ICMM - International Council on Mining & Metals

CASE STUDY

Restoring a forest after bauxite mining

Background

Alcoa World Alumina Australia operates two bauxite mines at Willowdale and Huntly in the Darling Range of southwestern Australia, 80 - 140 kilometres south of Perth. The Huntly mine is the largest bauxite producer in the world. The mine pits range in size from one hectare to tens of hectares. Alcoa has been rehabilitating its bauxite mines since 1966; today some 550 hectares are mined and rehabilitated annually. The technology of rehabilitation has been improved continuously over the years – from plantations of exotic pine trees to a sophisticated state-of-the-art rehabilitation programme.

Alcoa’s aim after bauxite mining in these areas is to re-establish all the pre-existing land uses of the forest: conservation, timber production, water production and recreation. Re-establishing a jarrah forest on the mined areas that is as similar to the original forest as possible was determined to be the best way to achieve this goal.

The Jarrah Forest

The jarrah forest is renowned for its diverse flora, being one of the most plant-species-rich forests in the world outside of tropical rainforests. It has a high conservation value, is the basis of a major sawmilling industry and is widely used for recreation pursuits. Restoring botanical richness is thus seen as an important component of re-establishing a jarrah forest.

A jarrah forest contains at least 784 plant species. Alcoa’s research and monitoring showed that among the vegetation types mined by the company there were approximately 300 plant species. Monitoring of rehabilitated bauxite mines found that the long-term vegetation of the site was controlled by the species first established there. The vegetation and the individual plant species are very resilient to natural forms of disturbance, so it is important to establish the correct flora early on.

A Good Record – But Not Good Enough

Efforts to improve plant richness in rehabilitated mines commenced in the mid-1970s, when the first studies were made of the seed content of forest soils. Ways to preserve seed viability in the soil and to separate the seed-rich topsoil from the remaining overburden were soon developed. In the late 1980s Alcoa started to monitor botanical richness in rehabilitated mine areas regularly. In 1990 the company recorded 65 per cent as many plant species in newly rehabilitated areas as in adjacent native forest – and this was using best-practice rehabilitation methods of the time. The company’s determination to do better than 65 per cent led to a 10-year research and development programme to improve rehabilitation practices.

Alcoa developed and implemented many innovative practices and technologies in the areas of seed treatment, seed application, topsoil handling, mine planning and native plant propagation. Collaborative projects to develop the science further were established with academic staff and students.

The Rehabilitation Process

The rehabilitation process starts with shaping the mine pit to produce a landscape that blends with the surrounding forest. Seeds of local plants are spread throughout the rehabilitated mine pit. Nursery-grown plants are also added, in the case of species for which seed is not a viable method of establishment.

Research in the late 1970s and the 1980s established that directly returning topsoil to a rehabilitated area greatly increased botanical richness. But planning for direct topsoil return can be complex, and operational constraints can result in topsoil being stockpiled. So part of the challenge was to improve planning processes and to implement plans to maximise the direct return of topsoil. Improvements had to be made at all stages of rehabilitation. This involved refining existing practices, developing new practices, developing better mine planning tools, developing new technology and further increasing environmental commitment.

Five important components of Alcoa’s approach to restoring the jarrah forest are worth noting:

• Identify opportunities to improve the number of plant species.
• Select research projects. Some projects were major investments, with the involvement of universities and other research organisations; other research took place solely within Alcoa.
• Build the infrastructure and equipment. In the development phase, infrastructure such as a micropropagation laboratory was built, and equipment such as mechanical seeders and large-scale soil screens were designed and constructed.
• Track changes to botanical richness. Monitoring occurred every year using a scientifically based sampling regime.
• Set clear targets. Stating an objective for the rehabilitated areas – to restore a functional jarrah forest ecosystem that matched the pre-mining land uses – was a significant step forward for the company.

A Restored Forest

The programme started with five-year improvement milestones. The first milestone was to achieve 80 per cent of forest-species richness. When this was accomplished, a new milestone was set for 2000 – that on average 100 per cent of the indigenous plant species found in representative jarrah forest sites would also be found in a 15-month-old rehabilitation, with at least 20 per cent of those found being from a recalcitrant-species priority list.

Alcoa reached its goal. In 2000, at the two operating mines at Huntly and Willowdale, the company achieved an average of 100.7 per cent – in other words, all the rehabilitated areas had on average the same number of indigenous plant species as found in nearby jarrah forests. The goal now is to maintain this good record and thus the botanical richness of the area after mining there.