Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)

Abstract

Abstract. Repeated long-term censuses have revealed large-scale spatial patterns in Amazon Basin forest structure and dynamism, with some forests in the west of the Basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the Basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR) has been developed. The model incorporates variations in tree size distribution, functional traits and soil physical properties and runs at the stand level with four functional traits, leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) used to represent a continuum of plant strategies found in tropical forests. We first applied the model to validate canopy-level water fluxes at three Amazon eddy flux sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for large trees. At the stand-level, simulations at 40 plots were used to explore the influence of climate and soil fertility on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. However all three measures of stand level productivity were positively related to annual precipitation and soil fertility.