OOS 47-6 - The response of tropical forest function and carbon cycling to warming: Insights from an elevation transect study in the Andes and Amazon

Friday, August 12, 2011: 9:50 AM
17A, Austin Convention Center
Yadvinder Malhi1, Patrick Meir2, Norma Salinas3, Javier Silva-Espejo4, Cecile Girardin5, Michael Zimmerman6, Luiz EO Aragao7, Daniel B. Metcalfe8, Filio Farfan-Amezquita4, Walter Huaraca-Huasco4, Liliana Durand4, Marlene Mamani4, Adan JQ Ccahuana4, Christopher Doughty5, William Farfan9, Karina Garcia9, Amanda Robertson10, Kenneth J. Feeley11, Michael Bird6 and Miles R. Silman12, (1)Environmental Change Institute, University of Oxford, Oxford, United Kingdom, (2)School of Geosciences, University of Edinburgh, Edinburgh, United Kingdom, (3)Universidad San Antonio Abad del Cusco, Cusco, (4)Universidad San Antonio Abad del Cusco, Cusco, Peru, (5)School of Geography and Environment, University of Oxford, United Kingdom, (6)School of Earth and Environmental Sciences, James Cook University, Cairns, Australia, (7)School of Geography, University of Exeter, (8)Swedish University of Agricultural Sciences, Umea, Sweden, (9)Department of Biology, Wake Forest University, Winston-Salem, NC, (10)Biology & Wildlife Department, University of Alaska, Fairbanks, AK, (11)Fairchild Tropical Botanical Garden, Coral Gables, FL, (12)Biology, Wake Forest University, Winston-Salem, NC
Background/Question/Methods

The response of the tropical biosphere to climate warming is one of the greatest sources of uncertainty in predicting 21st century climate change. A key aspect of the uncertainty is the sensitivity of tropical forest biomass, productivity, soil and necromass carbon cycling to temperature. Elevation transects in tropical forest regions can offer insights into this sensitivity, both for long-term equilibrium response from in situ measurements of plant and soil processes, and for transient responses through translocation experiments. Here we report results from such a carbon cycling study along a 3000 m elevation gradient in the Andes-Amazon region of SE Peru.

Results/Conclusions

In situ measurements of forest carbon cycling along the gradient show that gross (GPP) and net primary productivity (NPP) decline with elevation, but carbon use efficiency (the ratio of NPP to GPP), and the allocation of NPP, remains relatively constant. The decline in GPP is largely consistent with the expected temperature sensitivity of photosynthesis. The sensitivity of heterotrophic processes was analysed through translocation studies of soil organic matter, leaf litter and fine wood material. The three heterotrophic processes were well described by an exponential sensitivity to temperature, with a higher sensitivity (Q10 ~ 3) than usually incorporated in terrestrial ecosystem models. The higher temperature sensitivity of heterotrophic decay processes over autotrophic production processes results in a decline in soil and necromass carbon stocks with warming temperatures. We incorporate insights from these studies into a simple empirical carbon cycling model. We assume that similar temperature sensitivities persist for further warming in the lowlands, and use this model to explore how current and future warming may affect soil and vegetation carbon stocks in montane and lowland tropical forests. 

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