My point is this mate, yes vegetation does have an effect....but what is it? how much wieght do you put on it and what are the specific elements of the specfic case in question?
Soils particularly clay soils react to relative moisture changes with and without the impact of vegetation. Evapotranspiration occus in all living vegetation plants move moisture from the soil but they can only do this to a certain extent....the chemical and physical nature of the soil also controls the movement of moisture up down and through the soil profile itself. The suction pressures in soil are measured in pF values, Southern and SouthWestern Australian soils studied by the Footings and Foundation Society of Victoria have been shown to retain or hold miosture at 7pF...the wilting point of native trees falls within the 3.5-4pF range these values are logarithmic, so in other words the trees cannot remove the last portion of soil moisture so critical to dramatic alterations in soil volume and compaction, other factors are at play.
It may be that in this case, the Goode case, that the tree was a major factor, but there is no evidence given to prove this...just comfy statements about the impressive resume of the expert..I would have been demanding that the expert show the evidence. As for the Australian standard for footings on expansive clay soils, would we be speaking of the same standard that talks of tree heights as an important factor in determining species suitability???
The experience documented by PG Biddle in his book "Tree root damage to buildings" of long term monitoring case studies over 20yrs after remedial work (often tree removals) for building subsidence has helped me to understand a little of the complexity that exists between soils, vegetation and the effects they can have on buildings. Hopefully such long term and balanced research will inform the changes to the UK building codes standards and regulations, and then we can wait for Oz to copy them....
I have read so much bunk written by so called experts on the ways trees are supposidly to blame without substantive evidence that I always want to see the evidence first, before the conclusion is made not the other way around.
__________________ Sean  Trees are poems that earth writes upon the sky,
We fell them down and turn them into paper,
That we may record our emptiness.
- Kahlil Gibran
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