In mid-September Canopy Keepers was contacted by a distressed resident from Palmgrove Rd, Avalon, regarding the deliberate poisoning of a magnificent tall grey gum on public land. It is always devastating to see such a selfish act, most commonly committed to achieve a “better” view. The tree still stands, with council planning to leave the dead trunk and branches as a reminder that killing a tree for a view often results in a worse one. But we have an additional plan!
Dead trees can still provide a valuable habitat service, because they often contain hollows that suit a variety of birds, mammals and even insects. Veteran trees with natural hollows are always the best, but with a little expert help, younger trees that have given up the ghost before their time can also house wildlife.
It’s been a long-term mission for Sydney Arbor Trees, who have turned their chainsaws and cherry pickers into instruments of preservation; creating artificial hollows inside the trunks and branches of dead trees. Their hollows are creative, well researched and functional, providing a variety of carved out spaces ranging from ‘bat flats’ and ‘mazes’ for microbats, to made-to-measure homes for small and large parrots and native mammals, with species specific ports of entry. The arborists also choose the most desirable orientation of the habitat for each animal, considering exposure to different weather conditions and predators.
Canopy Keepers are hoping to raise the funds to transform the dead tree into a multi-level home for a variety of animals. In the meantime, we talked to chief arborist Greg Thallon to find out more…
Why did you decide to start adapting dead trees for homes?
Sydney Arbor Trees (SAT) decided to get involved in Habitat Creation after attending a workshop in late 2013 held by the City of Sydney and former Marrickville Councils, run by arborists Ben and Phil Kenyon – the arborists that developed Habitat Creation for Australian applications.
At that time, Sydney’s tree population was being severely impacted after the introduction of the RFS’s 10/50 code, and the schools’ safety audit that was undertaken in reaction to the death of a student in Pitt Town, and SAT was becoming concerned over the increasing rate at which mature trees were being removed. SAT saw that Habitat Creation works were not being undertaken in NSW and decided to target that niche, for the benefit of our industry, the livability of Sydney, and the critters we share the urban environment with.
How does the creation of these hollows have a beneficial effect beyond the animals it houses?
Healthy ecosystems rely on a diversity of creatures to maintain balance, and urban environments are no exception. Ecosystems rely on vegetation for water and air quality, and vegetation relies on other organisms for services like pollination and controlling ‘pest’ populations. For these other organisms to be able to provide these services, they require places to shelter from predators and raise their young.
Dead wood and vegetation is the basis of most food webs, providing food for all manner of organisms which in return become food for larger organisms. Retaining dead trees and wood onsite – standing or as logs – retains this food source, and also allows the nutrients in the wood to be recycled back into the soil to be used by other vegetation.
Is it safe to leave a dead tree standing?
This usually depends on a few factors, and can be quite a complex assessment to make, and so should always be made by a qualified and experienced arborist.
The following need to be assessed at a minimum:
- The location of the tree and any nearby ‘targets’ (people of property that could be impacted if it fell over).
- The health of the tree, or if it has died, the likely cause.
– If the cause of death/decline is suspected to be any kind of root damage and/or dysfunction, the tree should not be considered for retention as a habitat stag unless there are no targets.
– If the tree still has a full canopy (whether poisoned or still alive) it can be safely assumed that the tree will remain standing after the canopy removed, as the forces acting on it (wind and gravity) are greatly reduced.
- The ability/willingness of the client to undertake ongoing monitoring of the tree (by a qualified and experienced arborist) to ensure the structure of the tree has not deteriorated.
It is important to understand that all trees are inherently dangerous (where targets exist), and so should be regularly maintained and monitored by a qualified and experienced arborist, especially after any significant events or changes at the site, such as construction works or severe storms or bushfires.
What’s the first thing you look at when you assess a tree for habitat creation?
There are 4 important questions to answer during the assessment of habitat tree candidates.
- Is the tree safe to retain (as described above)?
- Which animal/s would the client like to provide habitat for?
- Are those animals known to inhabit the area?
This often involves a search of the NSW Office of Environment and Heritage ‘Wildlife Atlas’, filtering for species that rely on hollows.
- Does the tree (once the canopy is removed) have branches/trunks with diameters and heights sufficient to install hollows to the specifications those animals prefer?
In instances where the tree does not have a suitable structure to install hollows for the desired species, a list of suitable animal species is provided for the client to choose from.
How do you go about creating a hollow?
Animal species tend to have specific requirements hollows they select, including (a) the internal height and diameter of the hollow, (b) the height above ground of the entrance, (c) the diameter of the entrance, (d) the orientation of the entrance, and (e) the proximity to other vegetation.
Once the animal species is decided, a suitable trunk/branch is selected and the arborist gets to work. SAT uses chainsaws to install hollows, but there are other tools and methods being developed and used elsewhere.
The installation process can be varied, but generally involves the following 4 steps:
- The removal of a ‘faceplate’ off the outside of the trunk/branch.
- The boring out of the internal chamber/s to the desired species’ preferences.
- The drilling of the entrance to the desired species’ preferences.
- The reattachment of the faceplate.
It should be noted that steps 1 & 2 involve ‘bore cutting’, which involves the insertion of the nose of the chainsaw blade into timber. This can result in ‘kick back’, which is extremely dangerous and should only be undertaken by experienced and proficient chainsaw users.
Is this something anyone can do with a handy chainsaw and a ladder? (what risks)
Definitely not. As described above, the selection of a good candidate tree should be undertaken by a qualified and experienced arborist, so as not to create hazards in the process. Similarly, the removal of the canopy should be undertaken by qualified and experienced arborists. Also as described above, bore cutting should only ever be undertaken by experienced and proficient chainsaw users.
As for a ladder, it is never recommended that tree work (other than maybe hedging) be undertaken off a ladder. Chainsaws and ladders often result in hospital visits when used together.
Have you been back to check on your creations – how do you know they work?
Approaching nests and hollows in trees should only be undertaken with appropriate scientific licensing, which SAT does not have, but where SAT has been involved in follow-up maintenance of habitat trees, we have observed signs of habitation such as egg shells, feathers and droppings.
Some habitat trees have been fitted with cameras, and some are inspected by ecologists at the clients’ behest, and we often receive feedback and photos from clients in relation to hollow uptake by animals. It is always a proud moment for us.
What are some of the more interesting animals that have taken up residence?
Given that the client decides which animal/s to install hollows for, and usually chooses animals they regularly see at the site, the animals that we tend to see taking up the hollows are the more common species such as Rainbow Lorikeets, Sulphur-crested Cockatoos, Galahs and Brushtail Possums.
We have installed hollows for all manner of interesting animals –Powerful Owls, Greater Gliders, Feathertail Gliders, Superb Parrots to name a few – but have not received feedback as to their uptake at this stage.
How is it possible to adapt living trees?
Given that the weight above where the hollow is to be installed must be reduced as much as possible, it is not possible to install hollows into a trunk of a tree that still has a full canopy. It is however possible to install hollows in branches that have had their end weight removed, but this often means removing a lot of foliage, which could impact the health of the tree.
SAT generally prefers not to work on live trees, as the work does not comply with the Australian Standard for tree pruning, although we hope the Standard may be modified to include habitat pruning in the future.
There are other ways of enhancing the habitat value of trees without cutting into them however. Probably most important is the concept of connectivity between canopies, so that animals can move between trees without having to come to the ground and expose themselves to predations from cats and dogs. This can be done by planting vegetation with a range of heights and canopy densities, or by installing ropes between trees for mammals to get around on.
Generally, SAT thinks the best form of creating habitat in trees is to leave the tree alone unless absolutely necessary for safety reasons. After all, trees have been creating habitat for millions of years without our help. The best we can do is promote good tree management and ecosystem health to increase the likelihood of trees living into maturity.