Impact of Rising Temperatures on the Biomass of Humid Old-Growth Forests of the World

Abstract Background: Understanding how warming temperatures are influencing biomasses in the world’s forests is necessary for quantifying future global C (carbon) budgets. A temperature-driven decrease in future C stocks could dangerously strengthen climate change. Empirical methods for studying the temperature response of forests have important limitations, and modelling is needed to provide another perspective. We modelled current and future AGB (old-growth above-ground biomass) in humid lowland areas of the world by dividing GPP (gross primary productivity) and a measure of energy needed to support a given about of biomass called here MCB (maintenance cost per unit biomass). Results: Based on the modelling, we predict a temperature-driven increase in both GPP and MCB, except in the tropics, where GPP will decrease. Their ratio, and therefore also ABG, is expected to decrease in all other regions except the boreal. The AGB is expected to decrease 41% in the tropics and 29% globally.Conclusions: The estimated drops in AGB are dramatic. However, we did not include the fertilisation effects of increasing CO2 (carbon dioxide) and N (nitrogen) that potentially mitigate the temperature-caused drop in AGB.