Using growth-form attributes to identify pre-settlement woodland trees in central NSW, Australia

Old-growth woodland trees perform many important ecological functions, by providing critical fauna habitat and in sustaining biological diversity. Australian woodlands are dominated by box Eucalyptus species, which are difficult to age accurately using dendrochronology and other well-practiced methods. We aimed to develop a simple field method for identifying pre-settlement (old growth) Eucalyptus trees in south-eastern Australia, using measurements of tree growth-form attributes. We used TwoStep cluster analysis to classify and independently assess trees, and logistic regression analyses to develop models to identify pre-settlement trees in the field based on recorded attributes. Post-settlement (regrowth) trees tended to have a very uniform appearance, whereas the growth-form of older pre-settlement trees greatly varied, in terms of the number of stem and pipe hollows, and number of primary and secondary branches. This clear discrimination between cohorts of trees is discussed in terms of historic changes to disturbance regimes, and resultant impacts on remnant woodland structures. Our results provide a robust method for reliably identifying pre-settlement Eucalyptus trees in the field using tree growth-form measurements, and have broader implications for identifying age cohorts of forest and woodland trees elsewhere