Age structure and growth of Dracaena cinnabari populations on Socotra

Unique Dracaena cinnabari woodlands on Socotra Island—relics of the Mio-Pliocene xerophile-sclerophyllous southern Tethys Flora—were examined in detail, especially with regard to their age structure. Detailed statistical analyses of sets of 50 trees at four localities were performed in order to define a model reflecting relationships between specific growth habit and actual age. The problematic nature of determining the age of an individual tree or specific populations of D. cinnabari is illustrated by three models relating to orders of branching, frequency of fruiting, etc. which allow the actual tree age to be calculated. Based on statistical analyses as well as direct field observations, D. cinnabari populations on Socotra do not regenerate to a great extent and their age structure generally indicates overmaturity. The unique Firmihin D. cinnabari woodland will reach the stage of intensive disintegration within 30–77 years with 95% probability. According to our analysis of dead trees, it is evident that, on average, D. cinnabari in populations at Firmihin dies after reaching 17 orders of peripheral branches.