Evaluating the ecological and operational basis of vegetation condition assessments


  • Emma Gorrod

Evaluating the ecological and operational basis of vegetation condition assessments. Emma Gorrod School of Botany, University of Melbourne, Parkville, Vic. 3010, Australia, and NSW Department of Environment & Conservation, PO Box 1967, Hurstville, NSW 2220, Australia. Email: e.gorrod@pgrad.unimelb.edu.au.

Key words: habitat, management, uncertainty, vegetation condition.

Vegetation condition assessments as management tools.  Vegetation condition can be defined as the capacity of a site to provide habitat for all the indigenous species that may reasonably be expected to use it. Quantitative information on vegetation condition has recently been incorporated into policies and legislation for native vegetation management in Australia (ANZECC 1999; Natural Resources and Environment 2003; NSW Native Vegetation Regulation 2005). The general aim of each of these policies is to achieve a ‘net gain’ in the quality and extent of native vegetation. Indices of vegetation condition have been developed in a number of jurisdictions for this purpose, including Habitat Hectares (Parkes et al. 2003) in Victoria and BioMetric (Gibbons et al. 2005) in New South Wales.

Habitat Hectares aims to assess how ‘natural’ a site is by comparing it to the same vegetation type in the absence of major ecosystem changes that have occurred following European settlement of Australia (Parkes et al. 2003). BioMetric aims to assess the value of native vegetation for terrestrial biodiversity at a range of scales (Gibbons et al. 2005). Both indices score a similar set of site and landscape context attributes, with different scoring systems and index construction. Human value judgements are embedded in the selection of attributes and scoring methods of these indices.

Evaluating the ecological basis of vegetation condition assessments.  A number of theoretical and practical methods will be used to evaluate the ecological basis of vegetation condition assessments, commencing with an analysis of the ecological theory and assumptions that underlie these indices.

The properties of the indices will be investigated by constructing a matrix to assess the correspondence between the attributes scored in condition assessments and habitat requirements for a range of species that may be expected to use a patch of grassy woodland. This will help to identify groups of species and groups of habitat attributes for which vegetation condition assessments theoretically perform both well and poorly.

I will assess vegetation condition assessments in patches of grassy woodland in a range of condition states on the Cumberland Plain. I will also record presence of groups of organisms including plants, birds and invertebrates and additional habitat information. These data will be used to validate the predictions of the matrix analysis and potentially lead to recommendations for improving the indices’ sensitivity to habitat suitability for groups of organisms.

In addition, the relationship between vegetation condition as measured by these indices and the contribution of a patch to population viability of will be examined for selected species.

Evaluating the operational basis of vegetation condition assessments.  The various types of uncertainty associated with vegetation condition assessments, including both epistemic and linguistic uncertainties, will be evaluated. Operational uncertainties will be examined by comparing conducting vegetation condition assessments carried out by different assessors in the field. I will investigate how uncertainty may be incorporated into these indices through relatively simple methods.

Management implications.  This research is intended to improve understanding of the strengths, weaknesses and sensitivities of indices of vegetation condition. The implications for achieving management objectives, particularly ‘net gain’ in native vegetation quality, will be considered.