Improvements in native vegetation establishment on rehabilitated land at Eneabba are advancing with a multi-pronged approach of experimental assessment, training and trialling innovative methods. Nearly 700 hectares of land remain to be rehabilitated to native vegetation. The establishment of the native vegetation of this region – known as kwongan – is difficult given the diversity of plant species present and the nutrient poor sandy soils that hold little water and are prone to wind erosion. Revegetation of kwongan previously relied upon the harvest and spread of native mulch, which stabilised the soil surface against wind erosion, provided niches for germinating seed, and contained seed from bradysporous species (plants that hold their seed in the canopy). Mulch became unavailable at Eneabba after 2009 so alternative revegetation methods are being adopted and trialled. These methods, some of which are quite innovative, are already delivering improvements in the diversity and density of establishing seedlings.
The rate of revegetation at Eneabba is limited by seed availability. Iluka has increased the seed quantity, quality and diversity of species collected over recent years by training an in-house rehabilitation team. The team has been assisted by an expansion of the Eneabba local provenance (the region from which seed collection can occur) in 2015 that considered the latest scientific information and was approved by the regulating government authority. This gave the rehabilitation team access to more seed while ensuring seed collection minimises impact on the remnant native vegetation.
There is much potential in the broadcast seed used in revegetation. Experimental assessment at Eneabba in 2015 indicated that seven to eight times more seedlings emerge under ideal nursery conditions than from broadcast seed. Unlocking this potential is a key focus of trials in Eneabba revegetation.
Controlling both wind and water erosion has been critical for ensuring seedlings emerge and establish in the field. To control wind erosion Iluka changed from using cereal rye as a “nurse crop” – which was adopted to replace mulch but was demonstrated to inhibit native seed germination by an allelopathic chemical exuded from cereal rye roots – to applying a crust of dilute non-toxic bitumen emulsion to the sandy soil surface. This non-toxic crust degrades over a few years but does not inhibit germination. It allows seedlings to emerge and establish, protecting them from wind erosion. Combining this crust with the water erosion preventing techniques of ripping and mounding on sloping terrain in 2016, increased seedling establishment almost twofold in comparison to previous years.
Further improvements in seedling emergence and establishment have been shown in 2017 by trialling innovative methods. Soil imprinting, a technique developed in the 1970s, reduces rainfall run-off and increases infiltration and nutrient/organic matter accumulation thereby improving seedling emergence and establishment. However, the imprints erode too quickly in sandy soils such as found at Eneabba. A trial of soil imprinting in combination with a bitumen emulsion crust improved seedling emergence and establishment more than twofold on the practices adopted in 2016. These innovative methods will be adopted in future years to increase the quantity and quality of native revegetation at Eneabba.