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

Preface to the first edition


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.


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.


I touch on several closely allied fields including construction methods, forestry, fruit tree culture, garden design, historic landscape, qualifications in arboriculture, regulatory matters and wildlife. There are numerous entries on the natural environment and on climate change, practical matters for anyone interested in 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 www.treeterms.co.uk and you can email via the form there, or write to me at the publisher’s address.


Lyminge, March 2013

Preface to the second edition


This second edition is almost half as long again as the first. It contains more entries for air quality, alien invasive species, biomechanics, climate change, common land, damage to trees, environmental impact, the benefits of green space, tools and equipment, landscape character, professional bodies, silvicultural systems, tree risk assessment and wildlife conservation, among other topics.


I have also revised many of the original terms, each revision often having repercussions elsewhere in the A–Z.


No terms have become obsolete, but one or two have become redundant where I have organized the content slightly differently. Several new terms are relatively recent, at least in Britain, such as ‘biological concrete’, ‘biophilic cities’ and ‘BS 8545 (2014)’.


With regret I omit a term proposed by an Australian colleague for the aversion to perceived tree risk to which the elderly are particularly prone, ‘Geriatrica paranoia’.


I have continued to follow a line of enquiry to my personal satisfaction, for instance to understand what exactly is meant by natural beauty in the term ‘area of outstanding natural beauty’, to find that a protist, a simpler organism than a moss, can comprise a kind of forest up to 55m tall, and to explore the reasons for the continued destruction of the natural environment.


Lyminge, July 2015

Preface to the third edition


This third edition has many new entries dealing with the increasingly adverse effects on tree growth of extreme weather events, and the related topic of tree growth on harsh urban sites. Entries to do with the water relations of trees and their adaptations to drought have been overhauled accordingly, as has much of the rest of the content.


Some of the new terms have gained currency in the UK relatively recently, such as ‘forgiving road’ and ‘endotherapy’; I have used my discretion to introduce ‘mulm’ and ‘subjective presence’; and I continue to come across terms that turn up only occasionally in professional practice. For instance, a ‘bomb crater’ might be difficult to distinguish from a ‘dew pond’, while ‘rammed earth’ is recognized as a ‘sustainable building material’. Other new terms, like ‘transparent wood’ and ‘liquid smoke’, are curiosities.


Occasionally I continue to stretch the A–Z format by giving several entries under one head-term, as under ‘chalara die-back of ash’, ‘wildwood’ etc., and by venturing more relatively long entries.


Some entries that at first sight lack relevance arise from others to broaden a perspective. For instance, grass competes strongly with trees in the tropics as well as in temperate regions, hence ‘savanna’ as well as ‘grass competition’. ‘Stilt roots’ and ‘prop roots’, also found in the tropics, are included to help define ‘functional column’. And according to the ‘red list’ ‘rabbits’ are more endangered than ‘great crested newts’, which led to ‘maquis’.


I continue to take more care in citing references, to establish authority and facilitate further enquiry. Many journals continue to restrict full access to their articles but full texts can often be found elsewhere on the internet. Old Arboricultural Advisory and Information Service and Forestry Commission publications are also archived online.


Where modern or colloquial usage conflicts with literal usage, etymology or precedent, as in ‘monolith’, ‘pesticide’ and the apostrophe in Magistrates’ Court, I have preferred the modern or colloquial, in these three cases largely disregarding the dictionary, the Food and Environment Protection Act 1985 and HM Courts Service.


For this third edition I have removed most of the entries on the wider environmental topics of global warming and other human environmental impacts, but still include those most relevant to arboriculture and forestry.


To clarify a common misunderstanding many of the entries are not definitions, but for those that are you are not invited to define them only that way. The A–Z is just a convenient format for partitioning the subject matter, avoiding fuzziness and overlap as far as possible.


Lyminge, December 2020.