Local and regional climatic signals recorded in tree-rings of Chukrasia tabularis in Bangladesh

We developed the first tree-ring chronology of Chukrasia tabularis from a moist tropical forest in Bangladesh, spanning the 102-year period 1911-2012. The species showed wood anatomically clear annual tree-ring boundaries which crossdated between tree individuals. Bootstrapped correlation analyses revealed that the ring-width index was significantly negatively correlated with current year mean and minimum temperatures. This relationship was stronger during the dry season (November-March), the pre-monsoon (February-April) and the post-monsoon season (September-November) than during the main monsoon season (May-August). We interpret this result as an indication that temperature-driven higher evapotranspiration outside the main rainy season leads to water stress limiting tree growth. This is confirmed by negative correlations of the ring-width index with the Palmer Drought Severity Index (PDSI) during the dry season. Precipitation did not show significant relationships to tree growth, except in current year June. However, cloud cover strongly negatively affected tree growth, likely by reducing photosynthetic capacity particularly during the rainy summer (May-August) monsoon season. On a regional scale, the ring-width index was correlated with both Indian Ocean and Pacific Ocean sea surface temperature (SST) anomalies, but during different seasons. Ring width of C. tabularis was also significantly correlated with the El Niño Southern Oscillation (ENSO). Monthly Niño 3.4 region positive temperature anomalies enhanced current year tree growth but negative temperature anomalies reduced tree growth in the following year mainly through modulating local climate. Hence, tree-ring variations of C. tabularis in Bangladesh record local and regional climate signals and are a potential proxy to reconstruct local and regional paleoclimatic variability during the past centuries.