In the final article of this series on the importance of getting the basics of rehabilitation right, Astron’s Rehabilitation Principal Scientist, Katina De Sousa, provides some advice to clients on what is required to achieve success. Previous articles covered the first seven steps of the ten step rehabilitation process proposed by Toy and Daniels (1998) (Read Part 1, Part 2 and Part 3). In this article, the last three steps of the process relating to revegetation, irrigation and site monitoring and maintenance are discussed.
- Site characterisation
- Rehabilitation planning and engineering
- Material management
- Topographic reconstruction
- Replacement of topsoil or soil substitute
- Surface manipulation
- Addition of soil amendments
- Site monitoring and maintenance.
The development of a stable, self-sustaining vegetative cover is the principal goal for most rehabilitation projects. Three sources of propagules are available for rehabilitation: topsoil containing a soil seed bank, application of seed and tubestock (nursery produced seedlings). In Western Australia, active return of plant species is generally required because if seeding does not occur the resultant flora only reflects the soil seed bank and species that are able to disperse to a site, such as native and exotic ephemeral species (Norman et al. 2006, Standish et al. 2007). If the soil seed bank was depleted because it had been stockpiled then few plants would establish from this source (Koch et al. 1996).
Detailed discussion of revegetation techniques is beyond the scope of this article, however key areas to consider are:
- Application of a diverse seed mix is important as the vegetation composition of rehabilitated areas will likely strongly reflect the initial species mix and will not become more similar to the adjacent undisturbed vegetation over time – that is the initial floristic composition determines future shifts in dominance (Norman et al. 2006).
- Many native species cannot be established readily from seed or may require specific treatments to ensure germination (Commander et al. 2009, Turner et al. 2013).
- Seed collection needs to be planned in advance to ensure adequate volumes are available when required.
- Timing of seed sowing, particularly in arid regions, can profoundly influence seedling emergence (Commander et al. 2009, Turner et al. 2006). Seeding should be undertake at the optimal time and immediately following surface preparation before a surface crust forms.
- Materials with high salinity levels may need to be left to leach prior to seeding.
- In Western Australia seeding is often done in conjunction with ripping using a seeder box mounted on the back of the dozer. Seeding can also be conducted using a helicopter or by hand if areas are not too large, though walking on uneven ground can prevent a HSE risk.
Irrigation is not commonly used in rehabilitation at mine sites in Western Australia. However, in some situations where rapid establishment is required, such as establishing a visual screen around the boundary of a site, irrigation may be worth considering.
When you finally get to the end of the rehabilitation process it is important to consider how long you are likely to have to monitor a site for before being able to get the regulator to sign off on the success of your rehabilitation. Monitoring needs to be efficient and affordable if it has to be conducted over multiple years. Current monitoring methods are often criticised by being too focussed on small transect areas that are not necessarily representative of how a landform is performing as a whole. This is often observed in the field when a transect is located right next to an erosion gully, but as the gully is outside the transect the monitoring data may indicate that the landform is stable and at a stage ready for sign off by the regulator. Wherever possible, new technologies such as remote sensing should be considered so that monitoring can be undertaken at a landscape scale, with the added benefit of potentially being able to reduce monitoring costs.
Well that ends our four part series on the ten steps of the rehabilitation process...Stayed tuned for more information on the contribution of vegetation mulch to successful rehabilitation.
|Conducting rehabilitation monitoring, Mid West||Rehabilitation in the northern Goldfields (WA)||Rehabilitation in the northern Goldfields (WA)|
Commander, LE, Merritt, DJ, Rokich, DP and Dixon, KW 2009, ‘Seed biology of Australian arid zone species: Germination of 18 species used for rehabilitation’, Journal of Arid Environments, vol. 73, pp. 617-625.
Norman, MA, Koch, JM, Grant, CD, Morald, TK and Ward, SC 2006, ‘Vegetation succession after bauxite mining in Western Australia’, Restoration Ecology, vol 14(2), pp. 278-288.
Standish, RJ, Cramer, VA, Wild, SL and Hobbs, RJ 2007, ‘Seed dispersal and recruitment limitation area barriers to native recolonization of old-fields in western Australia, Journal of Applied Ecology, vol. 44, pp. 435-445.
Toy, TJ and Daniels, WL 1998, ‘Reclamation of disturbed lands’, in RA Meyers (ed) Encyclopedia of Environmental Analysis and Remediation, Wiley, New York.
Turner, SR, Pearce, B, Rokich, DP, Dunn RR, Merritt, DJ, Majer, J and Dixon KW 2006, ‘Influence of polymer seed coatings, soil raking and time of sowing on seedling performance in post mining restoration’, Restoration Ecology, pp. 267-277.
Turner, SR, Steadman, KJ, Vlahos, S., Koch, JM and Dixon, KW 2013, ‘Seed treatment optimizes benefits of seed bank storage for restoration-ready seeds: the feasibility of prestorage dormancy alleviation for mine-site revegetation’, Restoration Ecology, vol. 21(2), pp. 186-192.