Tree hollows and significant habitat trees in Australia

Loss of hollow bearing trees is a significant factor in the extinction and near extinction of many species.

The purpose of this project is to provide data to protect existing and future hollow-bearing trees and significant habitat trees, and to display their beauty and function.

The records of the locations and nature of the trees can be used by a number of organisations whose activities impact the survival of these trees.

For instance, forestry and rural fire services can implement strategies to protect the trees during hazard reduction burns in the same way that they check for, and protect, listed endangered ecological communities.

Councils made aware of hollow bearing trees on development sites can give consideration to the trees' protection when deciding development applications, and can safeguard trees in the lands that the councils manage.

The records of the trees will assist land managers generally to manage hollow resources sustainably.

Tree hollows

Tree hollows are used by more than 300 vertebrate species native to Australia, for whom the hollows provide thermal protection, shelter, sites for rearing young and facilitate ranging behavior and dispersal, protection from predators and sometimes food and water sources.

15% of all native terrestrial vertebrate species use hollows. More than 100 of these species are listed as rare, threatened or near threatened in state or federal legislation.

It has been observed that at least 27 amphibians, 79 reptiles, 114 birds and 83 mammals species are obligate users of hollows. 13% of terrestrial amphibians, 10% of reptiles, 15% of birds and 31% of mammals use hollows. (1)

Tree hollows form as a result of natural events such as fires, windstorms and lightning that damage the trunk or branches. Termites, fungi and bacteria then invade the ‘wound site’ and promote the decay of wood.

The process of hollow formation takes a long time. Hollows suitable for vertebrate species rarely occur in eucalypts less than 120 to 180 years old.

Small hollows with narrow entrances (less than 5cm), suitable for small animals such as the brush-tailed phascogale, take more than 100 years to fully form.

Hollows of a medium size (5-15cm), suitable for animals such as parrots, may take up to 200 years to fully form.

And the larger (greater than 15cm), deeper hollows occupied by animals such as the powerful owl will take at least 220 years to form.

Tree hollows are becoming rare as the number of old trees continues to diminish. In cities, towns and gardens, due to fears of falling branches, not many trees are allowed to reach the age at which they start to form hollows.

This project includes observations of tree hollows in living and in dead trees, and in significant logs.

A note in the Observation fields asks whether European honey bees are seen swarming at the hollow. Scientific committees in Australia, both state and federal, have recommended listing the feral European honey bees as a key threatening process under endangered species legislation.

European bees not only compete with native species for pollen resources, but they also compete for tree hollows. They swarm, stinging, and engulf the native occupants of hollows until they leave or die, in order to set up hives in the hollows.

The other question in the Observation fields asks for an estimate of the the size of the hollow, either in approximate dimensions or by considering the size of an animal that the hollow might be big enough to house. ie Would it be suitable for a small bird like a wren, a medium sized mammal like a Ringtail possum, or a large bird or animal like a large Brushtail possum or a Powerful Owl.

An additional note giving estimates of the approximate dimensions of the hollow entrance would be an interesting addition, especially for large hollows..

Significant habitat tree

A significant habitat tree has been defined as “standing live or dead trees providing ecological niches (microhabitats) such as cavities, bark pockets, large dead branches, epiphytes, cracks, sap runs, or trunk rot”(3). These microhabitats are used by a number of animals, plants, and fungi as a place to live, forage, and breed.

These trees may be important sources of nectar, foliage, fruits and seeds.

The tree’s branch structure may provide roosting and nesting sites

The bark might be deeply fissured, or may be shedding in long ribbons, providing shelter, nesting material and hunting grounds for many reptiles, birds, bats and insects.

Mature habitat trees also contribute significantly to the litter layer and fallen timber in patches of native vegetation

Even if only single paddock trees remain, they may provide habitat that is critical to the survival of native plants and animals, including threatened species.

Dead standing trees can be significant habitats by providing shelter and perching sites for wildlife. This supports social interactions, such as mating and territorial displays, and predators such as raptors use the clear lines of sight for observation.

Features of habitat trees may include dead branches, lichens, mistletoes, moss mats, epiphytes, fungal fruiting bodies, conks and other fungi, basal cavities, off ground cavities and fissures, vertical and horizontal spaces, delaminating bark, large vertical cavities, small horizontal cavities, ferns and green foliage, and understorey plants.

Habitat features of trees may be noted if they are not apparent in the photos of observations added to this project.

...............................................................................................................................
Banner photo of possum in branch hollow by Matt Anderson at
https://www.inaturalist.org/observations/41749584

Icon photo of possum in trunk hollow by Tanya Hattingh at
https://inaturalist.ala.org.au/observations/114176238
…………………………………………………………………………………………………………

Please also see the associated iNaturalist project:

Unusual or unnatural shelters used by Australian wildlife at
https://www.inaturalist.org/projects/unusual-or-unnatural-shelters-used-by-wildlife-in-australia
………………………………………………………………………………………………………….

References

1 Tree Hollows and Wildlife Conservation in Australia Philip Gibbon and David Lindenmayer CSIRO 2002 https://www.publish.csiro.au/book/3010/#:~:text=Tree%20Hollows%20and%20Wildlife%20Conservation%20in%20Australia%20is%20the%20first,practical%20approaches%20for%20land%20management.

2 Recognising Habitat NSW Local Land Services 2016 https://www.lls.nsw.gov.au/__data/assets/pdf_file/0011/1277498/8340_PPW_LLS-Recognising-Habitat_compressed.pdf

3 Habitat trees: Key elements for forest biodiversity Bütler, R., Lachat, T., Larrieu, L., & Paillet, Y. (2013). In Focus—Managing Forest in Europe (2.1). https://www.researchgate.net/publication/308050296_Habitat_trees_Key_elements_for_forest_biodiversity

4 Features of habitat trees, Arboriculture International 2015 http://www.arboriculture.international/environmental-1#environmental

5 Feral European bees background, Western Australian Museum
https://museum.wa.gov.au/explore/online-exhibitions/cockatoo-care/feral-bees less ↑