Treel ne
The International Society of Arboriculture UK and Ireland Chapter Official Magazine Spring 2013
Basics of Typical Resistance-Drilling Profiles by the widely celebrated Frank Rinn
Part 1 of Geoffrey Donovan’s Relationship Between Trees and Human Health Cass Turnbull’s Exception To The Rules Part 1, Topping and Heading
As part of the UK&I Chapter’s 21st Birthday year celebrations, the
Renowned experts in their field, Jeremy Barrell and David Lonsdale have acted numerous times as experts at the very highest levels in cases related to tree safety. For the very first time they share a platform to discuss their experiences and the implication for the modern Arborist. The day will start with Jeremy and David each sharing their thoughts on tree safety based on recent court decisions. They will invite questions from the audience and co-host an open forum to discuss the issues raised and this format will form the bulk of the day.
Cost;
Members (Chapter, CAS and MTOA) Non-members Students (first 20, recognised courses only)
Venue; Date; Time; Book;
The Jodrell Theatre, RBGKew (click for map) Tuesday 25th June 2013 9.30am to 4.30pm ISA, 148, Hydes Road, Wednesbury, West Midlands, WS10 0DR +44 (0)121 556 8302 enquiries@isa-arboriculture.org www.isa-arboriculture.org Supported by: EQT Booking Form.
Tel; Email; Web; Eform;
£55.00 £75.00 £25.00
Contents 4
President’s Pulpit
A few words from Alexander Laver
6 Events Calendar
Notable events for this year
7 Contacts
The people to call with your queries
30 Editor’s Comment
A few words from Charlotte McDermott
Features 8
Basics of Typical Resistance-Drilling Profiles
By Frank Rinn
14 The Relationship Between Trees and Human Health (Part 1)
By Geoffrey H. Donovan
20 Plants in Cities are an Underestimated Carbon Store
By Becky Allen, Press Release
21 ATF Summer Conference Flyer
Held by Ancient Tree Forum
22 Do Tree Stems Freeze In Winter?
By Micheal Snyder
24 ‘Towards Professional Amenity Tree Valuation’ by Dr. Heuch
A Review by Mark Chester
27 Exceptions To The Rules (Part 1)
3
By Cass Turnbull
President’s Pulpit It’s a busy time of the year right now, the dark winter has passed and a few milder days tease the world into spring. The end of year budgets are stretched, contractors are waiting longer into the year for the fresh growth of Aprils new budget burst, and tree officers are having to plan and fight for every penny. Over the winter the Chapter has been doing a lot of structural fruit pruning to try and reshape our apple trees, to help bear more fruit to share with our members. Two big structural branches have been reduced, Treeline and the website. The website was looking tired and was declining; it was also complicated, making it hard to maintain and fill it with fresh new shoots, but with hard work over the winter we know we have a brand new website and we have updated the online shop. The content pages are now easier to view and navigate for specific information for the reader, and the search power is far better pulling in hits from a broader audience. The platform is also far easer for the Chapter volunteer board and committee members to keep fresh and up-to-date, saving valuable time and minimalising frustration. This new website also boasts an improved shop; the old online catalog is gone. You will now find an online shop more familiar to users, easier to navigate, search and buy from. The is also a wider range of payment options: Credit or Debit Card, PayPal, and for those who like their personal touches you can check stock on line and then call Jean to place your order. This new web shop now provides membership renewals, event bookings and payments, and Certification exams, so go and have a look! Remember your ISA member number to get you up to 30% discount. Here is the link to the website: http://www.isaarboriculture.co.uk The next branch we have worked on was Treeline, with costs of layout and printed media going up, readership and circulation numbers was a catch 22, so this in turn hits the advising revenue that we need to keep this great publication rolling out to the members and then to the wider industry. We tried a few E-copes last year, but with some short-comings we felt a real change was needed. So here you are read the results. Our new Chapter Treeline is built as an e-doc from the start, making perfect to read on desktops, laptops, tablets or smart phones. This makes Treeline so much more user friendly. I can tell you about an event here and you can type in the link and go visit the site for more information. We can spread the hard work our volunteer contributors do further, as we are setting up a network with many other Chapters around the world to make it available to global ISA members. We will also be publishing on our own website as a download, a short time
after we send it out to the members, to reach a wider UK&I industry audience. This is all good news for those who want to find good places to advertise products or events to reach the people they want, and to help root traffic straight to their home page. If this sounds good to you and you want to advertise here, please visit the website. Our next job this spring is to work on the social media side of our communication; to reach further and atract more attention to the chapter, so lets grow a good crop of new followers and members. We will need your help to do this, so share Treeline, events, photos, articles, and products, forward it to friends, link it, like us, hash-tag it, and put it on your Facebook, Twitter, Linked In, and Instagram accounts! The chapter is a community and we need a strong community spirt to take ownership. Volunteer a second to click and share something or an afternoon on the stand chatting to others. It’s going to be easy if we all do a little. I would like to finish by thanking Sybs at THE STYLE DESIGN COMPANY for all the hard work on the web site and training the board and committee members. Also, I’d like to welcome our new Treeline Editor, Charlotte, who is already doing a top quality job with this as her first issue, as well as helping all the out-of-touch old tree-people throughout the board to get themselves geared up for the social media chapter revolution. By Alex Laver
4
All Ground Based & Aerial Training Delivered
Experienced Trainers, Friendly Service, Exceptional Results 1 Day - Emergancy First Aid 3 Day - First Aid at Work
Events Calendar Upcoming Events for the Busy Arborist April 1st 19th/20th 20th 26th-28th 30th
2013
Arborday – organise an event where you live Celebration of Trees, Capel Manor College Certification Exam, Capel Manor college SSA Tree Climbing, Easton College 3ATC, Sparsholt
www.arborday.org/ www.celebrationoftrees.co.uk/ www.isa-arboriculture.org/ www.isa-arboriculture.org/ http://3atc.trees.org.uk/
May 14th 3ATC, Myerscough 25th-27th UKI Chapter TCC finals, Highclere
http://3atc.trees.org.uk/ www.isa-arboriculture.org/
http://3atc.trees.org.uk/ www.isa-arboriculture.org/
www.trees.org/ www.isa-arboriculture.org/
June 1st 4th 5th 14th-15th 25th
3ATC, St Asaphs Certification Exam, Leicester UK&I Chapter Board Meeting AA Trade Fair, Cirencester Ask the Experts, Kew
Contacts Who’s Who?
Contact list for the chapter volunteers President
PA Reps CAS MTOA
Alex Laver
President-Elect
Jess Herbert
Vice-Presidents
Bob Widd Vacant
Past President
Russell Ball
Editor
Charlotte McDermott
Exec. Director
Ian McDermott
Office Manager
Jean McDermott
Above and right: trees from Highclere
Bob Widd Tim Wetherhill
Standing Committee’s TCC Ian Morgan SSA Stuart Phillips Officers Rise for Research Tree Fund Certification AFAG Commercial EAC
Website: Email: Tel:
7
Russell Ball Glynn Percival Dan Yeomans Alex Laver Jon Tonks Craig Johnson
www.isa-arboriculture.org Enquiries@isa-arboriculture.org +44 (0)121 556 8302
Basics of Typical Resistance-Drilling Profiles By Frank Rinn
atives into wooden utility poles The basics, potential uses and by pushing thin needles into the limitations of the resistance-rewood, to create channels for the cording drilling method, for tree inspection and risk manage- The first series of portable resistance chemicals. This method has since ment, can best be understood drills were sold to arborists worldwide become established worldwide, by reviewing its history of de- in 1987. Ehlbeck and Görlacher (1990) and is known as “In-Sizing”. It is velopment and technical speci- proved a linear correlation of its drilling especially useful for species like profiles to wood density. spruce (Picea) where wood prefications. These matters are reflected in the different properties of the currently servatives do not penetrate well, even under presavailable models of the instrument. In addition sure, because the connections between the wood to understanding the technical specifications, an cells close when they’re dying. The chief engiequal understanding of wood anatomy and me- neer at WESERHÜTTE, Thowald Kipp, observed chanical material properties is definitely required that some needles broke, while others penetrated for the proper application of this method, as well quite easily. He concluded that the recorded penas being able to reliably interpret the results. etration resistance could reveal something about wood condition and its strength. WESERHÜTTE, Manual resistance drilling used by carpenters which specialized in large machinery, realized that it was virtually since the 1920s is not described here because impossible to deit does not provide recordable data, and thus velop a wood diagis not used by professional tree risk assessors. nostic method for their application. Origin and purpose of resistance drill-
ing
Years later, two Today, it seems obvious that the penetration retired leading enresistance of drilling with thin needles (drill bits) can correlate to the condition of the wood. A needle shaft diameter of 1.5mm with a flat tip 3mm However, the evolution from the concept of the wide were found to be a good compromise for achieving maximum resolution and stability, while causing the first working prototypes to their development, least damage to the sample. bringing us to the current models of the present, took quite a bit of time, research, and effort. gineers of WESERHÜTTE (W. Kamm, S. Voss) Based on the idea of Prof. Gersonde, who worked received permission from the company to apply at German Federal Material Testing Institute for a patent describing the idea of needle resist(BAM, Berlin) during the 1970s, the German ance-drilling. Although this 1985 patent was later company WESERHÜTTE AG developed a ma- declared invalid by the German Patent Supreme chine for improving the penetration of preserv- Court, it triggered a flurry of development that Sketch of a KAMM-VOSS-resistance drill from 1984: a scratch pin (S) was fixed at a spring- (F) loaded gear box (G) between the motor and needle (N), creating a 1:1-scaled resistance profile on a wax-paper strip (P) housed within the machine’s casing. Resonance and threshold effects due to the springloaded recording mechanism delivered systematically incorrect and misleading profiles. Consequently, KAMM and VOSS abandoned this approach and switched to electric recording of the motor’s power consumption.
8
ultimately led to the first operational resistance speaker and headphone connected to the drilling drilling machine (Rinn, 1986) and the first series motor. They applied for a patent and asked Gerof portable drills (Rinn & FEIN, 1987). In 1984, man electric tool companies if they would be inKamm and Voss developed a drill that recorded terested in buying the intellectual property rights. the penetration resistance of a thin needle using a spring-loaded gear box connected to a scratch FEIN of Stuttgart/Germany, the company that pin. Nevertheless, resonance effects of the re- invented the first electric drilling machine in the cording spring mechanism (triggered, for exam- 1880s, was interested in their offer, but wanted ple, by tree-ring density variations) led to inac- an independent opinion from a University as to curate readings and profiles that were too high whether the needle resistance method could work. in late-wood and too low or even zero in softer In a joint project of the tree-ring lab at Hohenearly-wood. Such misleading spring-resonance heim University and the Environmental Physics effects can be partially reduced by compensation Institute of Heidelberg University, the resistance springs, but this introduces stimulus thresholds drilling idea was further developed, with the aim into the recording system, causing another sys- of measuring the intra-annual density variations tematic and inherent error: drill resistance values of tree-rings for climate reconstruction (Rinn, below the threshold are suppressed and not dis- 1986-1988). Early measurements clearly showed played, or plateaus appear in the profile where that electronic regulation and recording of motor the curve does not change even though the local power consumption are required to obtain reprowood properties are changing. If the spring-re- ducible profiles and reliable results, which can be corded profile drops down to zero in soft (but linearly correlated to wood density, as opposed intact) early-wood, for instance, this is likely to spring-loaded recordings which were shown misinterpreted as insect damage or decay. As a to be unreliable and systematically inaccurate. consequence, profiles from intact yet soft wood (commonly found in the centers of most conifers Technical basics or in the sapwood of many other species) are of- The power consumption of both electrical motors, ten misinterpreted as being decayed. These me- one responsible for the feed and the other for the chanically recorded profiles had thus been shown rotation of the needle, was measured individually as nonlinear, non-reproducible, imprecise, incor- and recorded whilst the needle was moving forrect, and unreliward and backSuch a high linear correlation between mean value of the resistable. More im- ance-drilling profile and mean density of the penetrated wood (kg/m続) ward, producing portantly, such is the basis for reliable evaluation of wood condition by interpreting the four curves per systematically displayed curves. It was proven that only drills using electronic regulation m e a s u r e m e n t . wrong profiles and electronic, linear recording without resonance and damping effects Detailed com(as common in the original spring-recording devices) can accurately can never be the measure wood density and deliver profiles that can reliably be interpreted. parative analybase for a reliasis showed that ble evaluation the variations of of wood condithe power contion and stabilsumption of the ity. Due to this, feed-motor at Kamm and Voss constant speed, developed a new and of both modrill in 1985 with tors, whilst pullan electrical reing the needle cording mechbackwards did anism, startnot contain siging with a loud nificant addi-
9
tional information (Rinn, 1989). detect thin tree rings because the Consequently, resistance drills tip would rotate in early-wood from then on usually measured and late-wood of two or even and recorded the electrical powmore rings at the same time. As er consumption of a direct-cura result, the measured resistance rent, needle-rotation motor whilst cannot differentiate between the penetrating wood. This value is density of individual early-wood proportional to the mechanical With this needle, it was possible to and late-wood zones and it would torque at the needle, assuming drill up to a depth of 1.5m (~5ft) be impossible to identify thin the motor acts linearly. This re- into old oak trees and still detect tree rings. Therefore, for tree tree-rings narrower than 0.5mm quires a correspondingly linear (Rinn 1990). ring identification, the needles type of electric direct-current moshould be as thin as possible. tor. If the needle’s tip is flat and twice the diameter of the shaft, the torque mainly depends The needle had to be kept as narrow as possible to on density at the major point of contact at the minimize damage to the test-tree. Unfortunately, needle’s ‘front line’ while penetrating the wood thin needles (<1mm) are often deflected by wood at a high rotational speed (Rinn et al, 1991). rays, knots or other wood anatomical features and The ratio between rotational speed and thrust did not maintain a straight path. Regarding the was shown to be critical to achieve a high lin- ability to penetrate hard-woods, needles obviousear correlation to wood density. This allows a ly had to be thicker and stronger. After thousands reliable interpretation of the obtained profiles. of tests, a shaft diameter of 1.5mm and a 3mm Since the goal was to determine radial density profiles at the highest possible resolution, drill resistance must be measured at one point of the drilling path at a time; therefore the end of the needle had to be flat. A thin centring tip was added to the end of the needle to guide it along a straight path. Due to tree-ring borders not being linear-laminar (arranged in a linear or flat manner, but are concentric or even undulating), the width of the needle’s tip determines the radial resolution by tangential averaging and should therefore be as small as possible. A wider needle would not allow the method to
tip was found to be a good compromise between minimizing damage and maximizing information in the profiles (Rinn, 1989a; Rinn et al, 1990).
All subsequent profiles used in this document have been obtained using a resistance-drill that records and is regulated electronically. It was also equipped with a flat tipped 1.5/3mm steel needle, as described above. Although the resistance-drilling method was developed for tree-ring analysis, its ability to detect decay now drives the market. Several thousand drills have been sold worldwide since 1987 by different manufacturers, but they differ dramatically in size, weight, resolution, precision, applicabiliIf the needle penetrates the tree rings of conifers radially inward (perpendicular to the stem), the profile clearly reveals differences in density ty and price. A linear correlation between earlywood and latewood. In this profile of a spruce tree felled in to wood density (as a mandatory 1986, the extremely dry summer of 1976 can be identified by the correpre-requisite for reliable profile spondingly narrow tree-ring with only a few latewood cells. interpretation) was demonstrated only for electronically regulated and recording device types (Winnistorfer and Wimmer, 1995).
Ability to detect tree rings and decay If the needle’s geometry follows
10
the guidelines as described here, local wood density at the point of the needle’s tip is the main factor influencing mechanical penetration resistance. Consequently, due to density variations between early-wood and late-wood, tree-ring structure and penetration angle determine the shape of the obtained profiles. Therefore, it is necessary to understand basic wood anatomical properties in order to interpret resistance profiles correctly. In addition to needle geometry and electronic regulation, the drilling This superposition of a radial x-ray-density profile (resolution angle determines the ability to detect 1/100mm) of larch (Larix) with a resistance drilling profile shows that local wood density determines the resistance value. The slope of the tree-rings. Maximum resolution of resistance profile at the tree-ring border represents the resolution limit tree-ring structures is provided by of detecting tree-ring (~1/10mm) when penetrated perpendicular (Rinn radial drillings, so that the needle et.al. 1996). penetrates the tree-ring borders radially inward (perpendicular to the stem). The lution radial x-ray density profiles, it showed more the drilling angle deviates from 90°, the that electronically regulated and recorded reless clear the tree-rings appear in the profiles. sistance-drills produce profiles linearly correlating to local wood density, revealing tree-ring density variations down to a width of about Wood anatomy 1/10mm or even less. That is assuming the neeRegarding wood material properties and the dle is equipped with a flat tip that penetrates cutting mechanism at the needle’s tip, lothe tree-ring borders radially (Rinn et al, 1996). cal shear strength may be even more closely related to the measured drill resistance valThe combination of the following wood anue. However, in comparison with high-resoatomical properties determines the appear(Left) Wide conifer rings are usually dominated by soft early-wood. Due to an age trend in ring width (Bräker et.al. 1978), conifers (trees, beams and poles) are mostly much softer in the center. The corresponding decline in drill resistance can only be distinguished from a decline due to internal decay if the intra-annual density structures are revealed correctly. This requires a high resolution profile that is linearly correlated to density, which can only be achieved by measuring and recording drill resistance electronically. Otherwise it would lead to misinterpretation and an inaccurate evaluation of trees and timber. Therefore, only machines that provide high resolution and linearly scaled profiles, can be used for reliable evaluations. The use of the early spring-loaded versions had to be abandoned because they lack these capabilities. (Right) Because earlywood width usually does not vary much, the wider rings of oak (Quercus) have denser latewood, leading to a higher mean profile level. In ring-porous trees, narrow rings may consist entirely of earlywood, and thus provide low density readings. Consequently, the resistance-drilling profile is lower for thinner tree rings, and higher for wider tree rings. This reflects the fact that ring-porous trees have a higher density if they are growing faster.
11
The angle between penetration direction and tree ring borders influences the ability to detect tree rings as shown here for spruce (Picea). In areas penetrated tangentially, the profiles cannot show differences between earlywood and latewood. Decay or insect damage can be identified by the drop of the profile below that for the earlywood level. It can be seen here in the bottom profile when the needle penetrates the soft pith and subsequently the crack.
ance of typical radial resistance profiles, which are concurrent with density profiles: • In general, late-wood is much denser than early-wood. Wide tree rings are dominated by: o early-wood in conifers and o late-wood in ring-porous species. • Due to the age trend, the average ringwidth declines with tree age and remains at a relatively low level throughout maturity. • In the case of narrow conifer rings, the relative amount of late-wood is higher and the density, as a direct result, is also higher. Consequently, slow growing conifers are mostly denser and stronger. The width of early-wood in ring-porous trees predominantly does not show strong variations. Therefore, the relative amount of early-wood is higher in narrow oak rings. The narrowest of oak rings are composed primarily of very soft early-wood. Consequently, the wood of slow growing ring-porous trees is low in density and lacking in strength. • Wider oak rings contain more latewood and are higher in density. Thus the faster ring-porous trees are growing, the higher their density and the higher the strength of their wood. • The consequence of slow or fast growth in terms of density is opposite in conifers and ring-porous species.
Wide rings of ring-porous trees are dominated by dense latewood. Due to an age-related trend, the wood of ring-porous trees, including stems, branches and beams, is denser in the center. This leads to a corresponding increase drill resistance. Narrow oak (Quercus) rings are dominated by soft earlywood, leading to a drop in density and drill resistance profiles. High resolution electronic resistance-drills, thus are mandatory for distinguishing such zones of narrow but intact rings from areas of decay, where the profile drops below that for earlywood. The spring driven recording mechanisms of the early resistance drill models led to resonance fluctuations where the profiles dropped down to zero in earlywood, making it impossible to distinguish between intact but soft and decayed parts.
There are many other consequences of the combination of these wood anatomical properties for tree inspection: conifer stems, for example, are commonly soft in the centre and stronger in the outer areas of the cross section, the opposite applying to oak and all other ring-porous species. Most importantly for resistance-drilling is that radial profiles deriving from conifers naturally tend to drop down in the centre. This is not a sign of decay and can only be distinguished reliably from a profile drop caused by internal decay, if the profile is linearly correlated to density, and the resolution is high enough to clearly differentiate between early-wood and
(Left) In diffuse-porous species, such as beech (Fagus), tree ring structures can be clearly visible in the profiles due to changes in wood density between earlywood and latewood. But, there can be tree rings where the tree did not build significant latewood layers thus leading to small or even no variations in parts of the profile. Therefore, it is impossible to determine number and width of tree rings. (Right) Sometimes, density variations within the ring may be in the same order of magnitude as at the tree ring border, and sometimes latewood is very thin or even absent, so that no peak is obvious in the profile to identify the tree ring as seen in this example from a drilling in poplar (Populus).
12
file cannot be interpreted, a reference drilling further up the stem may help, although the number of drillings should be limited The anatomical properties for the three wood-type groups (coniin order to minimize damage to the tree. fers, ring-porous and diffuse-porous trees), in combination with the trend for decreasing ring width with age, are important factors determining the typical radial density trend across stems and branches: These trends lead to typical mean resistance profiles because drilling resistance mainly reflects wood density along the drilling path. This aspect has to be taken into account while interpreting every profile and it underscores how important it is to know the species being tested, and the angle of the needle’s path in relation to the tree rings. Individual trees can have different mean profiles, for example if the tree was growing suppressed in early years. When in doubt, a reference drilling at another point on the tree may help. Reference drilling should be done in the same fibers further up or down the stem.
late-wood zones. If the profile drops down below the lowest early-wood resistance level, this indicates decay, a crack, or the pith as shown above. In ring-porous wood, such as oak (Quercus), the profiles are commonly very low in the wet and soft sapwood with narrow rings, containing primarily soft early-wood. They rise up in the centre of the cross sections. Again, a high resolution and linear correlation to wood density is required to differentiate between intact, but soft sapwood and decay.
Resistance profiles derived from tropical species, without distinct tree-rings, and they are similar to most diffuse-porous trees from moderate climate zones, but tend to rise up slightly in the centre. Thus, in general, three types of wood have to be distinguished in terms of typical profile shape: • temperate conifers, • temperate ring-porous wood and • diffuse-porous wood and wood of tropical trees without distinct tree-rings. These typical trends have to be taken into account whilst interpreting resistance-drilling profiles. At Typical radial resistance drilling the same time, profile of intact beech (Fagus). the influence of the angle of the needle’s path, in relation to the tree-ring borders, has to be considered. If a drilling pro-
13
Summary
Needle penetration angle, in relation to tree-ring borders and wood anatomical properties of the tree species, determine the typical shape of the resulting resistance drilling profiles. Only profiles of electronically regulated and electronically recording resistance-drilling machines have been shown to linearly correlate to wood density, allowing the user to interpret correctly and evaluate reliably. Thus, technical properties of resistance-drills have to be taken into account before purchasing and using a resistance-drill. Proper evaluation requires knowledge about the species’ specific and typical density trends within the tree-rings and along the drilling path. Wood anatomical properties differ strongly between the three wood-type groups (conifers, ring-porous and diffuse-porous). These properties influence the resistance-drilling profiles, as well as the mechanical behaviour of trees in general. Ring-porous trees have the highest strength values in the centre, and are much weaker outside. Conifers are just the opposite. This aspect influences all technical measurements of mechanical properties and behaviour of trees, not only by resistance-drilling, but also stress-wave-timing (sonic tomography) and static-load tests. This has to be taken into account whilst estimating strength and eventual strength loss due to decay (moisture content plays an important role, too). Thus, high-resolution resistance-drilling profiles reveal valuable information about intact and decayed areas, increment growth rates and mechanical properties of wood. Frank Rinn holds a degree in physics and is the owner of RINNTECH, a technical expert, researcher and manufacturer. Rinn, who resides in Heidelberg, Germany, is also the Executive Director of ISA, Germany. He has been recognized internationally for his advancements in technical wood analysis and has received four innovation awards for his contribution to the industry.
The Relationship Between Trees and Human Health By Geoffrey Donovan
Evidence from the Spread of the Emerald Ash Borer Introduction
There is increasing evidence from multiple scientifıc fıelds that exposure to the natural environment can improve human health. However, existing research has often been hampered by cross-sectional study design and a failure to adequately address confounding factors. Quasi-experimental designs, such as the pioneering work by Ulrich, who showed that patients recovered faster from surgery in a room with a view of natural scenery than those without such a view, are needed to provide stronger evidence of a causal link between health and the natural environment. To address this gap in the literature, a longitudinal study design was used to quantify the public health effects of an introduced forest pest, the emerald ash borer, which has killed tens of millions of ash trees since it was fırst detected in the U.S. in 2002. The spread of the borer is a unique natural experiment allowing the evaluation of the effect of changes in the natural environment on public health. The goal of the study was not to track the borer per se, but to use it as a proxy for tree loss. Natural experiments approximate RCTs, as the mechanism determining exposure is independent of the outcome, therefore common prior causes of exposure and outcome are equally distributed between those exposed and those unexposed. The borer spreads directly from county to county, but it is spread also by accidental transport — typically on fırewood — which results in satellite populations (Figure 1). This accidental spread adds an important random element to the current natural experiment. Nonetheless, natural experiments remain observational studies and cannot
prove causality.
This study examined whether the spread of the emerald ash borer is associated with increased mortality, related to cardiovascular and lower-respiratory-tract illness. These two types of health issues were chosen because they are the fırst and third most common causes of death in the U.S. and there are plausible mechanisms linking these types of deaths with trees. Specifıcally, the natural environment has been shown to decrease stress, increase physical activity and improve air quality. In turn, stress, lack of physical activities and poor air quality Figure 1. Counties where t have been linked been detected in 200 with cardiovascular and lower-respiratory-tract disease. The pioneering work in the fıeld by Ulrich found that patients recovering from gall bladder removal surgery in a room with a view of a natural scene recovered faster and took fewer pain medications than patients in a room with a view of a brick wall. However, extending Ulrich’s work has been problematic because most health outcomes of interest have causes that long precede the short surgical recovery period, and most people spend little time in environments as con-
14
trolled as a hospital room.
Observational studies of the relationship between the natural environment and health have examined a range of health outcomes. Mitchell and Popham found that, after controlling for SES, “greenness” was negatively associated with overall mortality in England. This relationship was particularly strong for cardiovascular-related mortality. Takona and colleagues studied the 5-year survival rate of 3144 senior citizens living in Tokyo. They found a positive association between survival rate and access to walkable green space in Holland, Maas et al reported a positive association between greenness and self-reported health. In a later study, Maas et al analysed the health records of 345,000 people. They found that those living in greener areas were less likely to be Extent of infestation — 2002 — 2007 diagnosed with 15 of the 24— 2010 the emerald ash borer had health outcomes 02, 2007, and 2010 examined. Results were particularly strong for anxiety and depression, for children and those with lower SES. Park and colleagues showed that walking in a forest reduced heart rate and cortisol levels. Finally, in New York City, Lovasi et al found that children who lived in areas with more street trees were less likely to have asthma. Two studies have examined the relationship between the natural environment and birth outcomes. Donovan et al found that mothers living in Portland or with more tree canopy within
15
50 meters of their homes, or who lived closer to open space, were less likely to have a baby that was small for gestational age. Dadvand and col-leagues1 conducted a similar study in Spain. They found that women with more greenness within 100 meters of their homes, or who lived within 500 meters of a major green space, gave birth to heavier babies, although results only held for women with the lowest level of education.
Emerald Ash Borer
The emerald ash borer, Agrilus planipennis, is a phloem-feeding borer native to East Asia. It was discovered in North America in 2002, when it was identifıed as the cause of widespread ash mortality (Fraxinus spp.) in Detroit MI and nearby Windsor, Ontario. By 2012, this borer had killed approximately 100 million trees in the U.S. (D. McCullough, Michigan State University, personal communication, 2012). However, its potential impact is much larger, as there are 7.5 billion ash trees in the country. In addition, the borer kills all 22 species of North American ash and virtually all infested trees, so it is a good proxy for ash tree death. For more information about this borer, see this video available online at www.ajpmonline.org.
Methods Study Area and Data
Data were collected from 1990 to 2007 and the analyses were conducted in 2011 and 2012. The study sample consists of the 15 states that had at least one confırmed case of the borer in 2010. Data was observed annually at the county level (1296 counties), from 1990 through 2007 (maximum number of observations = 22,032, but due to missing data, the actual number of observations = 21,080). This sample allowed observation of mortality before and after 2002, when the emerald ash borer was initially discovered in the U.S. By 2007, the U.S. Department of Agriculture (USDA) Animal and Plant Inspection Service had detected the bor er in 244 counties (once a county is infected, it remains infected; Figure 1). Two variables
were used to describe the presence of the borer: a dummy variable, which takes on a value of 1 in infested counties, and a continuous variable (06) that denotes the number of years it has been present in a county. Mortality data were obtained from the National Centre for Health Statistics and stratifıed by age (<18 years and (less than or equal to)18 years) and cause of death (major cardiovascular disease [ICD-10 codes I00-I78]; chronic lower-respiratory-tract disease [ICD-10 codes J40-47]; accidental death [ICD-10 Codes V01-X59, Y8586]). Demographic covariates were chosen based on neighbourhood determinants of cardiovascular and lower-respiratory-tract mortality. Demographic data was obtained from the 1990 and 2000 censuses and the 2009 American Community Survey. The authors estimated census variables for all other years by interpolation. The impact of the borer — on tree mortality and public health — depends on the number and distribution of ash trees in a county. Unfortunately, comprehensive data on ash abundance are not available. Therefore, a two-stage process was used to estimate ash-canopy cover, which is the area occupied by a tree’s crown when viewed from above. First, total tree canopy was estimated in a county using National Land Cover Data (NLCD) raster maps from 1992, 2001, and 2006. Tree canopy for all other years was estimated by linear interpolation or extrapolation from these 3 years. The NLCD maps were generated by processing 30-meter-resolution satellite imagery using class defınitions that have remained consistent through time26. Second, total tree canopy in a county was weighted by the proportion of ash in a state (ash as a percentage of total tree canopy varied from a low of 1.5% in Virginia to a high of 7.9% in New York). For example, if a county had 40% tree canopy and 5% of tree canopy was ash, then ash canopy was 2%. Data from the USDA Forest Service’s Forest Inventory and Analysis (FIA) program were used to estimate state-wide ash abundance. State-level data, as opposed to
county-level, were used to estimate ash-canopy cover, as some counties have little forestland and therefore have few plots.
Data Analysis
Two regression models were estimated relating the presence of the borer with rates of adult mortality related to cardiovascular and lower-respiratory-tract illness. Models of the following general form can be fıt to longitudinal data (where i denotes county and t denotes time):
Where Yi,t is the mortality rate (per 100,000 adults); Xi,t is a vector of independent variables; εi,t is an i.i.d. error term uncorrelated with the county-specifıc residual υi; and βs are coeffıcients that are estimated in the regression step. Typically, linear models of this form are estimated using either fıxed-effects or random-effects estimators. Fixed-effect estimators were used, as a Hausman specifıcation test showed that the assumptions underlying the random effects estimators were not met. Heteroskedasticity is a common problem in panel-data analysis. It can arise when observational units vary greatly in scale. In this analysis, mortality rates were used rather than number of deaths, which addresses the issue of scaling. However, in less-populous counties, mortality counts are low, which means mortality rates are sensitive to small changes in mortality counts (counties with low mortality counts were not dropped from the analysis). Therefore, a priori, error-term variance is expected to be higher in low-population counties. For this reason, model coeffıcients were estimated with heteroskedasticity-robust fıxed-effects estimators. Variables were selected for inclusion in the fınal model using iterative backwards selection. Progressively lower signifıcance thresholds were used with a fınal threshold of 0.1. A variance-covariance matrix was used to avoid including highly collinear combinations of variables in the
16
A tree-lined street in Toledo, Ohio in 2006, before emerald ash borer infestation. Credit: Dan Herms, Ohio State University
Three years later, in 2009, after the invasive insect spread to the neighborhood. Credit: Dan Herms, Ohio State University
iables met this threshold. In addition to controlling for potential confounders, all models included a linear time-trend variable (1-18 years) to account for broad trends in mortality — improved medical technology, for example — that would not be captured by demographic covariates In addition, a 1-year lag of mortality rate was included to address temporal autocorrelation (AR(1) correction). Finally, a variable denoting the amount of ash-canopy cover in a county was included, because if the borer does have a negative public health effect, then one would expect ash to have a positive effect, especially in counties not yet infected. Interaction terms between demographic covariates and both presence of the borer in a county and amount of ash also were included. This was done because past research has shown that access to greenness varies among demographic groups.30 Thus, the borer’s impact would be expected to depend on the demographic makeup of a county. Natural experiments provide stronger evidence of causation than observational studies, but it is still possible that the results were influenced by an omitted variable that is correlated with the spread of the emerald ash borer. Therefore, to provide an additional safeguard, a model was estimated with accidental death as the Table 1. Longitudinal regression model of adult lower-respiratry-tract disease–related mortality, adjusting for covari- dependent variable, because this is a type of ates, U.S., 1990–2007 death that the borer could not plausibly affect model. When similar demographic variables were (the same model selection criteria were used as co-linear (those describing income, for exam- those used for the cardiovascular and lower-resple), the variable from a group that had the lowest piratory-tract models). p-value when individually regressed against mortality was used. Please view the online version of Treeline to view the references for this report. The results Each variable that was dropped from the model and Frumkin commentary that accompanies this was checked to determine whether it varied sig- scientific report will be printed in the Summer nifıcantly between counties that were infested and edition, so please wait patiently, but in the meanthose that were not. If a variable did vary, then time you can email Geoffrey Donovan and his it was reintroduced and retained, if it caused the team: gdonovan@fs.fed.us coeffıcients on the two borer variables to change or you can visit the website: http://www.fs.fed. by more than 10%. None of the reintroduced var- us/pnw/news/2013/01/tree-human-health.shtml
18
DONâ&#x20AC;&#x2122;T FORGET If you have any queries regarding Treeline, or the ISA in general, please contact the chapter office on 0121 556 8302 and ask for the editor, Charlotte, or the chapter office manager, Jean, respectively and we will do everything we can to answer your questions and make your journey with the ISA a comfortable one. Donâ&#x20AC;&#x2122;t be afraid to call us, or email us at either charlottemcdermott@live.co.uk or jean@isa-uki.fsnet.co.uk.
Plants in cities are an underestimated carbon store By Zoe Davies
Vegetation in towns and cities can make a significant contribution to carbon storage and ecologists suggest that it could lock away even more carbon, if local authorities and gardeners planted and maintained more trees. The study, published in the British Ecological Society’s Journal of Applied Ecology, is the first to quantify how much carbon is stored in vegetation within an urban area of Europe. Using satellite data and information gathered by visiting local parks and gardens, the researchers surveyed vegetation across Leicester, including domestic gardens and council-owned parks, golf courses, abandoned industrial land, road verges and river banks. They found 231,000 tonnes of carbon (C) locked up in Leicester’s above-ground vegetation, equivalent to 3.16 kg C per square metre of the city, an order of magnitude greater than current national estimates. Most of this carbon pool is associated with trees. According to lead author Dr Zoe Davies of the University of Kent, “large trees are especially important carbon stores. Most of the publicly owned or managed land across Leicester is grassland. If just 10% of this was planted with trees, the existing carbon pool across the city could be increased by 12%.” “Trees, particularly large ones, should be protected and main-
tained and if more trees are planted in urban areas for their carbon storage value, they must be the right kind of tree planted in the right place, so that they have a long, productive life span and when trees die they should be replaced,” she added. The data, which until now was lacking, is particularly important because local government will play a key part in helping the UK government meet its target of an 80% reduction in greenhouse gas emissions, from 1990 levels, by 2050. According to Dr Davies, “currently, once land in the UK is considered to be urban its biological carbon density is assumed to be zero. Our study illustrates this is not the case and that there is a substantial pool of carbon locked away in the vegetation within a city – another reason why urban trees and green-spaces should be valued.” “Although it is not a panacea for emissions reduction, our results demonstrate the potential benefits of accounting for, mapping and appropriately managing aboveground vegetation carbon stores, even within a typical densely urbanised European city,” she supplemented. The study is an output from “4M: An Evidence Based Methodology for Understanding and Shrinking the Urban Carbon Footprint”, a £2.5m EPSRC-funded project by Loughborough University, De Montfort University, Newcastle University, University of Sheffield and the University of Exeter. Zoe G Davies et al (2011), ‘Mapping an urban ecosystem service: quantifying above-ground carbon storage at a citywide scale’, doi: 10.1111/j.1365-2664.2011.02021.x, was published in the Journal of Applied Ecology on 12 July 2011.
ATF summer conference June 12th and 13th 2013
Day 1 - ‘Looking forward with an eye on the past’
Knepp Castle in West Sussex has veteran trees set in the midst of a landscape-scale re-wilding project, where extensive grazing allows natural ecological processes to take place. We’ll consider the place of ancient trees and their associates in Neolithic landscapes, and think about how these ideas can help us manage ancient trees for the future.
Day 2 - ‘Populations in crisis: slowing the decline’
Ashtead Common in Surrey is home to 1200 oak pollards that are being managed individually in a programme of retrenchment pruning and haloing; we’ll have a chance to take a detailed look at the work to date. Topics will include specific management techniques, veteranisation and the current threats to trees. Both days will include a half day field visit and an indoor lecture session. Speakers include: Prof Lynne Boddy on decay fungi; Dr Helen Read on retrenchment pruning on beech; Dr Keith Alexander on invertebrate associates of ancient trees; Jon Stokes on ash dieback and other threats to trees; Dr Jeremy Dagley with an update on the management of ancient trees at Epping Forest; and Hugh Milner on the UK’s native lime species. And many more! Full list of speakers to follow. Booking essential - To receive a booking form please e-mail EventsATF@aol.com. Cost: £15 per day (£30 whole event). Ted and ‘the Belgians’ at Ashtead Common This is a non-profit making event and any surplus generated will be used by the Ancient Tree Forum to further its charitable aims of conserving our ancient trees and the species that depend on them. Full details, directions and accommodation information will be emailed with confirmation of booking. Anyone interested in arranging a poster display is welcome to email Luke Barley at luke.barley@cityoflondon.gov.uk For more information on The Ancient Tree Forum go to www. ancient-tree-forum.org.uk
21
Do Tree Stems Freeze in Winter? If So, Does this Damage the Tree? By Michael Snyder Trees are comprised of roughly fifty percent water, maybe a little less during winter, and if the temperature drops low enough the water in even the most cold-hardy tree will freeze. Since ice crystals can shred cell membranes, a hard freeze can be devastating to living tree cells, leading to dead leaves, dead branches, and even whole trees. However, most trees actually live through the winter, bearing up somehow despite prolonged exposure to brutally cold air, wind and snow.
So how do trees survive winter’s freeze? They can’t move south or generate heat like a mammal. The below-ground parts of a tree are kept insulated by a layer of snow and that is important to winter survival, but the exposed parts of a tree are obviously not protected in this way. To survive winter cold a tree begins its preparations in late summer as the length of the daytime shortens. Cold acclimation occurs gradually and includes a number of physiological changes in leaves, stems and roots. While fall colour seems to get all the attention, it’s what trees do later in autumn that is the most stunning, although harder to see.
some of the details remain a mystery to science, general mechanisms have been explained. Paul Schaberg, a research plant physiologist with the USDA Forest Service’s Aiken Forestry Sciences Laboratory in Burlington, Vermont, has led many investigations of cold tolerance in trees, particularly in the foliage of montane spruce and fir in New England. Schaberg’s work suggests three basic ways in which living tree cells prevent freezing. One is to change their membranes during cold acclimation so that the membranes become more pliable; this allows water to migrate out of the cells and into the spaces between the cells. The relocated water exerts pressure against the cell walls, but this pressure is offset as cells shrink and occupy less space.
The second way a tree staves off freezing is to sweeten the fluids within the living cells. Come autumn, a tree converts starch to sugars, which act as something of an antifreeze. The cellular fluid within the living cells becomes concentrated with these natural sugars, which lowers the freezing point inside the cells, while the sugar-free water between the cells is allowed to freeze. Due to the cell memSome of these later changes really do branes being more pliable in winter, seem to border on magic, and while they’re squeezed - but not punctured - by the expanding ice crystals. The third coping mechanism is altogether different. It involves what Schaberg describes as a “glass phase”: the liquid cell contents become so viscous that they appear to be solid, a kind of “molecular suspended animation”, that mimics the way silica remains liquid as it is super-cooled into glass. This third mechanism is triggered by the progressive cellular dehydration that results from the first two mechanisms and allows the super-cooled contents of the tree’s cells to avoid crystallizing.
A tree doesn’t have to keep all of its cells from freezing, just the living ones. This is significant, since much of a tree’s living trunk is made up of dead cells (though it’s strange to think of these cells as dead because they’re still involved in functions, such as sap flow, that keep the tree alive). Dead cells can and do freeze, but even the lowest temperature can’t kill an already dead cell and that’s the magic: while the overwhelming majority of a tree’s above-ground cells do indeed freeze regularly when exposed to subfreezing temperatures, the small percentage of living ones don’t. There are living cells in the trunk that remain unfrozen even though they are right next to – and at the same temperature as – dead cells that are frozen solid. This cellular magic of pliable membranes, sweet antifreeze, and glasslike super-cooling, with frost on the outside and viscous dehydration on the inside, helps trees avoid freezing injury to living cells, but it is not without consequence. According to Schaberg, the freezing of those dead cells does have implications for the tree’s health. For example, gas bubbles can form among them upon thawing, and these can prevent sap flow in spring, but Schaberg adds that trees have other means to overcome those temporary problems, and that it is far better for the tree to deal with these than to allow the water-based contents of nearby living cells to freeze and possibly kill the tree altogether.
Michael Snyder is the Chittenden (Vermont) County Forester.
This article is reprinted with the permission of Northern Woodlands magazine. A not for profit organization, Northern Woodlands seeks to advance a culture of forest stewardship in the northeast by increasing understanding of and appreciation for the All three cellular mechanisms are in- natural wonders, economic productivtended to keep living cells from freez- ity and ecological integrity of the reing. That’s the key for the tree: don’t gion’s forests. Subscribe or donate at allow living cells to freeze. www.northernwoodlands.org.
22
CPD
CEU’s
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.
‘Towards Professional Amenity Tree Valuation’ by Dr. Jon Heuch A review by Mark Chester Professional Members of the Consulting Arborist Society will be familiar with the principles of Amenity Tree Valuations. Valuing trees to the framework of the CTLA has been an established Area of Professional Competency for members. Dr. Jon Heuch has been working on the principles of valuing trees within the framework of asset valuation. In advance of an updated two day seminar on the subject, which will include assessing candidate understanding, Jon shared his thoughts. The review below is a summary of his talk, some of which will be covered in the pending seminar. The venue was Gristwood & Tom’s Shenley centre, for the fourth in the series of technical seminars being held in association with the ISA during 2012. Jon Heuch titled his talk ‘Towards Professional Amenity
ral Development. This includes the challenges of managing the trade-off between the needs of people and a desire to avoid environmental damage. So, what is valuation? Valuation is a decision making tool - a mechanism to assist us to provide advice and identify appropriate and optimum solutions. The valuation of amenity trees should not be undertaken in isolation of the valuation of other assets, including land. One of the problems with attempts to develop amenity tree values in the UK is that little attention has been given to reviewing attempts to value natural resources, particularly for government policy purposes. He summarised the development of valuation over the past few years, including Rodney Helliwell’s system that was first launched in 1974, CTLA (the Council for Trees and Landscape Appraisers, an American organisation), which was anglicised by Dr. Adam Hollis (2005-6). The ninth edition is presently being used and we are waiting for the tenth edition. We also have CAVAT and I-Trees. The commentary from the Royal Institu-
Tree Valuation’. Russell Ball began the seminar by thanking the hosts for holding the event and paying for generous catering and covering expenses, which ensured it could be delivered to delegates at no cost. He also thanked the speaker for giving his time to address the seminar on this pioneering topic. Jon's aim with the seminar was to explain the current situation and the problems. Stepping back, he then wished to consider what valuation is and where we should be going. He then planned to present proposals on a framework for Professional Arboricultural Valuation and identify the next steps. Jon began by explaining his background, experience and credentials for talking on the topic. His career started in the accounts department of Texaco petroleum in 1977. A management role led to him taking an MBA from 1997-2002, that included aspects of Financial Valuation. Since 1984, he has worked in Natural Resource Management and Ru-
tion of Chartered Surveyors (RICS), in its ‘Guide to Valuation for Amenity Trees’, has been instructive. Jon highlighted that valuations are often used in adversarial situations. He referred to a statement on a consultant’s website, referring to the practice used by CAVAT and Helliwell: ‘both systems have been tested in court, and are recognised throughout the industry as being the benchmarks for amenity tree valuation’. He commented that courts typically depend on the professions and experts to guide on matters such as valuation, but may establish principles upon which valuations are constructed. The fact that expert testimony has been accepted in Court may be reassuring to the expert, but does not mean that it will stand up to scrutiny by valuation experts. Knowing how to fill in the appropriate form/table for Helliwell/ CAVAT does not make one a valuation “expert”. Valuation as a subject area may be more familiar to some accountants, specialist chartered surveyors and/or economists who have an aca-
24
demic foundation in the subject and considerable practical experience. One of the challenges with arboricultural valuations for adversarial situations is that attendance of a two day valuation seminar provides a foundation of knowledge on which the professional has to build and, by itself, does not make one an expert on the subject. Further study/reading and experience is needed. Arborists cannot and should not consider that they can undertake valuations for legal purposes without being aware of appropriate cases, particularly Bryant vs Macklin. This case clarifies that compensation needs to be proportionate and fair to both parties. It is not about penalising the defendant but identifying what is reasonable. Citing a statement on the website of one professional association, about making those who damage trees pay for their actions, Jon explained that such a position is not sustainable. Much of the seminar involved Jon presenting examples of how trees can be valued by different groups, and some of the questions we as aspiring professional valuers need to consider. For example, one parish council in Kent, holds a meeting in the summer within the shade of a prominent local tree,
twenty years twice as valuable as one which provides amenity for ten years? (The answer is no). Is there value with â&#x20AC;&#x2DC;delayed gratificationâ&#x20AC;&#x2122;? If we could have a tree for ten years, now, or delay for ten years, then have a tree for the subsequent ten years, would there be a difference in value? The answer is, no. He explained the principle of depreciation, where an asset loses value each year. This does not favour trees, which exist in the long term, with life spans often measured in centuries. We then considered the main four valuation approaches. At present arborists have no coherent guidance on how a valuation exercise should be approached and what method should be chosen. The result is that different arborists use different approaches. Arborists need much more significant understanding of (any) foundations for a particular method, particularly in an adversarial situation. Jon came with much material and many slides to share. Time used for discussion ate into that avail-
25
which is particularly important to the community. He also showed photographs of a foreign street scene where tree cover is particularly valuable for summer shade. Power lines and shop signs intermingle with tree branches, in a way that would probably not be accepted in urban settings in the UK. Jon suggested that community support can be a key indication of the value of local trees. One tree officer he knows in the rural south east does not make Tree Preservation Orders for trees potentially affected by developments if the local parish council does not raise objections. This led to considerable discussion on the merits of allowing the public to influence tree policy. There was the view that those in our towns and cities tend to be less tolerant of issues such as leaf fall, shading, loss of satellite reception and the demand for space and most in the audience, whilst appreciating the benefits of community involvement in aspects such as tree planting, were reluctant to cede the role of tree protection to the public. He then looked at some basic economic principles, summarising both decades of experience and the contents of several substantial texts on the subject. Is a tree which provides amenity for
able and briefly he shared a proposal to take amenity tree valuation forward: Rather than focus on the valuation method, the valuation process should revolve around the type of problem that is being addressed - valuation for compensation for example is different from valuing for management purposes. For practical application, Jon will be delivering a new two day accredited seminar on Amenity Tree Valuation for the Consulting Arborist Society in April 2013. This will develop the material covered during the Gristwood & Toms seminar and will include delegates being appraised in the techniques for valuing based on the different methods. He will then explore interest in providing training to a wider audience. If you are interested in attending a future seminar on Amenity Tree Valuation, please contact the author at mark@consultingarboristsociety.com. The author is an independent arboricultural consultant practicing with Cedarwood Tree Care. He is also the Executive Director of the Consulting Arborist Society.
Tree Diseases
-biology, spread, future prospects and implications for the woodland manager This one-day event will cover the range of tree diseases currently affecting woodlands, including Phytophthora, Chalara and Acute Oak Decline. Speakers include Joan Webber (Forest Research), Nick Mainprize (Forestry Commission Plant Health), Peter Chappell (UPM Tilhill) and the Forestry Commission West Midlands regional team. The event is being held on Wednesday 24th April 2013, at
Herefordshire Group Training Association, Holmer Road, Hereford, Herefordshire, HR4 9SX The day starts at 10 am, and finishes at 4pm. The event costs ÂŁ10.00 which includes lunch and refreshments, and is targeted at woodland owners and contractors in the West Midlands . For more information or to book your place please contact the Heartwoods office on 01952 435860 or alternatively email harrietwood@smallwoods.org.uk
Heartwoods is a project of Small Woods (Registered Charity Number 1081874)
EXCEPTIONS TO THE RULES Part 1 Heading and Topping Trees By Cass Turnbull
At the International Society of Arboriculture’s conference in Portland I gave a talk on the work that PlantAmnesty has done to end tree topping. At the end of the talk someone asked the question, “Are there any circumstances where you consider crown reduction pruning is okay?” To which I replied, “Sure. There are even instances when tree topping is okay.” The fellow asked me for examples and I rattled off a few that I will include them below and in the next issue, but I sensed that he was more interested in my opinion on several hot topics being discussed in the arboricultural field, including at the conference. They include what is called ‘retrenchment pruning’ for very old trees, which are already starting to fall apart and look pretty shabby, topping and ‘spiral pruning’ of ‘edge’ or ‘release’ tree conifers to reduce the chances of blow-down, and topping and/or re-topping of defective conifers with ‘targets’. To that I would add topping of old apple and pear trees to bring them into production and the retrenchment pruning of declining live trees for the purpose of creating wildlife habitat. All this is to be defined and discussed in the following two part treatise by me, Cass Turnbull. The Beast
launched the campaign to end tree topping in King County as proof that it could be done. We went from I told my husband of my intentions of writing an arti- a city that had 90% topping to one of less than 10%. cle on when it is okay to top or crown reduce trees. He said, “Don’t do it!” - and I know why. Just talking Back to ‘the beast’: ‘the beast’ is in our DNA and about it feeds ‘the beast’. ‘The beast’ is the name the desire to control Nature has served us well as I give to the almost universal compulsion among a species, but it hasn’t worked out so well for Nathe peoples of the world to control their nature and ture. Gardeners and arborists want to control Natrees. Most often it is brutal, like tree topping, but it ture too; we are just more sensitive to our subjects can be seen in attempts to help trees such as the and work toward a more symbiotic relationship. perpetual hunt for the magic elixir, elaborate systems of cabling and propping, over-staking, paint- When is heading a tree okay? ing and wrapping trunks, drilling and filling cavities, wound dressings, and hundreds of other things, Firstly, the definition of heading, According the ISA some with and some without validity. I inwardly Best Management Practices Manual: heading is cringed when a gentleman at the conference came okay for training young trees, for example to force up to me and said with an earnest and passionate stare, “I save trees”; this is just the kinder side of the same beast. However, most importantly, the desire to control trees is responsible for the defining problem facing the tree care industry - the fact is that 90% of the work performed on trees worldwide is topping and it is unnecessary and shouldn’t be commenced, or in this case continued. I often wonder why the industry doesn’t spend more time, money and effort fighting the good fight; it could only result in a work increase and of better quality for the ethical and knowledgeable arborists, but I think I know the answer. It is because the problem is so huge and intractable no one wants to take it on, at least Unsuccessful heading of a conifer hedge. not on a large scale. Nevertheless, PlantAmnesty
27
Head temporary limbs for foot traffic. lateral branches to form low down on an apple or pear tree for easy harvest, and it is okay to head trees used as a formal hedge. Upkeep heading and/or shearing is annual and essential. In private conversations with people about their “pyramidalis” growing under the leaves, I’ve said that heading is a reasonable thing to do because these conifers do not rot readily, you can’t see the ugly round donut on top, and you won’t get a mess of watersprouts. However, the top will divide and thicken up, eventually becoming unmanageable. Still, it is a reasonable thing to do for a few years until such time as it will be removed altogether. Due to the thickening of the top, I do not recommend it for people who just want ‘to even out the top of their pyramidalis hedge.” It causes problems down the line. Unlike the headed and sheared Leland cypress hedge or beech hedge, the pyrimidalis hedge’s entire raison d’être is to not need shearing and heading all over every year. I guess this could be considered a grey area in the scheme of pruning ethics. A person also needs to head a young tree to develop a pollard. In future years the watersprouts are annually cut off to the pollard head. The ANSI 300 Pruning Standards has a loophole big enough to drive a truck and chipper through in this regard. It neglects to specify the size of the training cuts (no cut on a pollarded tree will ever exceed 2” in diameter). According to how it is currently written, a person could top a tree with the intent to cut off the watersprouts every year and correctly call it pollarding. It is not. Another instance involves the correction of a manmade weak trunk. Due to poor nursery practices
(over-staking and crown-raising) one can run across trees that, when planted and un-staked, flop over to the ground. Professor Richard Harris explored the problem within his standard text book Arboriculture: Integrated Management of Landscape Trees, Shrubs and Vines. Tree owners were often compelled to stake and re-stake the trees higher and higher up as they increased in height. Since those trunks were grown dependent on their ties, they never developed the requisite taper and strength to stand on their own. His final suggestion was to cut the young tree to the ground and let it send up a new, self made trunk. The tree owner would need to be careful not to get suckers from the rootstock of a grafted tree or allow a multiple trunked tree to develop (as they can fall apart many years later when they can do damage). Young trees (under 15 years) are all dynamic wood; they can easily compartmentalize after a heading cut, even topping, and outgrow the damage. On the other hand, heading your purple leaf plum, your hawthorn or your crabapple into a cute umbrella or ball is clearly wrong. Apparently these are considered a ‘grey area’ in the minds of many horticulturalists, but it serves no purpose other than to feed ‘the beast’. The plum will graciously die from it in the not-too-distant future. The crabapple, being a champion compartmentalizer, will go on to annoy the likes of me, forever, or until such time as the pruner gives up out of exhaustion.
When is topping a tree okay? A topping cut is a large internodal cut on tree. It causes rot to develop in the trunk and the epicormic shoots
28
(watersprouts) that are formed to replace the crown are likely to be weakly attached, even after many years, when they have turned into large, heavy branches. I can think of two cases when topping is a rational response to a tree situation. Birch trees often bend over in snow loads and refuse to straighten back up. If there is no target for the regrown top(s), it makes sense to top the stem and allow a new leader to grow. This happens naturally or it can be assisted by heading or removing the competing new leaders. Another instance occurred when a large conifer tipped in a severe storm. The arborist worked to wrench it back into the ground, at the owner’s behest, but could not. He eventually decided to top it to reduce the leverage. Since there was no target for the future, potentially less-well attached top(s), and since this tree compartmentalizes well (i.e. does not rot) this was a good decision and it worked. Then there’s those fruit trees again. It seems like I’ve spent a lifetime trying to convince people not to top their fruit trees. It’s not as if there would be any more fruit down low. There just wouldn’t be that wasted fruit up high where they can’t get it. Instead, PlantAmnesty classes demonstrated restoration pruning for the victims of previous top jobs. Those trees were an incredible mess. Their watersprouts had shot for the moon and only arched over and made fruit after they had re-attained their previous two story size. The apple and pear trees survived, mostly, with their hollow trunks, but the cherries would just die. Dr. Alex Shigo once said, “Some of the most abused trees in the world are fruit trees.” I had used the word ‘abuse’ as sort of a joke when applied to trees. Shigo didn’t. It helped me see small trees, including fruit trees, as deserving of respect, another favorite word of that great man. With that said, it can be a rational act to top an old apple or pear under certain circumstances (just not the ones you see everywhere, all the time). I do believe that the old trees at Pipers Creek Orchard were radically renovated (topped, or severely crown reduced) many years ago. This included a lot of dedicated follow up heading and thinning of the resulting explosion of watersprouts. The fruit is, I suspect, bigger and better as it receives more of the tree’s energy and sunlight and they look great. I have seen an illustration of topping an old apple tree in an OSU extension bulletin: what it failed to mention was 1) the tree might die and 2) if it doesn’t, you need to do a lot of follow-up pruning, otherwise your tree turns into a giant mess. The truth is that most people keep their apple trees for sentimental purposes, not maximum fruit pro-
29
duction, so such drastic measures don’t add up. Just last year a respected arborist, gardener and teacher of fruit tree pruning for PlantAmnesty announced his intent to radically renovate about 40 old fruit trees in a high use Seattle Park, next to the Good Shepherd Center and Tilth. His reasoning made perfect sense and I’m confident he would do the requisite follow up pruning, but when he asked if PlantAmnesty would participate, I had to decline. Such a public display of crown reduction/topping of trees would feed ‘the beast’. No matter what you tell people about the risks and required follow-up pruning, they just go and do what they see and ignore what you say. I feel certain that the primary result of such a project would be that hundreds of neighborhood fruit trees would be ruined by topping and the neglected mess watersprouts that follow. All of this begs the question, “What’s the difference between a radical reduction and a tree topping?” Seriously, a lot depends on the skill of the practitioner in weighing the risks and achieving the desired outcomes. All this is very interesting, but not really very important in the larger scheme of things, as far as I’m concerned. Grey areas are just that, and I don’t feel the need to codify the entire situational ethics of pruning. I just need to remind people to be careful in what they say and do, so that they don’t feed ‘the beast’. In the next issue, although it may feed ‘the beast’, I will address crown reduction on trees (same as drop-crotching) and conifer pruning. In the meantime, the factors to consider when making pruning decisions are: do you lock the plant owner into a high maintenance regime? Is the long term health of the plant assured? Does it look good? Does it preserve the long term safety of the tree, or are you making the tree safer now and more dangerous later (remember topping can do that)? Finally, does your pruning enhance or subvert the purpose of the plant (e.g. fruit production, beauty, screen)? Part 2 will be printed in the Summer edition, so please be patient for more from Cass Turnbull!
Editor’s Comment
I hope you have all enjoyed my first edition of Treeline as the new editor. For those of you that know me it’s a pleasure to make your reacquaintance, but for those of you that don’t my name is Charlotte McDermott, I’m twenty years old - so don’t let my youthful appearance fool you - and I’m an English undergraduate based in Birmingham. I’ve been familiar with the world of trees my whole life, but I’ll leave the climbing to the climbers, the consulting to the consulters, and the risk assessments to the risk assessors! I’m just here to bring it all together for you. My first edition has bought together a wide range of predominantly science-based articles for you to enjoy; from the wonderful Resistance-Drilling, The Relationship Between Trees and Human Health and Carbon Store, to Tree Stems Freeze and Exceptions, and the ad-
ditional Amenity Tree Valuation review, the authors of these amazing informative pieces of writing will illuminate the reader and bring to light some scientific aspect of trees and tree assessment that has previously been ignored or overlooked. Please tune in for the Summer edition, as a couple of the articles within this edition will be followed-up in the next; Geoffrey Donovan will be sharing his scientific results accompanied by a commentary, and Cass Turnbull will also be sharing the second part of her Exceptions, Crown Reduction. Don’t be afraid to contact us regarding any questions or general comments regarding the ISA and Treeline. I hope you will all get used to seeing a fresh face in Treeline (see left, cringe)! - Charlotte McDermott.
30
Bartlett Tree Research & Diagnostic Laboratory Because Pests and Disease are a growing problem
We are Bartlett Tree Research and Diagnostic Laboratory, with over 100 years of experience there isnâ&#x20AC;&#x2122;t a plant disease or insect pest we havenâ&#x20AC;&#x2122;t indentified, researched or managed. No matter the size or scope of your needs our diagnostic experts can identify and treat any pest or disease that threatens the health of your trees and shrubs. Every step of the way we bring a combination of local service, global resources, and state of the art scientific practices to make your landscape thrive.
B A RT L E T T S C I E N C E Disease & Insect Control | Pest & Disease Research | Product Trials Soil Nutrient Analysis (Heavy Metals, salt) | Soil Compaction Analysis | Plant Identification
For the life of your trees.
Prescription Fertilisation | Plant Health Testing | Phytophthora Testing | Scientific Advice
Head Office: enquiry@bartlettuk.com | 01444 892 900 Research Labs: research@bartlettuk.com | 0118 988 3032
www.bartlett.com