Bark thickness equations for five commercial tree species in regrowth forests of Northern New South Wales

Bark thickness at any point along the stem of eucalypt regrowth tree species is related to over-bark diameter at that point, height above ground at point of measurement along the stem, total tree height and breast height diameter over-bark. Equations have been derived for predicting bark thickness as a function of these variables and of over-bark diameter along the stem. Using these equations eliminates the need for routine bark-gauge measurements and their associated measurement errors and helps to accelerate the derivation of more precise stem volume functions. When used in conjunction with a tree or log taper function, the equations can provide estimates of the volume of bark resulting from harvesting and available for utilisation. Using data collected for taper and volume functions development for the Resource and Management Evaluation System at State Forests of New South Wales, nine different bark thickness equations were fitted for Eucalyptus pilularis, E. obliqua, E. andrewsii, E. saligna, and Corymbia maculata growing in northern coastal areas of New South Wales. Comparisons using fit statistics for all species and test statistics based an independent data set for E. pilularis, show that some equations were systematically biased for all species and it was recommended that they should not be used. The equation developed by Cao and Pepper (1986), labelled equation [8], was found to be the most consistent for all species.