Case study: Project 2
Planned installation of the Big Hat Tipi.
Instructions and Purpose
• Make suggestions to decrease the arboricultural impact of the proposed scheme on the retained trees during the design process.
• Detail the arboricultural impact of the proposed project.
• Prepare a tree work schedule to British Standard (BS 3998) 3998:2010 - Recommendations for Tree Work.
• Develop a tree protection strategy for the duration of the development including any demolition works.
Provision of the above information is designed to address the requirements of the LPA in terms of the arboricultural information necessary to register and determine the planning application.
In surveying the trees to the requirements of BS 5837, trees on and immediately adjacent to the site with a stem diameter over 75mm have been included. Large shrubs and hedges have been included where these are considered to be of significant amenity value. These are particularly important where they provide boundary screening. For clarity and ease of data interpretation, large shrubs have been classified as trees.
The trees were inspected from ground level and no climbing inspections were undertaken. Stem diameters were measured using a diameter tape at 1.5m from ground level
The quality and value of the tree stock has been broken down by BS 5837 quality grade. The grading system can be summarised as follows:
A Grade – trees of high quality and value with a life expectancy of more than 40 years
B Grade – trees of moderate quality and value, with a life expectancy of more than 20 years
C Grade – trees of low quality and value, with a life expectancy of more than 10 years
U Grade – trees usually for removal (unless otherwise stated), with a life expectancy of less than 10 years
The RPAs of the trees are included in the Tree Survey Schedule with reference to Table 1 of BS 5837. The RPA is the area, measured in m2, which is calculated in accordance with the BS 5837 using the stem diameter of the trees. This should provide retained trees with sufficient rooting environment to survive the proposed development. Section 4.6.3 of BS 5837 provides for the shape of the RPA to be modified from the starting point of a circle to account for site features where rooting may be restricted, as long as the total area remains the same.
Diagrammatic Representation of a Restricted Root Protection Area
Impediments to Normal Rooting
T1 and T4
Existing hard surfacing
Arboricultural Impact Assessment
This section comprises an assessment of the impact the proposed works detailed in Section 2 above have on trees. It considers the arboricultural impact and how this may be mitigated.
Incursions into Root Protection Areas
The table below summarises the significant incursions into the RPAs of noteworthy retained trees. The ‘Action’ column details how the incursion has been mitigated and why it is considered acceptable. Incursions may be fully invasive (where specialist methods are not used and some root loss is considered acceptable) or low invasive (where specialist methods are used to minimise damage to or loss of roots). Full details of how the works will be carried out without causing damage to the trees are given in the AMS.
Type of Incursion
T1, T4 and T5
A permeable low invasive surface consisting of hardwood woodchip will be installed on top of the existing soil level with pinned timber edges to limit root disturbance to an acceptable level.
Summary of Incursions into RPAs
Arboricultural Method Statement
Introduction to Arboricultural Method Statement
To safeguard the retained trees (both above and below ground parts) during the development works and preserve the soil structure of areas which could be allocated for new planting, it will be necessary to implement tree protection measures.
The basic principle is that the area inside the tree protective fencing is to be protected for the duration of the works.
A copy of this AMS shall be maintained on site at all times and made available to all site personnel.
All site personnel shall be made aware of the key impact of this AMS and be given an arboricultural induction by the Site Manager. A copy of the Induction Form will be signed by all site personnel to confirm that they have understood the issues involved.
As of 2005, Local Planning Authorities have powers to serve Temporary Stop Notices if agreed tree protection measures are not carried out. Adhering to this AMS will ensure that such costly and time consuming action is avoided.
A pre-commencement site meeting, involving the Client and an Arboricultural Consultant will be held to ensure that all aspects of the tree protection process are understood and agreed. A record of the meeting will be communicated to all parties by the Arboricultural Consultant within five days of the meeting.
All tree works will be carried out in accordance with BS 3998:2010 ‘Recommendations for Tree Work’ (as amended) and to current arboricultural best practice. Tree works will be carried out by a suitably qualified and experienced Arboricultural Contractor holding the necessary insurance cover. This contractor should carry out the relevant site specific risk assessments and record such information prior to commencement of tasks and work in accordance with current health and safety standards, practices and legislation. A list of such contractors is available from the Arboricultural Association at www.trees.org.uk.
Tree Protective Fencing
Tree protective fencing is used to ensure that the RPAs of the retained trees are safeguarded. These measures may also be employed to protect areas of ground for new landscaping.
The positioning and specification of the fencing is shown in Appendix 2. In this case, the default specification of BS 5837 consisting of fixed Heras or plastic barrier fencing would be effective.
The protective fencing will remain in position for the duration of the development. Clear signs will be attached to the fencing once erected – suggested wording will be ‘Construction Exclusion Zone No Access’.
The area shown for low invasive surfacing should be covered by heavy duty ground protection where access for machinery is required.
Site Access/Hard Surfaces
The existing vehicle and pedestrian accesses into the site are suitable for ingress during demolition and construction and no damage is anticipated to the root systems of the retained trees.
There is no requirement for demolition within the RPAs of the retained trees.
There is no requirement for any services within the RPAs of the surveyed trees.
There is no requirement for any foundations within the RPAs of the surveyed trees as the low invasive surface is to be retained with pinned timber edges that will sit on top of the existing soil levels.
There is no requirement for additional construction or hard landscaping that will affect the retained trees.
Subject to all of the above tree protection measures being implemented, construction works may proceed without risk of damage to the retained trees.
Soft Landscaping/Boundary Fencing
Soft landscaping will be undertaken when heavy machinery has been removed from site and tree protective fencing taken down. The following points will be observed:
• Care will be taken not to compact the soil within the RPAs of the retained trees or where new tree planting is to be carried out.
• No changes in ground levels will occur within the RPAs of the retained trees.
• Unwanted vegetation will be removed manually or using contact herbicides that will not damage existing tree roots.
• No irrigation or drainage pipes will be installed within the RPAs of the retained trees.
Sequencing/Supervision, Responsibility and Incident Reporting
Effective tree protection relies on following a logical sequence of events and arboricultural inspection/supervision.
Works which have the potential to affect trees will be supervised by a suitably qualified and experienced Arboricultural Consultant. Regular inspection visits will also be undertaken to ensure that tree protection measures are being adhered to. The final details of supervision and the frequency of inspection visits will be agreed at the pre-commencement meeting. The Arboricultural Consultant will make a record of visits, which will be attached to the site copy of the AMS for inspection and communicated in writing to the Client within five days of the site visit.
Daily inspection of the physical tree protection measures will be carried out by the on-site Arboricultural Liaison, who does not have to be a trained Arborist, but will be responsible for the implementation of the approved tree protection. Any deviation from the approved methodologies will need to be agreed by the Arboricultural Consultant who may need to visit site to authorise the revised tree protection measures. It is the responsibility of the Client or the Arboricultural Liaison to instruct the Arboricultural Consultant to attend site for the key events requiring supervision or monitoring.
Any damage to stems, branches or any size roots of the retained trees will be reported immediately by email and telephone by the Arboricultural Liaison to the Arboricultural Consultant. The Arboricultural Liaison will take photographs of the damage and send these to the Arboricultural Consultant who will visit site to assess the scale of the damage and report to the LPA Tree Officer. Mitigation for the damage will be agreed with the LPA Tree Officer.
Sequencing and Supervision
Issue arboricultural report to site manager
Give Arboricultural Consultant (AC) at least a week’s notice of pre-commencement meeting
Site Manager, Tree Officer and AC
Arboricultural induction and appointment of the Arboricultural Liaison
Carry out tree works
Erect tree protective fencing and construct timber edging for the low invasive surfacing
AC to inspect
Install low invasive surfacing using ground protection to access the site within the RPAs of the retained trees
AC to supervise
Carry out construction of the Big Hat Tipi
Remove tree protective fencing
Site Manager to brief landscaping company on site and supervise
Carry out soft landscaping