More than 200 delegates attended the first ever National Tree Officers Conference - organised by the Institute of Chartered Foresters, the London Tree Officers Association and the Municipal Tree Officers' Association - in Telford, Shropshire, on 9 November. The event provided updates on planning and street tree policy, contract management and pest and disease issues.
Wycombe District Council natural environment officer Philip Simpkin discussed the challenges in meeting the Buckinghamshire authority's ambitious target of 25 per cent tree cover.
"In Wycombe we want around 34 dwellings a hectare and with that density we can get to around 25 per cent tree cover, in line with our strategic objectives," he said. "But you can't plant 25 per cent now. You have to project forward to an eventual canopy cover. Whether that's the maximum possible figure or that expected after, say, 25 years, is something we are working on."
Anticipating practical problems with this approach, Simpkin posed the questions: "Do we refuse a proposal if it doesn't meet the target, or have zones with different targets? Do we factor in other measures such as green walls?"
Giving an inner-city perspective, Camden tree officer Riccardo Arnone said the inner north London borough manages 28,000 trees, principally mature London planes, Prunus and Acer, each on a database and mapping system.
"Subsidence can be expensive for the council and we have some very big trees close to properties," he added. This prompted a study to establish the correlation between expenditure on tree maintenance and frequency of insurance claims to justify retaining this budget. "Claims did indeed go down after maintenance spend, then went up again when spending was cut. In all we cut costs to the borough by around half."
As a result, a regular programme of pollarding began three years ago, combined with gradual replacement of species less tolerant of such treatment such as alder and Ailanthus, especially in subsidence-prone areas, said Arnone. "Ultimate size is important - 6m is sufficient for street trees," he added, suggesting Prunus 'Pandora' and Liquidambar styraciflua 'Gum Ball' to meet this. "To counterbalance this we can plant larger trees in parks, housing estates and even new-builds where subsidence isn't an issue.
"Diversity is key to resilient tree populations. But 50 per cent of our trees are made up of acer, Platanus, Prunus and Tilia. They are hard to get away from and we are reliant on Rosaceae for smaller trees." Meanwhile, he warned that a diversity of trees in a single street can lead to "a mix-and-match appearance".
Local authority tree managers "have great powers which we shouldn't underestimate" in dealings with contractors, said Barnet trees and woodlands manager Andy Tipping. "A good contract is vital. I see many cases of good contracts working well, bad ones not so well. There are rules on procurement so check you are compliant and talk to peers in the industry about what is and isn't working."
A recent contract renegotiation in his outer north London borough "was an opportunity to tear it up and start again", he explained. "We now have a biosecurity clause, which ensures a new tree spends at least a year on the nursery first. The public sector has millions of trees and we should show responsibility. You can also make them employ local subcontractors."
On young tree maintenance he added: "Big arb firms won't do a good job of nursery-type work so keep planting and young tree care separate. Most tree officers like me have come from the contracting world, but there is currently a lack of skilled arbs and a high turnover. Where the next generation of tree officers is coming from is a concern."
In light of the controversy around Sheffield's long-term tree and street maintenance contract, Merton borough arboricultural manager Dave Lofthouse suggested that "20-plus years is ridiculously long" for such contracts, to which Tipping replied: "We are probably all of the opinion that it's a silly idea. You have contractors managing their own contract."
Disease - Conference delegates updated on threats from canker stain of plane as well as acute oak decline
Tree officers should be vigilant for signs of canker stain on plane, caused by the fungus Ceratocystis platani, Transport for London senior arboriculture and landscape specialist and London Tree Officers Association (LTOA) chair John Parker told the conference.
"It’s hard to spot, it can kill trees pretty quickly and there is no cure," he said. "You are looking for problems in the canopy — retained, desiccated leaves. If you scrape away the bark you will see staining in the wood. But it requires a lab diagnosis to be certain."
He urged delegates to obtain a copy of a new LTOA guide to detecting and identifying the disease. "It’s mainly spread through infected tools and can live for two-to-three years as a saprophyte in sawdust. But they are still planting planes in Italy.
The cultivar Platanor appears resistant and is very quick-growing." The UK was granted protected zone status by the EU two years ago, restricting imports of plane saplings on condition that monitoring for the disease is maintained.
"LTOA has done surveying across London," said Parker. "This year we have surveyed over 2,000 trees, with no C. platani found."
On acute oak decline, Guildford Borough Council tree and woodland officer Geoff Monck said: "It’s a disease complex that we still don’t completely understand, a combination of biotic and abiotic factors including mildew, drought stress, lack of soil organic matter, run-off from roads, nitrogen depositions and even dog fouling."
Nitrogen and phosphate inputs appear to harm trees’ mycorrhizal fungi, while "there is a strong correlation with areas of low rainfall between 1971 and 2000, with hardly any in Devon, Cornwall, Wales, the Pennines and Lake District".
A Treework Environmental Practice trial of mitigation treatments with The Royal Parks found that organic amendments to leaves and soil "had a positive effect, with greener leaves and extension growth", though trees included as controls "now also show improvements, suggesting it’s episodic".
Institute of Chartered Foresters development director Russell Horsey said: "We’ve been 18 months putting this together and aimed to make it affordable for hard-pressed local authorities." The organisers will consider holding similar events depending on delegate feedback.