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Stable carbon isotope ( δ 13 C) series were developed from analysis of sequential radial wood increments from AD 1850 to AD 2009 for four mature primary rainforest trees from the Danum and Imbak areas of Sabah, Malaysia. The aseasonal equatorial climate meant that conventional dendrochronology was not possible as the tree species investigated do not exhibit clear annual rings or dateable growth bands. Chronology was established using radiocarbon dating to model age–growth relationships and date the carbon isotopic series from which the intrinsic water-use efficiency (IWUE) was calculated. The two Eusideroxylon zwageri trees from Imbak yielded ages of their pith/central wood (±1 sigma) of 670 ± 40 and 759 ± 40 years old; the less dense Shorea johorensis and Shorea superba trees at Danum yielded ages of 240 ± 40 and 330 ± 40 years, respectively. All trees studied exhibit an increase in the IWUE since AD 1960. This reflects, in part, a response of the forest to increasing atmospheric carbon dioxide concentration. Unlike studies of some northern European trees, no clear plateau in this response was observed. A change in the IWUE implies an associated modification of the local carbon and/or hydrological cycles. To resolve these uncertainties, a shift in emphasis away from high-resolution studies towards long, well-replicated time series is proposed to develop the environmental data essential for model evaluation. Identification of old (greater than 700 years) ringless trees demonstrates their potential in assessing the impacts of climatic and atmospheric change. It also shows the scientific and applied value of a conservation policy that ensures the survival of primary forest containing particularly old trees (as in Imbak Canyon and Danum).

In a first step to obtain a proxy record of past climatic events (including the El Nino- Southern Oscillation) in the normally aseasonal tropical environment of Sabah, a radial segment from a recently fallen dipterocarp (Shorea superba) was radiocarbon dated and subjected to carbon isotope analysis. The high-precision radiocarbon results fell into the ambiguous modern plateau where sev- eral calibrated dates can exist for each sample. Dating was achieved by wiggle matching using a Bayesian approach to calibration. Using the defined growth characteristics of Shorea superba, prob- ability density distributions were calculated and improbable dates rejected. It was found that the tree most likely started growing around AD 1660-1685. A total of 173 apparent growth increments were measured and, therefore, it could be determined that the tree formed one ring approximately every two years. Stable carbon isotope values were obtained from resin-extracted wholewood from each ring. Carbon cycling is evident in the 'juvenile effect', resulting from the assimilation of respired car- bon dioxide and lower light levels below the canopy, and in the 'anthropogenic effect' caused by increased industrial activity in the late-nineteenth and twentieth centuries. This study demonstrates that palaeoenvironmental information can be obtained from trees growing in aseasonal environ- ments, where climatic conditions prevent the formation of well-defined annual rings. Copyright 2004 John Wiley & Sons, Ltd.