A mining history spanning 150 years has helped to spare significant areas within an Adelaide Hills mine from land clearance. Now a strategic program is building on this with a highly successful formula of seed collection, propagation, weed and feral animal control.
“Over 2013 we trialled a topsoil-removal/ direct seeding process to rehabilitate a former haul-road within the mine and an area we owned adjacent the mine. In both cases, dense stands of relatively weed-free native vegetation established over the following 18-months.” Nearly 350kg of native seed was harvested from the seed multiplication area in its firstyear, providing valuable seed stocks for the mine’s 2015 direct-seeding program. Hillgrove says the haul-road’s understorey is now vigorous and last year it supplemented this with tube-stock plantings of mid and uppercanopy species.
A long mining history together with an abundance of rocky outcrops has ensured large areas of native woodland and grassland remain on Hillgrove Resource’s 440 hectare Kanmantoo copper mine including the largest grove of untouched native Woodland in the Adelaide Hills. The vegetation of the mine spans two rainfall zones, providing an unusually broad range of high quality plant species. Current mining activities are set to disturb around 29 ha of remnant vegetation, however Hillgrove is offsetting this by establishing 200 ha of new native vegetation within the mining lease and surrounding properties. This ensures the mine provides the community with a locally-delivered Significant Environmental Benefit (SEB), protected by a Heritage Agreement for future generations to enjoy well beyond the time of mine closure. Existing native vegetation within the mining lease is being improved and extended through a program of weed and feral animal control and new plantings and this is also increasing the environments available for native animals. Several years ago, Hillgrove established an ambitious program of seed collection and propagation. The aim was to achieve the mine’s SEB target and ensure it had adequate, locallysourced seed to supply tube stock propagation and feed the mine’s large-scale direct seeding programs on cropping land and rehabilitated mine landforms. “An annual wild-seed collection program within and near the mine provides species diversity for our ‘Foundation Seed Mixtures’, while seed grown within the mine’s seed production area, and its five hectare seed multiplication area, provides most or our seed to establish new native vegetation dominant stands,” explains Catherine Davis, Environmental Manager at Hillgrove. So far this year the company has direct-seeded 20 ha using more than 350kg of native seed – all farmed at Kanmantoo or collected during wild-seed collection programs. ISSUE 01 RESOURCING SA Spring 2015
“Cropping land has a notoriously large weedseed bank and contains fertiliser residues that will challenge and swamp unwary native seeds without a little help”
Studies conducted by Hillgrove in collaboration with the Adelaide Botanic Gardens Seed Conservation Centre revealed that the bulk of weed seeds in the area originated from the top 80-120mm of soil. Therefore removing 100150mm of topsoil left a seed bed relatively free of both weeds and agricultural fertilisers.
Steve McClare, CEO and Managing Director of Hillgrove Resources says “it was essential that we engaged our local community in the planning of our re-vegetation program,” Catherine adds.
Scarifying using a grader’s tines, followed by soil conditioning with a tractor-towed ‘power rake’ provides a good seed bed for direct seeding.
“This provided us with a clear understanding of the local community’s expectations of us as custodian of the natural environment both in and around the mine.” Several members of the local community have also been actively involved in the program, with local Landcare volunteers helping to recover areas earmarked for disturbance. “Some of the rescued species were planted in our seed production area to provide future seed sources, with others transplanted to woodland areas,” says Catherine. Plant rescue days also recovered 95 rare Diuris behrii Donkey Orchids, now being propagated by the Native Orchid Society of SA. As a result, nearly 100 propagated orchids were returned to the mine during the winter of 2014 and a further 100 this year.
“This year we removed and direct seeded a further 13ha of top soil using graders and scrapers, which efficiently remove at least 100mm of topsoil from alternating strips though ex-cropping paddocks,” Catherine explains.
“We then hand broadcast the native seed mix. This provides a natural looking sward of native plants and avoids the linear ‘mechanical’ appearance of conventionally direct-seeded patches.” This year, the northern slopes of Kanmantoo’s tailings dam became available for planting, providing an opportunity for the mine to trial a high efficiency, direct seeding/land stabilisation technique which combines hydroseeding with an acrylic co-polymer binding agent. Steve explains “approximately eight hectares of the final landform was prepared and divided into 21 plots, with seven of these randomly selected and finished with either topsoil, subsoil or mine waste. “These areas will be monitored over the coming years to measure seed establishment and weed competition,” he says.
Catherine says the conversion of cropping land to native vegetation and the rehabilitation of mine landforms with native species, demands effective and efficient planting techniques based on broad-acre equipment and know-how.
“If the plots containing mine waste only with no top soil prove successful, then hydroseeding could provide an effective way for us to establish large areas of native vegetation over the mine’s waste landforms.”
“Cropping land has a notoriously large weedseed bank and contains fertiliser residues that will challenge and swamp unwary native seeds without a little help.
While justifiably proud of its achievements, Steve says Hillgrove will remain innovative and always on the lookout for better ways to nurture and grow its natural environment.
Published on Sep 25, 2015
This is the launch issue of Resourcing SA, a magazine focused on the people, communities and stories surrounding South Australia's dynamic m...