A-Z of tree terms: A companion to British arboriculture

This volume developed over several years from my work as an arboricultural consultant based in Kent in the south-east of England. I hope it will be useful as a primer to those starting out in this field as well as to other colleagues, allied professionals, students and interested lay people.

I began with the terms I had used in my reports then expanded on them to include the things I talk about to clients during site visits. I then put in the sorts of things I might cite in my reports or might talk about, and finally the A–Z took on a life of its own.

Philip Wilson, the author of Tree Terms

I concentrate on the staples of arboriculture – tree management, tree hazard, trees and development, structural movement, planning matters – and include many related terms that are basic but useful to know. For instance, elements of mechanics help to explain why trees fall over (or not), familiarity with plant-water relations helps in understanding drought stress, and numerous site factors affect tree growth and form. Similarly, relevant metric units are defined to help understand, say, the heating value of firewood or the force that roots can exert, and I stretch the point to include many terms describing the structure and function of trees.

In some cases sets of things are largely complete, like types of fences or rights of way; in others I have arbitrarily chosen the most prominent examples only, as in species of decay fungi and UN conferences. With a few exceptions there are no entries for individual tree species, hybrids or cultivars, individual people, the many technical terms used by tree surgeons or specific legal cases.

Many terms are not cut-and-dried even within the context of British arboriculture: the term ‘tree’ is problematical because it is a composite of other terms; the simple-sounding ‘log’ and ‘clay’ each have three meanings; a historical perspective is helpful in understanding terms like ‘forest’ and ‘park’; and one thing may grade continuously into another, like ‘soil creep’ and ‘landslip’. Many definitions depend on the specific context or are distinguished only by their human purposes.

On occasion I have invented a term (or think I have) such as ‘catenary fence’, and elsewhere I use my discretion to minimize overlapping meanings. Thus, for instance, my definitions of ‘storm damage’ and ‘windthrow’ are separate and mutually exclusive even though the latter is actually a kind of the former, and I sometimes give a term less latitude than the dictionary to sharpen a distinction.

My aim throughout has been to make the content clear, not to create authoritative definitions under all circumstances.

Two comparable volumes have been published, Glossary of arboricultural terms by the International Society of Arboriculture and Dictionary for the management of trees in urban environments by the Institute of Australian Consulting Arboriculturists. There is surprisingly little overlap between this volume and those because, leaving aside differences of size, style and emphasis, many arboricultural terms are in fact quite parochial.

Any one country has its own legal framework, technical guidance and planning system, and the trees, soils, wildlife, landscape history, building practice and so on are also quite different. Where a term is used in two or more countries, its meaning or usage may differ for historical or legal reasons: for instance, a footpath in the Australian dictionary is ‘a dedicated pedestrian way, usually constructed of concrete’.

This raises the question: what exactly is the jurisdiction of this A–Z? I generally use ‘British’ to mean Great Britain (which I abbreviate to Britain), but some entries apply to the UK and some to Britain and Ireland. Some again do not apply to all of Britain. In particular I rarely address the administrative and legal differences between England, Scotland, Wales and Northern Ireland.

At times you will find that a term of interest is not included, a definition will be either irritatingly obvious or difficult to understand, and one will ramble while another is too short. To minimize such complaints I try not to pad out the A–Z with everyday terms like ‘hard hat’, or those, like some botanical terms, that are unimportant for the present purpose. I also assume that you can recall your school science and have an ordinary dictionary to hand if you need one. Where I can I enliven an entry, or help to justify its inclusion, with examples and practical perspective.

The end result, however, is little more than what I personally find useful and interesting. How many readers really want to know the difference between scrub and woodland, or care a fig for crinkle-crankle walls? Frankly I have no idea. Thus, it is not a mere politeness when I ask you to draw my attention to errors or other shortcomings in the A–Z, or to suggest new terms. An abridged version is freely available at and you can email via the form there, or write to me at the publisher’s address.

Philip Wilson
Lyminge, January 2013