The 53rd National Amenity Conference

To a member of the public, the canopy is often the part of the tree they pay the most attention to and it is usually the first place an arborist looks when trying to assess its health.

However, what the diverse mix of talks from a broad array of impressive speakers proved, is there is far from one school of thought when it comes to proper crown and canopy management.

The trade exhibition was held in the Forum Street, where refreshments and lunches were served.

TREE POPULATION AND CANOPY COVER

Chaired by Kew’s Tony Kirkham, the first session of the day began with a critical examination of the use of canopy cover targets in urban forest governance by Cecil Konijnedijk, professor of urban forestry at the University of British Columbia, Vancouver.

Looking at both the strengths and pitfalls of a canopy target approach, he lamented the idea of targets being set by city politicians picking numbers out of the air, commenting: “Canopy targets have their value, but we have to use them in much more sophisticated ways, looking at the city in terms of its different types of land uses, different socio-economic regions, different canopy targets across the city, but mostly thinking what is realistic for our urban forest legacy?

“What does a specific canopy target really represent? We want to link the full set of ecosystem services and benefits, not just cooling or climate change. I know climate change is on everybody’s minds, but we have to be careful that we keep that narrative much broader and realise that, when it comes to the individual person, it’s about those cultural, spiritual, personal, historical relations to trees. That’s what builds support for urban forestry.”

Forest pathologist Paul Barber followed with a look at the use of innovative technologies such as Arborflight in the measurement, monitoring and sustainable management of crowns and canopies.

Pointing to predictions that 2.5 billion people will be living in cities by 2050 as temperatures and extreme weather events increase, he said: “Urban planners, landscape architects, urban foresters, arboriculturists and forest pathologists all have a great responsibility to ensure we’re adopting the latest approaches, utilising them and getting accurate data that can be used in management.”

During breaks, delegates were able to explore the university grounds, spotting a wide variety of trees.

Following the coffee break, delegates returned to the Alumni Auditorium to hear Bryan Cosgrove recount his part in the development of a tree and woodland strategy for Greater Manchester through City of Trees, described as a ‘movement’ aimed at re-invigorating the city’s landscape through private sector funding.

He said: “My role is about using spatial data to develop green infrastructure plans. We have a target to plant three million trees within a generation – that’s a tree for every person in Greater Manchester. We also have a target to bring 2,000 hectares of existing woodland back into active management.”

He described how City of Trees used i-Tree, with the participation of members of the public and paid interns, to gather canopy data across the region and develop a 25-year strategy that will hopefully be embedded in the planning system of Greater Manchester.

Continuing with urban tree management – but several thousand miles away – Robert Northrop, extension forester for the University of Florida, then spoke about his own involvement in the urban tree canopy within the Tampa Bay Watershed.

“Urban conservation is primarily a social endeavour,” he said, speaking about his own approach to urban tree management. “The work we do with science and technology is, in fact, an artistic practice, in which our job is to bring forth on the landscape the vision and the values of the people that we work for and represent.”

A focus on values, he said, had been critical to his success in Tampa, where politicians are rarely persuaded by facts and figures, and, during the subsequent Q&A, he encouraged delegates not to lose sight of this.

Reflecting on urban canopy change across Great Britain through 10 case studies, Annabel Buckland, a member of the Urban Forest Research Group at Forest Research, delivered a presentation on her own research using photography to map changes in urban canopy cover across the decades.

She told how Forest Research has now created a canopy cover webmap, aiming to map urban canopy cover by percentage and ward for all urban areas in the UK.

“This is a citizen science project and it’s had a fantastic response. It’s been up and running since January and we’ve already completed 16 per cent of the urban areas of the UK.”

NATURAL FUNCTION

The afternoon’s session, chaired by Chris Quine of Forest Research, got underway with a presentation from chartered arboriculturist Luke Steer titled ‘Tree physiology for arborists: how trees work and what happens when parts are removed or damaged’.

His extremely detailed talk explored what happens when a tree becomes functionally unbalanced and concluded that pruning is a “compromise” which may increase mechanical stability but reduce biological viability.

Dr Duncan Slater, senior lecturer in arboriculture at Myerscough College, Lancashire, delved further into the subject, inviting delegates to think carefully about natural bracing and bark inclusions.

“Most people in here have cut a tree down or ordered one to be cut down by someone else,” he said. “We’ve all got the power to condemn trees or to look after them. If you follow certain rules – particularly non-scientifically-backed rules, you may be doing the wrong thing.”

Running through a series of examples, he argued against unnecessary pruning and felling, urging arborists to challenge old theories and their own thinking on axillary wood, natural bracing, bulges and forks.

Ana Perez-Sierra provided a six-year overview of tree diseases through her work at the Tree Health Diagnostic and Advisory Service at Forest Research, which identifies pests and pathogens on trees across England, Scotland and Wales, and provides impartial advice to the public and private sectors.

This was a job that had kept her very busy, she said.

“New threats to plant health keep emerging every single year,” she said, detailing her work to identify new and emergent pests and diseases, trends and changes in common varieties and ‘unknowns’ aka ‘the new problems of tomorrow’. “If you see something that is not normal, tell us. We’d rather have to tell you it’s nothing than miss something that could be important. You work with the trees and you know when something is not right. And if we detect something early, then we’re able to do something about it.”

Jon Banks brought the session to a close with an illuminating exploration of chlorophyll florescence and plant health, which included a colourful, practical demonstration.

The Forestry Commission’s Max Blake led delegates on a pests and diseases walk as part of Wednesday’s practical sessions.

CHALLENGING CURRENT PRACTICE

The second day’s talks got underway with a typically animated keynote address from Ted Green MBE, presenting a selection of pictures of trees and recounting the stories behind them in an effort to address the question ‘what’s pruning?’

It would prove to be a good question, with the subject dominating much of the afternoon’s session and the following day’s, but first Stefania Gasperini from Italy presented two case studies on morphophysiology, which she described as a useful tool for the management of veteran trees.

Pruning was the subject of Ted Green MBE’s keynote speech.

Ancient trees specialist Vikki Bengtsson, who introduced herself as the ‘tree torturer’, explained the nature conservation practice of ‘veteranisation’ (damaging live young trees to study the effects).

“We’re not aiming to kill them,” she said. “We just want them to suffer.”

Techniques she described included making nest boxes, ring-barking large branches and drilling into the trunk to mimic woodpecker holes. Though damage attracted an abundance of wildlife, in a study where 980 trees were tortured, only three died.

“Everything I’ve done with this project makes me trust trees more than ever,” Vikki said.

Next in the session, chaired by Mick Boddy, Kwok-on Tsang shared expertise from Hong Kong, expounding on the city’s pruning strategy for its iconic Stonewall Trees, making the preservation of natural heritage a key part of arboricultural practice.

Echoing Duncan Slater and Vikki Bengtsson’s message to “trust the trees”, professional climber Jon Harthill, whose arb company is based in Sweden, examined the consequences of reduction pruning with some interesting examples, particularly the controversial felling of ‘Sweden’s oldest street tree’, the Radio Oak in Stockholm.

He said: “It’s impossible to climb, revisit and section-fell trees daily without observing that trees violate any principles that we attempt to supply to them. It also seems, as a profession, that we are too ready to accept simple rules and principles, then implement them, without fully understanding what they really mean or the potential consequences.

“I think, from my experience, that by applying simple formulas for stability, we’ve undertaken recommended work which we probably never needed to do and we’ve lost some valuable trees.”

Reg Harris, director of arboriculture at Urban Forestry (Bury St Edmunds), then turned delegates’ attention to the subject of retrenchment pruning which, for a variety of reasons, was now “off the menu” for his company.

“Our trees have never been under so much stress,” he said. “We all need to join forces – the ecologists, the arborists, the consultants – think more about this, have some research into it, and hopefully we can leave these trees resilient for the future.”

PRUNING #1

Henry Kuppen, Ed Gilman, Tony Kirkham, Vaibhav Raje, Jaroslav Kolarik and Keith Sacre (chair).

After teasing the subject in the morning, pruning moved front and centre after lunch, in the session chaired by Keith Sacre of Barcham Trees.

Ed Gilman, from the University of Florida, captivated the audience by sharing his experiences with formative pruning and research on shade trees in the US. A big advocate of pruning, he walked the audience through best practice. Crucially – perhaps controversially – he urged arborists to prune at planting.

“I know this is going to make some people mad,” he said. “But many failures and branches that interfere with the environment are on the tree when it’s planted. Think about it. The branch architecture at planting may not be ideal.”

He was followed by Tony Kirkham of the Royal Botanic Gardens Kew, who examined the responses of different species to pruning phenology.

Amid much back and forth on the subject of when to prune, when not to prune, and all the unintended consequences for plant health, Henry Kuppen, MD of consultancy Terra Nostra, provided a bit of respite by focusing his talk squarely on the aesthetic delights of pruning, in particular the maintenance of the Netherlands’ charming – and occasionally spectacular – pleached trees.

Jaroslav Kolarik, CEO of Safe Trees, provided an informative update on efforts to develop a European Tree Pruning Standard, which was followed by an illuminating presentation from Vaibhav Raje, founder of Treecotech, about the burgeoning arboriculture industry in India, particularly his home city of Mumbai.

PRUNING #2

Tree champion Sir William Worsley spoke to a packed house on Wednesday morning.

With the Arboricultural Association’s conference dinner and awards taking place on Tuesday evening – and continuing into the small hours of the morning – a drop-off in attendance for Wednesday’s early talks could be anticipated. However, the auditorium was packed for the keynote address from the UK’s tree champion, Sir William Worsley.

“I’m struck by the sense people have that we’re at a critical and crucial time for the management of forestry – and there are exciting opportunities for the future,” he said.

“A key focus for me is to look at how the future environmental land management scheme will work for the creation of woodland and for its management, after we exit the European Union. We want a future policy to deliver an improved natural environment and I’m determined that forestry woodland creation and its sustainable management will play a crucial role.”

The final session of the conference, which was followed by practical workshops in the afternoon, was chaired by Vikki Bengtsson and began in earnest with a talk from Philip van Wassenaer, principal consultant for Urban Forest Innovations, calling for arborists to ‘reduce the crown, save the tree’.

Referring back to the previous day’s talks, he said: “My understanding of retrenchment pruning is it’s not for risk abatement, it’s not to save the whole tree. The purpose is to help stimulate the lower crown. Sometimes we need to help old trees get smaller. The challenge is deciding the dose.”

Staying on the subject of crown reduction was Paul Muir from Treework Environmental Practice, who advocated for statics as a useful tool to help assess a tree’s likelihood of failure and posited that crown reduction is often an inevitable response to uncertainty.

Martin Dobson, Andrew Benson, Philip van Wassenaer and Paul Muir.

Is pruning an effective tool for controlling subsidence risk? This is the question consultant Martin Dobson posed, running through a series of examples of trees causing subsidence damage to properties and assessing whether any could be retained.

He concluded: “Pruning can be used as a reasonable way of minimising risk and preventing the first instance of subsidence, but once damage has occurred, pruning is not a consistently reliable means of mitigation. However, if you want to prune rather than fell after subsidence, then you’ve got to do a 40–50 per cent crown reduction.”

Andrew Benson brought the session to a close by dropping from the heights of the canopy back into the soil, detailing his own research into root pruning.

All presentations across the three days were recorded and are due to be made available for all members in January.

The focus of the Arboricultural Association’s 54th National Amenity Conference in 2020 will be ‘Trees and Society’. Keep up-to-date at www.trees.org.uk.