Experts urge native species rethink in urban Perth parks amid growing polyphagous shot-hole borer threat

The tiny beetle destroying Perth’s trees can be combatted if a diverse mix of natives are planted as replacements, experts say. The polyphagous shot-hole borer has been wreaking havoc, forcing the mass cutting of some of the city’s favourite canopies. More than 6000 trees across Perth are infested, with 130 affected species, at least 30 of which are Australian natives, in almost 200 suburbs. There are around 200 infected trees in Hyde Park alone, including well-loved Moreton Bay figs. But the key to beating the beetle is planting a diverse range of native trees, according to Murdoch University environmental scientist Jane Chambers. “Diversity is the key in replanting. Being careful choosing the right species and choosing a wide diversity of species is probably our best opportunity to beat this,” she said. Dr Chambers is among the environmental and industry experts closely watching the State’s $44 million eradication program. “It affects the exotic trees by preference – but it will also attack native trees. Some are reproductive hosts and unfortunately, that includes trees like marri and red-flowering gums, which we would love to plant,” she said. But amid the loss of thousands of trees, there is an opportunity to prepare our parks for Perth’s increasingly dry summers. UWA School of Biological Sciences associate professor Nicki Mitchell said reimagining them to be more native heavy would ensure they were more drought-friendly in the summer. “I would hope we would see this as an opportunity as well as a bit of a catastrophe. There’s a huge opportunity to redesign parks to require less water,” Professor Mitchell said. The advice comes with a major tree-cutting operation starting on Monday at the Mount Eliza escarpment in Kings Park. Lover’s Walk is expected to be closed until the end of the month as crews work on the stretch of bushland from the Old Swan Brewery to the Kings Park apartments. To date, the borer has been detected in 241 trees across Kings Park. The restoration program will focus on returning native species to the scarp, with about 18,000 new shrubs and trees across 16 species already replanted. Beyond its cutting program, the Department of Primary Industries and Regional Development is also testing chemicals, latex paints, traps and pruning to see if trees can be saved or infestation slowed. DPIRD deputy director-general sustainability and biosecurity Mia Carbon said the department was also liaising with local governments and international experts to track any new developments. Dr Carbon said the department remained cautious about recommending trees to plant as the host list was ever-evolving. “Wherever the borer has gone in the world, it has found new host trees to live in. The pest certainly poses a significant threat,” she said. Agriculture Minister Jackie Jarvis said she had confidence the department was pulling out all the stops to fight the borer – and had been doing so since its first detection. It comes after several local governments questioned the speed of the State Government’s response and rollout of the eradication program. Among the leaders vocal on the issue was City of Perth Lord Mayor Basil Zempilas, who has slammed DPIRD’s pace on the response, labelling it “woefully behind”. The city is currently testing its own techniques in the hope it can save any heritage trees attacked by the borer. Ms Jarvis accused any opposition to the government’s response as “complete fear mongering”. “I would have thought that as a national biosecurity threat – this is an emergency – we would actually get bipartisan support,” she said. “They should be focusing on actually backing our efforts to eradicate this pest. I am absolutely shocked that they are playing politics with this.” She added that the rhetoric was “insulting” to some of the country’s top scientists working on the eradication program. “We are in the middle of an eradication process. This is a major biosecurity threat. They’re muddying the waters.” Dr Carbon said it was “understandable that people are concerned” about the borer. “It’s something that we should be concerned about and why we’re working so hard to eradicate it.”