Part 3 - Alternatives to Analogue Ecosystems
Part 2 of this series of articles finished with the question “Is comparison with analogue transects the best way to assess rehabilitation success?” This is an issue that many within the environmental field have been grappling with. There is currently no guidance or agreement on what is an acceptable standard for rehabilitation and each mine site is expected to develop site specific completion criteria based on the unique characteristics of the site.
Although comparison to analogue ecosystems has conventionally been the basis for setting completion criteria, it may not be the most appropriate method for assessing rehabilitation success in all situations. A couple of alternatives to comparison with analogue sites are discussed below.
Comparison with Rehabilitation in the Region
In many areas of Western Australia rehabilitation has been done for 30 years or more over hundreds of mine sites. There is now a substantial body of knowledge regarding rehabilitation techniques and what can be achieved. Therefore, comparison of a site with the best rehabilitation performance that can be achieved in the region may be an appropriate basis for assessing rehabilitation success.
However, this concept does come with two major disclaimers:
- A reasonable level of effort needs to have been put into ensuring that rehabilitation will be a success. Poor rehabilitation performance in an area to due inadequate effort cannot be used as the basis for setting low standards for completion criteria. This may make this concept only suitable for sites or geographical areas that have a track record of rehabilitation success.
- Individual sites or landforms need to be compared to other areas with similar materials and levels of disturbance. For example, rehabilitation of a waste rock dump constructed of saline, sodic material can never be expected to have the same result as rehabilitation of a borrow pit in lateritic material.
Astron has worked on a project where a mining company set criteria for rehabilitation performance based on comparison to rehabilitated landforms within their site; for example, species richness reaching 70% of the best achievable species richness at the site within each individual rehabilitation area. See the graph below for an illustration of how this type of criterion can be assessed.
Comparison with a regional database of rehabilitation performance would provide an even more robust basis for setting completion criteria based on comparison with existing rehabilitation rather than only comparing within a site or company. The setting of an absolute minimum standard that must be achieved may also be required.
Identification of Key Environmental Values or Services for the Proposed Post-Mining Land Use
Another basis for developing completion criteria is to consider what is really required for the land to serve its proposed post-mining land use. If the post-mining land use is to return a self-sustaining native plant community that is as close as possible to the original then comparison with analogue or reference sites may be an appropriate basis for judging rehabilitation success.
However, in many areas where mining occurs in Western Australia the proposed post-mining land use is a return to pastoral land. For this post-mining land use, the land needs to be returned to a state which will support grazing with low stocking rates. The key aspects to measure for this land use could be focussed on two key areas:
- Are the plants present suitable for grazing?
- Are they present in high enough numbers to be sustainable and support the required stocking rate?
In this instance the species to be returned should not necessarily be driven by what is present in an analogue ecosystem – it should be driven by what can actually be grown post-mining (hopefully some trials have been done to test what can be achieved) and what is palatable to stock (or what species the post-mining land owner wants returned). Similarly, the target vegetation cover or density should be based on what is required to suit the post-mining land use and is sustainable, not necessarily what occurs in an analogue or reference ecosystem.
This concept can also be applied to other post-mining land uses and land owners/managers. For example, land that will be reverting to management by Traditional Owners may be focussed on returning the species they have identified as important for their use of the land, such as bush tucker or traditional medicine plants.
Stay tuned for the final article (Part 4) in this series where some of the advantages of landscape scale monitoring and how it can be used for rehabilitation monitoring no matter what the basis for assessment of success will be discussed.