We have a new paper out in Global Change Biology, the first spatial comparison of productivity and carbon cycling from our GEM plots in lowland Amazonia. The plots spread across five sites in Peru, Bolivia and Brazil, spanning gradients from wet to dry, and from infertile soils in eastern Amazonia to moderately fertile soils in western Amazonia.
The GEM approach gives us insights into the full carbon budget of forests, from total photosynthesis or GPP, through its allocation to NPP or plant respiration, through the allocation of NPP to canopy, wood or fine roots, and through to biomass stocks and mortality rates. In this paper we explore to what extent these processes are simply related to each other. Can growth rates of a forest be predicted from photosynthesis rates, can biomass be predicted from growth rates?
We show that there is little simple linkage between growth and photosynthesis, because shifts in carbon use efficiencieny (the fraction of photosynthesis used for biomass growth) and the allocation of NPP matter. There is also no simple linkage between growth rates and biomass - in mature forests in Amazonia the spatial patterns in biomass are determined more by the spatial variation in tree biomass residence times (or mortality rates) matters more than variation in production. To predict biomass, we need to understand why trees die more than how trees grow. This unfortunately is a much harder challenge.
The paper represents a huge effort by GEM field teams in all three countries, who spent many weeks per month over four years collecting and processing data (and continue to do so). It was supported by the Gordon and Betty Moore Foundation, and also the EU project GEOCARBON. The paper can be accessed below.
Malhi Y., C. E. Doughty, G. R. Goldsmith, D. B. Metcalfe, C. A. J. Girardin, T. R. Marthews, J. del Aguila-Pasquel3, L. E. O. C. Aragão, A. Araujo-Murakami, P. Brando, A. C. L. da Costa, J. E. Silva-Espejo, F. Farfán Amézquita, D. R. Galbraith, C. A. Quesada, W. Rocha, N. Salinas-Revilla, D. Silvério, P. Meir and O. L. Phillips (2015) The linkages between photosynthesis, productivity, growth and biomass in lowland Amazonian forests. Global Change Biology, DOI: 10.1111/gcb.12859. Supplementary Information.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University