Print PageThe 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.
