Mount Eliza stripped bare as borer destruction forces major works in Kings Park

If you’re wondering why your commute along Mounts Bay Road has been looking a little less lush in recent weeks, it’s because of the sesame seed-sized polyphagous shot hole borer.

An infestation of the pest along the Mount Eliza escarpment has resulted in the removal or pruning of 42 trees, including large fig trees, with work wrapping up this week.

The trees’ removal has prompted fears of land slipping on the escarpment forcing the permanent closure of the popular Lover’s Walk and Mounts Bay Road access to the Kokoda trail stairs.

Now the Kings Park and Botanic Garden Authority must start site restoration works, including replanting flora and changing the entire shape of the escarpment slope.

An authority spokeswoman said the works would transform the site into a natural attraction for visitors, with more than 80,000 plants to be replanted along the escarpment.

She said no land slipping had been recorded to date, but geotechnical engineers were keeping a keen eye on the area, and rock catch and exclusion fencing was being installed to protect pedestrians and motorists.

“The coming months will see slope reshaping to reduce slope angle, installation of erosion control matting and planting of over 20,000 plants grown from seed collected from the scarp,” she said.

Work is wrapping up on the removal of 42 trees along the Mount Eliza escarpment in King’s Park.Credit: Ross Swanborough

The impacts on the escarpment are perhaps the most public reminder of the shot hole borer invasion in Perth after it was first detected in Fremantle in 2021.

Parks like Kings Park, Hyde Park and the Perth Zoo, which feature many foreign trees, are some of the worst impacted areas because the borer prefers exotic trees over WA’s natives.

The authority spokeswoman said small areas of infestation have been found in the park, generally restricted to boundary areas, and 159 trees have been removed since the start of the response.

Cut down trees on the Mount Eliza escarpment.Credit: Ross Swanborough

“In the same timeframe, BGPA has planted over 900 trees within the park, with an additional 500 planted at Mounts Bay Gardens in 2024,” she said.

“This is in addition to the more than 30,000 plants grown and planted within the Kings Park bushland and WA Botanic Garden annually.”

A fig tree cut down because of the borer infestation.Credit: Ross Swanborough

She said the tree removal and pruning program in Kings Park was showing evidence of success.

“Department of Primary Industries and Regional Development surveillance recorded a significant drop in PSHB presence in traps following the tree removals on Mt Eliza Escarpment in March 2024.”

Neither the authority nor department would reveal the total cost of the Mount Eliza operation, but said it came from the $44 million national biosecurity response into the borer coordinated by the Commonwealth.

More than 4500 trees were mulched in 2023 and 2024 to stop the march of the borer, which has so far been contained to the Perth metro area where there are two quarantine zones still in place.

More than 1000 trees have been pruned.

A department spokeswoman said there had been a decrease in borer activity across Perth during summer, consistent with international observations during hot weather.

Start the day with a summary of the day’s most important and interesting stories, analysis and insights. Sign up for our Morning Edition newsletter.