Climate-induced hysteresis of the tropical forest in a fire-enabled Earth system model
Mathematisch-Naturwissenschaftliche Fakultät
Tropical rainforests are recognized as one of the terrestrial tipping elements which could have
profound impacts on the global climate, once their vegetation has transitioned into savanna or grassland
states. While several studies investigated the savannization of, e.g., the Amazon rainforest, few studies
considered the influence of fire. Fire is expected to potentially shift the savanna-forest boundary and hence
impact the dynamical equilibrium between these two possible vegetation states under changing climate.
To investigate the climate-induced hysteresis in pan-tropical forests and the impact of fire under future
climate conditions, we employed the Earth system model CM2Mc, which is biophysically coupled to the
fire-enabled state-of-the-art dynamic global vegetation model LPJmL. We conducted several simulation
experiments where atmospheric CO2 concentrations increased (impact phase) and decreased from the new
state (recovery phase), each with and without enabling wildfires. We find a hysteresis of the biomass and
vegetation cover in tropical forest systems, with a strong regional heterogeneity. After biomass loss along
increasing atmospheric CO2 concentrations and accompanied mean surface temperature increase of about
4 ◦C (impact phase), the system does not recover completely into its original state on its return path,
even though atmospheric CO2 concentrations return to their original state. While not detecting large-scale
tipping points, our results show a climate-induced hysteresis in tropical forest and lagged responses in forest
recovery after the climate has returned to its original state. Wildfires slightly widen the climate-induced
hysteresis in tropical forests and lead to a lagged response in forest recovery by ca. 30 years.
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