Tree Hollows - update


In response to suggestions and requests from a number of people, we have recently enabled the recording of 'trees hollows' on NatureMapr.

And with the launch of the Mapping Glossy Blacks project, mapping tree hollows now has a clearly defined purpose.

Tree hollows can vary in size and type, from tiny knot holes to huge open spouts. Hollows of all sizes provide important habitat. However, it is the larger hollows which are of most interest and concern.

And it is these large, open hollows which we particularly encourage you to record as sightings.

Why is it useful to map tree hollows?

Large hollows form in large trees, and most often in senescent or dead trees.

And large dead or damaged trees are the very trees that tend to be lost from the landscape. They are deliberately burned or felled, or ultimately decay through natural causes. Given their critical importance to many species – including to Glossy Black-Cockatoos - trees bearing large hollows are deserving of protection. 

Knowledge of the location of such trees can assist land managers in decision making and planning. 

How do I record a Tree Hollow sighting?

Photograph the hollow, and the whole tree. Also include photos of the bark, leaves, and any (accessible) fruit or flowers.

Here is an example of recording a tree hollow sighting in a tall eucalypt. 

Note that with all plant records you are asked to specify the plant size (i.e. height). In this example, it's a large tree.

Flower dimension is probably not relevant, as any flowers present are likely to be well out of reach. This can be left blank.

Hollow type is important information. For example, Glossy Black-Cockatoos favour spout hollows.

Finally, measure the diameter of the tree at chest height. 

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Why not just add 'tree hollow' as additional information under tree species?

We did consider this approach, and it has merit. After all, the whole concept of the database recordings are built on identified species. This is the approach adopted by Canberra Nature Map.

The Atlas of Life groups have chosen to make Tree Hollows a special case, because many of the most valuable hollows are in long-dead trees which cannot be readily identified to species.

Whichever system is used, the recordings provide valuable data.

More information about tree hollows

Many animal and bird species are dependent on tree hollows, as nest sites during breeding season, or as year-round retreats and roosts.  

Here is an extract from a conservation management note published by the National Parks & Wildlife Service in 1999.

  • Hollow formation is dependent on a tree’s history, its species and location. Generally, small hollows with narrow entrances suitable for small animals such as the brush-tailed phascogale (Phascogale tapoatafa) and the eastern pygmy-possum (Cercartetus nanus), take about 100 years to form. Hollows of a medium size and suitable for animals such as parrots will take around 200 years to form, and the larger and deeper hollows occupied by glossy black cockatoos (Calyptorhynchus lathami) and other larger animals such as masked owls (Tyto novaehollandiae) can take a lot longer (Mackowski 1984; Menkorst 1984; and Scotts 1991). 
  • Valuable hollows for wildlife are generally found in mature and dead trees. Openings range from as small as 2 cm to as large as 75 cm, with depths ranging anywhere from 10 cm to 10 metres (pers. comm. Kavanagh). 

Some of the facts about the formation of tree hollows, and the extent to which species depend on them, may come as a surprise. The short paper is well-worth reading in full - click here to download as a pdf.

Examples of a range of hollows
From this collection, highest priority should be given to mapping A, C, D, F, G & H. 
These hollows are all located within two hectares of forest in the south of the Atlas of Life region.