Open Cut » Environment
Beyond the stage of reshaping spoil piles and other mine waste dumps to create landscapes that will ensure environmentally acceptable erosion and water quality control, one of the major challenges facing the rehabilitation of land disturbed by mining is the re-establishment of a self-sustaining vegetative cover. Given that the targeted post-mining land use for much of the coal mining area of eastern Australia has been one of returning the land back to grazing, most of the research emphasis in terms of species selection for revegetation programs has focussed on exotic pasture grasses. Due recognition of the importance of trees in a rural landscape has fostered a number of studies on tree establishment on coal mines and there is now a considerable bank of knowledge on the types of upperstorey species that may be suitable for re-establishment in a broad spectrum of mine media. Where neighbouring pastoral activities have not been as dominant and/or where the mine is in close proximity to uncleared forest or woodland communities, the use of tree species has been a more prominent component of seed mixes.
More recently, however, there has been an increasing interest in returning native communities in their entirety to disturbed and/or degraded landscapes, and as such, an increasing awareness of understorey species and their importance and relevance to biodiversity. This stratum of species has received considerably less attention than the major tree genera in revegetation programs, but is critical to ecosystem stability and functioning as it supports soil microbial and mesofaunal communities (essential for effective nutrient cycling), assists in erosion control and improving soil structure, and provides food, shelter and habitat for fauna.
Little is known about the basic biology of many of these species, let alone their ability to re-establish on disturbed landscapes. Therefore, with the financial support of the Australian Coal Association and the New South Wales Minerals Council, and the logistic support of nine mine sites, a research project was developed to address and understand the key issues that would assist in establishing native understorey on post-mined land. The project was divided into four stages. The first stage involved the formulation of lists of native understorey species in the surrounding areas of each of the mine sites involved. Species which were able to be supplied by commercial seed suppliers or were relatively easy to collect were obtained for use in the germination trials, which made up the second stage of the project. Those species which had the best germination results were then used in the third stage which involved glasshouse trials in the media commonly used for rehabilitation purposes at each mine. The fourth stage saw those species used in the glasshouse trials subsequently used in field trials set up in spring 1996, autumn 1997 and spring 1997. The aims of this research have been to first understand the germination characteristics of the species, followed by determining what the rate of emergence could be in ideal conditions, assessing the abilities of the species to cope with the chemical and physical properties of the various mine media likely to be encountered, and thereafter monitoring their actual performance in the field.
The nine New South Wales mines involved with the project were Hunter Valley No. 1, Mount Owen, Ravensworth and Warkworth (Hunter Coalfield), Baal Bone and Clarence (Western Coalfield), Westside (Newcastle Coalfield) and Tahmoor and West Cliff (Southern Coalfield). From across these sites, fifteen mine media (either one or two from each site) that were likely to dominate the surface of the post-mining landscapes were used in the glasshouse and field trials.
n addition to the information gained on species performances from the laboratory, glasshouse and field trials, the project has also produced a database reviewing the literature on the germination requirements and ecology of plant species occurring within New South Wales, and currently holds 780 records representing 519 species from 48 families. A CD version is being produced that includes information on seed availability, degree of success on mine sites and other disturbed areas, and a photographic record. For many species, the information from this project will be the only entry. A further output from the project is a herbarium, which consists of over 100 species and includes photographs and pressings from the understorey species at various stages of development. Since a fully functioning native species community is maintenance-free, the coal industry may benefit from a rehabilitation option of lower long-term cost. Beyond this, the wider community will also benefit through the transfer of the technologies developed into other arenas of degraded land rehabilitation, and also through the project's significant contribution to our basic knowledge about the characteristics of many species of native flora.