More than 100,000 were planted in 2021 alone.
The total tubestock planted since rehabilitation began 13 years ago is now more than 750,000.
MRM health, safety, environment and community manager Adam Hatfield says there is a strong “local flavour” to the tree-planting program – the on-site rehabilitation team is made up solely of Territorians; two of the team are Indigenous trainees from the local community, with two more locals due to join soon; and more than 95 percent of the seeds are collected locally and propagated in the mine’s on-site nursery.
He says the rehabilitation of the river banks and installation of large woody debris are key factors in the river’s health.
“This milestone highlights the considerable commitment and work MRM is continuing to do to rehabilitate the McArthur River channel,” Adam says.
“We are continuing to see the number and diversity of fish, such as barramundi and freshwater sawfish, in the river channel reflect other sites in the region, which shows that our rehabilitation plan is working.
“At the same time, independent expert reports have found that the McArthur River is healthy, the water quality is good and fish from the river are safe to eat.”
MRM operates a plant nursery, which produces tubestock of native plant species for use as part of the mine rehabilitation program.
The nursery includes three shade houses, one used for seed propagation with 75 percent UV shade cloth and the other two used for tubestock growth with 30 percent UV shade cloth, and a hardening-off area where plants are exposed to full environmental conditions before being planted.
In 2020 and 2021, MRM continued to upgrade the nursery to support the revegetation program, including:
extending the existing hardening-off area, increasing capacity by about 30 percent
installing a concrete floor throughout the hardening-off area
constructing a perimeter fence to enclose the nursery and prevent access by animals
installing a water recovery system to capture irrigation runoff from the hardening-off area and shade houses for reuse, significantly reducing potable water use
laying concrete slabs for a new green shade house, which will be installed this year
The nursery is capable of supplying more than 150,000 tubestock a year, which will increase to about 200,000 when the new shade house is operating.
Trees planted are acacia, inkberry, whitewood, freshwater mangrove, bean tree, ghost gum, river sheoak, river red gum, coolabah, gutta-percha, river fig, cluster fig, white berry, northern swamp box, paperback, Leichhardt pine, river pandanus and wild plum.
Grasses are river grass, tall Tamil grass, golden beard grass and speargrass.
Selection of trees to be planted takes into consideration local availability of seed; surrounding vegetation to recreate a consistent riparian community; climate, including water availability; key species for threatened animals; soil availability and fertility; potential for erosion control; and landform, such as slopes and floodplain.
Seedlings propagated as tubestock have proved to be the most successful method of planting.
Planting is carried out along the waterline of the McArthur River diversion channel from a small boat at the start of the dry season.
As the channel’s water level lowers during the Dry, revegetation targets the banks of the channel where irrigation has been installed.
The minimum planting density is usually two grasses and two trees or shrubs per square metre.
Tubestock are planted with a slow release natural fertiliser tablet and water crystal, if required, to promote fast adaptation and health.