Age estimation of juvenile stages of Dracaena cinnabari Balf. F., the last stone in the mosaic of knowing its lifespan

Abstract

This article presents the methodological approach of age estimation of juvenile Socotra dragon’s blood trees (Dracaena cinnabari Balf. F., DBT) for the first time. To date, only the model for the age estimation of the tree crown after the first flowering event has been published. The DBTs were measured on Socotra Island (Yemen), on the Firmihin Plateau. A set of three indirect growth models was used for the estimation of the juvenile phase duration. The first model shows the relationship between the proportion of stem cavities and diameter at breast height (DBH). The second model describes the relationship between the DBH and stem height of juvenile trees. The third model expresses the radial stem increment with an increasing number of branch orders. The first model estimates the ratio of the stem cavity and secondary vascular tissue. The second model serves to retrospectively estimate the DBH of the tree at the time of the first flowering event according to the height of the stem. Extrapolation of the third model enabled us to estimate the duration of the juvenile phase that corresponds to the thickness of the secondary vascular tissue. A non-destructive methodology for juvenile DBT age estimation was developed, although the calculated absolute values are not precise. The same approach can also be used for the other arborescent dragon tree species. The validity of our assumption should be verified by repeated measurements on trees from different age groups. And thus, more precise model with less uncertainty about the parameter estimates could be obtained in the future.