LTOA & Arboricultural Association Position Statement Jan 2012

The LTOA Massaria Working Group (LTOA MWG) has been set up to look into the problem of Massaria Disease of Plane (MDP) and communicate its finding with a view to ensuring good management practice is maintained in order to safeguard all the benefits and contribution to the community derived from the Capital’s London Planes.

MDP is a recent problem affecting the capital’s London Plane trees, which, though not particularly harmful for tree health, causes branches to occasionally decline, die and fall. It is thought to be a host specific fungus that occurs naturally in Planes, in a latent (endophytic) form, with a soft rot decay developing in certain affected branches that can result in brittle fracture. It appears that the symptoms of MDP are first observed on small diameter branches and if moisture availability continues to decline it may affect larger diameter branches. Notably, the period between initial expression and eventual branch failure can be short. Therefore, the prevalence of MDP requires a high level of awareness, knowledge and effective management techniques to determine the appropriate action. This warrants collaboration, sharing of reliable information and production of guidance to ensure that public safety management is a balanced and proportionate response to a problem and not one that is risk-averse and over-reactive (see NTSG guidance).

The MWG will develop a guidance document for tree managers providing a balanced and proportionate response to the problem. Members of the LTOA MWG include Mike Turner (The Royal Parks), Chair, Neville Fay (Treework Environmental Practice) Jake Tibbetts (London Borough of Islington), Peter Holloway (Arboricultural Association), Patrick Prendergast (London Borough of Harrow), Neil Taylor (City of Westminster).

This Position Statement outlines the LTOA’s stance to ensure that unnecessary and inappropriate intervention is avoided and that there is a measured and well-informed basis for managing and communicating the risks that may arise from MDP. The guidance document will aim to provide a framework for understanding the problem affecting London Planes, and for gathering and communicating evidence about the disease. This approach will underpin the formulation of both short term and long-term management guidance, inspection protocols, and inform professionals involved in managing individual trees and populations of Plane trees. It will support community based and professionally interested stakeholders for the benefit of maintaining the public environmental, contribution to health and wellbeing of London’s Plane tree population.

The LTOA MWG believes that the biggest risk posed to the London Plane tree population is from a disproportionate response to the problem, driven through fear of an over exagerated perception of public safety risk. This is because the unnecessary pruning or felling of London’s Plane trees would be significantly detrimental to both the tree and human populations of London.

London’s Plane tree population is generally subject to existing management which contributes to the very low public safety risk. Management of the risks associated with MDP requires no more than the application of existing management approaches. Management is also concerned with how resources are prioritised and allocated and needs to take account of the cultural care of the trees and their growing environment. Not to do so is to put future generations of Londoners at risk from loss of canopy (and its associated impacts on quality of life).

Massaria Working Group Core Principles:

• The MWG believes that there need be no loss of Plane trees as a result of MDP.
• Inappropriate management of MDP affected trees could have serious social, economic, environmental and political impacts SAME
• London Planes are a key component of the Capital’s urban forest making a vital contribution to the heritage, amenity, biodiversity and human health and wellbeing.
• MDP involves a fungus-host relationship that requires biological understanding and monitoring
• MDP presents a low risk to tree health – there is a greater threat to tree health and sustainability from misunderstanding the problem and inappropriate intervention
• Disproportionate management will result in tree loss and runs counter to the LTOA advised approach SAME
• While MDP presents a public safety risk, this should be assessed and managed in a reasonably practicable way - management should therefore be based on knowledge of the real risks (see NTSG)
• Tree management needs to be evidence based and take account of sustainability principles

This Position Statement aims through analysis and assessment of current evidence being accumulated in the UK and mainland Europe, to develop assessment, recording and management guidelines that will assist tree owners and managers to deal with MDP, and to identify research needs.

General Massaria Symptoms:

• A strip of dead bark starting at the branch collar and stretching along the top of the branch. The width of the dead strip varies but nearly always tapers to a distinct point.
• On smaller diameter branches (100 to 150 mm), death can occur within a year; these are normally obvious from the ground due to young twigs, seed clusters and sometimes ‘droughted’ leaves still being visible on the dead branch. Dead flaking bark is also often present, rapidly exposing the orange coloured sapwood.
• Larger diameter branches may not exhibit any symptoms and the dead strip of bark is mainly on the upper side of the branch which makes it difficult to identify from the ground.
• It is most frequent on shaded lower order branches which are in the mid to lower canopy level.
• Symptoms are seen affecting mature trees over 40 years of age

General Management Conclusions:

• Symptoms are not typically seen in trees with maintained reduced crowns (such as street pollards).
• MDP is associated with branch failure from decay and may occur rapidly within 4 months.
• MDP causes branch failure and poses a measure of public safety risk.
• Managing MDP for public safety can pose a threat to the health of affected trees.
• Managing MDP should not be treated in isolation but should be consistent with current public safety guidance principles (see NTSG), which include consideration of the benefits from affected Planes.

Factors influencing the disease incidence include:

• Tree health/canopy condition
• Age class/branch diameter
• Pruning history/branch loading
• Branch orientation/shading
• Soil rooting environment/hydrology
• Climatic effects/moisture deficit
• Proximity to other trees/competition

Proposed Management and Research

The presence of MDP of London Plane demands a thorough understanding of the disease and its development over several years if we are to prevent costly over-reactive and potentially damaging impacts upon affected trees.

Given that water availability, drought and tree vitality appear to be significant factors it is vital to ascertain ways to improve disease resilience, such as through irrigation and improved soil porosity.

The long term effects of pruning are unclear with regard to their impacts upon tree health and long term viability/disease spread. This needs to be considered when developing appropriate tree work and arboricultural practices – including retrenchment pruning (where it is considered this may improve the health of trees by reducing moisture stress), irrigation, improving soil environment and moisture retention.

Research programs are being developed for application in The Royal Parks and London Borough of Islington that aim to provide improve our knowledge in these areas.

MWG Objectives

The LTOA MWG objectives are to:

• Support stakeholders with common interests in the health and sustainability of the London Plane tree population.
• Provide information as we gain knowledge from experience and research
• Develop the LTOA MWG guidance document to address processes, procedures and management recommendations and options for tree management, titled Managing Massaria Disease of Plane.

Summary

The LTOA MWG objectives will aim to ensure:

• An adopted approach to ensure the retention of mature Planes wherever practicable.
• A sustainable Plane tree population for public benefit.
• A framework and principles for good practice.
• The development of short and long term control strategies.
• A balanced, proportionate and cost effective approach to inspection and pruning.
• Tree management that is not risk averse.
• A balanced and proportionate approach that is formulated to manage the real risks considered, along with the benefits from the trees.
• Management guidance to enhance tree vitality and longevity.
• A cost-benefit approach

A guidance document for tree managers will soon follow sometime in 2013.