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Vikki Bengtsson is an ecologist and has worked professionally with nature conservation since 1992. Up until 2003, she worked in England and now works primarily in Sweden. Vikki has worked throughout her career with issues relating to practical management and restoration of ancient trees and trains arborists, landscape architects, site managers and planners in the care and management of ancient trees. She has also also project managed the European VETree and VETcert projects developing training and a certification system for veteran tree professionals.
Philip van Wassenaer, B.Sc. Environmental Sciences, Master of Forest Conservation, is the principal consultant for Urban Forest Innovations, Inc., which specializes in the preservation, enhancement, and management of the urban forest using a research- and science-based approach. He is an ISA Certified Arborist, member of ASCA, a Past President and Director of the Ontario Urban Forest Council and a 2009 recipient of the ISA True Professionals of Arboriculture Award.
The presentation examines aspects of crown reduction from several different perspectives. An understanding of tree morphology and natural tree survival strategies can inform management approaches for aging trees. Statics Integrated Assessments or tree pulling tests are used to determine the uprooting or breaking safety of mature trees with compromised root systems or significant stem decay. These assessments are also used to prescribe pruning approaches to retain troubled trees.
Many mature trees have structural constraints that are not correctable in one pruning application. These trees can however be improved over time, utilizing crown reduction and thinning techniques. Large pruning wounds can lead to significant decay and structural weakness but if too little is cut, the tree may break, also causing large wounds. How do we find the appropriate dose? The techniques used for maintaining aging trees can also be applied to younger trees and trees damaged by storms. Case studies and examples will be presented to illustrate the concepts and techniques described above. The audience will leave with a further understanding of how thoughtful crown reductions can be incorporated into their repertoire of techniques to help conserve trees rather than removing them.
Having been lucky enough to have worked with the team at Treework Environmental Practice since 2001, Paul has had the opportunity to become involved in a diverse range of pioneering and ground-breaking projects, in accordance with the ethos promoted by the company’s directors Neville and Luke Fay. Treework Environmental Practice have been associates of the SAG Baumstatik Group of European consultants specialising in tree statics since 2005 and Paul has been a full member of this group since 2010. Paul has undertaken static load tests to assess the structural condition of over 200 trees throughout the UK and Europe and has presented his understanding of the principles of tree statics widely at events throughout the UK as well as in Europe, Asia, Australia and New Zealand.
Treework Environmental Practice have had a profound impact on the direction of the arboricultural industry in the UK having been involved with founding the Ancient Tree Forum, promoting new ideas from around the world, through the company’s pioneering seminar series and initiating the drive for a new industry approach to risk management that culminated in the creation of the National Tree Safety Group and industry guidance document ‘Common Sense Risk Management of Trees’. The company first introduced tree statics to the UK in 2004 and Paul has been promoting this new approach to tree assessment for over a decade. The implications of tree statics for the management of trees is dramatic and far-reaching.
Reducing the crown of a tree lowers the wind load that is borne by the stem and roots. However, all pruning has negative consequences for the physiological health of the tree, disrupting water relations and depleting the resources available to increase stem strength through adaptive growth. Reducing the wind load of a tree that is already perfectly capable of carrying that load therefore has only negative consequences due to this physiological impact.
Recommendations to reduce wind load via a crown reduction without quantifying the load or attempting to assess the load that a tree is able to carry is a precautionary approach. By definition, a precautionary approach is based on a lack of information. This uncertainty, and the reaction to it (the crown reduction), has serious negative consequences for trees with defects. In the worst case, trees that might have maintained acceptable safety factors for decades despite decay become vulnerable to being tipped into a spiral of decline.
Individual assessments, applying the principles of statics to more than 200 trees over 13 years, have shown that whilst strength loss attributable to defects (such as stem and root decay) can be clearly demonstrated to have had a negative impact on the structural integrity or stability of a tree, safety factors often remain acceptable and frequently remain reassuringly high. For late mature trees with large stem diameters, residual safety factors (after defects are taken into account) are higher than safety factors for defect-free trees in earlier life stages with smaller stem diameters.
The management recommendation that has been made, with great confidence, for the majority of the trees assessed using static load tests over the last 13 years, is therefore to simply retain the tree and to do nothing further than monitor.
Quantifying loads and estimating safety factors are essential components of determining whether a crown reduction is an appropriate management approach. For late mature trees with defects, crown reductions will rarely be necessary to maintain adequate safety factors. Where safety factors for such trees are reduced to such low levels that a crown reduction is genuinely required to achieve an acceptable likelihood of failure, the prospects for longevity are poor and removal is probably a more appropriate approach.
Martin started his career in arboriculture at Forest Research (part of the Forestry Commission) before working for two years at the Arboricultural Advisory and Information Service. He launched his own arboricultural consultancy in 1997 and from the outset tree-related subsidence was a key element of his work. Over the last 22 years he has prepared hundreds of reportson subsidence and has appeared asan expert witness in some notable court cases. Martin delivers lectures and courses on trees and subsidence for the Arboricultural Association, MBL Seminars, RICS and Portsmouth University.
This presentation will review research directed at determining whether pruning of trees can prevent subsidence damage occurring and will go on to present the speaker’s experiences of the success, or otherwise, of pruning where trees have been implicated in subsidence and monitoring of cracks and/or levels has been carried out. It is highly desirable to have trees in our urban landscape and a balance often has to be struck between maintaining a tree’s visual amenity and controlling its water uptake by means of crown reductionin areas of shrinkable clay. Recent legal cases have provided an insight into where the line might lie between a tree being regarded as posing a reasonably foreseeable ‘real’ risk and a notional or ‘possible’ risk which it might be legitimate to ignore or do nothing about. If a tree is regarded as posing a real risk then the tree owner will likely face a financial liability if it goes on to cause subsidence damage. But if the tree can be maintained by pruning to keep it within the ‘Goldilocks zone’ liability for claims may be avoided. Clearly a cost-benefit analysis may be required to see whether the expense of pruning is outweighed by the savings in payouts for claims.
Andrew grew up in the United Kingdom, and after graduating with a degree in Biochemistry in 2002, found himself working outdoors with trees. After three years as a climbing arborist in Wales, Andrew emigrated to New Zealand where he now holds citizenship. In 2011, he graduated with distinction in an arboricultural degree course through Myerscough. Since 2011, he’s worked as a consultant in Auckland, New Zealand with a focus on tree protection and developments. Since 2016, Andrew has been a full-time student in a Ph.D. program at the University of Canterbury undertaking root pruning research yielding several publications to date.
In the modern urban environment, trees along roadsides or in parks are frequently exposed to ground alterations which may result in root removal. Severing roots can have an array of negative effects on urban trees and it is important for practitioners to understand these effects in order to make appropriate tree management decisions. This presentation will review some of the existing literature and outline what we know and what we don’t know about root pruning, as well as taking a look at the findings of some recent research.
Afternoon Practical Workshop Sessions will consist of 2 x 1hr 15min sessions each with a choice of speakers.
Dr Ana Pérez-Sierra has more than 20 years of experience in plant pathology (agriculture, horticulture and forestry). From 1995 to 2003, she worked as a plant pathologist at the Royal Horticultural Society, Wisley Gardens. From 2004 to 2013, she was the coordinator of the Spanish Reference Laboratory for the Identification of Plant Pathogenic Fungi under the authority of Spanish Ministry of Agriculture, Food and Rural Environment. Since 2013 when she joined Forest Research she has been actively involved in developing early warning systems for the detection of tree pests and diseases in Britain.
As in previous years this workshop will be an opportunity to discuss pests and diseases present on the campus. We will do a walk looking at symptoms and signs in trees that might indicate the presence of insects or other microorganisms (fungi, bacteria, oomycetes…). Give that many attendees may have joined previous walks around this site, we will bring additional resources to facilitate the discussion of tree health related matters.
Jon Banks is a researcher for the Bartlett Tree Expert Company Ltd. He has been involved in Bartlett research and diagnostics at the University of Reading since 2010. He was awarded the Gatsby Summer Bursary for his undergraduate research on plant stress mitigation and the R. F. Addey Memorial Prize for Horticulture. He is vice chair of the Research Advisory Committee for the charity Fund4Trees and a member of the London Tree Officer’s Associations Biosecurity Working Party. He has presented his research at numerous conferences including two presentations at the International Urban Tree Diversity Conference in Alnarp, Sweden and a keynote address at the 2018 Myerscough research conference; in addition, he chaired the tree health session at the Arboriculture Associations annual conference in 2016. He has also managed the unmanned aerial division, coined TB7, which was licenced by the civil aviation authority for two years. He recently completed his PhD assessing drought and variation in drought tolerance within the Acer genus. His role now includes managing the Bartlett research and diagnostic laboratory; keeping Bartlett representatives informed and updated of recent developments in tree pests and diseases, management and maintenance.
Dr. Stefania Gasperini, agronomist and arborist, is the owner of AR.ES. since 1996, an Italian company qualified in Urban Arboriculture for municipalities and private owners. Gasperini is specialized in tree risk and tree stability assessment and in management of veteran trees. She is a speaker at many conferences and workshops, board member of SIA (Società Italiana di Arboricoltura), 1st Vice-Chairwoman of EAC – European Arboriculture Council, board member of SAG Baumstatik e.V. and member of ISA – International Society of Arboriculture. She is ISA Certified Arborist and TRAQ Qualified (Tree Risk Assessment Qualification).
Some individual trees will be selected in the external area for an outside workshop session in order to demonstrate what was exposed during the talk about trees architecture and crown morphophysiology.
Dr. Giovanni Morelli, agronomist and arborist, owner of Progetto Verde since 1994, is a consultant in urban arboriculture, specialized in tree risk and tree stability assessment and in management of veteran trees. He has written numerous articles and he is a lecturer in University. He has been a speaker at about 100 national and international conferences. He is a member of the International Society of Arboriculture (ISA), of the Società Italiana di Arboricoltura (SIA), and of SAG Baumstatik e.V.. He is ISA Certified Arborist, ETT – European Tree Technician, Board Certified Master Arborist (ISA) and TRAQ Qualified (Tree Risk Assessment Qualification).