Climatic fluctuations trigger false ring occurrence and radial-growth variation in teak (Tectona grandis L.f.)

摘要

The objective of this study was to examine the interaction of extreme growth years in teak (Tectona grandis) with climatic conditions of current, antecedent and subsequent years, in order to explain the nature and the effects of climatic variability on teak growth in northeastern Thailand. A 33-year tree-ring index was constructed and extreme growth years during the period 1976-2008 were identified. A superposed epoch analysis (SEA) was used to study the interaction of climatic data and extreme growth years. Extreme growth years were derived from eight wider and seven narrower annual rings identified using the Cropper’s method. Seventeen false rings were detected using the threshold value ≥ 80% of false ring occurrence for all samples in each growth year. False ring occurrence was associated with narrow ring width formation and triggered by increasing maximum and mean temperatures at the beginning of the rainy season (May to August). In the third year after false ring formation, we observed a pattern of wet year occurrence when annual rainfall and relative humidity in September to December were higher than in adjacent years. Moreover, in the sixth year before false ring formation, a wet year was observed when relative humidity in September to December was higher than in adjacent years. Wider ring width index occurring in a particular year was found to be triggered by a decrease in maximum and mean temperatures in May to August of the current year, suggesting that wet years promote teak growth. The third year after the formation of wider rings was characterized by a low annual rainfall. Our results showed that drought years trigger false ring and narrow ring formation, while wet years trigger wide ring formation in teak. A cycle of wet years between the sixth year prior to, and the third year after, the formation of false rings was also observed, as well as the occurrence of drought in the third year since the formation of wide rings. False ring, narrow ring and wide ring occurrences appear to be good indicators of a 3-6 year climate fluctuation pattern, similar to that of the El Niño-Southern Oscillation (ENSO) cycle in this region.