes woodlands. Each state
and territory has its own method and data for reporting on forest type and extent.
Currently, there are two major national forest reporting systems:
• The National Forest Inventory (NFI) compiles state and territory forest mapping
information using eight broad types of forest. These maps are the agreed Australian
Government data used in international reporting on forest sustainability.
• The National Carbon Accounting System (NCAS) was developed for international
(Kyoto Protocol) reporting on carbon emissions. It uses woody vegetation cover
data, based on Landsat imagery since 1972, to monitor trends in deforestation and
forest regrowth, taking into account human and natural causes. ‘Forest’ is defined by
NCAS as native and non-native vegetation that has at least 20 per cent canopy cover
and could grow to at least two metres tall over a minimum area of 0.2 hectares. It
does not include native grasslands.
The Australia’s State of the Forests Report 2008 (Montreal Process Implementation
Group for Australia 2008), based largely on NFI data, found that the nation has
147 million hectares of native forest, dominated by eucalypt (79 per cent) and acacia (7
per cent) forest types (Figure 2.5). Around one-third of Australia’s native vegetation in
the intensively managed agricultural and urban zones has been cleared or substantially
modified over more than 200 years of European settlement. Native vegetation in these
areas is highly fragmented.
Figure 2.5 Forest extent and types
23
Source: Bureau of Rural Science 2008
The NCAS data indicate that, nationally, deforestation is gradually falling from a high in
the 1970s and 1980s. NCAS shows an ongoing annual net loss of woody forest cover
(Figure 2.6), but the rate of loss has decreased since broad-scale clearing regulations
came into effect in Queensland and New South Wales.
Figure 2.6 Extent of forest cover 1972–2006 as estimated by NCAS
Source: NCAS, Department of Climate Change
Changes in forest cover, as defined by NCAS, between 2002 and 2006 occurred in
several bioregions (Figure 2.7). Net losses occurred in eastern Queensland, the Northern
Territory, south-west Western Australia and eastern Tasmania. These patterns concur
with known occurrences of land use change, wildfires and other pressures that deplete
forest cover.
24
Figure 2.7 Change in percentage forest cover between 2002 and 2006 by IBRA 6.1 regions as estimated by NCAS
Land use change and clearing
Over much of southern Australia, intensive agricultural systems (using introduced crops
and pastures) have largely replaced native vegetation. In contrast, the extensive livestock
production systems across the rangelands of central and northern Australia, have
historically been based mainly on native grasses and shrublands.
Overall, land use change since European settlement has had comparatively greater
impact in the intensive land use zone of southern Australia, through clearing and
modification of large areas of native vegetation. Many of these southern regions retain
less than 50 per cent of the pre-1750 extent of native vegetation, and much of this occurs
as patchy, isolated remnants. However, although native vegetation remains throughout
the rangelands, the extent and composition of species and communities and the condition
of the native vegetation have been widely and substantially affected by grazing.
The Queensland Government regularly and consistently monitors woody vegetation
cover using satellite-based monitoring and extensive ground truthing. Case study 2.1
illustrates the value of building good baseline and monitoring systems for native
vegetation. It also shows that rates of clearing are now falling in regions where rates
were recently among the highest in the nation.
25
Case study 2.1 Queensland’s Regional Ecosystem survey and mapping program (Butler and Accad 2008)
In Queensland, a concerted effort over the past decade has produced a seamless map of land classes or regional ecosystems (REs) covering more than 80 per cent of the state at a scale of at least 1:100 000. REs were first described by Sattler and Williams (1999) as ‘vegetation communities in a bioregion that are consistently associated with a particular combination of geology, landform and soil’. The RE classification has been modified as it has been used, as mappers identified new REs or modified RE descriptions. The up-to-date RE classification can be accessed via the web-based Regional Ecosystem Description Database (Environmental Protection Agency 2008).
The RE framework and mapping are key resources for conservation planning, and also facilitate environmental protection through the Vegetation Management Act 1999 and the Environmental
Protection Act 1994. RE mapping is carried out by the Environmental Protection Agency (EPA) through the Queensland Herbarium and draws on aerial photography, satellite imagery and land cover change analysis from the Department of Natural Resources and Water, particularly the Statewide Landcover and Trees Study (SLATS).
The mapping provides data on the pre-clearing distribution of REs and also on their distribution as ‘remnants’ for specified years. Remnant condition is based on the structure and composition of the RE’s ‘predominant canopy’, the vegetation layer that contains the most above-ground plant biomass. For example, in woodland, the tree layer is the predominant canopy. To be remnant, a patch of a woodland RE must have a tree layer with at least 70 per cent of the height and at least 50 per cent of the cover typical of uncleared woodlands of the same RE, and the dominant species must be characteristic of the RE’s uncleared canopy (Neldner et al 2005).
Outcomes
The rate of remnant clearing in Queensland peaked in 1999–2000, just before the introduction of laws controlling vegetation clearing on freehold land (Figure 2.8).
26
Figure 2.8 Changes in the rate of remnant clearing from 1997 to 2005 for Queensland and the three bioregions in which clearing is concentrated
-
100,000
200,000
300,000
400,000
500,000
600,000
700,000
1997-99 1999-2000 2000-01 2001-03 2003-05
Period
Rate
of re
mn
an
t cle
ari
ng
(h
ecta
res/y
ear)
Queensland
Brigalow Belt
Mulga Lands
Desert Uplands
Source: unreleased EPA mapping, RE version 6.0
The distribution of remnant clearing has also changed markedly since 1997. Three regions, covering about 35 per cent of the state, accounted for nearly 90 per cent of the remnant clearing in Queensland between 1997 and 2005 (Figure 2.9). The largest of these, the Brigalow Belt, covers 21 per cent of Queensland but contributed 40 per cent of remnant clearing between 1997 and 2005. The other two key regions are the Mulga Lands (11 per cent of Qld, 35 per cent of clearing) and the Desert Uplands (4 per cent of Qld, 13 per cent of remnant clearing).
27
Figure 2.9 Changes in the rate of clearing by IBRA 6.1 subregions from 1997 to 2005
Source: unreleased EPA mapping, RE version 6.0
Wilson et al (2002) assessed a RE-mapping time series spanning 1995 to 2000 and noted that remnant clearing was increasingly occurring on more marginal country. At the state scale, this trend is indicated by a shift in clearing towards more arid lands, especially the Mulga Lands. The rate of remnant clearing in the Brigalow Belt dropped substantially after 2000, and has dropped slightly in the Desert Uplands too, but has tended to increase in the Mulga Lands.
The Mulga Lands have been Queensland’s remnant clearing hotspot since 2001. Anecdotal evidence suggests that much of this clearing occurred under an exemption to the clearing laws, allowing trees to be used as fodder without the need for a permit following drought declaration. The exemption has now been tightened, and remnant clearing across the state has been strictly controlled, including prohibition of broad-scale remnant clearing for most agricultural purposes since the end of 2006. Figure 2.10 shows the extent of remnant vegetation across Queensland in 2005, just before broad-scale tree clearing ended.
28
Figure 2.10 The extent of remnant vegetation across Queensland in 2005 as a percentage of the area of IBRA 6.1 subregions
Source: unreleased EPA mapping, RE version 6.0
Future directions
The RE mapping program is set to achieve full coverage of Queensland at a scale of at least 1:100 000. Ongoing mapping is also improving the scale of data in intensive land use regions concentrated along Queensland’s east coast. The team and technology developed for the RE mapping effort have also been involved in an ongoing wetland mapping program that links closely to the RE mapping.
2.3.3 Monitoring vegetation condition
The condition of native vegetation is a surrogate indicator of the health of ecosystems,
and the richness, diversity and resilience of communities and species. Native vegetation
condition is, however, an inherently value-based concept, and it is important to clearly
state the values of the stakeholder. For biodiversity values, the ‘naturalness’ of
vegetation is an important quality. ‘Naturalness’ is an outcome of a complex range of
environmental variables and pressures, such as land use, drought, fire, pests and disease.
It is not a static condition, but will vary naturally in landscapes that are constantly
changing.
Much progress has been made since 2002 in the collaboration between national, state and
territory jurisdictions in improving Australia’s vegetation information including
approaches to modelling, monitoring and mapping vegetation condition, at national and
more localised scales. The Executive Steering Committee for Australian Vegetation
Information (ESCAVI) is developing an approach to monitoring native vegetation
condition around this emerging consensus. This approach focuses strongly on the habitat
value of vegetation using reference-based, documented benchmarks for vegetation types
29
that describe the expected values of a range of attributes in a long-undisturbed, ‘natural’
state.
Site-based pilot studies under ESCAVI (publication can be accessed at
The pilot study in Tasmania involved implementing the modified Habitat Hectares
method, now called the TASVEG Vegetation Condition Assessment (TASVEG VCA).
During the trial, the method was used in forests, grasslands and wetlands. The work
resulted in a practical and repeatable method that can produce useful information in the
Tasmanian context including assessing non-forest vegetation.
Tasmanian benchmarking methodology
The Habitat Hectares approach uses a set of reference sites, or ‘benchmarks’ against
which vegetation communities are assessed, allowing a vegetation condition score to be
33
developed for each community (Parkes et al 2003). The first step for Tasmania was to
develop these benchmarks.
Benchmarks for 139 communities were created using TASVEG community descriptions
(Harris and Kitchener 2005), existing ecological datasets and input from a large number
of vegetation scientists with expert knowledge of particular communities. The use of
TASVEG communities was advantageous as the 158 communities are well described,
mapped at a 1:25 000 scale and used by a diverse client base. In some cases, several
benchmarks were required for one TASVEG community due to identifiable floristic
variations over the communities’ range. Benchmarks were then refined through field
testing and further input from experts. Vegetation benchmarks were created on a priority
basis, with the highest priority given to communities with distributions in the agricultural
and more intensively settled areas of the state and to listed ecological communities on
private land.
Parkes et al (2003) developed seven ‘site condition components’ that are used in
developing site condition scores. They include vegetation attributes of the location: large
trees, canopy cover, understorey cover and composition; litter layer, presence of logs;
presence of weeds; and recruitment of overstorey species. These are known collectively
as the site score. Three of these were not relevant to a treeless community, and are not
included in the Tasmanian non-forest methodology. The remaining three components
assess the spatial context of the vegetation in the landscape. In the TASVEG VCA
method for non-forest vegetation, the site condition components ‘large trees’ and ‘tree
canopy cover’ were replaced with a ‘dominant life form cover’ component. The third of
these non-relevant components is the log component; in non-forest communities this is
not assessed, and site scores are standardised for this using the Victorian correction
factor.
In the TASVEG VCA method, a ‘persistence potential’ component is measured in non-
forest communities, rather than the assessment of forest recruitment developed by Parkes
et al (2003). This assesses the natural regenerative capability and sustainability of the
vegetation; qualifying this score depends on the integrity of community structure and
composition.
Outcomes
The creation of benchmarks, initial trial and subsequent modifications of the Habitat
Hectares method comprised the first step in developing a state-wide approach to
assessing and monitoring vegetation condition in Tasmania. A regional natural resource
management (NRM) strategy for the assessment and monitoring of native vegetation
condition has subsequently been prepared.
The final TASVEG VCA method is objective, consistent and defensible. The TASVEG
VCA is suitable for use by non-specialists who have basic botanical skills. A fitness-for-
purpose analysis of the TASVEG VCA method is currently being carried out for the
Tasmanian Department of Primary Industries, Parks, Water and Environment.
34
Assessing native vegetation condition using the Bushland Condition Monitoring Method and South Australian Biodiversity Assessment Tool (Milne 2008b)
The Nature Method and the South Australian Biodiversity Assessment Tool (SABAT)
address the lack of techniques for measuring the condition of key vegetation
communities in South Australia, and provide an innovative approach to building
community capacity in vegetation management. The Nature Conservation Society of
South Australia (NCSSA) method was specifically designed for use by non-professional
volunteers and land managers. The method allowed for identification, assessment and
scoring of a range of key benchmarked indicators. The NCSSA method:
• builds the capacity of conservation volunteers, managers and extension professionals
to understand and manage native vegetation through a training and support program,
and
• enables reporting of the condition of native vegetation in South Australia at a
regional and state scale and is compatible with the approach to the monitoring of
native vegetation condition for the National Native Vegetation Condition Indicator.
Figure 2.12 Volunteers on the Bushland Condition Monitoring Assessment in coastal vegetation, Waitpinga, South Australia
Photo: Janet A Pedler
35
The SABAT was developed by the South Australian Government around the NCSSA
method to assess sites in Bush Bids program. It is a powerful tool that:
• at an individual site level, can provide site-based reports on
− current vegetation condition
− change of vegetation condition
• at a regional/state scale
− can provide a central repository for Bushland Condition Monitoring data
− can collate and report regional data on a number of attributes related to
vegetation condition.
Outcomes
Data have been collected from more than 500 sites across five different NRM regions.
The program has also trained more than 300 people from 42 different community groups
and organisations. Preliminary analysis from tests of surveyor consistency indicates that
the method provides valuable and reliable data that can be used to assess and monitor
changes in specific attributes of bushland that are well-accepted surrogates for
biodiversity value (Milne 2008a).
Case study 2.2 Mapping native vegetation condition in the Murray Catchment, New South Wales (CSIRO)
Historically, regional-scale vegetation assessment and mapping programs have focused on assessing the extent and composition of native vegetation. However, there is increasing demand for maps of vegetation condition (Oliver et al 2002, Parkes and Lyon 2006). Such maps are needed to support native vegetation management, including providing regional context for site condition assessments, assisting with regional planning or conservation target setting and monitoring the effectiveness of interventions (e.g. fencing, grazing management, remnant enhancement) (Zerger et al 2006).
This project has developed a native vegetation condition mapping methodology that improves upon existing approaches and uses recently available high-resolution satellite imagery (SPOT-5). Site-based assessments are integrated with remotely sensed data (SPOT-5 and Landsat 5 TM) and explanatory GIS data in a predictive modelling framework to build maps across two 1:100 000 mapsheets in the Murray Catchment of New South Wales. The BioMetric site assessment methodology has been used to ensure that results integrate with tools commonly used in New South Wales. Particular attention has been paid to developing a stratification that captures the disturbance gradients in the landscape to ensure that field sites capture the full range of vegetation condition states. The project examined the operational limitations of building such vegetation condition maps and the importance of site data density on modelling, and evaluated the use of regional-scale GIS data for mapping.
The project objectives included:
• development of an operationally feasible technique for mapping native vegetation condition at catchment and regional scales, using site-based condition estimates, remote sensing and predictive modelling
36
• identification of data requirements for effective native vegetation condition mapping in the case study regions, and
• assessment of the potential use of regional-scale and national-scale spatial information for building regional-scale vegetation condition maps (i.e. at the catchment management area or statewide levels).
Outcomes
Results have shown that, for some vegetation condition attributes (volume of fallen logs and native grasses), it is reasonably difficult to obtain strong predictive accuracies (greater than an r2
of 0.5) when building regional-scale spatial predictions. For the models tested in this study, spectral remote sensing indices were always selected as significant predictors of native vegetation condition. Remote-sensing data senses primary attributes of native vegetation, rather than surrogates for disturbance as with most GIS-derived variables (e.g. topographic position).
The capture of Biometric-type data over such study domains is estimated to cost approximately $50 000. Satellite image acquisition, assuming a coverage of six SPOT-5 scenes, will add another $30 000. GIS data for such regions are generally already available (e.g. 25-metre DEMs, land use mapping, tenure), but time needs to be allocated to data preparation and satellite image classification (woody vegetation mapping). The modelling component is a relatively small part of such a project; the primary costs are for data acquisition and preparation.
Relying on archival satellite imagery such as SPOT-5 and Landsat TM has inherent limitations, as it is difficult to obtain neighbouring scenes of similar seasonality that are cloud free at regional scales. Image seasonality plays an important role in determining the effectiveness of modelling. SPOT-5 imagery is of limited use compared with Landsat TM imagery: owing to the scale of Landsat TM imagery, there are no seasonality issues between neighbouring scenes. For operational purposes, it is therefore more efficient to work with Landsat TM data at regional scales.
A limitation in such modelling is the difficulty in obtaining spatial historical information about disturbance and vegetation management activities (e.g. revegetation, remnant enhancement), which will impact upon the accuracy of the final model. As modelling relies on spatially explicit surrogates of vegetation disturbance, users need to be aware that the models are regional summaries of vegetation condition with inherent limitations in temporal and spatial accuracy and precision. However, the investment in plot data, which underpins such research, may be justified if it serves multiple purposes. For example, appropriately stratified Biometric-type plot data could serve the needs of a vegetation monitoring and evaluation system, while also acting as a primary input to developing regional-scale maps of native vegetation condition.
Future directions
This is the second such native vegetation condition project completed, and predictive model performance is comparable between studies. Improvements in plot data density, stratification or use of different modelling methods may not yield significantly improved results. However, we believe that time-series satellite imagery has significant potential for improving predictive performance (see Figure 2.12). To date, projects have relied on the use of single epoch imagery (from a single timeframe, and therefore not showing trends). Including some understanding of temporal change in native vegetation attributes may improve the accuracy of regional-scale predictions.
37
Figure 2.13 Spatial prediction from Murray Catchment Management Area modelling: volume of fallen logs
Source: Zerger et al 2007
Key conclusions from the pilot studies
The ESCAVI process for developing nationally consistent approaches for monitoring
vegetation condition has successfully piloted a methodology based on the Victorian
Habitat Hectares approach using well-accepted surrogates. The approach is flexible and
has wider application to meet many of the needs for condition monitoring.
It will take significant, well-targeted effort to establish baselines and begin monitoring of
trends in key vegetation communities. Meanwhile, modelled datasets based on surrogates
of condition can provide valuable insight into the condition of vegetation at national,
state and local scales and can provide useful immediate information to meet the needs of
policy makers and natural resource managers.
Rangelands condition reporting
Case study 2.3 Land condition in rangelands and links to biodiversity (Fisher 2008)
The complexity of relationships that define biodiversity responses to changes in vegetation condition and the challenges in defining appropriate indicators, particularly for national reporting, are well illustrated by recent research from the Australian rangelands. Fisher and Kutt (2006) identified a number of limitations to using land condition or other simple measures such as groundcover as surrogates for biodiversity health in the rangelands.
The rangelands cover roughly 80 per cent of Australia’s land area and contain much of Australia’s biodiversity. There is no comprehensive rangeland biodiversity monitoring program comparable with existing pastoral monitoring schemes, but substantial decline in rangeland biodiversity has been reported and is thought to be ongoing (Woinarski and Fisher 2003).
38
Land condition and rangeland biodiversity
‘Land condition’ is a key indicator for assessing the sustainability of pastoral land management. It includes a number of elements such as the composition of the ground layer (e.g. the density of palatable, perennial plants), the amount of bare ground and the condition of the soil surface. These elements also contribute to the concept of ‘landscape function’ (i.e. a measure of the landscape’s capacity to capture water and nutrients).
There are well-developed monitoring programs for pastoral land condition in each of the rangeland jurisdictions (NLWRA 2001). These generally rely on plot-based assessment of vegetation cover, frequency of perennial plants, floristic composition and/or demography and soil-surface condition at representative sites throughout the pastoral estate. For example, the Western Australian Rangeland Monitoring System covers approximately 1620 permanent sites (Watson et al 2007). Some jurisdictions also use satellite imagery to assess condition over large areas.
The Australian Collaborative Rangelands Information System (ACRIS) report, Rangelands 2008
– Taking the Pulse (Bastin and the ACRIS Management Committee 2008), collated and synthesised monitoring data to present the first national assessment of change in Australia’s rangelands. This assessment reported on the indicator ‘landscape function’, which was measured directly at pastoral monitoring sites in some jurisdictions, or derived from other data on groundcover. During the 1992–2005 reporting period, landscape function was stable or improving in most rangeland IBRA regions for which data were available. This result must be carefully interpreted, as rainfall variability is one of the major drivers of change in the rangelands. However, after correcting for seasonal quality, a generally positive picture of rangeland condition emerged. What does this mean for biodiversity?
Land condition and rangeland biodiversity
It is often assumed that pastoral monitoring acts as a good surrogate for biodiversity monitoring: if pastoral land condition is good or improving, then rangeland biodiversity is likely to be in good health. This assumption has rarely been rigorously tested.
A detailed study (Fisher and Kutt 2006) examined the relationship between pastoral land condition and biodiversity in two important pastoral regions of the tropical savannas of northern Australia. A broad range of biota was sampled at sites in three condition states (‘poor’, ‘moderate’ and ‘good’) in several land types in the Burdekin Rangelands (Queensland) and Victoria River District (Northern Territory). The study identified a number of constraints to using land condition (or other simple measures such as groundcover) as a surrogate for biodiversity health in rangelands:
• Components of biodiversity are likely to respond in a complex fashion to the spatial configuration of land condition across the landscape. Biodiversity status will be poorly predicted by limited point assessment of land condition.
• The history of land condition, other management influences such as fire frequency and fine-scale climate variability are factors that are not necessarily reflected in current condition.
• Some important threatening processes, such as feral predators, operate independently of condition.
• Simplistic categorisations of land condition cannot adequately encompass the range of responses found in many biotic groups across different habitats.
• Perceptions of condition (and changes in condition) may diverge from ecological and production viewpoints (e.g. in relation to introduced pasture and woody thickening).
• Rangeland condition assessment generally fails to capture the condition of rare and restricted ecosystems, although these are generally areas of high biodiversity significance.
39
Although land condition clearly has some influence on biodiversity, the response of biota to land condition is complex and highly variable between taxa, land types and locations. Not surprisingly, land condition is most strongly predictive for components of the biota whose ecology is closely linked to characteristics of the ground surface and density of ground layer vegetation, such as plants and ants. The inconsistent response to condition of many species and functional groups makes it difficult to identify components of the biota most susceptible to degradation, or identify ecological traits that may be indicators of susceptibility. Land condition, by itself, will therefore be a relatively poor indicator for the condition of rangeland biodiversity. Similarly, a single group of animals or plants is unlikely to be an adequate surrogate for a broader range of taxa in any rangeland biodiversity monitoring program.
Findings
• There are pastoral monitoring programs in each of the rangeland jurisdictions, based on regular sampling of representative ground sites, and in some cases augmented by remote sensing. These monitoring programs use indicators relating to groundcover, vegetation composition and landscape function to assess pastoral land condition.
• Results from pastoral monitoring sites may also give a misleading picture of regional biodiversity ‘health’ because they are biased towards extensive and relatively stable land types under moderate grazing pressure. Ecotones and restricted, but biodiverse, landscape elements are generally poorly sampled in these programs.
• Although existing pastoral land condition monitoring provides some useful information about biodiversity, comprehensive biodiversity monitoring programs at regional or jurisdictional scales, which include the direct assessment of selected biota, are required in the rangelands. Further research is also required to develop more useful ‘habitat condition’ metrics appropriate for rangeland biota and ecosystems.
40
Figure 2.14 Sites in eucalypt open woodland in the Victoria River District of the Northern Territory in ‘good’ (top) and ‘poor’ (bottom) pastoral land condition
