Existing Trees on Sites (including regulated and significant trees)
Introduction The Australian community has become increasingly committed to the conservation of the environment and there is now a considerable body of legislation which is designed to protect our flora. Professional service contractors need to make decisions about the natural environment including decisions about larger individual trees and other artefacts or vegetation which are on the proposed site. These decisions should be made in the context of applicable legislation and from a site assessment encompassing a tree audit. Once it has been agreed that a tree is to be retained in a development, steps need to be taken to ensure that no harm will come to that tree as a result of the project either through the design or through lack of proper care and attention during construction. Any tree work that is required as a result of design or construction is to be carried out by an arborist. If it is proposed to remove tree/s then the requirements of the Development Act 1993 should be considered as detailed in the following section.
Regulated and Significant Trees South Australia's significant tree controls came into effect on 20 April 2000. On 17 November 2011 the Development Act 1993 and Development Regulations 2008 were amended to introduce ‘regulated trees’ in addition to ‘significant trees’ which allows for a two-tiered system of tree classification and assessment. The Development Act 1993 provides that any activity that damages a regulated or significant tree is development. For any such activity a development application is required and will be assessed by the local council. A regulated tree is: any tree in metropolitan Adelaide and/or townships in the Adelaide Hills Council or parts of the Mount Barker Council with a trunk circumference of 2.0m or more measured at a point 1.0m above natural ground level (in the case of trees with multiple trunks, it is those with trunks with a total circumference of 2.0m or more and an average circumference of 625mm or more measured at a point 1.0m above natural ground level). A significant tree is a regulated tree that is: any tree in metropolitan Adelaide and/or townships in the Adelaide Hills Council or parts of the Mount Barker Council with a trunk circumference of 3.0m or more measured at a point 1.0m above natural ground level (in the case of trees with multiple trunks, it is those with trunks with a total circumference of 3.0m or more and an average circumference of 625mm or more measured at a point 1.0m above natural ground level); or any tree identified as a significant tree in the Development Plan of the City of Adelaide, City of Burnside, City of Prospect or City of Unley.
0f2112a313e10d70a7d6df05ccff65b4.doc Updated in June 2012 Existing Trees
An application for development approval should therefore be made seeking approval for any tree damaging activity of a regulated or significant tree. Tree damaging activity means: the killing or destruction of a tree; the removal of a tree; the severing of branches, limbs, stems or trunk of a tree; the ringbarking, topping or lopping of a tree; any other substantial damage to a tree; and includes any other act or activity that causes any of the above to occur. It is considered that the definition would include substantial damage to the root system due to trenching for services or other construction activity. Tree damaging activity does not include: maintenance pruning of less than 30% of a tree crown; the removal of dead or diseased wood; or the removal of branches that pose a material risk to buildings or areas frequently used by people. Exemptions also apply to: all trees located within 10m of an existing dwelling or existing in-ground swimming pool unless the tree is either a Willow Myrtle or any Eucalyptus; a list of 24 tree species considered to have medium-high or high risk for limb failure and infrastructure damage (these are considered exotic species or are common trees planted in urban areas); a regulated or significant tree that is dead; and a regulated or significant tree located within 20m of a dwelling in medium or high bushfire risk areas. Urgent tree damaging activity is permitted in order to protect a person or building. However, if this activity is undertaken, then: the person who undertakes the work must notify the relevant authority; the work must be undertaken to cause the minimum damage to the tree; and thereafter, the owner must seek the appropriate development authorisation.
Likely Damage to Trees This guide note provides information on the ways trees can be damaged followed by methods to prevent that damage from occurring. In the case of trees, prevention is always better than cure as when damage is inflicted on a tree, it may be too late to apply a cure. Trees survive best when subjected to the least amount of damage.
Damage to Tree Roots The severing or scarring of a tree's roots will significantly shorten its life. Such damage may take 3-4 years to be noticed and it can take up to 10 years before tree death occurs.
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Root damage poses two concerns. Firstly, major root severance threatens a tree's stability (roots act structurally as anchors) and secondly, lesser roots supply moisture and nutrients and act as a food supply line. If either is removed, the tree will shed limbs, the crown will die back, leaves will shrink in size, the canopy will thin and the tree can quickly become unsafe. It may also die. Roots need air and water to survive. Soil compaction may deny the tree roots access to these two vital elements, hence no activity should occur on a building site which causes compaction, or trafficking within a tree's root zone. Where necessary works or proximity of new works and the presence of retained trees requires vehicular access, it should be undertaken with vehicles with low axle loads or deflated tyres. Failing this, protective planking, plating or mulching needs to be considered. Department of Planning, Transport and Energy (DPTI) contracts require the contractor to care for retained trees under threat from ground level activity. Trenching should not occur within the root zone. Where this too is impossible to avoid, a risk to the tree will exist and should be pointed out to the Lead Agency. To minimise this risk, trenching near structural roots should occur below them, not through them. Where tree roots are exposed to air for exploratory or trenching purposes, they should not be left exposed for more than two hours on hot days. They should be wrapped in wetted hessian while exposed. When backfilled, the backfill density should not exceed the density of the natural soil. Trees should not be deprived of their normal water supply. If this is likely, the contractor should provide a supplementary source of water. The specification should ask the contractor to keep the tree root-zone moist, at all necessary times, noting that irrigation, after rain, can do more harm than good.
Damage to Tree Canopy Contractors should not touch the Lead Agency's tree canopy without an instruction to do so. Such instructions should not be given without specialist advice that such action is either warranted or advisable.
Damage to Tree Trunk If plant and machinery are kept away from trees, bark damage should not occur. It is important to avoid damage as it permits pathogen entry, decay and cavity development and shortens the life expectancy of the tree. Bark damage is also unsightly and large wounds may not heal and require a bark-graft. A specialist arborist may be needed to carry out this kind of repair. While small wounds may heal naturally, bark damage should be avoided.
Contractors in the Way of Trees Trees belong to the owner and are not a site amenity for the contractor. Workers, plants, materials, site offices and compounds do not belong within a tree's zone of influence and should not be put there.
Trees in the Way of the Contractor When scheduled for retention, a tree should not be pruned or interfered with in any way for the contractor's convenience. The contractor should allow in his tender for the untouched survival of the tree.
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Where one or two limbs of a retained tree interfere with the eaves of a building or where plant or scaffolding are unavoidably required, this should first be agreed with the DPTI Project Risk Manager and the Lead Agency. If agreed, the situation should be referred to a tree specialist for advice on how to provide access with the minimum disturbance to the tree. An offending limb may be able to be tied back temporarily or perhaps minor surgery is acceptable. Any work agreed to should only be carried out by an arborist.
Professional Service Contractor's Responsibility The professional service contractor is responsible for: site assessment; compliance with the Development Act 1993 and Development Regulations 2008; tree audit; achieving agreement with the Lead Agency on the trees which are to be retained; design which encompasses the results of the site assessment and tree audit and makes adequate provision to protect those trees which have been nominated for retention; drawings and specification which adequately reflect the design intent with respect to trees and detail what is expected of the contractor; managing that all subcontractors adhere to the guidelines expressed above and for coordinating their input; managing that during construction there are adequate practices implemented by the contractor to protect trees and that expert advice is sought to ascertain if there are any potential problems to the health of trees, e.g. to the crown, trunk or roots of a tree; providing written advice to the Lead Agency about the long term management of the trees which are to be retained; and informing the Lead Agency of any trees identified as regulated or significant (refer to paragraph, Tree Audits below) and/or trees which will require special care and management.
Tree Audits A tree audit is a health and safety check for a tree in the context of its surroundings. The check is to include tree work which is needed to improve the tree's quality of life or to reduce any risks to life and property from its presence. The tree audit should be comprehensive because it not only gives an account of the tree's condition at audit, but it also enables that tree's condition to be reviewed by future audits so that a tree's initial condition may be compared with its present condition. Hence, any trends in the tree's response to its surroundings can be monitored, giving the owner an opportunity to alter or eliminate any adverse circumstances affecting either the tree or its surroundings. Trees have various safe lifespans and even with good tree management eventually the tree will reach the end of its safe life. Acceptance that tree cycling is needed for a permanent tree presence is an important concept for managers/owners to accept. Tree audits give information about the health of a tree and make recommendations for retention or removal. Tree audits can form a data base from which to choose suitable replacement trees and from which to avoid problem species when re-planting is being considered.
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A tree audit should contain the following data:
Basic References Botanical name. Common name. Location on a drawing. Height and spread of canopy. Girth of trunk at 1m above ground. Classification as a Regulated or Significant tree where applicable.
Tree Condition General description of tree. Description of limbs removed by pruning. Description of limbs removed by storm damage or natural limb shedding. Description of limb and trunk wounds. Description of cavities and presence of decay. Notification of any nests, animal occupied cavities or presence of bees. Notification of any broken but attached limbs (called hangers). Notification of dead limbs. Notification of any cleft forks. Notification of any split forks or splits in stems or limbs. Notification of any disease of infection. Notification of any chlorosis or necrosis. Notification of any co-dominant stems. Notification of any loss of cross section of stems of limbs. Notification if the tree is leaning (how many degrees). Notification of any visible roots or loss of roots.
Tree Environment Notification of any underground services in or near the root zone. Notification of any surface irregularities like slopes or retaining walls. Notification of any nearby buildings and structures. Notification of any limbs overhanging or abrading buildings or structures. Notification of any footpaths and limbs overhanging them. Notification of any fences and property boundaries and any limbs or roots encroaching over the boundary.
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Adverse Tree Condition Notification of any adverse characteristics such as spiny limbs, poisonous fruits, likelihood of limb loss or collapse. Notification if the tree is partially unsafe or totally unsafe and any adverse conditions caused by the tree such as damage to building, structures, paved surfaces, underground or overhead services, fences or neighbouring properties.
Tree Work Notification of any tree work which is required to improve the tree or to reduce any risks to persons or property. Assessment of whether the tree work needs to be done immediately for personal or property safety, or requires attention in the next 12 to 24 months. Differentiation between the work that can be carried out by the owner and the work that should be done by a contractor.
Risk Management Action Following an Audit Should a tree audit highlight the need for removal or remedial treatment of a tree, it is prudent to carry out such recommendations using two levels or urgency as follows. For personal and property safety, action should be without delay through the Project Risk Manager. Refer also to Part 4—Development assessment, Division 1—General scheme, Subdivision 1—Approvals of the Development Act 1993 for details regarding approvals that may be required. For action benefiting the tree or for routine maintenance, action should be included in the contract documents.
References For further information regarding Regulated and Significant Trees please refer to the following links. Regulated and Significant Trees http://sa.gov.au/subject/Housing %2C+property+and+land/Building+and+development/Building+and+development+applications/ Heritage+listing+and+significant+trees/Regulated+and+significant+trees Protecting Regulated and Significant Trees http://sa.gov.au/upload/franchise/Housing,%20property%20and %20land/PLG/Protecting_Reg_and_Sig_Trees_Comm_Info.pdf
Contact For further information contact:
Adrian Swiatnik Supervising Civil Engineer Phone: 08 8226 5376 Email: [email protected]
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