The Sensitivity of Wet and Dry Tropical Forests to Climate Change in Bolivia

Abstract:

Bolivia's forests contribute to the global carbon and water cycle, as well as to global biodiversity. The survival of these forests may be at risk due to climate change. To explore the associated mechanisms and uncertainties, a regionally adapted dynamic vegetation model (LPJ-GUESS) was implemented for the Bolivian case, and forced with two contrasting CMIP5 RCP8.5 climate change projections. The CNRM-CM5 projects an rainfall increase of about 5% in lowland Bolivia, while IPSL-CM5A-LR projects a decrease of about 17-26%. Changes in carbon stocks and fluxes were evaluated, factoring out the individual contributions of atmospheric carbon dioxide ([CO2]), temperature and precipitation. Special attention was paid to the effect of rising temperatures on photosynthesis, respiration, and the atmospheric demand for transpiration.

Impacts ranged from a strong increment to a severe loss of vegetation carbon (Cv), depending on differences in climate projections, as well as the physiological response to rising [CO2], see figure. The simulated loss Cv was primarily driven by a reduction in gross primary productivity, and secondarily by enhanced emissions from fires and autotrophic respiration. In the wet forest, less precipitation and higher temperatures equally reduced Cv, while in the dry forest, the impact of precipitation was dominating. The temperature-related reduction of Cv was mainly due to a decrease in photosynthesis, and only to lesser extent because of more autotrophic respiration and less stomatal conductance as a response to an increasing atmospheric demand. Tropical dry forests were simulated to virtually disappear, regardless of the fertilizing effect of rising [CO2], suggesting a higher risk for dry forest loss along the drier southern fringe of the Amazon. Implications for climate change adaptation and mitigation measures are discussed.