UKTC Archive

Re: [EXTERNAL] Tree failure potential assessment study WAS Civil cases for nuisance or damage to property

Subject: Re: [EXTERNAL] Tree failure potential assessment study WAS Civil cases for nuisance or damage to property
From: Simon Pryce Arboriculture
Date: Jan 15 2020 20:28:54
If you look at the subsidence data from Cutler & Richardson and Mercer roots can clearly spread well beyond RPA distances e.g. 30m for species oak and poplar.  Those are distances to which roots have spread in sufficent quantities to damage buildings, so the farthest edge of the root systems will no doubt be well beyond that.  Basing RPAs on trunk diameters is attractive because the diameter is the about the easiest thing to measure, but that assumes that the root spread / trunk diameter relationship is linear.  One of my forestry lecturers used to point out dbh is pretty inaccurate as a measure of trunk volume, but can at least be measured easily while the tree is still standing.

I played with some of my own subs data a while back, which suggests that it isn't linear, at least with the sort of established trees that get implicated in subsidence cases.  Distance / diameter is greatest in relatively small early mature trees and less in older, larger ones, which is consistent with our understanding of tree biology.

The NHBC assessment of the range at which trees might damage buildings is based on their height, while BS5837's assessment of building work damaging trees is based on their trunk diameters.  Go figure.  Fortunately both systems have sufficient safety margins that either can be used with reasonable success without engaging the brain too hard and the trees frequently forgive us, which isn't bad compared with many other human endeavours.

By the way please stop putting "nature" and "design" too close together in the same post.  The way the internet works we'll be getting creationists, flat earthers and maybe even Richard Dawkins joining in.


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