Conservation & Ecology
Trees in high risk areas require monitoring
An owner/manager should decide a policy appropriate to their site, which is influenced by levels of use and the importance of the trees. Trees with structural faults which are valued for their amenity value will, of course, require greater monitoring and possibly specialist advice. It is reasonable to inspect trees within falling distance of well used areas such as roads, footpaths or on golf course greens and tees. Zoning allows resources to be allocated to areas of high risk. An inspection may take the form of informal observation, formal or detailed inspection. Following zoning, it is necessary to identify the type of inspection required. Initially, this can be carried out by walking the site. Trees that require further inspection can be identified depending on their location in relation to risk, their size and condition. If there are any doubts at this stage then specialist advice should be sought.
Assessment should also take into account the species of tree. For example, and as a rule, poplars are far more likely to fail than oaks. Ground conditions should also be assessed; if an area is wet, then there is more likelihood of a tree suffering from wind blow. It may be wise to involve a specialist in the zoning process. However, once the plan is in place then an annual informal visual inspection can be undertaken in-house, and any trees which are of landscape or amenity value that show symptoms of disease or potential for failure can then be monitored by a specialist. This ensures resources are allocated cost efficiently. Technology can be used where the
retention of important amenity trees is desired. (See detailed inspections)
Informal Inspection
In certain areas of low risk, informal observation may be all that is required and, given the general low risk posed by trees, this may be considered reasonable and appropriate. However, choosing to implement a system of informal inspection is not justification to do nothing. Informal inspections should take place and be recorded.
An informal inspection should take the form of a visual assessment of a trees general health, structural stability and position with regard to risk. Any observation which causes concern should then be acted upon and a formal inspection made. Likewise, any reports regarding tree issues by either staff or the general public will
inspection is not justification to do nothing”
“Choosing to implement a system of informal
require action; this would normally involve a formal inspection by a competent member of staff or by a specialist. Informal surveys can be carried out by a person with good local knowledge regarding usage of the site (owner, greenkeeper, groundsman, agent) and, therefore, areas of high risk. This does not require a specialist, although any potential problems that are identified should be acted upon.
Formal Inspections
A formal inspection is one where a person visits a tree for the sole reason of assessing that tree, for either inventory or health and safety purposes. This will normally take the form of a ground level inspection looking at the general health and stability of the tree; assessing die back, uprooting or structural defects. This provides a cost effective means of identifying trees which present a risk and require a detailed inspection. In order to undertake a formal inspection, a general knowledge of trees and the ability to identify poor health or structural weaknesses is required. Further, the capacity to assess the height and falling distance of the tree is also essential in order to establish the element of risk the tree provides. The ability to identify visible signs of ill health or structural weakness, such as cavities or heave (root plate movement), is also necessary as they may cause the tree to fail.
Detailed inspections
Detailed surveys should be carried out by a qualified specialist who is experienced in the field of investigation. The landowner should satisfy themselves of the specialist’s qualifications and experience and ensure that they have the necessary insurance to carry out the tasks required.
Generally, an initial ground level visual assessment will take place to identify signs of structural failure. This may result in the need for further specialist investigation comprising either soil and root assessments, aerial surveys or the use of diagnostic tools such as resistograph drill. Detailed surveys are generally confined to
trees of high amenity value to the landowner.
Recording details
Records should be kept to provide evidence of due care and attention. They should not be onerous, but should record date and type of inspections along with any actions required and subsequent remedial works as appropriate. They do not need to include every tree, but it would be advisable to list individual trees that present risk, listing and identifying them and their location, the findings of detailed inspections and the actions taken to minimise risk.
Resistograph testing
The resistograph is an instrument that detects decay and cavities in trees and timber. The arborist is able to detect wood decay, stages of rot, cavities, cracks and ring structure. It can also be used in certain species to measure growth rings and bark diameter. The stability and health of the tree can then be assessed much more accurately. As the micro drill enters the tree, the
resistance of the wood changes the rotation speed of the drill. These variations are translated into a graph. The tiny drilling hole closes itself up without any damage to the tree. This then provides written evidence which, combined with the experience of the arborist, allows a rational decision to be made. There is no substitute for experience, as the drill provides evidence of only the area where it is used. The arborists experience will tell him, depending on the pathogen, where the greatest likelihood of failure is liable to be. Different fungal bodies attack different areas of the tree; some favour roots and butts, whilst others may favour branches or limbs. It is, therefore, important to ensure that the arborist you use has sufficient experience to assess the tree before detailed surveys are undertaken.
For further information contact John
Nicholson Associates on 01913 842557 or 07967 818719
APRIL/MAY 2013 PC 55
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