Patrick J. Baker, Sarayudh Bunyavejchewin, Chadwick D. Oliver, and Peter S. Ashton. 2005. Disturbance history and historical stand dynamics of a seasonal tropical forest in western Thailand. Ecological Monographs 75:317–343.

Appendix B. Description and evaluation of Duncan’s (1989) method for estimating the distance to the pith from an incomplete tree core.

For a tree core that has missed the pith, the length of the missing radial distance to the pith is obtained using the following equation:

where L is the length of and h is the height of the largest complete ring arc (Duncan 1989). The number of rings to add was calculated by dividing the missed distance to the pith by the mean annual radial increment. To assess the accuracy of Duncan’s age adjustment technique, we compared the tree-ring age and estimated age to the pith in those trees in which at least one core struck the pith and at least one core did not. In general, Duncan’s method generated very good total age estimates. Of the 45 cores tested, only 13 (28.8%) had adjusted ages that were >5 yr different from the true age. Adjusted ages tended to be slightly greater than the true ages (Fig. B1). In addition, variation in the age adjustment errors increased with increasing age, although there were no obvious biases in the age adjustment errors relative to missed distance from pith (Fig. B2). Overall, these results suggest that age adjustments to account for missing the pith based on Duncan’s method were a minor source of error in estimating the establishment date of the study trees.

FIG. B1. Assessment of Duncan’s method for estimating number of missing years in incomplete tree cores. Ages are compared for individual trees in which at least one core struck the pith and at least one core did not.  For the cores that did not strike the pith the distance to the pith was calculated using Duncan’s (1989) method. The missing number of years was obtained by dividing the distance to the pith by the mean annual radial increment of the entire core. The line in the graph represents a 1:1 relationship in which true age (taken from the core with the pith) equals the adjusted age (calculated for the cores that missed the pith).

FIG. B2. Comparison of age adjustment errors and estimated distance to the pith. Age adjustment errors were calculated for those trees in which at least one core struck the pith and at least one core did not.

LITERATURE CITED

Duncan, R. P. 1989. An evaluation of errors in tree age estimates based on increment cores in kahikatea (Dacrycarpus dacrydioides). New Zealand Natural Sciences 16:31–37.