Biology & Paleo Environment Events

Twenty years of tree-ring research in Southeast Asia has resulted in near-millennial length reconstructions of the regional hydroclimate using the rare cypress (Fokienia hodginsii) found growing along the length of the Annamite Range from 12° ‒ 23° N latitude. These records led to discoveries of severe climate anomalies that gripped the region and contributed to the demise of the Khmer at Angkor by the early 15^th century, and the collapse of all major polities of the Indochina Peninsula by the late 18^th century. Three published records of spring (March ‒ May) hydroclimate from north, central and southern Vietnam Fokienia represent the most robust and well-replicated tree ring records from anywhere in the global tropics, with two additional Fokienia records from north and central Vietnam currently in preparation for publication. Additional Fokienia collections from Lao PDR are being developed. We have also developed teak records from Myanmar, Thailand and Indonesia, and multiple records from Pinus species from Myanmar, Thailand, Cambodia and Laos.

This talk focuses on new developments in the methods we use to analyze tropical tree ring data. We are now able to account for discrete seasonal reconstructions of climate beyond the spring season, and include variability of the summer, autumn and winter seasons. In particular, Blue Light Intensity (BLI) is a proxy for wood density, and has been widely used in the high latitude forests where summer temperature dominates the growth response. We apply this technique to the earlywood of Fokienia hodginsii samples from Vietnam and find a response to winter (Dec-Apr) temperature strong enough to allow for robust statistical reconstruction. We interpret these results as reflecting a cavitation-avoidance response of this species, such that higher than average temperature during the annual winter dry period results in a reduction of lumen diameters during the springtime flush of growth (an interpretation supported by ongoing ecophysiological research). Stable isotope analyses of δ¹⁸O from Fokienia and Pinus species are revealing summer hydroclimate seasonality (May-Sep), while earlywood and latewood measurements from Pseudotsuga sinensis from northern Vietnam reflect autumn rainfall. The ability to analyze discreet seasonal climate variability from the tropics is new, and is a major development for studies of climate over Southeast Asia.

Fall 2017: