Removal of trees infested with shot-hole borer in Kings Park has surprising outcomes

Australia Broadcast Center

3 days ago

The removal of beloved trees from Kings Park has left a scar across the escarpment and made it vulnerable to dangerous landslides.
But it has also created an opportunity to future-proof the popular attraction amid a drying climate.
Like thousands of trees in Perth, around 42 Moreton Bay figs and coral trees — which once towered over visitors to the inner city park — fell victim to the polyphagous shot-hole borer beetle, which was detected in WA in 2021.
Principal landscape architect for the Botanic Parks and Gardens Authority, Bel Foster, said the trees had huge canopies that had sheltered the ground for decades.
Ms Foster said their disappearance meant large areas of the escarpment were now exposed to rainfall for the first time in many years.
"Because the soil underneath is really dry, it's got lots of humus," she said.
The escarpment is a fragile geological system, and one that, with the busy Mounts Bay Road sitting at the bottom, required special planning.
Ms Foster said authorities were working collaboratively with geotechnical specialists, civil engineers, restoration experts and Wadjuk traditional owners to come up with a solution.
Ms Foster said while the removal of the trees was distressing for many people, it meant some positive changes could be made at the site.
"We've been able to remove a lot of aging or end-of-life infrastructure that was down there, some very old retaining walls and other things that were actually causing challenges," she said.
"With the re-profiling works, we've actually been able to achieve something that's got a really long, sustainable life span for us from an environmental, but also an asset, perspective."
Part of the project has involved inserting custom-designed drainage cells below the soil surface at the top of the hillside to slow water infiltration.
That measure is intended to prevent water running off the slope and causing landslips, while also holding water at the top to quench the thirst of trees and vegetation.
"We know with climate change, drying climate and more irregular rainfall patterns, these kind of improvements are really important to the ongoing resilience of our collection," Ms Foster said.
The bare landscape also allowed workers to revegetate the slope with native plants.
Ryan Glowacki, acting manager of biodiversity conservation at Kings Park, said thousands of plants had been propagated from seeds and cuttings that were collected from vegetation in the area.
"This year we've got just over 20,000 plants to put back in, which is a great achievement," Mr Glowacki said.
That number is on top of 20,000 that were planted in a different location last year, and there are plans for 30,000 per year for the next few years.
Mr Glowacki said there was now a good opportunity to replace introduced species with natives, which were more suited to the humid climate while providing stability.
"All these species, because they've adapted to the environment already, they've got this ability to bind soil with their root systems," he said.
"They provide great stability in that area and they can protect the space from small slippages in the sand, particularly with water run-off."
Ms Foster said the escarpment was a significant area for the traditional owners, the Wadjuk people.
While elders were monitoring the works, authorities found remnants of Perth's past, such as bricks and old bottles — but also something surprising.
"One of the most exciting things for us in the project is, through the removal of some of [the] aging infrastructure, we've actually had a new freshwater spring emerge down at the toe of the escarpment," Ms Foster said.
"An aspiration from the traditional owners for a long time has been to have that water flowing again as opposed to being contained in the fountains, so it's just a really fabulous kind of outcome from this project that we weren't anticipating.
"It's a really important step towards that kind of story about healing country.
Frogs have already returned around the spring where elders have installed habitats for them.
A stand of 20,000 trees, shrubs and other ground cover, which was planted a year ago, has thrived, with some plants already three metres tall.
Ms Foster said native fauna were returning to the area which had historically been frequented by pests.
"With our fauna-monitoring cameras we've seen our possums coming down to drink, we're seeing more native birdlife down there," she said.
Now that the final planting is complete, the tracks and paths will be opened back up to the public, who will be able to watch the transformation continue.