UKTC Archive

Rocking in the wind

Subject: Rocking in the wind
From: Chris Hastie
Date: Feb 05 2002 10:21:42
On Tue, 5 Feb 2002 Edmund Hopkins <edmond.hopkins@xxxxxxxxxxxxxxx.gov.uk>
wrote
Is it appropriate and necessary to periodically reduce large trees growing
in the pavement not far from houses in order to address the risk posed by
windthrow? I am mindful that these trees have asymmetrical root systems
with little lateral support on the road side.

A related (perhaps inspired by the same tree?) question I have could by
phrased more or less the same, but prepended by the word "When".

Or more specifically, how much movement is acceptable in a tree in high
wind. Towards the end of last week I looked at several trees that were
visibly moving in the ground. Small cracks in the soil were opening and
closing near the base of the tree as the wind gusted.

Trees do move. I believe that oft times it is a constant gentle tapping
by the root system that causes retaining walls to fail, not sustained
pressure from growth increment. Someone recently mentioned this
continual movement gradually turning the soil to porridge until the tree
topples.

So how much movement is acceptable, and how is this observed? Is a
slight cracking in the soil near the base always alarming? Or is to be
expected?

Back to Edmunds original question, I would argue that if the root system
has not been disturbed it is probably up to the job, despite its
asymmetry. The problem is, of course, how many street trees have
undisturbed roots? The one I'm thinking of, by the way Edmund, is
surrounded by a traffic calming scheme that was not very carefully put
in about three years ago.
-- 
Chris Hastie
OakWood Arboricultural Consultancy

http://www.oak-wood.co.uk

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