Effects of fire and CO2 on biogeography and primary production in glacial and modern climates.

Dynamic global vegetation models ( DGVMs) can disentangle causes and effects in the control of vegetation and fire. We used a DGVM to analyse climate, CO₂ and fire influences on biome distribution and net primary production ( NPP) in last glacial maximum ( LGM) and pre-industrial ( PI) times., The Land surface Processes and eXchanges ( LPX) DGVM was run in a factorial design with fire 'off' or 'on', CO₂ at LGM (185 ppm) or PI (280 ppm) concentrations, and LGM (modelled) or recent climates. Results were analysed by Stein-Alpert decomposition to separate primary effects from synergies., Fire removal causes forests to expand and global NPP to increase slightly. Low CO₂ greatly reduces forest area (dramatically in a PI climate; realistically under an LGM climate) and global NPP. NPP under an LGM climate was reduced by a quarter as a result of low CO₂. The reduction in global NPP was smaller at low temperatures, but greater in the presence of fire., Global NPP is controlled by climate and CO₂ directly through photosynthesis, but also through biome distribution, which is strongly influenced by fire. Future vegetation simulations will need to consider the coupled responses of vegetation and fire to CO₂ and climate. [ABSTRACT FROM AUTHOR]