Chopped wood lay on the ground at a school. Upon closer inspection I saw that it was infested with Polyphagous Shot Hole Borer (PSHB). There were a number of infested trees on the property. I spoke to the principal this morning who was unaware of the infestation – the trees had fallen during a storm and the wood would have been sent to an ordinary dump site. Given that Jo’burg City has not allocated specific sites for borer infested wood I suggested that he may want to chip and compost it on site, on a concrete base. I also suggested that he look at the JUFA website for additional information.
I could have suggested that he contact Andrea Rosen (JUFA) yet I am aware that she is dependent on the city allocating a designated site. This is an urgent necessity. Yet if it fails we have to find alternative sites.
Now that I know what PSHB infestation looks like I notice the dead and dying trees where ever I go. I want to start marking these trees with an orange mark.
Why orange?
Not all dead or dying trees are infested. Even those that are may be at different stages of infestation and the degree of urgency would be different. I prefer a graded response which includes doing what we can to save as many trees as possible, rather than chop them down. The orange mark could be painted over with green if it recovers. If it needs to be chopped down it can be painted over in red.
In addition, trees on pavements and in public spaces fall under the auspices of the council; no-one may remove them without written permission for each tree is a protected environmental asset. On private property people are free to do as they wish making options more diverse. Those with the interest and the means may choose to use poisons in the hope of saving their trees. This is a costly option and it is best to consult with a registered arborist.
Others merely cut them down and dispose of them any old how, spreading the borer outwards. This is mostly done in ignorance. Prof de Beer, the expert leading local research, stated in September 2018 (YouTube video) that Jo’burg had committed to allocating designated dump sites within a week of that interview. It has not done so leaving concerned citizens to deal with the challenge themselves.
No one is quite sure of the extent of the infestation for the borer does its work from the inside and often the trees look healthy until the very end; it is the tree immunity that is compromised.
Until such time as city officials respond to requests for designated sites here are a few suggestions:
JUFA’s Andrea Rosen has piloted a composting method that entails hot composting (minimum 45º) wood chips to destroy the borer. She has managed to get her experimental piles to over 60º. This must be done in a ‘quarantined’ space so that the infected wood chips do not come into contact with the earth. She has used plastic sheeting.
What though of the long-term vision for our man-made urban forest?
Do we still want it or are we happy to become a concrete wasteland, with no shade, no birdlife, no insect life, no clean air to breathe?
I certainly want to preserve our urban forest and since healthy soil is the basis of healthy plants perhaps this is an aspect in our tree maintenance that we want to invest in. Building healthy, organic soil is a good in itself and is something we can all strive for.
From a carbon sequestration perspective our trees are a necessity. Retaining and maintaining our urban forest is not a luxury we can do without, it is an essential component of our on-going sustainability.