Raise your hand if you too had your wedding photographs taken among the roots and underneath the shade of the vast Moreton Bay Fig at the Arderne Gardens.
If so, consider yourself lucky, because if the Polyphagous Shot Hole Borer (PSHB) manages to infiltrate the arboretum and public park, the “Wedding Tree” stands to be among the first to be infested.
READ | Polyphagous Shot Hole Borer: What does the science say?
Speaking at a “Celebrate the biodiversity of the Western Cape” event, co-hosted by The World Wide Fund for Nature (WWF) and the Friends of the Arderne Gardens (Fotag), Francois Krige, chair of Fotag, said that research done in Perth, Australia, had shown that the Moreton Bay Fig was among tree species vulnerable to PSHB attack.
Until recently confined to the Garden Route and Somerset West in the Western Cape, the tree-killing beetle was discovered infesting a Boxelder Maple (Acer negundo) on a private property in Newlands just over a month ago.
In his address given at the event held last week Thursday (23 February), Krige shared that the beetle had already spread to Wetton Road, Wynberg.
ALSO READ | Concern as tree-killing beetle spotted in southern suburbs
According to the City of Cape Town, the Invasive Species Unit had recorded a total number of 128 infested trees by Tuesday 21 February.
According to Krige, the arrival of PSHB in the southern suburbs poses the gravest threat to the arboretum at the Arderne since the original trees were planted in the 1850s.
“We are incredibly concerned about the proximity of this. It literally surrounds us. The scariest part for me is that we have so many rare trees here, so we don’t even have adequate data as to which trees to protect.”
On Friday 17 February, Fotag began their counter-attack by hanging about R35 000 worth of repellents on the Wedding Tree. Lures and traps will be deployed around the garden’s perimeter shortly.
Krige explains that passing beetles are sexually attracted by the lure pheromone mimicker in the traps.
“Should they not be enticed, they will, hopefully, be fooled by the verbenone repellent sachets tied in the canopies of the champions. These pheromone mimickers attempt to trick the beetle into thinking that the tree is infested already and is not an attractive host,” he says.
As part of pre-emptive measures, Fotag are planning to remove Acer negundo (a category three invasive) within the garden along with a few other low-value, reproductive host species, such as the decayed oaks on the Herschel boundary, and some viburnum shrubs.
Krige says that Acer negundo accounts for over 90% of infested trees in the surrounding area, and accounts for 100% of the outlier species, and 100% of the severely infested species.
“They are referred to as ‘amplifier’ species. To borrow from Covid terminology, they are the super-spreaders of PSHB. Removing them also helps us to have more resources available for fewer and more special trees.”
Funded by Fotag and its donors, the removal of these low-value, reproductive hosts will begin next week.
“The City of Cape Town has given us their blessing. The project will be ongoing and the number of lures and repellent deployed, and the number of trees propagated, will be determined by the amount of money we can raise,” says Krige.
ALSO READ | Invasive beetle to hit municipalities and property owners where it hurts
With PSHB now firmly lodged in the southern suburbs, Krige says, in a few years’ time, the future of Cape Town’s treescape will be very different from what we know.
“No more English oaks, no more London Planes, no more Boxelder maples, no more Poplars; that is 40% of our treescape gone.”
He shares that Fotag has a little propagation programme going where they are collecting other rare trees from around the world that are PSBH resistant.
“For some time now, we have been collecting seeds of rare trees. We have been propagating them at the tiny nursery space at Arderne and at Kirstenbosch.
“Once they are successfully germinated or cuttings have successfully rooted, we grow them on at the nursery at Platbos Forest Reserve.”
He says programmes like these will be incredibly important going forward.
“We now urgently need to expand this project; to grow the PSHB-resistant, climate-change resilient trees to replace those that we will lose, to improve the diversity of exotic trees in the arboretum and to research and make available the trees that will be planted in our streets in the years to come, once this terrible disease has run its course.”
Researchers who have studied PSHB infestations for the past 10 years, as they have struck in California, Israel and South Africa, have all come to the same heart-breaking conclusion.
Despite best efforts, the loss of thousands of trees is inevitable.
Krige put it most eloquently at last week’s event: “We must not be remembered as those who failed our Giants, but as those who replaced them. All the trees in Cape Town were planted by human hands. We have the hands to do more planting.”
