Habitat tree retained, a joint AGL Southern Hydro - McConnell Dowell environmental initiative
A large, mature Alpine Ash (eucalyptus delegatensis) has been retained as part of a joint AGL Southern Hydro and McConnell Dowell initiative to minimise impacts of the Bogong Power Station construction on the surrounding environment.
The tree which has been retained offers significant habitat to a range of native species with potential roosting, nesting, refuge and breeding sites in its limbs and hollows.
From a safety perspective the tree has been identified as unstable and at risk of falling, though recognition of these habitat values has lead to works being undertaken to support and retain this valuable asset.
Safety - Hazard identification and risk assessment
As part of McConnell Dowell's hazard identification and risk assessment process, a qualified arborist (tree doctor) was engaged to carry out an inspection of the structural stability of all trees on and surrounding the main work sites. The purpose of this inspection was to identify and trees that had the potential to impact on site workers, site plant and infrastructure.
The main finding of this arborist's inspection was that this large Alpine Ash located below the viewing platform at the Power Station site was quite unstable and was at risk of falling. The instability of this tree has been caused as a result of fire damage, insect attack and the tree's limb position, all combined with old age.
Other findings of the inspection have led to the pruning of overhanging tree limbs and tree canopy reduction works on other trees around the work sites. The Alpine Ash (habitat tree) was the only tree recommended for removal or to have works undertaken to support and stabilise it.
Tethering the habitat tree - 6th June 2007
The habitat tree has three slings attached to its main trunk. The slings are made of polyester which combined with the width of each sling aims to minimise rubbing and further damage to the tree.
The top and bottom slings have cables attached which run to a second tree upslope with the same type of slings fitted around the base. This second tree is structurally sound and will act as an anchor point to support the habitat tree. The cables can be tensioned if required via turn buckles. Care has been taken to leave these cables loose enough to allow natural movement of the tree in windy conditions.
The third, middle sling on the habitat tree has a separate cable attached and this cable runs to the base of another structurally sound tree across the slope to the north. Again this cable is attached via the same type of sling and has a turn buckle in line as a tensioner. The aim of this cable is not to anchor and support the habitat tree but to influence the direction of fall should the habitat tree fail. It is thought that less damage to plant, people and infrastructure will occur if the tree falls in this northerly direction rather than directly down slope onto the work site.
The tree will be monitored during the project to detect any significant movement that may suggest further instability and an increased risk of failure.
At the end of the project, when there are no personnel, plant etc. left on the site, the slings and cables will be removed from the habitat tree. It is hoped that the tree will defy its declining condition and continue to stand for many years to come as a habitat for local wildlife.
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Four species of quolls occur in Australia. Most parts of Australia were once inhabited by at least one quoll species and they were among the first native animals to be described by European scientists.
The tiger quoll, or spot-tailquoll, is the largest marsupial carnivore (a carnivore is an animal that preys on other animals) surviving on mainland Australia.
All quoll species have declined in numbers since European settlement in Australia. This is because of habitat loss and habitat change across the land, and due to introduced predators such as foxes.
What do they look like?
Tiger quolls are more than 50% larger than other quolls and, unlike other quoll species, have white spots that extend along their tail.
They have a pointed snout, a long tail and are lively and sometimes aggressive. They have bright eyes, a moist pink nose and many sharp teeth. Their fur is a rich rufous (red-brown) to
dark brown above, with white spots of varying size, pale below. Their fur also has a coarse texture.
Where do they live?
The basic requirements for most species are food, shelter and space. Tiger quolls are found
in a range of forest habitats, from rainforest to open woodland. They require forest with
suitable den sites, such as rock crevices, boulder tumbles, caves, hollow logs, burrows and tree hollows.
The tiger quoll has a large home range and can cover considerable distances (over 6km) overnight. They are largely nocturnal and solitary.
The tiger quoll was once common throughout south-eastern Australia, including Tasmania. However, since European settlement, they are now rare across most of their range.
What is threatening them?
Adult tiger quolls have a ‘territory’ of up to 500 hectares. There are few areas where such territories exist without quolls encountering the effects of humans. This makes them particularly susceptible to a number of threats. These include:
- Scattered populations: Populations of tiger quolls are now scattered and hence vulnerable to chance events such as bushfires and disease.
- Land clearing: Loss and fragmentation of habitat are a primary threat to this largest of Australia's marsupial carnivores, especially areas of suitable forest with sufficient numbers of den sites and prey.
- Introduced competitors: Competition for food with introduced foxes and cats, as well as possible predation on young quolls by these introduced species may also threaten them, although whether this is a problem is still unknown.
1080 baits: 1080 baits are used to control fox and wild dog numbers. Unfortunately, female
and juvenile quolls are especially susceptible to 1080 baits. It is vital that when 1080 baits are
used, best practice management guidleines are employed, in order to keep impacts to native
species to a minimum.
- Fire: Since tiger quolls favour dense habitats with maximum fuel loads on the forest floor, burning is also likely to threaten the species.
For more information, please see the Australian Threatened Species Fact Sheet.
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