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Applied Seed

There are several ways plants can be returned to rehabilitated bauxite mines;
  • natural seed that is contained in the returned jarrah forest topsoil
  • seed that is collected from plants and then spread on the mined areas
  • plants that are grown in the nursery and then planted out
  • natural colonisation from the surrounding forest into the mined areas.
Each year Alcoa spreads over five tonnes of native seed onto bauxite mine rehabilitation areas.  More than four tonnes of this is zamia (Macrozamia reidlii) which has a large seed the size of a small egg.  The rest of the seed mix of normal small seeds is applied at a rate of approximately 1.3kg per hectare. The seed mix includes the two dominant tree species, jarrah and marri, banksias, sheoaks and approximately 50 to 90 species of the ground flora.  All of this seed is collected within approximately 20 kilometres of where it will be used because this ensures that the same genetic diversity that was present before mining is re-instated. This use of this local provenance seed is an important factor in restoring the conservation value of the forest.
Some species such as the dominant jarrah and marri trees re-establish well from untreated seed, but many jarrah forest plant species are dormant and require different conditions or treatments to germinate.
Species from the Pea family, often called legumes, for example, require a heat treatment before they will germinate. This natural adaptation allows them to germinate after fire or other disturbances in the forest. Testing of all species is carried out to determine the optimum heat treatment for the hard-seeded legume species.  Many other native jarrah forest plants also germinate prolifically after forest fires, but did not respond to simple heat treatments. In 1994, researchers at Kings Park and Botanic Garden discovered that smoke is the stimulant, not heat. Alcoa helped fund this research and was directly involved in field and laboratory studies which found that some plant species in our seed mix germinate better after smoke treatment. Accordingly, all seed is given the appropriate treatment before being incorporated into the seed mix.
The timing of seeding is important in the establishment of plants from applied seed. Based on the time-honoured agricultural practice of applying seed when the soil was wet, seeding had always taken place in early winter. This meant seed was falling on ground that had already developed a crust after autumn rains. However laboratory and field trials identified benefits of sowing seed in the summer, immediately onto the tilled soil. Seed burial and contact with the soil is improved and for some species the natural cycles of soil heating, cooling, wetting and drying also appear to improve germination rates.
Alcoa uses a computer controlled air seeding machine, attached to the ripping bulldozer, which has removed the strenuous task of manually spreading seed over all rehabilitated areas. A key feature of the machine is its ability to handle mixed seed of various size and shape from very fine to larger seeds, although because of their size Zamia seeds are still applied separately by hand.
Seed is now spread directly onto freshly ripped ground from the bulldozer, combining two tasks into one with far better results.

Preparing the rehabilitation seed mix

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Preparing the rehabilitation seed mix at Marrinup Nursery.

smoke treatment of seed

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Aerosol smoke treatment of seed to improve their germination rates.

Zamia seed

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Due to its size, the Zamia seed must still be spread separately by hand in the rehabilitated areas.