Recent trends in the intrinsic water-use efficiency of ringless rainforest trees in Borneo

Abstract

Stable carbon isotope (d 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 agegrowth 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).

Carbon isotope discrimination in C3 land plants is independent of natural variations in pCO2

“…One recent study that did attempt to account for such factors (Frank et al, 2015) concluded that p CO2 has no effect on tree d 13 C (-0.55 ± 0.67 ‰/100 ppmv; Supplementary Information), in good agreement with results here. Although susceptible to individual idiosyncrasies, cellulose records from individual trees from the Borneo rainforest (Loader et al, 2011;MAP c. 3 m/yr) also imply a p CO2 -effect indistinguishable from zero (0.0 ± 0.2 ‰/100 ppmv; Supplementary Information). Early Eocene isotopes of angiosperms further support p CO2 -independence (Diefendorf et al, 2015).…”

1982–2010 Trends of Light Use Efficiency and Inherent Water Use Efficiency in African vegetation: Sensitivity to Climate and Atmospheric CO2 Concentrations

“…We found a strong positive VPD trend (from WFDEI) over the central African forest and the northern savannahs during 1982-2010 probably related to rising temperatures. This iWUE* increase, related to the positive VPD trend, reflects positive physiological responses of plant functional types to environmental changes, as found in previous studies in steppe or rainforest [28,72,73].…”

Conclusion: applying South East Asia Rainforest Research Programme science to land-use management policy and practice in a changing landscape and climate

“…(b) Assessing and modelling impacts of climate change The papers by both Mercado et al [5] and Loader et al [6] provide advances in methodology in assessing the effects of rising carbon dioxide and climate change on forest vegetation. The findings of Mercado et al [5], demonstrating the importance of nutrient availability as a factor influencing net primary productivity across Amazonia, will be fundamental in improving global Review.…”