Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

Teak forms xylem rings that potentially carry records of carbon sequestration and climate in the tropics. These records are only useful when the structural variations of tree rings and their periodicity of formation are known. The seasonality of ring formation in mature teak trees was examined via correlative analysis of cambial activity, xylem and phloem formation, and climate throughout 15 years. Xylem and phloem differentiation were visualized by light microscopy and scanning electron microscopy. A 3 month dry season resulted in semi-deciduousness, cambial dormancy and formation of annual xylem growth rings (AXGRs). Intra-annual xylem and phloem growth was characterized by variable intensity. Morphometric features of cambium such as cambium thickness and differentiating xylem layers were positively correlated. Cambium thickness was strongly correlated with monthly rainfall (R-2 07535). In all sampled trees, xylem growth zones (XGZs) were formed within the AXGRs during the seasonal development of new foliage. When trees achieved full leaf, the xylem in the new XGZs appeared completely differentiated and functional for water transport. Two phloem growth rings were formed in one growing season. The seasonal formation pattern and microstructure of teak xylem suggest that AXGRs and XGZs can be used as proxies for analyses of the tree history and climate at annual and intra-annual resolution.