A model investigation of vegetation-atmosphere interactions on a millennial timescale

Abstract

Abstract. A terrestrial biosphere model with dynamic vegetation capability, Integrated Biosphere Simulator (IBIS), coupled to the NCAR Community Atmosphere Model (CAM2) is used to investigate the multiple climate-forest equilibrium states of the climate system. A 1000-yr control simulation and another 1000-yr land cover change simulation that consisted of global deforestation for 100 yr followed by re-growth of forests for the subsequent 900 yr were performed. After several centuries of interactive climate-vegetation dynamics, the land cover change simulation converged to essentially the same climate state as the control simulation. However, the climate system takes about a millennium to reach the control forest state. In the absence of deep ocean feedbacks in our model, the millennial time scale for converging to the original climate state is dictated by long time scales of the terrestrial carbon stocks, biomass and soil carbon. Our idealized modeling study suggests that the equilibrium state reached after complete global deforestation followed by re-growth of forests is unlikely to be distinguishable from the control climate. The real world, however, could have multiple climate-forest states since our modeling study is unlikely to have represented all the essential ecological processes (e.g. altered fire regimes, seed sources and seedling establishment dynamics) for the re-establishment of major biomes.