A limited range of native plant species have been tested for revegetation purposes on coal mines in the Hunter Valley, with exotic grasses and native upper canopy species representing only a few families and genera being utilised for rehabilitation. In contrast to the high maintenance requirements of areas dominated by improved pasture grasses, the introduction of a greater richness of native species will reduce the ongoing maintenance and increase the likelihood of the development of a self-sustaining vegetation community. The aim of this study has thus been to assess the establishment success of a range of native understorey species on land following coal mining in the Hunter Valley, New South Wales, and to determine key factors affecting establishment.
Twenty-three species representing nine families were selected for this study. Seven species were from the Mimosaceae family, four from the Fabaceae, three each from the Casuarinaceae and Asteraceae, two from the Myrtaceae and one each from the Sterculiaceae, Rutaceae, Meliaceae and Bignoniaceae families. All species were commercially available and local to the mining areas that were the focus of this project. The selected species were tested for viability and germination under laboratory conditions and also monitored for emergence in a range of mine media under glasshouses conditions. On-site studies commenced in spring of 1996 and 1997 to assess the emergence and survival of these same species under field conditions at four mine sites: Hunter Valley No. 1, Mount Owen, Ravensworth and Warkworth Mines.
Higher levels of emergence were recorded for most species in the laboratory and glasshouse studies than in the field, mainly due to the non water-limiting conditions of the controlled environments. Based on the results obtained in this study, total field emergence of 1% or greater was used as a benchmark for species success. Highest emergence was obtained for Acacia cultriformis (>12%). Other species which had greater than 1% field emergence were Allocasuarina littoralis, A. verticillata, Hardenbergia violacea, Kennedia prostrata, Swainsona galegifolia, Melia azedarach, Acacia decora, A. falcata, A. longifolia, A. salicina and Bractiychiton populneus. Many of these species persisted for at least the three-year monitoring period and could be considered for inclusion in seed mixes for revegetation purposes on site.
Of those species which showed field emergence of less than 1%, some could still be considered for inclusion in the revegetation program. High rates of success under glasshouse conditions indicates the potential for improved field emergence in more favourable climatic conditions. In addition, a number of species with dormancy mechanisms identified could be included if appropriate pretreatments to break dormancy are found to be feasible and practical prior to broadscale seeding.
Species emergence and survival success was influenced by the substrates in which they were sown. Overall, the Mount Owen topsoils and spoils supported highest emergence. The topsoil from Mount Owen Mine is considered highly favourable for species emergence and survival, due to its more favourable chemical and physical characteristics and limited exotic seed content. Of the remaining mine media used in the glasshouse and field trials, best results were obtained from the non-topsoil materials, a direct result of a lack of competition from exotic pastures and weeds.
The diversity of species currently utilised for mine revegetation purposes can be increased given the success of the selected species tested in this study. Many other species may also be found to have potential, given the appropriate testing. Thus, further research on native understorey species for the revegetation of degraded land and for the enhancement of biodiversity in general, is recommended.