Drivers of recent forest cover change in southern South America are linked to climate and CO2

Widespread changes in forest structure and distribution have been documented in northern Patagonia over the past century. We employed LPJ-GUESS, a dynamic global vegetation model (DGVM) to investigate the role of climate, atmospheric carbon dioxide (CO2), and fire on simulated forest cover during the twentieth century. Our objective was to assess the drivers responsible for forest change to temperature, precipitation, radiation, fire and atmospheric CO2 Simulations using observed changes in climate and CO2 from 1930 to 2010, showed an increase in forest cover under changing climate and CO2, because of higher carbon assimilation and net primary production. The model results were compared with a remote-sensing-derived biomass map and ‘greening’ indices from the normalized difference vegetation index. Model simulations and satellite data both show increased greening at high and low elevations. In contrast, simulations using pre-industrial climate and CO2 conditions resulted in a decrease in fire frequency and lower simulated biomass than is reflected by present-day vegetation. Our simulations shows that climate is the primary driver and CO2 fertilization is the secondary driver of forest expansion in northern Patagonia. We suggest that rising CO2 mitigates climate-induced drought stress due to increases in water-use efficiency.