Alcoa’s rehabilitation mosaic

Bauxite mining in the Northern Jarrah Forest

As the most abundant metal in the Earth’s crust, aluminium is all around us from the planes, trains and cars we use to navigate, to the computers and phones we use to connect. As a plentiful, lightweight, durable and infinitely recyclable material, it will continue to stick around, especially given its emerging role in renewables energy technology.

According to the International Aluminium Institute, aluminium is one of the most recycled materials on earth, with almost 75% of the 1.5bt ever produced still in use today.

As a major input for solar panels and wind turbines, we need aluminium that will last into the future. As a result, aluminium is increasingly tied up in long-life products, meaning there is still growing demand for sustainably produced aluminium.

The process to make aluminium begins with mining bauxite, which occurs in certain locations globally including WA’s Northern Jarrah Forest, where Alcoa Corporation (ASX: AAI) has mined for bauxite since the 1960s.

Alcoa has now found itself with a dual responsibility: to provide the bauxite needed to enable essential technologies and propel us to net-zero while also taking special care of the ecologically significant environments it operates in.

As a result, the company has committed to an extensive forest rehabilitation plan across its operations, involving robust monitoring, prolific research and holistic remediation approaches.

The Australian Mining Review had a first-hand look at the company’s Huntley mine site to see Alcoa’s rehabilitation efforts up close.

Forest footprint

Alcoa expects to clear less than 8% of its mineral lease which spans an area east of Perth, down to Collie. Despite this, the company is fervently committed to leaving the forest better than it was found.

Working collaboratively with government, research institutions and other stakeholders, the company has developed a leading rehabilitation program with the goal of ensuring optimal return of plants and animals where mining has finished. Over 500ha are now rehabilitated annually, with plans to double that rate by 2027.

Although the forest is home to ecologically and culturally significant old growth stands, 98% of the Jarrah Forest has been historically harvested in the past, according to Alcoa. Alcoa only mines in areas that have been previously logged, avoiding old growth forest, national parks and areas of high conservation value.

The company has rehabilitated 75% of mined areas, with a focus on species richness and understory diversity. The goal is to establish self-sustaining forests similar to unmined areas. Once rehabilitation is completed, determined through agreed completion criteria, Alcoa will return the forest to the State.

Alcoa has been adapting to an ongoing evolution of rehabilitation criteria for Jarrah forests since its first rehabilitation efforts in 1966. There has been a shift in priorities over time, from high-density timber plantations to biodiversity-focused approaches.

Now, rather than focusing on growing as many straight and towering trees as quickly and closely as possible, key metrics include native flora, understory species richness and tree density that allow the forest more room to breathe.

Since 1988, only local native species, such as Jarrah and Marri, have been used in Alcoa’s rehabilitation. This proliferation of local species not only better reflects the forest’s pre-industrial state, but also creates a more resilient environment that can bounce back against potential threats such as die back and fire. Alcoa is the first mining company to achieve 100% plant species richness return.

What is rehabilitation, really?

Rehabilitation isn’t simply about planting millions of trees, it is about supporting a continuously evolving, dynamic and diverse environment. This takes many forms and with it comes a variety of challenges.

There is general concern over the strength of rehabilitation outcomes when it comes to bauxite mining, as the soil substrate is effectively dug out for bauxite processing. To overcome this, Alcoa has developed an approach that first focuses on returning the soil to a more natural state.

Following bauxite mining, landscaping takes place. This is where mined out pits, haul roads and any supporting infrastructure are reshaped to better blend with the surrounding topography. Alcoa achieves this using 3D technology. This technology is employed to design the pit area, ensuring the land is shaped correctly to retain water.

After landscaping, deep-ripping takes place. This relieves ground compaction from mining. The benefits of this are two-fold: rainfall can better infiltrate the soil and the roots of plants can better penetrate the soil, allowing for improved establishment and survivability.

What stands out the most is Alcoa’s soil return, which follows landscaping and deep-ripping. During the mining process, Alcoa collects and stores overburden and topsoil. This is crucial, as the soil topsoil not only supports but also defines how the forest can evolve. The topsoil, which is the top 75-150mm layer, is considered the “gold” for rehabilitation as it contains the seed bank and nutrients.

This fresh topsoil can only be stockpiled for up to 3 months during summer, as longer storage can degrade the seed bank and nutrients. After landscaping and contouring, the overburden is first returned, with the topsoil applied on top of it.

Returning the original topsoil for rehabilitation ensures the landscapes reflect what was previously there as closely as possible, both in nutrient composition, soil profile and plant species present. This topsoil is the lifeblood of the rehabilitation process, with about 70% of plant species richness returned from the reintroduction of the fresh topsoil. The other 30% comes from collected seeds and nursery-raised seedlings.

Following the soil return, habitat return is conducted, where logs and rocks that were previously moved are returned to create fauna habitats, encouraging the return of reptiles and mammals that help re-establish forest ecological processes.

Then, contour ripping is conducted. This creates wave-like grooves and ridges as the area is ripped on contour to help water infiltrate into the soil, assisting in seedling establishment.

Next, plant return takes place. There are multiple steps involved in returning native plant species that make up the forest ecosystem beyond the seeds found in the fresh topsoil. Collected seed. including species that have undergone heat or smoke treatment, is applied with an air seeder or by hand.

There are some plants, known as recalcitrant species, that are difficult to establish from seed. Alcoa takes the extra step of carefully growing these species in labs and then introduces them to the rehabilitation site roughly 12 months after initial seeding. This ensures the establishment of more challenging plant species to achieve the desired forest structure and biodiversity in the rehabilitated areas.

Natural fauna return to the rehabilitated areas is another important aspect of the process. According to Alcoa, all mammal species and about 90% of birds and reptile species have so far been recorded in the rehabilitated forest.

Monitoring of the rehabilitated sites is ongoing and includes assessments at nine months, 15 months, and 24 months post-establishment, with remediation if criteria are not met.

Nine months after the first winter season, ecologists assess the rehabilitation quality.

A small amount of fertiliser is applied once to 15-month-old rehabilitation in late winter or early spring to balance growth and diversity. At 15 months, ecologists also reassess the rehabilitation quality to ensure it is on track to achieve the agreed completion standard.

At 24 months, Alcoa monitors the landscape for any erosion issues. The company then continues to monitor for bare areas using aerial imagery.

Good things take time

Once rehabilitated sites are at least 12 years old, Alcoa can assess whether it meets the completion criteria to be handed back to the State.

The completion criteria are expansive, concerning evolution over time, tree form, understory diversity and species richness. The youngest rehabilitation in a given forest block must be at least 12 years old before the entire block can be considered for handback. The goal is for the rehabilitated areas to be integrated into the standard forest management practices of the State, including activities like controlled burning and thinning.

During rehabilitation, Alcoa hopes to encourage ecological succession, the gradual process of change in the species that make up an ecological community following a disturbance to the existing habitat, in this case, bauxite mining.

Following rehabilitation establishment, the next stage of ecological succession is early establishment, between 1-5 years. At year three of rehabilitation, there should be a dominant shrub layer, emerging tree saplings and early development of fauna refuge.

Following early establishment, the forest is in its juvenile stage from 5-15 years. At year nine, the canopy layer should be developing, with young trees, reaching up to 10-12m in height. At year 12, there should be a distinct overstory, while the midstory and understory develop further. At year 14, the visual effects of mining should be minimal, thanks to the growing canopy.

After the juvenile stage, the forest is in its resilience stage from 15-30 years. At year 16, Jarrah and Marri trees should grow to 15m in height. At this point, prescribed burning may be conducted by an external agency.

Back to the bauxite

This approach to rehabilitation doesn’t just change the environment, it has also fundamentally altered Alcoa’s bauxite operations for the better.

One way the company is looking to improve its practices is through the process of decoupling. This means Alcoa is decoupling the mining and processing of bauxite ore, allowing the company to accelerate the rehabilitation process so that it can begin while mining is still ongoing, thus speeding up the entire rehabilitation timeline.

Traditionally, Alcoa would mine an area and immediately process the bauxite ore. With decoupling, ore will be mined and then stockpiled. Alcoa can then begin the rehabilitation process, without waiting for the mining to be entirely completed at a certain pit. This also means pit lifespan may be slightly longer.

Alcoa’s holistic and sustainable approaches to its mining and the environments it operates in are just part of what has earned the company the reputation of being among the lowest carbon dioxide emitting alumina producers.