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School of Geography

Roel Brienen Dr Roel Brienen

Contact details

School of Geography
University of Leeds
University Road
Leeds LS2 9JT   UK


+44 (0) 113 34 33381

Student hours:

Work in progress

NERC fellowship “Climate change and the Amazon: assessing the impact of climate on tree growth using tree ring widths and isotopes”

Responses of tropical trees to elevated [CO2], predicted temperature increases, or an increased drought frequency are highly uncertain due to a lack of appropriate data. Nevertheless, some recent projections indicate large-scale die-back of the Amazon rainforest over the coming century. As the Amazon stores large amounts of carbon, such a die-back would significantly affect atmospheric CO2 concentrations, with important consequences for the rate of climate change.

In my research fellowship I will use novel, proven methodologies to determine the past sensitivity and resilience of Amazonian tree growth to increased [CO2] and climate fluctuations with a view to helping to make improved predictions for the future. This involves the acquisition of tree ring data from forests located along the major precipitation gradient within the Amazon (i.e. total annual rainfall and rainfall seasonality) and across a range of species, representing the dominant functional axis of tropical trees. Using tree rings permits the extension of annually resolved historical records of tropical tree growth to the past 200 years. Responses to external controls will be evaluated from comparisons with local and large-scale climate and atmospheric data such as [CO2], rainfall, temperature, solar radiation and ENSO and AMO-indices. Long-term trends in carbon isotope (δ13C) of tree ring cellulose will reveal the extent on long- and short-term (annual) variations in tropical forest tree photosynthetic carbon isotope discrimination (Δ), probing directly the link between photosynthesis and climatic variability, as well as providing the first centennial-scale test of the CO2-fertilisation hypothesis for tropical forests. The δ18O of tree ring cellulose finally is linked to large-scale controls in precipitation, and will thus provide independent climate information which I will use to evaluate tree responses to climate over longer time-scales.

My study will contribute to obtain a more rigorous understanding of growth and physiological responses of tropical trees to [CO2] and climate and provide a solid base-line for validating and improving individual based growth models or Dynamic Global Vegetation Models (DGVMs).