Open Cut » Environment
Restoration can be defined as 'replacement of an ecosystem that was totally destroyed with one of the same kind' and 'the new ecosystem must be entirely reconstructed on a site that was denuded of its vegetation' (Clewell et al. 2005). Ideally restoration should allow transformation from a disturbed state to a state with structure and function similar to that which existed prior to the disturbance (Redi et al. 2005). However, a complete transformation is seldom attainable and “…a commonly accepted goal is one of rehabilitation-the reconstruction of an ecosystem that is a self-sustaining entity, requiring minimal or no maintenance or management, but that does not necessarily attain an exact pre-disturbance species composition…
The difficulty for rehabilitation performance assessment lies in determining that this goal has been reached. International guidelines on how to measure restoration success (SER 2004) listed nine ecosystem attributes, comprising three main groups - vegetation structure, species diversity (fauna and flora) and ecological processes (or ecosystem function) (Ruiz-Jaen and Aide 2005; Ruiz-Jaen and Mitchell Aide 2005). It is thought that if vegetation structure and species diversity (flora and fauna) match that in reference sites or are tending towards the values for reference sites, then a functional self-sustaining ecosystem has been restored.
Rehabilitation success relinquishment in the Bowen Basin will require some or all of the following biological criteria to be met (Nichols 2004):
- An indication that sustainable vegetation has been achieved, and that keystone plant species are established and reproducing (e.g. eucalypt canopy-forming species for woodlands);
- Presence of a range of faunal groups found in native vegetation with similar abundance and responding in a similar fashion to perturbation (natural or anthropogenic), and that certain keystone groups are present (e.g. hollow-forming termites; predators - spiders, wasps, ants; soil-forming groups - termites, ants; decomposer groups - springtails, mites).
Furthermore, rehabilitated lands must show development of similar fauna, or at least be shown to be proceeding towards development of similar fauna based on a comparison with reference sites comprising target end-use vegetation, e.g. grazing lands, remnant vegetation or forestry (McCoy and Mushinsky 2002; Patten 1997).
Invertebrates are key building blocks upon which ecosystem functioning and higher fauna such as vertebrates depend, and thus represent an important component of any determination of success or otherwise within rehabilitated landscapes. They contribute to a number of ecosystem processes (Daily 1997) including soil formation, nutrient recycling, decomposition, pollination, propagule dispersal, herbivory, food for vertebrates and a host of others (Majer and Brown 1998). It is these aspects of their ecology which makes them most useful as bioindicators of ecosystem functioning. If a viable group of invertebrates is present then the ecosystem is likely to be functioning properly, but the difficulty lies in establishing what a viable group of invertebrates constitutes. There is no easy way to do this, and ecological understanding of different habitat types is far from giving a complete picture of which elements are essential. The standard approach is to select reference sites located within a comparable landscape matrix to the rehabilitation under assessment, sample them simultaneously with identical sampling techniques, and compare assemblages. The metrics used for analysis can either be univariate (such as taxa richness, diversity indices, abundance) or biological signatures (Dangerfield 2005) where assemblage composition (species or higher level taxa) is compared using multivariate statistics based on similarity indices and ordination (Clarke 1993; Clarke and Gorley 2001; Clarke and Warwick 2001).
Biological community dynamics are influenced by a range of processes including seasonal, successional and longer term cyclic or directional changes. Another aspect of community dynamics is resilience to ecosystem disturbance such as drought, fire, flood, climatic extremes and physical disturbance, and the ability to persist following perturbations is an important measure of rehabilitation success. Important criteria for selecting bioindicators are that they must be sensitive to these aspects of community dynamism and that they must change in a reasonable time-frame. Invertebrates have natural advantages for measuring resilience in that: (i) they have short generation times, (ii) they are dependent on habitat features that are sensitive to short-term drivers of ecosystem change and (iii) they are relatively biodiverse with functional redundancy within guilds.
The main objective of this project was to use a meta-analysis of existing datasets to develop a sufficient understanding of the variability of invertebrate taxa within regional native vegetation to enable them to be used as target criteria for rehabilitated landscapes. Twenty datasets were assembled allowing insights into sampling protocols, identification of useful bioindicators, seasonal and interannual variation of invertebrate assemblages, spatial variation (within and between habitats) of these assemblages, reference site selection and approaches for assessing rehabilitation progress.