A preliminary investigation of the potential to determine the age of individual trees of Breonadia salicina (Rubiaceae) by relating xylem vessel diameter and area to rainfall and temperature data

The estimation of tree ages in southern Africa and in tropical, sub-tropica l and semi-arid areas in general, has been problematic due to the lack of d istinct growing seasons and corresponding climatic extremes. The lack of di stinct ring boundaries and the frequency of anomalous growth patterns have hindered the science of dendrochronology in southern Africa. An investigati on to determine the use of xylem vessel dimensions as a tool for tree-ring identification and age estimation of Breonadia salicina sampled in the Krug er National Park was made. Sections of stem disc samples were used. Trends in xylem vessel diameter (both radial and tangential) and area were examine d, both between trees and in relation to trends in rainfall and maximum tem perature data. It was possible to match anatomical trends between individua l trees by correlating chronological sub-periods from the discs. Similarly, linear regression analysis was used to match trends in xylem vessel diamet er and area to sub-periods of climatic pattern and thus determine dates for these chronological sub-periods from the disc samples. Of the three variab les measured, radial vessel diameter was the most sensitive to an annual ra infall mean (between July and June). Maximum temperature was found not to c orrelate to any of the three variables measured.