Using Banksia (Proteaceae) node counts to estimate time since fire

Abstract

In Australia, numerous methods have been used to determine the time since the last fire at a given site. One method involves counting the number of annual growth nodes on Banksia spp. that are either killed by fire, or regenerate from surviving rootstocks, to determine above-ground plant age. Although a number of studies have used the Banksia node-count method to estimate plant and therefore site age, no published data assess the reliability of this method. This study attempted to determine the accuracy of the method, with shrub-form B. marginata individuals from five sites of different age, in a south-eastern Australian sand heath. A significant relationship was found between modal node (internode) counts and the known time since fire, with internode counts at four of the five sites accurate to within 1 year of actual site age up to 21 years (n > 50 individuals per site). The results suggest that the Banksia node-count method is a useful tool for determining site age up to 21 years. However, sample sizes need to be appropriate for the area sampled, given the potential error in counting nodes and the inherent site variability in age classes.