CARBON CYCLING REFLECTED IN RAINFOREST CARBON ISOTOPE VALUES

The influence of the tropics in determining global climate has recently received renewed interest. In years of the El Niño-Southern Oscillation (ENSO), high pressure over the Indonesian region causes severe droughts on Sabah, Malaysia. Unfortunately climatic measurements are limited and therefore, proxy measures are required to reconstruct past drought events.

A radial segment was obtained from a recently fallen tree (Shorea superba Sym.) growing near to Lahad Datu, Sabah. Asymmetrical growth and indistinct rings resulting from an aseasonal climate prevented absolute dating. A time frame was established successfully by wiggle-matching high-precision radiocarbon dates to reject ambiguous values. Carbon isotope values were determined on the resulting 250-year time-series.

Carbon cycling is evident in the "juvenile effect" resulting from the assimilation of respired carbon dioxide and lower light levels below the canopy and, the “anthropogenic effect” caused by increased industrial activity in the late-nineteenth century. This research represents one of the first attempts to date the primary rainforest and reconstruct past environmental conditions on Sabah.