A 448-year teak chronology from northwestern Thailand is used to assess past changes in the strength of the summer monsoon. The chronology is based on 30 living trees that extend from 1604 to 2005, and a 47-stump chronology that spans from 1558 to 1903. We used methods of cross dating and chronology building that address problems specifically found in teak. The result is a robust chronology with strong signal strength back to 1600 AD, and with variability retained at the multi-decadal scale. Variability in annual growth in teak from this area is dependent on rainfall and soil moisture availability at both the beginning and end of the monsoon season as confirmed by comparisons with temperature, rainfall and PDSI data. These correlation analyses confirm that our record is a proxy for summer monsoon strength and/or duration, and highlight the importance of soil moisture availability in the seasons of transition. The chronology reveals two prominent periods of decadal-scale drought in the early and mid 1700s that correspond to persistently warm sea surface temperature anomalies in the tropical Pacific as derived from Galapagos Island coral records. Speleothem data from central India also indicate protracted periods of drought for the 1700s. While these broad-scale eighteenth-century persistent droughts may be related to protracted El Niñ o-like conditions in the tropical Pacific, regional climate forcing over the Indian Ocean and western Pacific sectors appears to be a strong contributor as well. Spectral analyses reveal power in the ENSO range of variability from 2.2 to 4 years, and at the multi-decadal scale at 48.5 years.

We present the first tree-ring chronologies of total ring width (RW), earlywood width (EWW) and latewood width (LWW) from Lao P.D.R., from 52 core samples from 26 mature pines (Pinus merkusii Junghuhn & De Vriese), from Phu Khao Khouay National Biodiversity Conservation Area northeast of Vientiane. The chronologies span the 262-year period from 1743 to 2005 A.D., and at least for RW and LWW exhibit strong signal strength back to the late 1700s. Correlation analyses with climate data from a composite of 13 nearby stations in Thailand indicate statistically significant ( p 0.05) negative correlation with prior year June rainfall, and positive correlation with August-September maximum temperature. Annual radial increment is also significantly negatively correlated with percent cloud fraction, leading us to believe that growth may be adversely affected by light availability (i.e., reduced growth during periods of low light) and not positively affected by high temperature per se. Spatial correlation with sea surface temperature fields highlights the influence of the central and eastern tropical Pacific Ocean, particularly for EWW. Wavelet analysis reveals multi-decadal scale variability between 30 and 60 years for all three indices, and higher frequency power for RW and LWW between 2 and 7 years, the typical range of ENSO. While RW, EWW and LWW all appear to respond to monsoon climate, we highlight the need for far more detailed ecophysiological response studies for this species, particularly with regard to the role of light availability and temperature during the peak monsoon. #

Abstract. Naumthong M, Palakit K, Duangsathaporn K, Prasomsin P, Lumyai P. 2021. Climate effects on the growth of Pinus latteri and Pinus kesiya at the Intakin Silvicultural Research Station, Chiang Mai Province, Thailand. Biodiversitas 22: 2512-2519. Relationship between the growth of two pine species, Pinus latteri and Pinus kesiya, and past climatic factors are studied. Standard dendrochronological techniques were used on 40 core samples obtained from 20 trees from each species to cross-date tree-ring width and determine the growth patterns of each species. Over a period spanning from 1980-2019 (P. latteri) and 1984-2019 (P. kesiya), the calculated mean ring-width values were 0.596 and 0.430 cm per year, respectively. An analysis of the relationship between tree-ring width of P. latteri and climatic data indicated a positive correlation with the relative humidity in April. However, a negative correlation was observed with the temperature in April and August. The factors limiting the growth of P. latteri the most were the temperature in August (r2=0.228; P<0.01). The index constructed for P. kesiya indicated a positive correlation with extreme minimum relative humidity in December and extreme maximum temperature in March. The factors limiting the growth of P. kesiya with a significant correlation, were the relative humidity in April (r2=0.173) and temperature in May (r2=0.184). These results can be used to plan the management of forest plantations and to select suitable areas for the cultivation of pine trees in Thailand

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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 treering 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.