Using tree hollow data to define large tree size for use in habitat assessment

ABSTRACT

Habitat assessments often require observers to estimate tree hollows in situ, which can be costly, destructive and prone to bias. An alternative is to count the number of trees above a specific size. The size at which a tree develops hollows differs substantially among tree species. To assist with setting standards for habitat assessment we defined a large tree as the size at which a species has a 50% probability of supporting a 2-cm diameter hollow. We estimated this size for 68 species using a meta-analysis based on 18 data sources. We found that large tree size ranged from 21 to 106 cm diameter at breast height (DBH). Each species was attributed to vegetation types (formations and classes) to explore variation in large tree sizes. Despite considerable variation within vegetation classes and formations, our results suggest that a large tree size of approximately 50 cm DBH may be appropriate for most vegetation types, with lower estimates in semi-arid vegetation (~30 cm) and higher estimates in wet sclerophyll forests (~80 cm). Our estimates provide empirical support for defining large trees at species vegetation class and formation levels within New South Wales, and highlights the need for more empirical data.

KEYWORDS:

• habitat quality
• tree cavity
• habitat condition
• vegetation condition
• biodiversity metric
• biodiversity indicator
• biodiversity benchmarks

Acknowledgements

We would like to thank Laura Kuginis for assistance with collating the tree hollow dataset; Shawn Capararo for collating and managing the OEH vegetation function dataset that is the basis for this work and Eve Slavich for statistical advice.

Supplementary Material

Supplementary datas for this article can be accessed here.

Additional information

Funding

This work was supported by the NSW Office of Environment and Heritage.