We’ve seen an unusual proportion of sudden branch failures over the last few weeks, presumably due to the phenomenon known as Sudden Branch Drop or Summer Branch Drop, both shortened to SBD. The mechanism for this is not fully understood, but it appears to relate to a combination of heavily loaded limbs, an internal or otherwise not very obvious weakness of some sort and adverse weather conditions during periods of high humidity. These factors working together can lead to otherwise healthy looking limbs (and they normally are quite large limbs) failing suddenly with only a few seconds warning. I’ve seen a number of these over the years, but amazingly they always seem to occur without causing injury or much in the way of damage, despite often being sizeable lumps of timber. In the last two weeks we’ve seen a large limb fail from a Cedar in Clyst St Mary, limbs fail from two Horse Chestnuts (one in Lympstone and one in Exminster) and a large limb fail from a Holm Oak in Exeter. All failed at structurally compromised limb unions (though not any obviously weaker than other unions in the affected trees), during hot, humid weather, some during quite gusty, windy conditions but others during calm weather.

If I had undertaken a safety inspection of the trees immediately before the failures would I have considered them hazardous?  Possibly, but maybe not. Safety inspections of trees are not intended to have the result of reducing all risks associated with inspected trees to zero. Trees, as large, dynamic woody structures will inevitably have some risk associated with them, some of these risks may be quantifiable or predictable but others will not. It may well be prudent in some cases to consider the risk of SBD in those species known to be prone to it, particularly in areas of high public use, but any works recommended must be balanced against the difficulty and cost of the operation and the impact of the works on the tree. The link below gives sensible advice for all tree owners as to how to responsibly manage trees where safety is a concern. If, after reading this, you are still concerned then contact us and we will be happy to advise.

http://www.forestry.gov.uk/PDF/FCMS026.pdf/$FILE/FCMS026.pdf

By Graham Joyce | August 23rd, 2013