Assessing vegetation condition

Classifying and mapping native vegetation communities is an important first step for planning and management at catchment or regional scale. Being reasonably confident about the condition of the vegetation adds another important dimension to our understanding of whether vegetation will persist in the longer-term and the services that it provides.

Improving techniques for describing the condition of native vegetation has been identified as a key outcome of the National Framework for Managing and Monitoring of Australia’s Native Vegetation 164. In this framework, the conservation of native vegetation and fauna is seen as central to meeting biodiversity objectives for Australia. The data attributes and protocols for vegetation extent and condition developed through the NVIS are to be used in the monitoring component of this framework. To adequately assess change in native vegetation cover and condition, a whole-of-landscape approach that incorporates both its biological and functional values may be needed.

Native vegetation condition is one of the resource condition indicators to support the matters for targets on native vegetation integrity 165. An Interim Approach to Native Vegetation Condition 166 has been developed to improve the consistency in the national assessment of the condition. The paper is based on the Habitat Hectares approach to monitoring although it is noted that other processes are underway, at varying stages of development, for monitoring native vegetation condition. Habitat Hectares was originally developed to assess the habitat quality of native woody vegetation in the intensive land use zone 167. The landscape context component is of most relevance to regional managers, although site-based characteristics dominate the habitat score (Table 8). The interim approach is not intended to be used as an indicator by regional groups in setting targets for native vegetation condition. It has been provided to indicate a possible way forward and may form the basis for the development of a full paper on indicators.

The Habitat Hectares approach has been widely adopted in various forms, for example, in the Heartlands project and as a basis for A Prototype Toolkit for Scoring the Biodiversity Benefits of Land Use Change 168. Approaches such as these are always evolving, and a recent review discusses some of the areas where improvements could be made  169. Further research has led to a more recent version of the Habitat Hectares approach 170, which supercedes all previous versions and is recognised as the official method for assessing native vegetation in accordance with the native vegetation management framework in Victoria. The manual provides a step-by-step approach to conducting assessments in the field and useful tips for ensuring consistency of application. For the first time, a method for assessing treeless vegetation is provided in an easily accessible form.

Table 8: Components and weightings of the habitat score used in the Habitat ectares approach



Source: D, Newell G, Cheal D (2003) Assessing the Quality of Native Vegetation: he ‘habitat hectares’ approach. Ecological Management and Restoration 4 (Supplement), pp. 29–38

An Interim Approach to Native Vegetation Condition 171 refers to the landscape classification described in Section 2.2b that uses the four states: relictual, fragmented, variegated and intact. It is important to consider different scenarios of landscape alteration such as these when choosing ‘landscape context’ (Table 8), or similar attributes. For example, for intact landscapes in the extensive land-use zone, ‘patch size’ may be irrelevant and landscape context may be best indicated by other physical disturbance measures like distance from watering points. Both site-based quantitative assessments and regional-scale estimates are required to facilitate on-ground management decisions and strategic overviews of vegetation condition, and must be linked to allow the strengths of each scale to be realised and the weaknesses to be mitigated. Site-based measures provide guidance for specific management issues and individual investment decisions, but can be ad hoc in coverage and limited by resources. Regional-scale measures provide a broadly comprehensive perspective but, through their reliance on surrogates, are limited in precision. The combination of both types of measure will allow the generality of regional overviews to be calibrated progressively with the specificity of quantitative site data.

	Action: 2.7
	Read the interim paper on assessing native vegetation condition for the national Matters for Targets and consider how the approach it proposes could be adopted for your region.
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National Vegetation Information System (NVIS) 172 data were used during activities to help review the condition of native vegetation at a continental and regional level. These are reported in the Australian Native Vegetation Assessment 2001, which shows that agricultural, pastoral and urban development has significantly and rapidly changed native vegetation since European settlement. Impacts have varied with land uses and include broadscale clearing for cultivation and grazing on improved pastures, forest modification through logging practices, rangeland modification through grazing practices and changes in fire regimes, the introduction of exotic species, and major alteration and loss of native vegetation due to the filling of wetlands in urban areas and transport corridors. Overall, the native vegetation has been modified significantly in many regions and catchments, especially the intensively-used areas of southern and eastern Australia.

Also building on the work of the Audit, a report in Science for Decision Makers has been developed to provide a summary of how vegetation condition can be used as an indicator of ecosystem health and natural resource productivity 173. This report concludes that there are four broad approaches to surveying vegetation condition, ranging from a one-off ‘snapshot’ assessment to repeated surveys over time that may or may not be compared to a baseline assessment.

A number of government agencies are now monitoring clearing of vegetation, by type, on a frequent basis including through the National Carbon Accounting System (NCAS) 174. For example, the NCAS is designed to reduce scientific uncertainties that surround estimates of land-based greenhouse gas emissions and carbon sequestration (especially in the form of vegetation). This system underpins the monitoring and reporting capabilities of the Australian Government in relation to climate change. The information collected through the NCAS includes data on vegetation condition at landscape level, and trends in condition over time. Information such as this can make an important contribution to the assessment of native vegetation condition.

	Action: 2.8
	Investigate how the condition of native vegetation has changed since European settlement of Australia and read the Science for Decision Makers report on measuring vegetation condition.
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Monitoring rangeland condition

Tracking Changes: Australian Collaborative Rangeland Information System 175 describes the Audit’s work in the less intensively used regions of Australia. It sought to define the elements of a comprehensive monitoring program that would provide regular Australia-wide reports and enable people to make better land use and management decisions in the rangelands. Existing information and monitoring systems have not comprehensively reflected the condition of Australia’s rangelands. The proposed system would involve a series of interlinked activities that build on new rangeland monitoring capabilities. In discussing how rangeland monitoring may work, Tracking Changes outlines State and Northern Territory monitoring activities and highlights individual case studies to demonstrate how monitoring systems are already being used to inform land use and management decisions at a variety of scales. The Audit developed new capabilities and approaches to rangeland monitoring. These include Developing an Analytical Framework for Monitoring Biodiversity in Australia’s Rangelands 176, an operational system using remote sensing that would enable monitoring across large areas of northern and central Australia, and an approach to rangeland management driven by how landscapes function, rather than how they are used.

Monitoring of vegetation condition in the Australian rangelands is considered in detail in relation to biodiversity in a recent study Biodiversity Monitoring in the Rangelands 177. The study, which builds on the work of the Audit, provides detailed information about monitoring and the significance of vegetation condition for biodiversity conservation. The study suggests that monitoring activities focus on:

• The integrity of native vegetation communities;
• Significant native species and ecological communities;
• Inland aquatic ecosystems integrity (rivers and other wetlands);
• Ecologically significant invasive species.

The study outlines a minimum set of biodiversity indicators including data trends in the cover of native perennial grass/native perennial ground layer vegetation; the abundance of exotic plant species; the condition of fire-sensitive plant species and communities; the abundance of grazing-sensitive plants; the abundance of listed threatened species; and the condition of listed threatened communities.

A major research theme is examining whether the indicators used for landscape function and pasture condition can be used as surrogates for biodiversity 178. The current body of monitoring work suggests that there may be some widely-applicable indicators of landscape health or pasture condition, most notably (in the northern rangelands) the extent of native perennial grass cover, landscape function analysis (LFA) score, and the value and temporal stability of reflectance scores or indices. In the absence of any other information, there is a widespread supposition that these measures may also relate to biodiversity and hence provide surrogates for biodiversity trends. In order to develop robust protocols for monitoring biodiversity ‘health’ in the tropical rangelands, it is important to test the validity and utility of these surrogates.

Identifying benchmarks

In the context of native vegetation management, benchmarks or reference areas are used to provide a standard against which the condition of local vegetation can be assessed. They are appealing because they provide a simple focus for management. In Australia, standards have included the extent and structure of vegetation as it was in 1750 (Figure 9) or 1990, a nominated reference site (if this exists for the vegetation type in question), or an ‘ideal’ state. Individual attributes are compared against the value of the same attributes in the benchmark, providing an indication of the direction and magnitude of change. At the regional and catchment level, they are mostly used to assess the extent and condition of vegetation types across their distribution compared to the benchmark or reference area. Because each vegetation type is different, a number of reference areas are needed in any one region.

Several mapping and assessment tools in the intensive land use zone rely on benchmarks that represent the average characteristics of the mature native vegetation that occupied the site before agricultural development, as far as this is known. For example, this is the benchmark used in Assessing the Quality of Native Vegetation: The ‘habitat hectares’ approach 179 and A Prototype Toolkit for Scoring the Biodiversity Benefits of Land Use Change 180. In Queensland, the definition used for mapping remnant vegetation is that the tallest vegetation layer is at least 70 per cent of the height, and 50 per cent of the cover, of that normally found for that layer 181. The discussion paper on native vegetation condition for the national matters for targets also states that reference points will be expressed as a benchmark that represents the average characteristics of a mature and apparently long undisturbed stand of the same vegetation type 165.

In some circumstances the current focus on ‘pre-1750 vegetation’, ‘pre-agricultural vegetation’ and ‘naturalness’ as benchmarks may limit efforts for assessing vegetation condition for biodiversity conservation. The following principal reasons have been put forward as to why using these benchmarks can be an issue when site-based methods are used 182. These are broadly applicable at the regional and catchment scale.

• The models used of pre-European vegetation are considered likely to be least accurate for vegetation types that have been most heavily degraded, cleared and fragmented.
• Routine adoption of pre-European condition/distribution and naturalness at the site level may lead to a devaluing of native vegetation that differs in type from that predicted to have existed on-site in 1750.
• Attempts to restore a modelled vegetation type may fail because the location where it was originally found has been significantly and effectively irreversibly changed due to altered fire regimes, degraded soil attributes and modified hydrological regimes.
• The philosophical complexity of the ‘naturalness’ concept may not necessarily be consistent with the most effective biodiversity outcomes.

In addition to these points, the nature of disturbance in Australia (see Question 3) makes it difficult to define a single meaningful benchmark, even for a single vegetation type. In a context of natural disturbance such as fire or flood, the properties of a system such as structure and floristic composition will change over time. Vegetation is dynamic and likely to have varied in composition and structure over time, even in its ‘natural’ state. Consequently, condition should be interpreted against the changes needed to achieve a desired state. These observations make the identification of benchmarks more complex than some approaches may suggest.

A flexible approach to identifying reference areas is described in Biodiversity Monitoring in the Rangelands 183. The report identifies the two most important criteria for selecting a reference area: representation of the characteristic landscapes and habitats of the region to be monitored; and minimal influence from all major pressures acting on the country type they represent. Where possible, they should also be of sufficient size to support large-scale processes that sustain native vegetation and its associated biodiversity. This may be more difficult in the intensive land-use zone than the rangelands, but is a worthwhile aim. The key message from this report is that reference areas are a relative benchmark of the ‘good’ current status and condition of biodiversity or native vegetation. Their greatest value is to represent standards for evaluating differences between areas under more or less pressure, in order to identify changes over time. In areas where entire landscapes are under pressure, such as those that are highly productive and/or restricted in extent, it is recommended that reference areas should be located to represent the ‘best-on-offer’ state of that vegetation type.

Figure 9: Pre-European major vegetation groups in Australia; pre-European is defined as that estimated to occur before 1750



Source: National Land and Water Resources Audit (2001) Major vegetation groups V1.0 (1km), National Vegetation Information System (NVIS), Commonwealth of Australia (http://audit.ea.gov.au/ANRA/vegetation/vegetation_frame.cfm?region_type=AUS®ion_code=AUS&info=veg_type)