Community response to the start of the removal of Polyphagous Shot Hole Borer beetle (PSHB) infested trees from City-owned land indicates that a troubled road lies ahead, with one camp warning against a knee-jerk reaction and another advocating taking even stronger, preventative action.
On Wednesday 8 March, the City of Cape Town began to remove the first trees, infested Boxelders (Acer negundo), along the Liesbeek River corridor, near the N2 highway and Liesbeek Park Way.
Eddie Andrews, the City’s Deputy Mayor and Mayco member for spatial planning and environment, says the City will prioritise the removal of Boxelders from City-owned land along major transport routes, as these pose the biggest threat of spreading the PSHB to other parts of Cape Town.
“We will not remove all of the infested trees at once, but will prioritise the heavily infested reproductive host trees, and trees that are dying and present a safety risk to people and properties. Based on our experience from infestations in the Somerset West area, Boxelder trees are on top of the list of trees that must be removed.
“It is difficult to say how long this process will take, but safe to say that we will keep on for as long as needed,” says Andrews.
By Thursday 9 March, the City had recorded 191 infested trees – 104 on City-owned land and 87 on private properties in the southern suburbs.
Most infested and affected trees are Boxelder, London Plane, English Oak and Grey Poplar.
Areas affected are Newlands, Kenilworth, Mowbray, Rondebosch, Observatory and Wynberg.
According to arborist Francois Krige, who is also the chair of the Friends of the Arderne Gardens, Boxelder by a huge margin, is the most susceptible of all species to PSHB.
Krige says, at present, it represents over 95% of all trees infested, 100% of all heavily infested trees, and 100% of the outliers.
“It allows the beetle to leapfrog into new areas and is the ‘super spreader’ within a few weeks of arrival. It acts as a lure for the beetle into your area and thereby makes your less susceptible trees more vulnerable.”
According to the management protocol drawn up by the City’s Invasive Species Unit, the priority is the swift identification and removal of highly infested trees to reduce the beetle population.
Infested trees must be chipped on site and may not be removed from the property as the removal of the chipped wood will spread the pest to other areas.
Clare Burgess, chair of TreeKeepers, however, urges caution when it comes to considering the removal of healthy trees from the urban forest. TreeKeepers is a citizens’ organisation that works to conserve trees in the urban forest.
“TreeKeepers is not, and never has been happy with the current trend in the city to remove healthy trees from the urban forest. Whether this applies to trees with the potential to become infected by PSHB or Pine and Gum trees, or other listed alien invasive plants that have been targeted in the past for removal,” says Burgess.
She says they prefer for each tree to be assessed and alternatives to removal to be considered wherever possible.
“Whilst we understand the principle behind the current attempt to create ‘sacrificial trees’, in this case the Acer negundo which is known to be a breeding host for PSHB and therefore an amplifier of the fungal disease that is killing the trees in which it breeds, we ask that everyone, including the council, consider the pros and cons of retention or removal for each individual tree.”
Burgess says TreeKeepers agrees with the former approved method of deciding whether trees should be removed or not by assessing their health and infection levels with regard to PSHB.
“If a tree is clearly going to succumb to the infection, then it needs to be removed as soon as possible. If there is a chance that the tree could survive, then this needs to be considered,” she says.
However, she says, their concern is not only for the way that this pandemic is handled, but also for the precedent that is set by applying a blanket statement to remove all trees of a particular kind. “There is considerable concern among the public, that this could be used as a way to remove trees that are healthy but troublesome for other reasons, such as blocking views, making a mess with their leaves or berries and getting in the way of building development.”
This damning evidence has led to some professional arborists recommending the removal of Boxelders from the local landscape – infested or not.
“The most important thing we can do is remove Acer negundo from the landscape. This is recommended within a kilometre of the infestation zone. An Acer in this proximity is pretty much doomed already,” says Krige.
He adds that it is also much more cost-effective to remove a Boxelder tree before it is infested.
“As it can be felled using conventional methods. Once infested, phytosanitary protocols must be followed.”
