Restoration of Akaroa Quarry – Tasmania – using a variety of methods

Todd Dudley  – North East Bioregional Network

In 2016 the North East Bioregional Network (NEBN) objected to a proposed re opening of a quarry to extract granite for an extension to the St Helens Point barway rock wall.

The mine is located in the St Helens Point Conservation Area and surrounded by coastal bushland in good ecological condition including Allocasuarina verticillata forest, Eucalyptus amygdalina forest and Melaleuca ericifolia swamp forest. Strangely mining is a permitted use under the Conservation Area tenure in Tasmania despite it being managed by Parks and Wildlife. Very few Conservation Areas have Management Plans which is an indictment on the Tasmanian Government’s priorities.

As with many coastal engineering projects the rock wall extension has been a black hole for millions of dollars of public money with minimal outcomes. Nevertheless, while the rock wall may have been a pointless exercise, NEBN were engaged in 2017 by Marine and Safety Tasmania (MAST) to rehabilitate the mine after the extraction was completed.

The mine site of around 1.5 ha, was relatively weed free. However it had been used by a local person to deposit their green waste so there was a small patch of weeds such as mignonette (Reseda luteola), Melalueca armillaris, Acacia retinodes and Scotch thistle present.

Our methodology for restoring the Quarry was as follows:

• Removal of garden waste and soil (there was one soil heap that was left and managed in situ by spot spraying because it contained mignonette and we did not want to spread it elsewhere)
• Ripping the quarry floor and some gentle slopes with an excavator to improve conditions for native plant establishment
• Applying jute matting to slopes to ensure there is minimal soil erosion
• Establishing a small sediment trap/pond and place rock in drainage lines to protect from erosion
• Collection and dispersal of local native seed-bearing branches of Allocasuarina verticillata, Allocasuarina littoralis, Melaleuca ericifolia, Banksia marginata, Kunzea ambigua, and Leptospermum scoparium.

The Allocasuarinas, Melaleuca and Leptospermum always have viable seed capsules on them which open within days after the branches are cut while Kunzea and Banksia seed is only available in late Summer/Autumn. Unlike many other Banksia, the Banksia marginata in this region sheds just about all of its seed every year.

The ideal time for direct seeding is mid-Autumn while it is still warm, but evaporation rates are declining so this gives plants a chance to get established in moister conditions (it can be very dry on the East Coast of Tasmania)

The branches also help to some extent to protect seedlings from browsing by wallabies

We have used this process on a number of quarry sites with good success.

The outcome has been excellent with all species establishing. In particular the Allocasuarina verticillata is growing vigorously with many trees over 3 metres in height 4.5 years after seeding.

In addition, natural regeneration of other species occurred due to the close proximity to native bush. Some of the other recruits included Acacia verticillata, Acacia sophorae, Monotoca elliptica, Olearia lirata, Kennedia prostrata, Correa reflexa, Pomaderris apetala and Muehlenbeckia gunnii to name a few.

The sediment trap/pond has hosted a good population of tadpoles this year (2022) due to the wet weather.

There was one hiccup in 2021 when the Environment Protection Authority (EPA) visited the site to monitor the progress of the restoration. After the inspection, the EPA deemed that a small section of the access road was not doing as well as the rest of the regeneration. They contacted MAST and directed them to import topsoil to be deposited on the road and then to plant it out.

Fortunately, MAST contacted NEBN and we produced a short report which was sent to the EPA explaining why this was the worst of ideas and that it would have most likely introduced a cocktail of weeds to the site as well ruining the prospects for both direct seeding and natural regeneration. While NEBN and MAST considered the restoration of the road access was satisfactory we ended up re ripping and re seeding the road and also caged some of the subsequent regrowth to keep the EPA happy.

For more information about the work of NEBN visit https://www.nebn.org.au/