14C dating of tree falls on Barro Colorado Island (Panama): a new method to study tropical rain forest gap dynamics

Abstract

A new method for investigating the age structure of the patch mosaic of a tropical forest by utilizing radiocarbon dating techniques on fallen trees is proposed. Aboveground nuclear explosions in the early 1960s, before the nuclear test ban treaty, created a spike in the 14C concentration content of the atmosphere. The amount of radiocarbon in the outer layers of wood collected from trunks of trees that had died in known years (1970–1989) on Barro Colorado Island (BCI) and Gigante Peninsula (Panama) was analysed to test the hypothesis that radiocarbon concentration was predictive of year of tree death. The date of tree death was negatively related to the level of 14C, following a trend similar to published data on tree rings from German and Amazonian trees. Combining our data with these data in a statistical analysis revealed a significant predictive effect of radiocarbon on year. Analysis of covariance showed that there was no significant difference among the slopes of the three groups of data, but there was significant heterogeneity among the intercepts. The differences suggest a need for site-specific calibration and refinement of field protocols. The technique shows promise and suggestions are made to improve its usefulness for future studies.