Prepared by Patrick and Philip Kenyon – VTIO Victoria
24 September 2010
Approximately 300+ species of wildlife use tree hollows throughout Australia. Tree hollows are of great importance as they are used as nesting sites, shelters and safe refuges. Hollows can present as a small crack or split into a very large cavity in the tree. (Gibbons & Lindenmayer, 2002).
The Arboricultural Industry has gradually become aware of the importance of habitat trees as part of an active ecosystem. The creation of artificial habitat hollows in dead, dying or living trees is developing rapidly within our Industry.
This workshop is aimed at habitat awareness and to further develop methods and ideas to create artificial habitat in trees whilst maintaining the trees basic integrity.
When managing large dead trees in the landscape, the current management practice is to reduce the tree to a point where it is unlikely to present a risk to people and infrastructure. These trees are usually dead, dying or declining and are left as habitat stumps. The habitat stump has a high proportion of sound wood (very little decay) which has very little value to wildlife, as there are very few usable hollows.
Natural hollows are formed by the process of failure and decay within a tree. It can take up to 120 -150 years in many tree species for natural hollows to develop (Mackauski 1984, Stoneman et al.1097, Warnington and Lamb1999 in Gibbons & Lindenmayer, 2002). By developing a range of strategies it is possible to shorten this long-term decay process and provide natural-looking habitat by creating artificial wildlife hollows.
We have so much to learn about the habitat requirements for many species of birds, reptiles, amphibians, mammals, and insects that utilize habitat in trees. It is hoped that this workshop will stimulate some research to further develop the level of knowledge and methods being used. There is a strong school of thought that trees that can develop habitat hollows are able to sustain better survival in some environments.
Without a doubt, habitat is a vital factor in the health of the overall urban forest.
List of points that may need to be considered (Some need further research)
- Entrance Vital (see attached chart.)
- Aspect. Openings faced away from worst weather.
- Temperature. Warm and ventilated.
- Waste drains out of nest.
- Landing platforms. Required by some hollow users.
- Escape ladder for young.
- How many habitat sites in each tree.
- How close can each site be situated.
- Discouraging feral and predator animals.
- Light exclusion for owls and some bats.
- Height of lip in the (Kookaburra chickens point their rear over the edge during toilet training)
- Complimentary planting to provide, food, cover and aesthetic screening.
- Retain any natural habitat if possible.
- Can habitat be created in live branches without compromising safety.
- Can a branch collar be developed by constricting sap flow at the collar site?
- Methods of removing branches and leaving ‘natural’ habitat ends.
Methods of creating habitat hollows and cavities in standing trees and branches.
Method 1: Trunk Hollows
This is a procedure to make artificial hollows in habitat stumps on vertical sections.
Identify a tree that can be retained as a habitat stump rather than complete removal. Remove the canopy back to a level that is acceptable to reduce the target area or risk of limb failure. Retain any existing hollows if possible. (See Figure 1 and Figure 2).
Identify suitable locations for new hollows.
Remove a faceplate approximately 30mm to 50mm thick and lower it to the ground. See Figure 3 and Figure 4.
The size of the face plate removed will determine the size of the artificial hollow
Choose the desired entrance hole and carefully drill through the faceplate. Pre drill two holes to attach the faceplate back on to the tree with screws. See Figure 5 and Figure 6
Mark out the size of desired cavity with boring cuts. Once you know the desired depth of the cavity, draw a line on the chainsaw bar with a marker pen, so that each boring cut is similar in depth. Carefully use a small chainsaw to carry out a series of horizontal boring cuts. (Rollomatic E Mini with picco micro chain is very good for boring cuts). See Figure 7 and Figure 8
Use a small crowbar and hammer to break out sections and form the cavity. Once this has been done, carefully tidy up the rough interior with the chainsaw. See Figure 9 and Figure 10
Retrieve the face plate and screw into position.
Method 2: Branch Hollows
First a suitable branch or stub is selected. Ensure the branch diameter is no less than 150 mm for this method
Remove the excess length of the branch safely, leaving a stub of at least 300mm in length.
Cut a sloping section off the end of the stub. Angle the cut at approximately 30 degrees. Cut a face plate off the stub following the same angle. The face plate should be approximately 20mm minimum depth. The face plate should be angled to shed water.
Use a small chainsaw to very CAREFULLY bore into the sloping cut end of the stub. This boring cut should only be undertaken by experienced operators.
Remove the core to create a hollow. The hollow can be left open or the face plate re-attached and an entrance hole drilled.
Select a spot for the entrance and use a suitable drill to bore an entrance hole. Entrance holes can be through the face plate, in the side or from the underside. Boring large holes is a little difficult. Reattach the face plate with screws or nails. Drainage holes may also be required.
- Gibbons, P. & Boak, M., 2000, The Importance of Paddock Trees for Regional Conservation in Agricultural Landscapes, New South Wales National Parks and Wildlife Service.
- Gibbons, P. & Lindemayer, D., 2002, Tree Hollows and Wildlife Conservation in Australia, CSIRO Publishing, Collingwood.
- Victorian Tree Industry Organisation (VTIO), 2010, Tree habitat sizes, www.vtio.org.au/Content/?s=habitat
- Grant J. 1997. The Nestbox Book, Gould League Of Victoria Inc.