Arboricultural Consultant

P.G. Biddle

Dr P.G. Biddle, O.B.E., M.A., D.Phil., F.Arbor.A.
Registered Consultant of the Arboricultural Association
Honorary Fellow, Insitute of Chartered Foresters

  Review - Prof. Cram

Prof. W.J. Cram

Department of Biological and Nutritional Sciences, University of Newcastle-upon-Tyne

Review in Arboricultural Journal Vol. 22, (4), 1998.

"The author sets out his intentions from the start - "to provide a comprehensive analysis of how the interaction of trees, soils and water can cause foundation movement and damage to buildings". This task, as the author points out, involves knowledge from at least ten professions. Presented this way, it might seem impossible. In reality the focus is on a single problem, whose solution, as persuasively argued by the author, will not be found without integrating knowledge from a range of disciplines. In this book Dr Biddle achieves such a synthesis admirably.

The book is in two volumes. Volume 1 covers the interaction of trees, soils, water and buildings; the methods of investigating damage; and means of remedy and prevention. Volume 2 presents the results of Dr Biddle's own investigations of the patterns of drying of clay soils near trees, evidence of which is used in the first volume.

After describing the relevant features of trees, root systems and soils, the effects of tree root systems on soil moisture and the development of persistent moisture deficits are described and discussed, followed by their effects on buildings. The weather, seasonal and year-by-year, is then explained as a crucial variable. A hierarchy of species with different 'water demands' is presented after discussion of the limitations of such an attempt in the face of the great diversity between individuals of the same species. Root pressure can also break pavements and disturb walls, and roots can invade and block drains. Such less frequent types of damage are described in a chapter of their own. Following the first ten chapters devoted to the cause of the problem, six are devoted to investigation and diagnosis (though it is suggested that working on remedy is one sure-fire way of refining diagnosis). A major point (made explicitly in the text and illustrated by the case histories described) is that effective solutions will be obtained only by correct identification of the cause, and that using one traditional stereotyped method alone will inevitably lead to mistakes. The crucial investigation method espoused is to measure accurately the extent and timing of movements of foundations: 'Level monitoring is the most useful, and cost-effective, part of any investigation and it should be a routine part of all investigations.' The chosen case studies support this recommendation. The author discusses the whys and hows of site investigation of the building (particularly monitoring of levels), of soil and trees, and the diagnosis and prediction of 'heave' following the release of a persistent water deficit.

The final four chapters concern remedial action after damage, concentrating mainly on tree management (with underpinning being a building/engineering activity outside the scope of this book), predicting and preventing damage, and the legal framework. The aesthetic impact of trees and the question of tree management versus engineering solutions is kept to the front throughout. The final chapter presents the author's view of the role of each of the professions concerned with the problem, where Biddle suggests new approaches and attitudes they each might take in order to achieve successful and cost-effective solutions.

At the end of each chapter is a case study illustrating various points made in the chapter or the book as a whole. The book is designed to help the practitioner, and the layout assists with this. Highlights within the text and pointed, short summaries at the end of each chapter make the main points jump out, and also allow scanning of chapters to check whether there are areas of importance to be absorbed. More importantly, this is the most coherently written technical/scientific book I have read. Every aspect discussed is to the point, and the cross-referencing between chapters and sections is extensive and maintains the relationship between the parts. In each chapter the author identifies the main point immediately, develops the idea, and at every step the relevance of what one is reading to the single overall problem of diagnosis and remedy is maintained. In turn this gives an added point to many of the subjects discussed. Evolution, the principles of naming and identifying plants and the practicalities of estimating tree height, to select just a few, are all given new interest by being tightly knit into what one can only call a narrative.

The writing is clear and punchy, the illustrations are beautiful. In other words, I found this a jolly good read and hope that others will find the same!

An original feature is a case study at the end of each chapter, each ending with lessons to be learned. Both the lively language and the series of trials reminds one of 'The Pilgrim's Progress'!

The author's approach to evidence demands comment. His ideas and conclusions are always explicit and quantitative where possible, with examples and tables. Where the evidence is scanty or subjective this is made clear, as in discussing the idea of putting tree species in a hierarchy of damage causation. It is helpful that the author never ducks behind the 'cop-out' of 'too difficult'. In fact, to have an idea crystallised in a table or graph, however uncertain, is very valuable. Progress depends on having preliminary hypotheses (otherwise known as 'Aunt Sallys').

The author, 'would always be interested to hear from anyone wishing to correct technical inaccuracies'. In the area of plant biology the presentation is accurate, well balanced and imaginative, and Biddle is clearly au fait with the other areas discussed. Some areas are more uncertain and controversial than others, as the author generally makes clear, and three comments seem appropriate:

Firstly, the question of genetic differences between tree species in water demand and other aspects of their physiology. The author, I think, goes a little far in asserting that 'phenotypic variation' (variation caused by the environment) 'will mask any attempts to identify the differences between... different species.' There will, nevertheless, be genetic differences which determine the potential of a species. Progress in agriculture depends on identifying such differences. For trees, it is a purely practical problem that genetic experiments take a long time.

Secondly, the effects of pruning. The author correctly identifies that fact that the fall in transpiration will generally be less than the fraction of leaves removed. It might be pertinent to remark that understanding of crop transpiration is fairly advanced, and transfer of the theory to trees, backed up by experimentation could be pushed ahead with advantage to the insurance industry.

Thirdly, the one assertion that the author makes without providing back-up evidence is that trees will tend to maintain their root to shoot ratio after pruning. Herbs may do, trees might, but there must be an important difference in timescale.