Rosanne D’Arrigo, Paul Krusic, Ashley Curtis, and John Sakulich

Tree-Ring Laboratory Lamont-Doherty Earth Observatory

Jonathan Palmer - Tai Tapu Canterbury New Zealand

Satria Bijaksana - Institut Teknologi  Bandung, Bandung, Java, Indonesia

La Ode Ngkoimani - Haluoleo University, Kendari, Sulawesi, Indonesia

Siti Zulaikah - State University of Jakarta, Jakarta, Java Indonesia

The Indonesian Archipelago is situated in the western tropical Pacific, one  of the  centers of action most strongly impacted by the El Niño-Nino-Southern Oscillation (ENSO) and the Asian Monsoon . Rainfall over much of  Indonesia  results directly from convection related to the Indonesian Low pressure cell, the western arm of the ENSO system.  Many Indonesian peoples are directly impacted by the rainfall extremes (drought and floods) which are associated with ENSO and related monsoon variability. Longer records from tree rings and other proxy data can extend existing climate information on ENSO and monsoon-related drought and floods back in time for Indonesia. These longer records can be used to better understand the tropical climate system and aid in climate prediction.

A remnant stand of old-growth teak in central Java.

Indonesia is one of the few tropical regions where tree-ring chronologies have been successfully used to study aspects of climate, including ENSO and the Asian monsoon. For this reason Indonesia is an important component of our current NSF-funded TRL-LDEO Asian Monsoon Project. The primary tree species used for dendrochronology in Indonesia is teak ( Tectona grandis ), a semi-deciduous tree that  is thought to have been introduced to Indonesia from India centuries ago.

Extracting increment cores from a teak tree.

Teak can reach significant age (several hundred years or more). Samples are also resistant to decay and subfossil wood can last for considerable periods of time.  As teak is also a very valuable commercial wood, much of the remaining natural stands have been logged and there are very few old growth teak left in Indonesia. Teak was first shown to be suitable for dendrochronological purposes in the 1930’s, when Berlage, a Dutch scientist, described the first tree-ring width chronology for this species from Java, dating back to 1514.

A pile of subfossil teak logs recently excavated in east Java.