Management Plan for the Trees of the ANU

Features of the ANU treescape

The most obvious and valuable landscape feature of the ANU campus is its vast and diverse treescape. There are approximately 10000 trees on the campus and they can be divided into 3 categories:

Original trees which pre-date white settlement

These trees are the remnants of the savannah woodland which was a feature of the higher ground on the site, particularly Acton Ridge. (It is interesting to note that the bulk of the site was grassland.) The original trees include five species, Eucalyptus melliodora (Yellow Box), Eucalyptus blakelyi (Blakely’s Red Gum), Eucalyptus bridgesiana (Apple Box), Eucalyptus manifera (Britle Gum) and Eucalyptus rubida (Candle Bark)

On the basis of heritage significance the remaining original trees are the most important trees to conserve and protect on the campus. They are also the ‘bones’ which support the landscape structure of the campus. However, they are also not the easiest of trees to manage safely in a populated environment due to their habit of occasionally shedding limbs (despite the most intensive arboricultural management). They are also particularly prone to accelerated senescence being caused by root disturbance in the form of trenching within the root zone or soil compaction.

The public risk factor associated with these original trees may be minimised by regular inspections to monitor the health of the trees, restricting public activity under the canopy of the trees and enforcing a policy of no development or disturbance in the root zone of the trees.

Native and exotic trees planted after white settlement in the pastoral phase and then the Federal phase of the site

Prior to the ANU being established significant tree planting had occurred on some parts of site particularly in the areas in proximity to the old hospital buildings. In the 1920’s Thomas Weston was responsible for planting a wide selection of trees to trial their performance for future use. The selection included Australian native species from various origins, exotic deciduous trees and exotic coniferous trees.

The bulk of these plantings are valuable assets to the ANU treescape. However, the extensive planting of Eucalyptus globulus spp. bicostata (Blue Gum) was unfortunate because this species has proved to be very difficult to manage from a public risk perspective. Blue Gums are prone to being infected by wood rotting fungi that may severely weaken the structural framework of the main trunk or major branches. Given that it can grow rapidly up to a height of 40 meters the public risk implications are obvious. In addition, on a species by species basis the management of this species of tree consumes the highest proportion of the budget for tree surgery each year.

Native and exotic trees planted after the ANU was established in 1949

Extensive planting programs have proceeded since 1949 in association with the development of the campus. Various tree themes have evolved within the campus with areas of predominantly Australian native species, others with mainly exotic deciduous trees or conifers and some with mixed planting. Perhaps the most enduring philosophy for the planting theme for the campus is based on an image of the native landscape of Black Mountain sweeping over the campus being interspersed with pockets and avenues of exotic species.

The planting programs have not been executed with any special regard to potential building development. The attitude in the past was to plant extensively and never mind if trees had to be removed subsequently for buildings. Also, no special care was taken to position trees where they would have the least impact on underground services or pavements. This rather random approach to planting has its merits but the budget constraints of the 1990’s have led to the evolution of a far more exact approach to what is planted where.

The aim of managing the ANU treescape

The aim of managing the ANU treescape is to conserve and maintain the trees on the campus to maximise their aesthetic and amenity values and minimise their risk to public safety and damage to the infrastructure of the campus.

There are three basic pre-requisites in achieving this aim. Firstly, to employ staff who possess the appropriate knowledge, skills and experience in tree management and arboriculture and secondly, to ensure that achieving the aim is given high priority as part of their duties. The third pre-requisite is to allocate an appropriate amount of funding to be reserved for tree management.

The staff and structure of the F&S Grounds Section satisfy the three pre-requisites described above. One of the principal functions of the Assistant Grounds Manager (AGM) is to monitor the health and condition of all the trees and program all tree surgery work. The AGM has qualifications in horticulture and arboriculture and has an appropriate level of experience.

In addition, within the staff of the Grounds Section several staff are formerly qualified in the field of horticulture and have practical skills an experience in the operation of chainsaws which facilitates basic arboricultural activities.

F&S allocates 10% of the total annual grounds maintenance budget to tree surgery operations. This figure does not include salaries and dditional funds are allocated to the replacement of trees.

Description of the current strategy for managing the ANU treescape

Inspections

For the purposes of monitoring the AGM conducts regular inspections of the site with the intention of identifying any urgent problems and schedule routine tree maintenance. Particular attention is given to trees that are identified as hazardous or have been known to be problematic in the past. The inspection generates a list of work that is illustrated on a site plan. The type of work falls into one or more of the following categories;

  • Deadwooding
  • Removal of poorly formed or defective branches
  • Crown thinning/weight reduction
  • Formative pruning
  • Lifting to enable pedestrian or vehicle access
  • Roofline pruning
  • Power line clearance
  • Cable bracing
  • Tree removal

During the process of carrying out tree surgery operations the opportunity to undertake an upper canopy inspection is exploited. This inspection often generates more work to a tree and is usually undertaken while the Arborist is up in the tree. The exception is when advanced wood rot is discovered and a tree must be removed completely on safety grounds, in which case the AGM is first notified.

Work Scheduling

Once the site inspection is complete the AGM schedules the work in order of priority. Although the bulk of the tree surgery operations on the campus are carried out by Arboricultural contractors, the Grounds Section also carry out a range of basic Arboricultural operations. Staff are fully set up and confident in performing these operations. The true value of having this capability is reinforced during emergency situations when contractors are not immediately available.

Naturally any work associated with reducing public risk is scheduled first. In situations where work considered urgent cannot be carried out immediately the area concerned is barricaded off from public use and warning signs erected.

Reporting

Arboricultural work is often generated through reports via the following channels;

  • OH&S Hazard or near miss reports – usually eye hazards or line of sight problems
  • Building maintenance workers – Branches overhanging gutters or plant rooms or
  • access issues around buildings
  • Electricity Authority – clearing of overhead powerlines.
  • Community members – report hazards high in the tree canopy which may only be seen from a window of a multi story building.

Hazard reduction

Formative pruning is a valuable technique used to reduce the incidence of structural defects. This technique aims to prune early and in accordance with the natural form of an individual tree. The principles behind this technique include:

  • Removal of poorly developed or diseased branches.
  • Removal of multi stemmed leaders.
  • Removal of crossing branches.
  • Removal of branches where included bark is evident at the crotch or where the branch intersection forms an acute angle.
  • Good cultural practices such as supplying adequate irrigation/drainage, mulching, fertilising and pest control maintains trees in good health, this in turn reduces the risk of limb failure.
  • Tree protection – it is imperative to protect trees from physical damage including soil compaction. These activities can introduce secondary effects placing the tree under stress and therefore increasing the hazard of limb failure.

Tree removal due to public risk

All trees have the potential to be dangerous, but it is the position of a tree in relation to people, vehicles and buildings that may necessitate the removal of a tree on safety grounds. The decision process is often difficult when concealed structural weakness are discovered in prominent trees that otherwise appear healthy.

The sudden removal of such trees can result in spirited criticism. In such situations it is essential that the local community is informed exactly what is going to happen and why. In some instances the opinion of the Forestry Department is sought or a consultant is commissioned to undertake internal investigationsto establish the extent of a suspected structural defect. If all the information gathered indicates that the tree is dangerous in its position then its removal is scheduled as soon as possible.

Storms

The occurrence of violent storms can prompt a change in priorities, when all available resources are directed towards the clean–up. Failed branches and crotches expose defect trees which forces decisions to remove particular trees following storms.

Tree removal due to development

In recent years the University has embarked on an extensive capital works programme. Although every attempt is made to design around trees (particularly significant trees), inevitably development causes the loss of hundreds of established trees annually. Where practical, successful attempts have been made to transplant established trees that would have otherwise been sacrificed. This practice is considered expensive and as a result is reserved for particularly valuable trees of smaller dimensions.

Tree Removal due to interference with services

As previously mentioned the early tree planting programmes did not consider the universities future plans or underground services. As a result many trees have to be removed because they now interfere with services such as overhead cables, water mains, stormwater and sewer lines. Large trees are also removed as they interfere with buildings, paths and roadways. Trees that interfere with views and prevent a clear line of sight for road traffic are may also be considered for removal if pruning does not suffice.

Tree management with a digital tree survey

In 1998 the ANU Department of Forestry was commissioned to undertake a digital tree survey of the ANU campus. This Database includes over 10,500 trees, each with detailed information including: genus and species, ID number, position, dimensions, health and a maintenance record of each tree. The use of the survey as a management tool is enhanced by its flexibility.

The type and range of information that the survey is capable of producing facilitates the processes of inspecting and scheduling tree surgery operations. The survey can produce images of all or part of the site with a variety of tree data ranging from all trees to a vast selection of fields such as individual species, all trees above a certain size, all remnant trees or unhealthy trees.

Prior to inspections the survey may also be used as a reminder of trees that have had problems in the preceding twelve months. Printed extracts from the tree survey are used to graphically describe tree maintenance work to contractors and staff. These plans identify individual trees and describe the specific nature of the work required. On completion these records are entered into the database. Following regular updating of the survey this data will form the basis for forecasting future budget needs.

The digital tree survey makes the task of managing the treescape a more exact process which is protected from the problems associated with a key member of staff leaving the ANU with all the crucial tree knowledge in his/her head. Having a detailed record including a history of events on each tree, aids when defending public liability claims or when pursuing compensation claims when trees have been damaged.

Classification of individual trees

For the purpose of organising and separating records each tree has been classified according to a particular value, these classes are separated further between deciduous and evergreen species. For the purpose of keeping an historical record, the identity and location of trees that have been removed remains within the database and their position is normally hidden. Trees are rated as EXCEPTIONAL, HIGH, MEDIUM OR POOR. These classifications have an influence over the development of the campus because a priority is given to retaining and protecting exceptional and high quality trees. Detailed information relating to the protection of trees during the development of the campus is contained in the landscape protection guidelines.

The following criteria is used to classify trees on the ANU campus:

Exceptional

To be classified as exceptional a tree must satisfy one or more of the following criteria -

1. Compositional
  1. The tree is a prominent individual in the campus landscape.
  2. The tree is one of a group which is prominent within the campus landscape.
  3. The tree or group is an element of a purposeful composition and this composition is a readily identified part of the campus identity.
2. Historical
  1. The tree is associated with a person or event important in the development of the University or, by implication, important in a realm beyond the University.
  2. The tree was specifically planted to commemorate a person or event important in the development of the University or, by implication, important in a realm beyond the University.
  3. The tree remains from a planting of the site prior to its use as a University campus.
3. Natural History

The tree is probably a part or a direct descendant of the forest cover of the site prior to non-indigenous occupation.

4. Rarity

The tree is a species that is rare in Canberra.

5. In Addition

No tree is rated as Exceptional if it is not in good condition unless it ranks so highly under one or more other criteria that special provisions (eg denying people access within its canopy) are warranted.

High

To be classified as high a tree must be well established, have good form, vigour, and health and be of sound condition. The majority of trees on campus fall under this category.

Medium

A tree may be classified as medium if it is immature and is not yet well established. A tree may also be classified as medium despite being well established if it shows poor form or has become suppressed.

Poor

Trees that are suppressed, diseased or are structurally unsound. A tree may be classified as poor despite having the general appearance of a high quality tree. Once identified as poor such trees are generally scheduled for removal particularly if the tree represents a public liability.

Summary

The trees of the ANU campus have high aesthetic and ecological value and are held in high regard by the management and general community of this university. Substantial funds are allocated each year to managing this natural resource that is in a constant state of change. The primary aim of the tree management plan is to maintain our trees in a healthy and safe state and to protect and retain them as a dominant feature of the ANU campus.