LTOA study to help maintain import ban
London’s abundant and distinctive plane tree population faces the potentially devastating threat of a disease which has wiped out thousands of trees across Europe, but is believed not yet to be present in the UK.
The London Tree Officers Association (LTOA), has released a position statement outlining its concern about what it describes as ‘a number of significant pests and diseases threatening the health of London’s trees’. Of chief concern among these is the canker stain of plane (Ceratocystis platani) or CSP.
CSP functions as a vascular wilt, similar to that of Dutch elm disease; the fungal pathogen enters water-conducting vessels of the tree, ‘causing barriers and chemicals to be produced [perhaps by the tree itself] and inhibiting the flow of water and nutrients to the leaves, eventually causing leaves to wilt and die with potential fatal consequences for the tree,’ the statement says.
‘A ban on importing London planes has been in place as of October,’ explains LTOA executive committee member and member of the organisation’s bio-security working party David Lofthouse. ‘We’re now trying to make sure that the ban is maintained by cooperating with Defra and the Forestry Commission,’ he adds, ‘and have recently completed a survey with the Forestry Commission, showing that this country is a [CSP] disease-free zone.’
CSP was introduced to Europe during the Second World War, since when it has become established in Italy and Spain, and has tracked north through southern France, while also affecting planes in parts of Greece, Switzerland and elsewhere in mainland Europe. The consequence has been dramatic, says the LTOA: ‘Thousands of mature planes lining the four hundred kilometres of the Canal du Midi in Southern France are being felled and burnt every year in an attempt to prevent the transmission of fungal spores’.
The LTOA’s Tree Health and Plant Bio-security Action Plan says of the CSP pathogen: ‘Once established in the UK, plane tree populations already abundant in urban forests will be at particular risk of infection, decline and death, and likely result in extensive, costly tree removal, and replacement with resistant species.’
The life cycle of a plane tree, as with our native oaks, may span 1,000 years, notes the LTOA. ‘Given that planes are the largest trees in London, that even our oldest planes may be just in their mature stage, and that the ecosystem services provided by trees increase exponentially with size as trees mature, there is a clear responsibility to maintain the health and well-being of our planes, to foster their long-term contribution to the urban forest.’
It is a ‘sad irony’, it adds, that the origin of London plane plantings in the capital ‘was partially due to its capacity to resist atmospheric pollution, and that this tree, that everyone until recently considered to be virtually indestructible, could now be exposed to a fatal pathogen just when the benefits and services it provides are most needed’.
The LTOA believes that the losses affecting the London plane population across the capital, should CSP take hold, ‘would be practically irrecoverable for three or so generations, with severe consequences not only for the visual beauty of the city but also for the services London planes provide to the quality of urban life’.
While another disease affecting plane trees, Massaria (Splanchnonema platani), is a weak pathogen and its effects long term may not be too damaging if managed appropriately, asserts the LTOA, CSP ‘is a true killer, impacting planes on a par with Dutch elm disease upon the elm population’.
The worst case therefore would be devastating for London. The costs would be astronomical in lost tourist revenue, loss of enjoyment of the streets, great parks and squares of London, of the vast carbon storage and carbon sequestration, and of the absorption of atmospheric pollutants.
While in such circumstances there might be talk of replacing London's plane tree asset, the reality would be different. The sheer cost of starting again to achieve a true replacement that would probablytake two centuries to achieve, focuses the mind on the true value of London’s plane tree population. While political intentions may be positive, attention to problems, timescales and budgets tend to be short term, all of which gives little confidence that were major losses to occur, there would be concerted long-term effort to restore the quality and extent of the urban forest to its former healthy condition.