TREEL NEThe International Society of ArboricultureUK and Ireland Chapter Official Magazine

Autumn 2013

This issue includes:Frank Rinn’s Shell Wall Thickness and

Breaking Safety of Mature Trees,Exceptional Yew Trees of England,

Scotland and Wales, andFrom the Treetops, a TCC and ITCC overview

Contents 3 Editor’s Comment

A few words fromCharlotte McDermott

4 Executive Director’s SayA few words from Ian McDermott

6 Events CalendarNotable events for this year

7 ContactsThe people to call with your queries

Features

9 From the TreetopsBy Charlotte and Ian McDermott

12 The exceptional yew trees ofEngland, Scotland and Wales

by Andy Moir, Toby Hindson,Tim Hills and Richard Haddlesey

19 Shell-wall thickness andbreaking safety of mature trees

By Frank Rinn

25 Mark Johnston Press ReleaseBy Julie Gaier

26 Connecting People inthe U.K. with Trees

Mark Johnston Biography

29 In search of the perfect report Part II

by Jeremy Barrell

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Editor’s CommentDear readers,

This is a picture of me from the ITCC on Centre Island in Toronto, which was a fantastic TCC to say the very least. Toron-to was an amazing place - albeit insanely expen-sive... - and seeing our very own Jon Turnbull make it to the finals was very exciting indeed.

In this issue there is, once again, an interest-ing technical article from Frank Rinn, an account of Mark Johnston’s award, part two of Barrell’s per-fect report search, an ar-

ticle on exceptional yew trees of the UK and an account of the ITCC in Toronto by yours truly.

I would personally like to thank Ian McDermott, Russell Ball, Glynn Percival and Nigel Smith - the four members of the editorial board - for continually supporting me throughout my time as editor, encouraging me and generally point-ing me in the right direction! Thank you all.

— Charley

Executive Director’s Say

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I always find writing these sorts of piece dif-ficult so I looked to the archives for the last time I wrote in Treeline and was shocked to see it was the summer of 2007, hmm, time certainly does fly by when you’re not look-ing and not much inspiration from a piece over 6 years old, or maybe there is?

In that last article I was talking about the Ar-boricultural Liaison Group (ALG) and the newly formed Arb. Policy Group. The latter was killed at birth by an overdose of lethar-gy and perhaps the reasons for the existence of that group were always a bit pretentious and perhaps the end was blessed. However the ALG tripped a few times in the recent past and was shelved for a couple of years but it is good to see it is back and function-ing pretty well.

The ALG is a forum for the terribly splin-tered arb. industry to come together around a table and talk about our commonalities and also to plan the calendars better so as events promoted by the member societies

do not clash too badly. The Chapter is repre-sented by Jess Herbert (President Elect) and also the Municipal Tree Officers Association (MTOA) and the Consulting Arborist Socie-ty (CAS) both professional affiliations of the chapter are also represented on the ALG, so there is good ISA presence, and along with the AA, ICF, LTOA, Lantra and quite a few others the group is now vibrant with their next meeting scheduled for mid-October. If you want to know more about this forum please let me know and we’ll place some in-formation into Treeline on a regular basis.

The Summer has been pretty busy from an ISA per-spective and damn enjoyable at times. We have had the UK&I TCC at High-clere, more of which is covered else-where in here and on the web, and that was just a great gig. Then ArborCamp at the JA Jones show. From there we were

Bill Kowalczyk and Ian Morgan in Switzerland

Executive Director’s Say

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at the ITCC in Toronto and then onto the ETCC in Switzerland. Put-ting the “I” in ISA can sometimes be enjoyable as well as worthwhile as the venues and the climbing skills were some of the best have seen in years.

One of the up-sides was the road trip to Swit-zerland with Ian Morgan the cur-rent TCC Chair-man and my old mate ex-President of the Chapter Bill Kowalczyk who was responsi-ble in 1993 for roping me into ISA – a day that changed my life forever! It’s good to see that three 50 something’s can still get out and about without Saga insurance and a walking frame.

The downside? You’re only as good as your next gig and we need volunteers to help make these things happen, so, you know the drill, contact us and make the offer, you nev-er know where you’ll end up.

For me though the highlight of the year will be the TRAQ course. I have been involved in the development of this qualification for over four years now and at times I found it to be one of the most frustrating experiences ever, but the result was worth the pain and I am really pleased that we have the first course right upon us now at Capel Manor on the 14th October and this will be the first

one in Europe and hopefully many more will follow.

TRAQ (Tree Risk Assessor Qualification) is the ISA’s newest and shiniest award and is their first ever qualification as opposed to a certification. This may not seem much to us here in the UK but is a HUGE shift in the way ISA do things, another example of the “I” in ISA becoming ever more important.

As you hopefully will have seen in the Sep-tember 5-minute update, we have next year’s annual meeting set out and this is something you must put in your diary – 2nd and 3rd of May again at Capel Manor college (easy to get to and some cheap digs available). There will be a great array of things to do and see, so block the weekend out of your diary now, ring the family and have a great weekend.

Mac

Bill and Stefan Kowalczyk in Switzerland

Events Calendar Upcoming Events for the Busy Arborist

2013September

7th-8th ETCC,Switzerland http://www.itcc-isa.com/events/regional/etcc/ etcc.aspx

9th–11th ArboriculturalAssociationConference www.trees.org.uk

12th–13th ConforWoodlandShow www.confor.org.uk

October

1st–2nd ExpoTCO http://www.treecentreopheusden.nl/expo/en/

9th–11th ISALeadershipWorkshop,Illinois www.isa-arbor.com 12th CertificationExam,Enfield www.isa-arboriculture.org

14th–16th TreeRiskAssessmentQualification www.isa-arboriculture.org

November

24th–2nd NationalTreeWeek www.treecouncil.org.ukDec.

December

7th–8th TreeDressingDay http://www.national-awareness-days.com/tree- dressing-day.html

11th HedgerowRegulations www.mtoa.co.uk

Contacts Who’s Who?

Contact list for the chapter volunteersPresident AlexLaver

President-Elect JessHerbert

Vice-Presidents BobWidd Vacant

PastPresident RussellBall

Editor CharlotteMcDermott

Exec.Director IanMcDermott

OfficeManager JeanMcDermott

PA Reps CAS BobWiddMTOA TimWetherhill

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Standing Committee’sTCC IanMorganSSA StuartPhillips

OfficersRiseforResearch RussellBallTreeFund GlynnPercivalCertification DanYeomansAFAG AlexLaverCommercial JonTonksEAC CraigJohnson

Website: www.isa-arboriculture.orgEmail: Enquiries@isa-arboriculture.orgTel: +44(0)1215568302

Phil Wade, Director – Sorbus International Ltd

Sorbus International Limited are leading suppliers of specialist & hi-tech equipment to the ar-boriculture, forestry, utility, grounds maintenance, landscaping & environmental care sectors in

the UK & worldwide.

In late 2012 the PICUS 3 was launched; the most compact, lightweight, fastest & user friendly PICUS system ever.

The PICUS 3 hardware is a complete re-design & the result of this and the new Q73 software

means time on site is effectively halved compared with previous PICUS systems.

Quentin Nicholls, Managing Director of Arbortrack Systems Ltd comments: “After 10 years of getting to know the PICUS, it was time for us to take the plunge and buy the PICUS 3.

The first thing you notice is the smaller case, which is now not much bigger than a standard briefcase. I found the PICUS 3 to be easier to use on site and there is no longer the need for a PC as the PICUS 3 will store the records of dozens of trees. The sensor belts are more stream-lined & easier to handle & it also has built-in GPS and a clinometer to accurately measure the

heights of trees.

I would also thoroughly recommend purchasing the electronic callipers as these are simple to operate and considerably speeds up the time taken for each inspection.”

Please contact Sorbus International Limited for more information on the PICUS 3 or go to our website www.sorbus-intl.co.uk8

The UK&I TCC

After witnessing many a year of Jonathan Turnbull’s terrific performances within the UK & I Tree Climbing Championships, it was no surprise when – once again – he was selected as our male representative at the In-ternationals in Toronto, Canada.

The Chapter competition at Highclere Cas-tle was a raging success with some blazing sunshine mixed with the strong winds, but the latter did not deter the climbers from giv-ing it their all, especially for the only female competitor in the competition, Josephine Hedger.

With no other female competitor Jo chose and was given the chance to compete along-side the men and proved her worth in the tree industry when she won the Aerial Res-cue event outright, but the results for the Masters climb placed her fifth out of the five males and herself, but as the only female she was automatically selected to go to Toronto in August along with the winner, Jon who was on very good form this year, read on.

The ITCC

The Internationals took place on Centre Is-land, Lake Ontario, and attracted the public in huge numbers as well as the climbers, their friends, family and acquaintances. The cli-mate for the ITCC was even nicer than that of the Chapter’s with uninterrupted sunshine throughout, so I’m sure some of the climbers had some sunburn to contend with in addi-tion to the very demanding trees presented to them by the ITCC committee. Not so small stunted trees on this particular island and the spread of some of the trees made for great climbing as well as great viewing points too.

The atmosphere was cheerful and optimis-tic, as it mostly always is, but for the final-ists their optimism paid off and gave them

From theTreetopsA TCC Overview

By Charlotte and Ian McDermott

9

Scott Forrest during the Masters

James Kilpatrick after his Masters climb

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all a glimmer of hope of becoming the Champion; for the five males, Giovanni Ugo, Scott Forrest, James Kilpatrick, Mark Chisholm and our very own Jon Turnbull, and the three females, Veronika Ericsson, Nicky Allen-Ward and Anja Erni, the Mas-ters climb would come to prove who was the best of the best.

Unluckily for our Jo, she didn’t quite make it into the final, but the word around was that she just about missed it – along with a couple of other climbers – by a fraction of a point. Better luck next time, Jo but there was a big con-solation and Jo emulated her performance in the Aerial Rescue by winning the event in Toronto also.

Unfortunately for Giovanni of Italy and Mark of America their climbs took a little too long and they both timed out, James’ climb was of a high standard but not high enough to com-pete against Scott and Jon. Scott’s climb was virtually perfect, which left Jon with a tough climb to compete against him, but in the end between these two fantastic climbers Scott once again came out on top and became the Champion, but Jon did the UK & I Chapter proud by representing us in the ITCC with his amazing climb which left him in a close

second place.

The chapter continues to provide the op-portunity to field such great climbers as Jo and Jon both nationally and internationally through sponsorship and a LOT of volun-teer effort, we will always need extra help so please consider volunteering when the 2014 competitions come around. If you want to see Jo, Jo, and the other members of the UK&I European team (Stef Kowalczyk and Steve Gale) then you still can at the ETCC in Switzerland in early September.

If that wasn’t enough, and you missed our last ArborCamp then our top climbers will be at the next ArborCamp at Capel Manor next spring – book early!

Scott Forrest during the Masters

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Left and above: Jon Turnbull, second

place

The exceptional yew trees ofEngland, Scotland and Wales

by Andy Moir, Toby Hindson,Tim Hills and Richard Haddlesey

SUMMARYWhile English yew Taxus baccata L. has become extinct or rare in many parts of Europe, Britain contains a large population of very large and old yew. We analysed 2,760 records of live yew trees to document this unique population and categorise by girth: 717 Veteran (5-6.99m), 204 Ancient (7-8.99m) and 55 Ex-ceptional (≥9m) yew trees. Indi-vidual trees are mapped, and both areas and habitats of the highest proportions are detailed. The loss of 223 notable trees from church-yards highlights a need for better safeguarding a unique habitat of the world’s largest yew trees.

IntroductionEnglish yew (Taxus baccata L.) is a slow-growing, long-lived (>1000 years), shade-tolerant species thatis able to withstand full sun. In a continental climate it is typically an isolated understorey tree, but inoceanic climates it can form dense stands (Thomas and Polwart, 2003). Over-use in past centuries,combined with unsuccessful re-generation, browsing pressure, ille-gal cutting and lack of appropriatemanagement strategies (Svenning and Magård, 1999; Dhar et al., 2006), have contributed to English yew being catalogued as a rare and endangered species over Europe (Hageneder, 2007).

In Britain yew is widespread, al-though yew woodland is restricted to the south and, to a lesser degree, the north of England, occurring on shallow, dry soils, usually on chalk or limestone slopes. Thomas and

Polwart (2003) show the distribu-tion of English yew in Britain. The Joint Nature Conservation Com-mittee (http://jncc.defra.gov.uk/)lists thirteen yew woodlands of Special Areas of Conservation (SAC). A large population of in-dividual trees and small stands are more widely spread, growing on more fertile soils.

Yew has been comparatively little studied, probably because it most often occurs as a codominant or subordinate species in other types of woodland, or as single trees (Tit-tensor, 1980). Ecological investiga-tions have been carried out on theyew woodlands on the North and South chalk Downs in south-east England (Williamson, 1979; Tit-tensor, 1980; Rodwell, 1991), but little has been published about woodlands on the magnesian limestone in Country Durham or on limestone pavements around Morecambe Bay. Age and dendro-climatological studies have been conducted on yew trees in the Privy garden at Hampton Court (Moir, 1999), woodland at Hap-py Valley (North, 2000) and some

churchyard yew in the south-east region (Moir, in preparation).

The natural distribution of yew in Britain is clouded by planting. The only significant stand in Scotland, on Loch Lomond, is considered to have been planted, and whether yew is native to Scotland has been debated (Dickson, 1994). Particu-larly large yew trees that often occur (presumably planted) near chapels, churches, cemeteries and other prominent areas have long been of interest, and their occur-rence, and often girth, document-ed. The aims of this research were to use records of a unique relic population of large-girth yew trees to quantify and map the popula-tion, to identify the most impor-tant areas and habitats of survival and to highlight recent losses.

MethodsThe earliest locations and descrip-tions of ‘notably’ large-girthed English yew come from a variety ofdocumentary sources, some dating back to the late 18th century. Since 2005 historic records, together with more recent identifications

Figure 1. Ankerwyke, Berkshire, recorded with a girth of 788cm. (Photo: Tim Hills)

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Figure 2. Frequency histogram of the girth of 2,208 live yew trees.

and girth measurements of notable yew trees, have been collected by members of the Ancient Yew Group (AYG) and volunteers, and entered onto the AYG database. With most historical records now entered, the fo-cus has turned to locating new notable yew trees and identifying where trees on previously recorded sites have been lost.

The AYG database, which may be viewed at www.ancient-yew.org, provides the most comprehensive archive 13

of information on large yew trees in this country. Tree girth has tra-ditionally been recorded at breast height (1.3m). However, the trunks of yew are notoriously irregular (Figure 1), and low branches can make girth measurements ex-tremely difficult, except when tak-en very close to the ground. The girth measurements of yew trees are therefore typically recorded at the minimum girth between the ground and breast height.

DataFor this study data from the AYG database was made accessible and retrieved in 2011. Seven fields of information: Site name, Area, Country, Site type, Tree Girth, National grid reference (NGR) and Notes, were transferred to a spreadsheet that was then edited, mainly to complete omissions, but also to help identify and correct errors. Girths recorded in inches were multiplied by 2.54 to convert to centimetres. National grid ref-erences were generally recorded to six figures, which gives a precision of 100 × 100m. However, where references were not recorded the NGR for the location name (typi-cally the nearest village) was used. In most instances, where a few large yew trees occur in a small discrete group, only a single entry for the largest tree was recorded. To enable the distribution of yew to be plotted with ARCVIEW GIS software, NGR grid references were converted to latitude and lon-gitude in a decimal degrees format. Records in the database for yew inIreland and France are not in the British NGR format, so these re-cords were not included in this analysis.

In Britain both the Tree-Register and Ancient-tree-hunt.org.uk cat-egorises trees into ‘Notable’, ‘Veter-an’ and ‘Ancient’. However, to high-light the exceptional rarity and importance of the largest-girthed yew, we have defined a further

category ‘Exceptional’ yew. Here we define five categories based on girth: Young (≤2.99m), Notable (3-4.99m), Veteran (5-6.99m), An-cient (7-8.99m) and Exceptional (≥9m) (Table 1). The 30 counties with the largest populations of yew were listed in rank order. The per-centage loss of trees has been cal-culated using the following equa-tion: (Lost/Live)*100.

ResultsA total of 3,041 records of yew trees were used in this analysis. Of these, 73% were of known girth, 18% of unknown girth, and 9% were lost trees. Distributions of the sizes of the 2,208 live yew of know girths are shown in Figure 2 and Table 1. Veteran, Ancient and Exception-al status yew trees form 32%, 9% and 3% of the records, respective-

ly. Just 35, 19 and one Exceptional yew trees are identified in England, Wales and Scotland, respectively.

The overall geographic distribu-tion of yew is shown in Figure 3 and quantitatively described in Tables 2 and 3. England is shown to contain 71% of the population of recorded yew, with the highest proportion at 17% in Hampshire and Kent. Hampshire and Kent between them contain 19% of the Ancient and 15% of the Exception-al yew trees. Wales contains 25% of the live recorded yew, but half thisnumber (12% of the total popula-tion) is located in the County of Powys. Powys contains high pro-portions of both Ancient and Ex-ceptional yew, accounting for 22% and 15% of these populations, re-spectively. Two other noteworthy

Figure 3. The distribution of 717 recorded yew of Veteran (black/small),Ancient (green/medium) and Exceptional (blue/large) size in England,

Scotland and Wales.14

high proportions of yew in Eng-land occur in the counties of Som-erset and Gloucestershire in the South-west and in Shropshire and Herefordshire of the West Mid-lands, which contain 19% of the total population divided equally between these two regions.

Comparison between the numbers of live yew and lost yew in differ-ent areas are shown in Table 2. We identify that, overall, 10% of previ-ously recorded yew have now been lost, but these levels are more thandouble in the worst affected coun-ties: Glamorgan, Yorkshire and Warwickshire. The highest num-bers of lost Notable yew trees re-corded are 23 in Somerset and 20 in Kent. While Scotland is shown to contain just 4% of the popula-tion, it contains the yew with the largest recorded girth at 17.06m (56 ft).

In terms of habitat, a total of 1,855 individual trees (67% of the re-corded population) are located in churchyards. Woodland and gar-den yew account for just 9% and 6% of the population, respectively.Churchyards also account for the highest number of all recorded lost yew, 223 (79%). In contrast, just three trees are recorded as lost from woodland.

DiscussionExceptional yewWhile it is recognised that our data records only a small part of the to-tal population of yew, it identifies a very high proportion of those trees considered most valuable in terms of conservation. Read (1999) de-fines veteran trees as those of in-terest biologically, culturally or aesthetically because of their age, size or condition, and suggests that oak specimens with a girth of more than 4.7m be considered vet-eran and valuable in terms of con-servation. Our defined category of Veteran yew should be considered in similar terms, while those cate-

gories of Ancient and Exceptional yew increase exponentially in rar-ity and value.

A further aspect to the importance of this largegirthed yew is age. Es-tablishing the age of yew is com-plicated by the general hollowing characteristic of trees over 4.6m in girth (Mitchell, 1972). How-ever, the use of partial increment cores and sections from both hol-low trees and solid trunk church-yard yew in the SE region provides reasonable empirical evidence that one metre of girth equates to around one hundred years of age (Moir, in preparation). This helps confirm previous estimates that suggest that yew trees categorised here as Exceptional are likely to be near or over 1,000 years old, which further highlights the importance of these trees.

The distribution of yewChurchyards contain 717 peci-mens (73%) of the total 976 re-corded yew with girth of 5m or more, highlighting this habitat as the most important for the preser-vation of large-girth yew. Exactly why yew is associated with church-yards remains unclear, but it has been suggested that the larger yew at such sites may be survivors from saint cells from the sixth to seventh centuries AD (Bevan-Jones, 2002). The small (3m x 4m) cells or her-mitages of early saints (which may have been little more than a few stones, or wooden constructions) can leave little archaeological ev-idence or may be incorporated into later churches. Wales has no examples of natural woodland yew (except in a few areas of cliff (Bevan-Jones, 2002)); therefore the abundance of large yew is most likely explained by planting. It is also of interest that, assuming one metre of girth equates to around one hundred years of growth (Moir, in preparation), then the drop after the peak frequency of yew (Fig-ure 2) coincides with the dissolu-

tion of the monasteries at the end of the medieval period (c.1539). Similar evidence for a relationship between churches and yew comes from a study using increment cores from the yew at the Dunsfold Par-ish church in Surrey (Moir, 2004). The study at Dunsfold concluded that the church and the yew were likely to be of the same age. Earlier studies on yew have also suggested a link between the planting dates of yew and their location in relation to a church (Chetan and Brueton, 1994).

Losses of yewSixty-seven percent of all record-ed yew are located in churchyards. However, 717 of the 976 recorded Ancient yew (≥5 m) (73%), and 50 of the 55 (91%) Exceptional yews (with girth ≥9 m) are locat-ed in churchyards. This research highlights the churchyard habitat as a critical habitat for the conser-vation of large-girthed yew trees. Rather startlingly, 10% of large yew trees previously recorded in churchyards are shown to have dis-appeared; the majority over the last one hundred years. The loss of yew trees from churchyards is increas-ingly being recognised (Green-wood, 2013). It is worth noting, however, that yew trees in promi-nent positions such as churchyards and historic sites are more likely to have been recorded, so the totals may be biased towards churchyard yew loss, while the more easily missed woodland yew losses may be under-represented. However, on balance, the general inclusion of multiple large trees into a single record in this study means that the full extent of large-scale losses at anumber of sites is likely to be un-der-represented. For example, at Sullington (Sussex) only one of six yews now remains, at Blaina (Monmouthshire) eleven substan-tial trees have all been removed, and at Strata Florida (Scotland) only two of what was once 39 yew remain (Bevan-Jones, 2002). It is 15

16

possible that these losses are in part a response to the pressure on churchyard space for burials and buildings. While it was considered beyond the scope of this study to quantify the timings and reasons for losses, this information is of-ten available, and analysis of these factors in the future is suggested to help identify simple strategies to help conserve yew. For instance, a total of 28 churchyard yews are re-corded as lost due to storms, there-fore it is hypothesised that pre-venting the removal of the lower branches may help mitigate the ap-parent susceptibility of these trees to wind damage.

The importance of the churchyard habitatThere are two general conserva-tion strategies for slow-growing long-lived species that are rare and confined to small geographical ar-eas: a) reinstituting the ecological processes important for the re-cruitment of new individuals (for example, removal of animal brows-ing pressure on seedlings), and b) protecting established individuals. From our data, hardly any large yews are recorded in Special Areas of Conservation of yew woodland, and just 9% of trees are located in woodland, demonstrating the lim-ited importance of these habitats in the conservation of Britain’s larg-est-girthed yew. It can be argued that the wide regional coverage of large-girthed yew shown here should be viewed as important for the long-term viability of the yew population in this country, due to the critical role they may play in regeneration. Yew seeds are pri-marily dispersed by birds (Iszkulo and Boratynski, 2004), therefore individual yew allow spontaneous germination under canopies of other tree species some distance from them. In a study on the South Downs of the Hampshire/Sussex border, Tittensor (1980) found yew woods often along parish bounda-ries and suggests their likeliest ori-

gin is from parental seed trees that marked those boundaries. Large-girthed yew also form a widespread interlinked network that produce abundant pollen that can be borne long distances by the wind, helping to preserve the genetic variation required to maintain population viability. The regeneration of Brit-ain’s younger yew woods and fu-ture yew wood is therefore likely to be interlinked with the health of the population of large individual yew.

Future researchInterestingly, in studies on the yew woods of the South Downs, Tit-tensor (1980) found 62% of yew on steep slopes, 90% on chalk and 80% of woods occurring in areas of high rainfall (>1000mm per year). The influence of factors such as rainfall, slope and substrate on the population of individual recordedtrees is highlighted for future in-vestigation. Also, despite Scot-land’s comparatively small popula-tion, the few examples of large yew identified there may be critical in helping to establish whether yew is native to Scotland. The relationship between planting yew and church-es may be significant and further research to explore the possible correlation between the establish-ment of churches and the girth of their associated yews is currently under way.

Conclusions1 This study maps all known yew trees of 5m or more girth in Eng-land, Scotland and Wales and highlights that just 55 ‘Exceptional’ yew trees (those with a girth of 9m or more) survive.

2 Previously known areas with high proportions of large-girthed yew in Hampshire and Kent are shown to contain 17% of the pop-ulation, while Powys has 12%. Pre-viously unrecognised areas with high proportions are identified in Somerset, Gloucestershire, Shrop-shire and Herefordshire, which between them contain 19% of the population.

3 67% of large-girthed yew trees are recorded in churchyards, and recent losses suggest a need to bet-ter safeguard the exceptional trees that survive in this habitat.

AcknowledgementsThis research was funded by Tree-Ring Services, UK. The Ancient Yew Group database is made acces-sible to the public as the Yew Gaz-etteer, thanks to the sponsorship of the Tree Register of the British Islesand the Conservation Foundation. We thank all those who submitted data to the Ancient Yew Group da-tabase. We are grateful to Lesley Trotter and an anonymous review-er for comments that substantiallyhelped improve this paper. 17

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Shell-wall thickness and breaking safety of mature trees

By Frank RinnAbstractThe acceptable level of trunk hollowness with regard to the breaking safety of trees has been debated for decades but remains unresolved for most tree ex-perts because of contradictory statements, theories, and publications. However, research and observa-tions clearly demonstrate that mature (large diam-eter) trees require much less remaining shell-wall thickness for reasonable stability, than younger trees still growing in height. Furthermore, stability of ma-ture trees is surprisingly independent of woodmaterial properties such as fiber strength.

Keywordsshell-wall thickness, one-third-rule, breaking safety, tree safety

IntroductionStorm events often lead to breakage of conifer trees in forest stands, even those with intact cross sections. Breakage, though, is probably more likely to occur if decay is present. (Fig. 1). On the other hand, old trees are known for having surprisingly thin shell-walls, often for many decades (Fig. 2), yet many survive even strong storm events — even trees that are quite tall or have large, wide-spreading crowns. These observations seem contradictory, but can be explained as subsequently shown.

The uncertainty about potential stem breakage safety was one of the reasons for developing mobile testing methods to detect internal decay, and for measuring shell-wall thick-ness. In 1984, two retired German engineers (Kamm & Voss) tested a drilling device using a spring-driven scratch pin, and which recorded a 1:1-scaled profile of the thin needle’s penetration resistance on a wax pa-per strip within the machine. These profiles allowed for the detection of large voids in trees, but were found to be systematically wrong in the more intact portion of the stem be-cause of resonance and damping ef-fects of the spring-loaded recording mechanism. Thus, evaluations of utility poles, trees, and timber products based on such profiles were

also systematically wrong and unreliable. For exam-ple, decay was identified were the wood was just soft (by nature), but intact. Consequently, Kamm & Voss developed a resistance drill that recorded data elec-trically. With that improvement, they then tried to sell the corresponding systematically wrong in the more intact portion of the stem because of resonance and damping effects of the spring-loaded recording mechanism. Thus, evaluations of utility poles, trees, and timber products based on such profiles were also systematically wrong and unreliable. For ex-ample, decay was identified were the wood was just soft (by nature), but intact. Consequently, Kamm & Voss developed a resistance drill that recorded data electrically. With that improvement, they then tried to sell the corresponding patent application (Kamm& Voss 1985). A company interested in the intellec-tual property asked a German University whether the concept, based on measuring needlepenetrationresistance, was practical. Starting in 1986, this idea became the patent application (Kamm & Voss 1985). A company interested in the intellectual property asked a German University whether the concept, based on measuring needlepenetration resistance, was practical. Starting in 1986, this idea became the subject of a physics graduate research thesis (Rinn 1988). This research resulted in further technical de-velopments and finally, patent applications describ-ing high-resolution machines and drilling needles (Rinn 1990, 1991). The results clearly showed that regulation of the machine, acquisition of measure-

Figure 1. In forest stands, internally decayed stems show a significantly higher breaking probability, but

even completely intact cross sections may break. 19

ment values and recording of the profiles must be done electronically to ensure a distinct (linear) corre-lation between the obtained pro-files and wood density— the major wood material property (Rinn et.al. 1989 & 1996). Only those profiles obtained in this manner, enable the user to correctly interpret results and reliably evaluate wood condi-tion (Rinn 1996). Thereafter, wood samples from all over the world were tested with these improved de-vices. It’s interesting to note that in stems of coconut palms (Fig. 3) it was found that approximately ⅓ of the trunk radius has a significantly higher density (andstrength).

Some years later, Mattheck and Bre-loer published statistical data (1994) claiming that breaking safety of tree trunks is significantly lowered if the remaining intact outer shell wall (t) is thinner than ⅓ the radius (R). This finding was interpreted as confirmation of a poten-tial natural mechanical design because the mechan-ical load characteristics of coconut palms are similar to slender conifers in forest stands.

Eventually, new analytical and computational meth-ods suggested that tangential tension stresses as a consequence of bending or torsional loads may ex-plain the increase of breaking failures of trees with a t/R< ⅓ (Ledermann 2003). This result was expected because torsional and shear strength of wood are comparatively low (Blass und Schmidt 1998).

Years later, critics claimed that there is no scientific proof of the socalled ‘Mattheck’s ⅓ -rule’ (Gruber 2007, 2008), and thus, no valid reason to fell trees if t/R< ⅓. Consequently, practitioners and experts became increasingly unsure about which method or ‘rule’ to apply for safety evaluation of trees.

Trunk and crown relationsThe mechanical bending load of upright tree trunks is mainly determined by wind load (Spatz & Bruechert 2000). Because wind speed tends to increase with height above ground, and drag is de-pendent on wind speed to the power of two, tree height is the dominating allometric wind-load fac-tor. Consequently, after a tree has reached maxi-mum height, wind load does not increase any more (White 1998), although old branches may locally

Figure 2. Large, old trees with very thin shell walls (t/R<1/5) often

remain standing for decades despite the loss of much of their stem cross

sections.face higher drag due to higher wood stiffness (Fratzl 2002). While the crown does not grow any more, girth usually continues to increase due to annual radial growth increments. That means the trunks of aging trees continuously gain load-carrying ca-pacity, while the load remains fairly constant. Consequently, the increas-ing girth of aging trees automaticallyleads to a steady increase in the trunk breakage safety factor (= load-carry-ing capacity / load). And this leads to the question: How hollow can a mature tree become, before the risk of stem breakage is unacceptable?

Numerical estimation (based onGere and Timoshenko 1997)Mechanical stress (S) in a cross sec-tion is usually defined as the acting

force (F) divided by the area (A): S = F / AIf a bending moment (M) is applied, stress can be calculated from S = M / WW characterizes the section modulus that is usually determined by an integral over the cross sectional area. For cylinders of diameter (D) and a central void of diameter (d), W can be calculated in a sim-ple form: W = π * (D4 – d4)/(32*D)Strain in the material is usually defined by changes in length (ΔL) divided by the observed distance (L):ε = ΔL / L At the same time, strain is a consequenceof external loading and strongly determined by the modulus of elasticity (E): ε = ΔL / L = S / EThis helps to explain the influence of material strength (= maximum applicable stress = Smax) on the maximum bending load that can be applied without causing damage: Mmax = W * S maxIn an intact cylindrical cross section (d=0), the de-pendence of the load carrying capacity on diameter and material strength is obvious: Mmax ~ D³ S maxTherefore, a doubling of the material strength val-ue of the wood (Smax) in the whole cross-section leads to a double maximum applicable bending load (Mmax). A doubling of trunk diameter, however, 20

leads to an eightfold increase in maximum applica-ble bending load: (2*D)³ = 8*D³Compared to the impact of diameter increase on to-tal load carrying capacity, higher material strength within a newly formed tree ring is only of marginal relevance. The influence of radial growth of a stem cross section in terms of dimension is thus, far more important than changes in material properties. Therefore, we can characterize the load-carrying ca-pacity of cylindrical cross sections in first order by its diameter.

Diameter growth with ageAs already shown by Bräker (1981), ring width of mature trees usually stabilizes as a nearly constant value. If we assume that ring width, after the tree has reached maximum crown height (time point y=0), is a percentage (p) of the diameter at this time (D1), we can estimate later diameters (D2), years (y) after D1 was reached: D2 = (1+ y * p) * D1

The corresponding section modulus can then be written as:

Now we can ask the most important question: at what point (level of hollowness) does a large old tree become unstable? For easier evaluation we trans-form diameter values into shell-wall thickness (t) and stem radius (R): t/R = 1 – d/DOnce we set W2! = W1 , we can calculate t/R-ratios equivalent to the ones at y=0:

With this formula we can determine the t2/R2-ratio at any given point in time of maturity (y>0), which is equivalent to a certain t1/R1-value at y=0.

Practical applicationIf we assume an intact (d1= 0) tree trunk has a di-ameter of D1= 60cm (about 24 inches) at the time when its crown reaches its maximum height (y=0), and then an annual ring width of 3mm (p = 0.5% of D1), the diameter of the trunk after y = 20 years

Figure 3. A resistance drilling profile of a coconut palm stem disk showing linear correlation to wood

density, and that approximately ⅓ of the outer radius has significantly higher

wood density.

will be D2 = 66cm. If this trunk cross section then (at y = 20) would have a central void of d2 = 47cm, it would have the same load-carrying capacity as the completely intact cross section at y=0 (Fig. 4) That means, if we assume the tree at y=0 is “absolutely safe in bending” (because it is completely intact), we have to grant the same level of safety 20 years later to this tree with a diameter of 66cm if there is a central void leading to a t/R ratio less then ⅓: t2/R2 = 9.5/33 ≈ 0.29, because these two cross-sections provide the same load-carrying capacity and thus, similar breaking safety.

If we assume a cylindrical trunk (D1= 60cm) has a central void of d1= 40 at y=0 (that means a t/R= ⅓), after y = 20 years and p = 0.5%, D2 would be 66cm. If this trunk then has a central void of d2= 52 (=>t2/R2≈ 1/5), it would provide the same load carrying capacity as with a t1/R1= ⅓ at y=0 (Fig 5). What this means in terms of bending safety for such trees is that: a t/R= 1/5 at y = 20 is equivalent to a t/R= ⅓ about 20 years earlier (y=0). If we believe a t/R= ⅓ is a measure representing sufficient ‘stability’ of a tree at y=0, then we have to accept, that 20 years later, a t/R= 1/5 represents the same amount of ‘stability’and relative safety.

Consequently, the critical t/R ratio is not a constant value, but strongly depends on trunk diameter and thus age (and crown size), as soon as the height does not increase any more.

Consequences and limitsEspecially in the urban landscape, risk of tree fail-ures, resulting in injury to people or property dam-age, resulting from tree failures, increases with age. Therefore, most trees that require a thorough assess-ment are more or less mature. Consequently, the ap-proach described here is relevant for the majority of urban tree inspections, especially for level 2 and 3 as defined and explained by the ISA tree risk assess-ment qualification (TRAQ).

The comparative shell-wall safety estimation meth-od as described above, shows that the so-called ‘⅓- 21

rule’ may be correct for a certain kind and age class of trunks, but has no relevance for mature trees, andshould not be used to justify felling or even exten-sive crown reduction to mitigate risk for such trees. In mature trees, a t/R= ⅓ is not even the starting point for being concerned about breaking safety, be-cause, as shown above, in terms of breaking safety, a t/R= 1/5 or even less can be equivalent to a t/R= ⅓ at the time the tree reached maximum crown height. This explains why large, old, hollow trees with very thin shell walls often stand for decades, despite large crowns and exposure to strong wind.

When we assume the ⅓-rule as being correct in de-scribing the point where the probability of breaking failures starts increasing significantly for central-ly decayed, thin, and tall, slender forest trees (and coconut palms), we have to accept that this start-ing point for concern shifts down to thinner shell walls once maximum height growth is reached, because tree /diameter continues to increase. In the second example described above, the starting point for concern would be a t/R= 1/5 (assuming that a t/R= ⅓ is the starting point of con-cern for younger trees as described above).

However, it has to be taken into account that this approach as pre-sented here is valid only as long as t/R>1/10, approximately. Below this ‘limit’, and if big, open cavities are present, more complex approaches and estimations have to be applied, because other failure modes may

Figure 4. (Left) These two cross-sections (sketch to scale) provide the same load-carrying capacity and thus the same breaking safety provided the same wind load is applied.

Figure 5. (Right) The left cross section of a decayed tree stem at year=0 provides a t/R≈⅓. The image on the far right shows the same cross section after 20 years of annual increment growth and further decay progression with a t/R≈1/5. Assuming the same wind load, these two cross sections (sketch made to scale) provide approximately the same load-carrying capacity, therefore, if an expert evaluates the left cross section as acceptable (‘safe enough’) at the time of inspection (y=0), the same grade of safety has to be granted to the tree 20 years later despite a thinner shell wall.

occur, and because longitudinal dimension of wood deterioration or other structural damages become more important (Niklas and Spatz 2012; 2013). This aspect shall be explained in future publications.

In addition, in terms of loss of load-carrying capac-ity (LCC), the location of decay (centered or uncen-tered) within the cross section, as well as cross-sec-tional shape, are more important than just the size of deteriorated parts (Rinn 2011). Comparatively small areas of decay in the outer sapwood of the stem, or on the upper side of a horizontal branch can lead to significantly greater losses of LCC and thus, have a greater impact on safety than large centrally located voids. Consequently, for assessing the stem breaking safety of mature trees, it is not enough to determineshell wall thickness by, for example, resistance drill-ing at just one point, or measuring fiber strain with

Figure 6. Two examples of decayed trunk cross sections of mature urban trees (left: Ulmus, right: Tilia). Decay columns are often asymmetric be-

cause they develop from trunk wounds or damaged roots. In addition, many mature urban trees do not have cylindrical cross sections. Thus, sim-

ple measurements of shellwall-to-radius-ratios, or the local assessment of strain by pull-tests can hardly be applied correctly for evaluating breaking

safety. In such situations, tomographic assessments are required for obtain-ing more precise results and more reliable evaluations.

22

only one elongation sensor during one pull-test. Both results are valid only for the point of meas-urement and cannot be extrapolated to the whole trunk. Results can be quite different in other areas of the same cross section, and even more so, up and down the trunk. If devices that can be calibrated are properly applied, both measurement methods (re-sistance drilling and pull test strain-assessment) candeliver valuable information, and significantly en-hance tree risk evaluation compared to visual grad-ing alone. But it has to be taken into account that each result is only valid for the point of measure-ment. In this sense, tomographic approaches deliver more information, but still have to be understood and interpreted correctly. (Fig. 6)

Without knowing the weakest point of the tree trunk under external loading, every localized measure-ment is just an approximation and cannot describe the mechanical behavior of the whole cross section, trunk or even tree. This limitation is valid for all technical methods and devices in a specific certain way, and has to be clearly understood, explained and communicated by the experts. The shell-wall-to-ra-dius-ratio (t/R) required for sufficient breaking safe-ty is not a constant value over time, but decreases as trees mature and increase in girth. Understanding and applying this aspect of natural tree architecture while inspecting and evaluating mature urban trees can prevent unnecessary felling or crown reduction as compared to current standards - for the good of nature, people, and municipal budgets. In this man-ner, trees can be retained longer to provide social and environmental benefits that enhance quality of life in urban landscapes, without endangering peo-ple and their property.

Frank RinnHeidelberg/Germany

23

Jon Turnbull during his ITCC Master’s Climb

One of the ITCC Masters bells

CEU’s CPD

WHERE MUNICIPAL ARBORISTS GO!

For regular technical meetings, on-line education, updates and networking.

MTOA, JOIN NOW. CONTACT THE CHAPTER OFFICE FOR DETAILS, CLICK HERE.

Professor and Re-searcher from United

Kingdom Honored with Education Award from the International Socie-

ty of Arboriculture.

CHAMPAIGN, Ill., U.S. (August 2013) – Dr. Mark Johnston, a professor and research fellow in arboriculture and urban forestry at Myerscough College in Lan-cashire, United Kingdom, is this year’s recipient of the Interna-tional Society of Arboriculture’s (ISA) prestigious Alex L. Shigo Award for Excellence in Arbori-cultural Education.

The Alex L. Shigo Award honors ISA members for enhancing the quality and professionalism of arboriculture through education. ISA President Terrence Flana-gan honored Dr. Johnston at a ceremony on Sunday, August 4th in Toronto, as part of the ISA Annual Conference and Trade Show, August 3rd–7th, 2013.

“Dr. Johnston has worked as a contractor, consultant, tree officer, and college professor to connect people with trees in schools and communities throughout Britain and Ireland,” says Flanagan. “He has helped hundreds of young men and women complete their degrees in arboriculture in addition to his development of online courses to make higher-learning availa-ble to students everywhere.”

Responsible for the Forest of London project, Dr. Johnston led Britain’s first city-wide ur-ban forest initiative and inspired other major urban forest pro-jects across the UK. His Trees in Towns II survey for the gov-ernment on urban trees in Eng-land is considered an influential policy and practice guide. He developed and led Myerscough College’s Master of Science pro-gram in Arboriculture and Urban

Forestry, the only post-graduate course of its kind in Europe.

Dr. Shigo, a renowned plant pa-thologist, was known through-out the industry for his studies on tree decay, which led to ma-jor changes in arboriculture. “I met Alex Shigo in 1980 at a joint ISA-AA conference in England and was fortunate to sit through his impromptu workshop,” says Dr. Johnston. “When I became a full-time lecturer, Dr. Shigo’s books, videos, and research papers were required learning materials for my students. This great man has not only had an influence on me, but also on the thousands of students I’ve taught.”

Johnston is one of eleven dis-tinguished professionals who make up the circle of winners for ISA’s Awards of Distinction, sponsored by Bartlett Tree Ex-perts. Robert Bartlett Jr., Chair-man and CEO of Bartlett Tree Experts explains, “Bartlett is proud to partner with ISA in sup-port of the 2013 Awards of Dis-tinction. These individuals are truly ‘champions of tree care.’ We applaud all of the hono-rees for their tireless effort in research, teaching, mentoring their peers, and dedication to the best daily practices of arbo-riculture.”

ISA has been honoring mem-bers and industry professionals with the Awards of Distinction since 1963. Nine categories rec-ognize candidates in such areas as research, publishing, educa-tion, and advancing the cause

of the organization. The winners are selected by a diverse group of experts in arboriculture. More than 20,000 members make up ISA’s organization worldwide.

ABOUT ISA

The International Society of Arboriculture (ISA), headquar-tered in Champaign, Ill., is a nonprofit organization support-ing tree care research and ed-ucation around the world. To promote the importance of ar-boriculture, ISA managesthe consumer education web site, www.treesaregood.org, which fulfills the association’s mission to help educate the public about the importance and value of proper tree care. Also, as part of ISA’s dedication to the care and preservation of shade and ornamental trees, it offers the only internationally-recog-nized certification program in the industry. For more informa-tion on ISA and Certified Arbo-rists, visit www.isa-arbor.com.

ABOUT BARTLETT TREEEXPERTS

The F.A. Bartlett Tree Expert Company was founded in 1907 by Francis A. Bartlett and is the world’s leading scientific tree and shrub care company. The organization’s current chairman, Robert A. Bartlett Jr., represents the third generation of Bartlett family management. Bartlett has locations in 27 U.S. states, Canada, Ireland, and Great Britain. Services include prun-ing, insect and disease man-agement, fertilization and soil care, cabling and bracing, tree lightning protection systems, and tree and stump removal. Its corporate offices are located in Stamford, Connecticut. To find out more, visit the company’s web site at www.bartlett.com or call 1-877-BARTLETT (227-8538).

25

It was the early 1970s and Mark Johnston was working on timber felling when he had a chainsaw accident. It was this mishap that got him thinking about the future.

“Do I really want to be doing this when I am 40?” Johnston recalls.The job was becoming increas-ingly demanding for him as he grew older each year. Johnston, who had left school early with no real qualifications, began to re-alize that he needed additional education to advance in a career. So, he made a decision.

“I signed up for a basic course in tree surgery that didn’t require any formal qualifications—only that I have experience,” he re-members. “When I passed that course, I was qualified to take another higher level arboricul-ture course and so I continued. I learned a valuable lesson—one I have always passed on to my students: get qualified and then anything is possible.”

From the time Johnston began his studies in 1975, he devel-oped a love for arboriculture and kept studying while working in the field. He eventually earned his Royal Forestry Society (RFS) diploma working as a London tree officer and then obtained his Ph.D. in urban forestry from the University of Ulster.

“Once I was involved in arbori-culture, I never looked back,” Dr. Johnston recalls. “For me, urban forestry was the perfect combina-tion—a concern for people and a concern for trees.”

Dr. Johnston began teaching ar-boriculture at various colleges in England and also as a visiting lecturer at the Chinese Universi-ty in Hong Kong. Today, many of his students in Hong Kong now hold high positions in parks man-agement and tree care. Since

his arrival at Myerscough Col-lege in Lancashire, England, Dr. Johnston has helped hundreds of young men and women complete their degrees in arboriculture. He is also responsible for developing and leading the college’s Master of Science in arboriculture and assisted in the development of online courses to make high-er-learning available to students everywhere.

“The master’s course at Myer-scough is unique as far as Eu-rope is concerned,” explains Dr. Johnston. “It’s the only post-grad-uate qualification of its kind here. We attract graduates in related subjects from many countries overseas. Our range of online courses is also unique interna-tionally drawing interest from all over the world.”

In addition to his teaching, Dr. Johnston is a dedicated research-er, involved in tree care projects and the study of urban forests.“The ‘Forest of London’ project was Britain’s first city-wide ur-ban forestry initiative, which had far-reaching impact in both Brit-ain and Ireland,” Dr. Johnston explains. “I launched it in 1987 and led the program, which em-phasized partnership working, community education, and in-volvement. The greenprint from this project was later adapted to other cities, including Dublin, Re-public of Ireland; Cardiff, Wales; Glasgow, Scotland; and Belfast, Northern Ireland.”

Dr. Johnston has published a number of papers related to his studies. In 2008, he wrote the influential “Trees in Towns II: A New Survey of Urban Trees in England and Their Condition and Management.”

“I was the lead researcher on this

major government study,” says Dr. Johnston. “The publication established a planned, system-atic and integrated approach to managing urban forests in Brit-ain. The research is expected to influence policy and practice for many years to come.”

Dr. Johnston has worked in arbo-riculture education for 18 years and is honored to have his work recognized by ISA. But it should also be noted that Queen Eliz-abeth II has commended Dr. Johnston for his contributions to arboriculture and urban forestry. Dr. Johnston is a Member of the Most Excellent Order of the Brit-ish Empire.

“I was particularly pleased that the citation mentioned my cross-community work in the For-est of Belfast project,” Dr. John-ston replies, “where I tried to use trees and tree planting as a uniting tool between divided com-munities. Although I was born in London of Scottish descent and have worked in Britain for most of my career, I have lived in Belfast for the past 20 years. My wife is Irish.”

For nearly 40 years, Dr. Johnston has dedicated himself to connect-ing people with trees all across Britain and Ireland, working as a contractor, consultant, a tree of-ficer, and a professor. The lesson he learned early on to discover as much as possible about the trees around us is one he wishes to pass on to future generations.“I would like the respective gov-ernments to ensure that all young schoolchildren in Britain and Ire-land learn about tree planting and basic tree care as part of their regular education. I think that could make a huge difference in their attitudes and behavior to-ward trees and the environment once they become adults.” –Dr. Mark Johnston

Connecting People in the U.K. with TreesDr. Mark Johnston — Alex L. Shigo Award for Excellence in Arboricultural Education

Professor, Research Fellow, Arboriculture and Urban ForestryMyerscough College

Preston, United Kingdom

26

ArborCamp

Join us on October 23rd in London

Ride for Research ....... get on your bike... plant trees with school children... raise money for tree research

www.Fund4Trees.org.uk

The ride is suitable for all abilities and open to anyone working in the forestry and arboricultural industries. There is a minimum requirement to raise £150 of sponsorship. Find out more at:

28

In Part l of this article writ-ten to accompany his semi-nar ‘Expert’s Question Time’ co-hosted with Dr. David Lonsdale at Kew Gardens on Tuesday 25th June, Jeremy shared his views on the im-portance of experience and the process of starting a new commission.

In part ll, he looks at the el-ements that need to be com-pleted before he begins to write the actual report.

Collecting and managing relevant information

The reality of many tree fail-ure cases is that they do not progress to formal legal pro-ceedings until some consid-erable time after the event, which in some instances can run to a number of years. Al-most invariably, with such a lapse of time, the tree or tree-part that failed is long lost and there is nothing left on site but a space where the tree once stood. Under such circumstances, ‘Why bother with a site visit?’ and ‘Is it re-ally necessary?’ are common questions asked by instruct-ing lawyers, keen on keep-ing costs to a minimum. The response is that a site visit is absolutely essential and I rarely take on cases where

one is not agreed.

When a tree fails, the immedi-ate surroundings and specif-ic circumstances are always a material consideration in assessing whether the event was reasonably foreseeable, and the only way to reliably get that context is to visit. In addition to the health and structural issues of the actual tree, matters such as exposure to wind, recent loss of shelter, recent root disturbance, fail-ure patterns in nearby trees and ground conditions, can all have a bearing on why a failure occurred. The default for me is always to visit, even on the lowest value cases or if the tree has gone, and it would be very unusual not to do so.

It is easy to get carried away with being an expert and fo-cus on the detail at the ex-pense of the wider context, and detailed investigations of tree parts that failed is a common area for making that mistake. The reality-check is that the courts rarely seem to be interested in what sort of fungus caused the failure, or the ratio of sound wood to decayed wood in a cross-sec-tion, or the retrospective ap-plication of this or that meth-od of assessing the level of

risk. What seems to be much more important is whether the cause of failure would have been discoverable be-fore the event, and the start-ing point for that aspect of management, as set out in the HSE SIM, is a “quick visual check”.

What could be seen by look-ing from ground level is what matters, and although detail of what could not be seen may be of passing interest, it is un-likely to influence any judg-ment. The only exception to that would be if there were discoverable visual indica-tions of a problem that would have triggered more detailed investigations, in which case it would be prudent to estab-lish what such investigations would have been likely to dis-cover. However, in the bulk of situations, my experience is that there is no need for an-ything more than recording dimensions and features that would have been visible from a ground based inspection.

More often than not, the only evidence of tree condition and the detail of the failure is in the form of photographs, and their interpretation can often dictate the course of a case. Indeed, two of my current cases have featured on TV

In search of the perfect report Part IIby Jeremy Barrell

reports of accidents, so imag-es can extend to high quality video footage as well. In the absence of the actual tree or part that failed, images have the potential to be extremely helpful for exploring detail well after the actual event.

Considering how pivotal im-ages can be, it is surprising how often the tree expert gets incomplete sets of poor qual-ity photocopies, and yet it is almost normal rather than the exception. The experienced expert will always ask for good quality copies and al-ways remind the instructing lawyers to request in writing from the other side that all images of the event are dis-closed. A more recent evo-lution of using images to as-sist expert analysis is to visit the location on Google, with Streetview often providing quite detailed views of road-side trees before the failure.

Legal proceedings always have a strong focus on doc-uments, sometimes running into thousands of pages, and managing such vast amounts of paper is a headache. This is often compounded by them being sent in dribs and drabs, without proper referencing, pages sometime duplicated or missing, and even the odd word being changed with-out any indication. Law-yers tend to leave all this to their administrative support, which is probably the root of

the problem, because to get document management right takes a lot of time and brain-power. It may be mundane to read every page and makes sure it is stored with the date received and the number of pages meticulously cata-logued, but being organised to this level is a core skill of effective experts. Invariably, the lawyers don’t do it, so you have to, and experts who pay very careful attention to this detail will be the ones who find that critical sentence or even a single word that can make the difference between winning and losing.

Writing the report: Phase l

The ultimate purpose of a le-gal report is to assist the court in understanding matters that are beyond its expertise, and it must be written for the court, not the entity paying for the service. It is a clear duty of the report-writer to discharge that task with com-petence, due care, integrity, independence and impartial-ity, and to present an objec-tive and balanced position to assist the court in making its decision on the matter in dispute. These are onerous constraints, but this is the framework that all legal re-ports must be constructed within. Indeed, all experts must be ever-mindful of this rigid duty in the process of evolving opinions and then presenting them as written

reports. Throughout the writ-ing phase, these requirements should be at the forefront of your thinking, setting the mental framework for every aspect of the exercise.

Legal cases are invariably complicated and that takes clear thinking to understand, assess and analyse. No doubt there are many ways to achieve this, and the ap-proach is bound to vary with each individual, but here are a few ideas that seem to have assisted me in improving my writing. As preparation, I always start by scanning the documents to give me a quick overview, which seems to help establish a rough frame-work of the issues very early on. I highlight matters that seem important, usually write short notes on the page near them and then tab the page so that I can easily find it again. All this is before the site visit, but I still take the full papers when visiting in case some-thing crops up that I missed in the scan. During this peri-od, I start to think about and locate technical references that I think may be useful in clarifying the issues that be-gin to emerge. I very rarely rely on books and publica-tions, but often they provide technical support for an ex-perienced-based opinion, so it is necessary to have copies and refer to them.

Been there, done that!

Congratulations to all those who recently completed the inaugural Tree Risk As-sessment Qualification at Capel Manor college on the 14th to the 16th October.

Pictured at the bottom during one of the written assessment from left to right are: Arron Sanderson, Alvan Kingston, Matt Stuart, Ian Barnes, Steve Maros, Colin Quinn, Hal Appleyard, Dan Yeomans,

Tim Wilcox, Russell Ball and Craig Johnson.

The food was good too (in the foreground and our very grateful thanks go to the ever helpful and friendly staff at the college. Of course, the bonus for the TRAQ is that Capel has some great trees, and be-low the students are pictured looking at one of the large Oaks in the grounds in preparation for the field assessment por-tion of the exam.

If you are interested in taking this course then please contact the chapter office to register your interest as we are now tak-ing names for the next one. Look forward to seeing you there.

TRAQ ReviewBy Ian McDermott

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