Executive summary
What the report is about
Biodiversity surrogates and related metrics are techniques which have been developed to rapidly assess vegetation structural and compositional status and to score or rank expected habitat biodiversity value.

The metrics include assessment of forest stands relative to regional benchmarks, and the connectivity to nearby remnant vegetation. This report examines the applicability of biodiversity surrogates and their compiled metric scoring systems to assessing forest condition, and hence the ecological sustainability, under different forest management inputs. Four private native forest case studies were examined in northern NSW, eastern Victoria and southern Tasmania.

The report provides recommendations for forest managers and regulators of the industry on those elements of the existing metrics which have value in a private native forestry context. It outlines a process for the development of surrogates and metrics which attempts to directly address the sustainability of private native forestry, rather than focusing on vegetation quality or condition as in the existing schemes.

Who is the report targeted at?
The report has direct relevance to private and public forest managers who are required to test, evaluate or benchmark their forest management activities against sustainability criteria which use biodiversity surrogates or metrics. It will also be of interest to researchers, policy makers and policy administrators involved in native forest and natural resource management. The metric scoring systems assessed in this report have intended application through Commonwealth?State natural resource management partnership agreements, and through implementation by regional catchment authorities.

Background
Governments are increasingly using biodiversity surrogates and their compiled metric scoring systems to support national and state-based vegetation management frameworks, to value and monitor market based investments in vegetation rehabilitation or restoration, and to monitor compliance with environmental standards and certification schemes.

Biodiversity surrogates offer a convenient means of assessing a forest stand’s structural and compositional status and its inferred ability to provide habitat and resources for local populations of plants and animals. Indices or metrics based on summarising these surrogates also offer a convenient way to rank or compare different stands and then translate those results into monitoring frameworks or onground actions. Habitat Hectares and Biometric are the two most widely used measures of vegetation quality or condition in Australia, with both schemes being customised to either formal policy frameworks or legislation. Biometric and Habitat Hectares were designed to implement vegetation policy instruments which seek to apply a ‘improve or maintain’, ‘no net loss’ or ‘net environmental benefit’ test to assessing vegetation change. These systems assess within a property vegetation type, the extent, condition and regional context where a landholder intends to clear native vegetation, to receive incentive management payments, or apply appropriate offset mechanisms for land use change.

The convenience of the above approaches and the tendency to relate index scores to stand management history and by inference a cause and effect relationship is problematic. Private native forests contribute a large component of hardwood supply in Australia as well as regional natural resource values, and are increasingly important as supplies from public native forests diminish – their management is important and occurs over long time periods. The suitability of the metric scoring systems to assess the ecological sustainability of different forest management actions such as clearfelling, thinning or selective harvesting, or measure the recovery of forest condition with time after these actions is debateable, when their primary focus is on the implications for vegetation condition of a change in land use.

Aims/Objectives
This study aimed to:

• undertake comparative analysis of the Habitat Hectares and Biometric data collected as part of three private native forestry projects funded by the Joint Venture Agroforestry Program
• improve understanding of the contribution that biodiversity metrics can make to the assessment of private native forestry sustainability.

The study focuses on the utility of the component biodiversity surrogate measures within each metric for assessing forest vegetation quality and condition.

Methods used
Data from four case studies was used to compare the performance of the site condition component of Habitat Hectares, and the site value component of Biometric, as measures of the sustainability of private native forestry.

The project methods were to:

• Review current knowledge and application of biodiversity metric scores to assessing the sustainability of forest operations, and examine the basis for existing biodiversity metrics within various vegetation policy instruments which seek to apply an ‘improve or maintain’, ‘no net loss’ or ‘net environmental benefit’ test to assessing vegetation change
• Compile all raw field data used to derive metric scores for Biometric and Habitat Hectares from the eastern Victoria, northern NSW and southern Tasmanian studies funded by JVAP
• Derive benchmark values for the variables in the Biometric and Habitat Hectares schemes, using regional data sets from the NSW Department of Environment and Conservation, the Victorian Department of Sustainability and Environment, and the Tasmanian Forest Practices Authority which are aligned with the sampled forest types in each study
• Test individual variables, surrogate scores and metrics with independent variables and indices summarising the condition of the vegetation and ecosystem properties and report using univariate and multivariate analyses
• Develop recommendations on the applicability of existing metric scores for assessing the sustainability of forest operations and recommend alternative scores or approaches.

In the four case studies, the biodiversity surrogates were assessed against the known forest management inputs, with a wide range of independent variables collected from detailed vegetation, ecological, fauna and timber assessments. The assessment of the Biometric and Habitat Hectares systems focussed more on their component biodiversity surrogates (e.g. plant species richness, fallen log volume) and less on their compiled metric scores, which are highly dependent on vegetation landscape context and the form of the additive or multiplicative terms used to derive the summary values. In order to provide a meaningful comparison, the analyses presented are limited to those variables in common across the studies, or those present in at least two of the studies.

Results/Key findings
The Biometric and Habitat Hectare systems differ in the nature of their biodiversity surrogates, and the degree to which the raw values for the biodiversity surrogates are converted into information based on benchmark values or predicted values over time or with a given management type (e.g. cattle grazing, weed control). In Biometric, the biodiversity surrogates are weighted largely upon their ease of replacement (e.g. hollow bearing trees or plant species richness); in Habitat Hectares they are weighted by vegetation quality criteria such as the existing cover and richness of plant life forms, the presence of large trees and site weediness. The Biometric system places more emphasis on vegetation and habitat condition using functional criteria, the Habitat Hectares system places more emphasis on vegetation quality or compositional criteria.

The empirical assessment of individual biodiversity surrogates often produced variable results or was highly context dependent. The majority of the surrogate attributes appeared insensitive to forest management, although their sensitivity was relative to the benchmark values adopted for the particular ecological community and the systems used to categorise and score the field values. A number of surrogates examined, for example hollow bearing trees, large trees in excess of the benchmark size class, and a small number of late successional faunal groups, were useful in discriminating between sites with different forest management treatments, that is, mature and regrowth forests.

The cumulative site metrics were able to demonstrate compliance with sustainability policy criteria such as the Victorian Native Vegetation Management Framework with relative ease. The implication was that harvesting systems which retain a component of mature forest stand structures, either via variable retention or patch retention systems, will be more likely to score highly in the offsets policy 10 year threshold. However this study does not interpret this as evidence that the forest management regime is sustainable or the policy requirement is appropriate. Too much uncertainty exists in the outcomes of forest management actions for a policy as simple as a site reaching 50% of the pre-harvest site quality score within 10 years to be considered ecological sustainable.

The highly variable results of the ecological surveys conducted in the regrowth and mature forest stands illustrates the difficulty of not only using surrogate attributes to predict species occurrences, but of interpreting complex species-environment relationships using additive or muliplicative biodiversity metric scores. Components of the site condition score of Habitat Hectares and the site value score of Biometric do however have the potential to form part of a reconfigured index or measure of the sustainability of private native forestry, once additional criteria such as stand structural diversity are included and ecologically sustainable forestry is elaborated in a form related directly to the individual surrogate measures and their benchmark values.

Implications for relevant stakeholders
The studies reported here represent some of the first available in eastern Australian to quantitatively assess, using independent data, the value of biodiversity metrics in predicting ecological change. The quantitative field data which was collected serves to illustrate the value of underpinning land management decisions with transparent metrics rather than expert-based systems or qualitative policies or prescriptions that are not amenable to such direct examination. Having documented, transparent and quantitative metrics means that the data can be critically examined, a key feature of any public policy instrument.

The results of this study indicate that biodiversity surrogates and to a lesser extent compiled metrics have considerable potential in the assessment and monitoring of private native forestry – such as environmental and operating compliance with standards for vegetation and ecologically sustainable forest management.

Components of the metrics and scoring systems were useful in examining the sustainability of private native forestry; however the framework they were developed for (vegetation quality or condition) is not the same framework needed to examine native forests managed for, among other values, a flow of wood products. Critics of these metrics need to be mindful. Both Habitat Hectares and Biometric were developed with a specific suite of policy and operation criteria, and any metric developed for a private native forestry application would need to do the same.

For a new biodiversity metric to be derived to assess the condition of managed private native forests, clear objectives and operational setting are required. An approach could be:
 

1. Define management or policy objectives and operational constraints.
2. Develop an appropriate conceptual framework for the ecosystems under consideration.
3. Select an appropriate suite of indicators or vegetation attributes.
4. Consider the options available for combining these into an index.
5. Use data collected at broader scales to place the site in a landscape context.

Recommendations

• Further development is required to define the most appropriate surrogates for forest sustainability in the context of management for harvesting, before certification schemes, regulatory agencies and reporting organisations could adopt them.
• The regional studies examined in this report indicate that the existing surrogates and metrics have varied applicability across the ecological communities and stand management types examined. Metric scoring must be based on realistic ecological classifications and benchmarks. As part of evaluation, it is important that sites which represent experimental controls and environmental stratification are included; without this control, the assessment of the sensitivity of the surrogates and metrics will be limited.
• If considered important enough to be applied to private native forestry, biodiversity surrogates and metrics must undergo prior testing against real long term ecological data collected over at least ten years to reflect the time frames and thresholds that current policies are using.
• There is an opportunity to use several existing long term, replicated and well managed ecological experiments to test how the surrogates reflect ecological changes over time, and to examine options for reconfiguring a metric to assess the sustainability of private native forestry. The experiments are at Cabbage Tree (East Gippsland, Victoria), Tanjil Bren (Central Highlands, Victoria), Warra and upper Florentine (southern Tasmania), Wauchope (mid north coast NSW) and Bago (southern NSW tablelands) and cover the range of forest types managed by private native forest growers. Pre-existing measurements would allow examination of the temporal response of different metric parameters, and importantly a range of independent variables to assess their surrogacy value for other forest values. Specific forest management activities could also be examined, for example fuel reduction burning and thinning, and retention systems which have the potential to be considered as part of the offset calculations.
• Several alternative approaches to the analysis of the data presented in this report are worthy of consideration. The a priori division of plots into management histories such as regrowth and mature in East Gippsland, or the revision of the stratification design used in north eastern NSW to characterise silvicultural treatment along a continuum using an independent measure such as dbh distribution or a size/age class diversity index could improve sensitivity of the analysis. This would aim to detect more subtle continuous variation between plots.
• In the regional case studies evaluated, the metric scores derived from the managed forest stands were highly dependent on how the metric was compiled, the method of deriving the benchmark threshold or range of values, and how the individual surrogate was measured in the field. Definition of consistent methodologies for assessing sites, benchmarks and forest management inputs is warranted.
• These metrics have direct applicability in certification audits because they are based on repeatable methods and measurable environmental outcomes, unlike other certification systems based on assessment of management inputs. Any proposed use of biodiversity surrogates and metrics for certification should consider:
• the costs for the private native forestry industry in adopting metric scoring systems to assess their ecological sustainability
• consistent monitoring and reporting systems to allow cross-compatibility and statistical power
• national reporting standards, adopted from one of the existing frameworks such as the Montreal Process, and reconfigured to resemble an offset policy outcome
• trade offs between dimensionality (how many parameters or surrogates), flexibility (can compromise sensitivity) and representation within environmental indices reconfigured to specific circumstances.

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