THIS WAS ONCE, THIS
Some of the landscapes we’re familiar with might not be what they seem. We assume they’re natural – stable coastal dunes, sweeps of banksia woodland, healthily diverse wetlands. And much of the time they are relatively untouched. But sometimes they aren’t. Many high conservation value wetlands, and highly disturbed coastal dune systems around Perth and the southwest have been rehabilitated following decades of human disturbance. Sections of both the Reid and Roe highways have also been given the treatment. When the Dawesville Cut was made at Mandurah, the five hectares of spoil was seeded and planted out to make it look as though the landscape had always been there, albeit now in a tidier format. Each of these sites happens to be the work of the collective of expertise which sits under the banner of Tranen Revegetation Systems. Since 2002, the team has delivered these amongst 740-odd rehabilitation projects. General Manager and natural area rehabilitation specialist Damian Grose describes what’s involved to transform bare earth to natural-like landscapes...
Listening to Damian describe what’s involved in getting these projects ‘right’ begins to sound like landscape version of horse whispering. He describes re-creating, as closely as possible, the look and function of natural systems. “We need to understand which plants should be growing where, and by looking at all the elements holistically, aim for optimum establishment and long-term success.”
By elements, Damian is referring to - amongst other factors - topography, soil, hydrology, and biology. He is foremost an environmental engineer, and that coupled with the Tranen team’s expertise in restoration ecology, natural areas, and project management means that no project is simply a case of putting plants into the ground.
Take the four-year long Melaleuca Park Wetland Offset project, completed in 2014. Here was an area of high conservation value wetland, surrounded by a former pine plantation. The client and Western Australia’s Department of Parks and Wildlife briefed Damian, James Lawton (project manager), and the team to create a landscape that would function to protect the 21 hectare wetland. The result is a 37 hectare indigenous species buffer.
“The actual wetland was under pressure both from the pines’ legacy and post-harvest weed invasion. The buffer we put in not only protects the wetland, but creates an ecological linkage to the Banksia woodland in the adjoining Melaleuca Park nature reserve.”
Careful appraisal of the area led to seven distinct revegetation zones being designed and planted, each with their own plant suites. The ecological linkages Damian describes needed to function as if Nature had put them there. Now the ideal plant communities are in the right place and are providing habitat supporting endangered native fauna: for example, nearer the wetland for the endangered Southern Brown Bandicoot (Quenda) and up on the ridge, the threatened Carnaby’s Black Cockatoo.
Carefully judging the landscape is critical: getting the right plant communities in the right soils in the right locations is a key part of the process.
Creating these zones wasn’t a matter of popping some tube stock into the existing landscape. “A substantial fence was installed around the perimeter of the site to exclude off road vehicles as well as the animals that would impact on our work - kangaroos and rabbits. The pine plantation had been harvested, but the stumps remained. Some were pulled out with an excavator in strategic locations, but there were too many so others were left in place. Pine wildlings also established after the harvest and encroached into the wetland – some of them 15 metres tall – and they also had to be removed.” The pine debris was mounded and burned, not only to clear the site for the new plantings but also to help rebalance the soil pH.
By anyone’s standards, these pine wildlings (above) are major weeds. They had to be removed and burned along with the rest of the pine debris (below), left behind after the pine plantation was cleared. Only then could the site be prepared further for planting.
Meanwhile, 120 kilos of seed from 107 local species was being provenance collected over a two year period by the Tranen team. This was then direct seeding by hand-broadcasting. “With direct seeding, if you get it right, you get it really right. But seeds may sit for some time before germinating even though we’ve given them specific pre-treatments to break dormancy. If you take into account loss through insects and birds, typically around 10% will become established.” In total 400,000 seedlings were also planted out over the four years to provide insurance for the direct seeding, and supplement the plant numbers post-installation. Planting seedlings is costlier but more reliable with a success rate quoted by Damian of between 70 and 90%.
This is how the professionals hand-broadcast seed that they collected over the two previous seasons (above). And this is how they plant the insurance tube stock seedlings (below).
And unlike most traditional landscape projects, Tranen factors irrigation out of the equation. “The cost of watering over one summer is the same as getting a plant into the ground in the first place.” The team offsets the no-establishment watering approach by applying all the expertise at their disposal: to put the right plant communities in the right situations, and to time the moment so that seasonal rainfall will do the job.
As for the Melaleuca Park Wetland Offset project, establishment initially went well when measured against the criteria set as part of the contract. “Our stem densities were almost twice the target, and the weed levels below. Species richness, was initially low, but further infill planting increased it to the target level.” So all was looking good until the second summer, the driest on record. Two thirds of the plants were lost across the site, either directly from water stress, or increased herbivore impacts.
But despite these losses the story has a happy ending. By the time the site was handed over to the Parks and Wildlife service to maintain, all the targets had been met or were just under and satisfied the proponents that a successful long-term result would be achieved. This was a terrific result given many other projects undertaken across Perth that year were decimated by the same drought period.
If there’s anything to note, having heard Damian’s tale, it’s that being across all aspect of a project, from collecting seed to sculpting and preparing the planting sites, pays off. Having a keen eye and field knowledge for what would thrive where is also a bonus.
Successful establishment of a diverse self-sustaining landscape is the goal. Species presently found in the wetlands project include the endangered Southern Brown Bandicoot (Quenda) and the Butter Orchid (Caledenia flava).