“Hi Jerry, During heavy wind and rain, my tree developed a 30 degree lean. I think it should be removed. I have attached images…Can you assist please?” Stuart in Sydney.

Hi Stuart,

Your tree is a Robinia pseudoacacia, aka robinia or black locust, a fast growing, widely planted, winter deciduous species. The absence of spines is common as trees mature. They exist on juvenile growth to deter browsing animals. It has small white, scented flowers in summer.

A thirty degree lean is not good. Robinia pseudoacacia is a legume and, just like wattle, unless planted as a seedling and ideally as tubestock, they may not establish a strong anchoring root system. They will, however, establish a leafy crown. This combination of inadequate anchorage and a large crown means that in heavy or persistent rain, or during windy weather when the soil is saturated, limbs may break, crowns may split, or trees may develop a lean.

This lean can sometimes be corrected by crown thinning which aims to reduce the weight and wind drag of the crown. Up to a maximum of thirty percent of the crown is removed, not by reducing the length of individual branches (which in following years will make matters worse), but by evenly removing one third of all the branches in the crown. This reduces wind resistence of the crown and gives the tree time to re-establish its loosened root system. This treatment can extend the useful life of a tree for decades, but if the location in which the tree is growing doesn’t permit it to grow a stronger root system (very poor, compacted, dry soil; shallow soil; a tree surrounded by concrete, etc), it may just give you an extra 5-10 years of trouble-free life.

Alternatively, the tree can be felled as you believe it should. The stump should be ground out and all the arisings (chipped wood) must be dug out and sent to the tip. Failure to do this invites root decay fungi to proliferate and if this includes Armillaria luteobubalina (honey fungus) it may take up residence and attack healthy trees and shrubs elsewhere in your garden for many years.

Felling and stump grinding is straightforward, but Robinia – like elms – are capable of producing root suckers, often in prodigious quantities. So be prepared to apply a systemic herbicide on emerging suckers. Or maybe invest in an urn so you can apply boiling water on suckers until they are slowly exhausted.

Please understand that it is difficult to provide an on line assessment, you need an on site tree inspection/ report.

However, when England’s Great Storm of 1987 occurred, I was managing an urban forest in London where I was involved in the successful salvaging of many Robinia pseudoacacia trees by applying the technique of crown thinning described.

Make sure to engage a competent arborist, this is not a task you can trust a tree lopper with. I suggest contacting Arboriculture Australia to have your tree inspected by someone qualified and take it from there.

Thank you for sending me useful, clear photos of your tree.

Kind regards,

Jerry Coleby-Williams
25th February 2020