Living in the gaps – the vital role of tree hollows

A Barking Owl (Ninox connivens) taking refuge in a hollow at South West Rocks. Photo by – Trevor Bullock

Across New South Wales, hollow-bearing trees are critical habitat for at least 174 native Australian species, including 40 that are listed as threatened[1]. These natural cavities are essential for a wide range of wildlife, including mammals, birds, reptiles, amphibians, and countless invertebrates. They offer safe spaces for shelter, nesting, and breeding. In many cases, the survival of these species depends on the availability of tree hollows.

The NSW Government, Department of Environment and Heritage has produced a page and a series of short videos showcasing the importance of hollows and how landholders can protect them. Head to the bottom of this article to check them out.

What Are Hollows and How Do They Form?

Tree hollows are holes that form over time in the trunks and branches of living or dead trees. These hollows result from natural processes such as wind damage, lightning strikes, fungal decay, and termite activity. They can take hundreds of years to develop and are not features that can be quickly replaced.

Small hollows, which may be suitable for species like the Brush-tailed phascogale (Phascogale tapoatafa) or Eastern pygmy-possum (Cercartetus nanus), can take 80 to 100 years to form.
Medium-sized hollows, used by birds such as the Superb parrot (Polytelis swainsonii), typically develop over 150 years.
Large hollows, which are deep and wide enough to support species like the Powerful owl (Ninox strenua) or Glossy black cockatoos (Calyptorhynchus lathami), may require 200 years or more to fully develop.

Hollows occur in a variety of native tree species, typically older eucalypts and other long-lived trees that dominate the Australian landscape. Because of this, the protection of mature trees is crucial.

Why Are They Under Threat?

Hollow-bearing trees are quickly declining due to ongoing pressures such as land clearing for agriculture, development, and infrastructure; intense and frequent bushfires that destroy mature forest; and a lack of recruitment, where younger trees aren’t given the chance to grow old enough to form new hollows.

With so few mature trees remaining in many areas, it’s becoming harder for wildlife to find the safe spaces they need to survive and thrive.

How Landholders Can Help: Fire Protection and Beyond

Landholders and land managers play a key role in preserving the ecological value of hollow-bearing trees. One of the most immediate threats is bushfire, which can destroy both living and dead hollow-bearing trees in a single event.

To help protect these vital habitats:

Clear leaf litter from around the base of hollow-bearing trees.
Wetting down the base of at risk trees and logs in preparation for a prescribed burn.
Avoid removing old or dead trees and fallen logs despite the impulse to ‘make tidy’ as they are likely still providing habitat.

For detailed guidance, download the Hollows fact sheet

The Benefits of Keeping Hollows on Your Land

By supporting wildlife, hollow-bearing trees provide direct and indirect benefits to the land:

Improved water and nutrient cycles and overall soil health.
Help maintain a biodiverse landscape, which supports pest control, seed dispersal, and ecological resilience.
Provide shade and shelter for livestock, improving animal welfare in hotter months.

Watch this short video from NSW Environment and Heritage to hear how local farmers are seeing real benefits from conserving hollow trees on their properties.