ARE TROPICAL FORESTS AN EXTREMISTAN ENVIRONMENT?

Abstract

Background: This study reveals the surprising impact of large trees on biomass modeling and estimation in tropical forests. Findings emerged from viewing tropical forests as an Extremistan environment—a domain where a small number of extreme events disproportionately impact overall outcomes. The aims were to: (i) determine whether humid tropical forests can be characterized as an Extremistan environment, (ii) quantify the impact of large trees on the biomass quantification, and (iii) recommend better practices to mitigate the impact of large trees. The methods included forest simulation, biomass model calibrated with multi datasets and extensive examination of the impact of large trees on model performance and mean biomass estimation.

Results: The select group of the 1% heaviest trees account for 25–35% of the total biomass, a concentration analogous to the wealth concentration in developed countries. Additionally, a “tyranny” of the 5% heaviest trees (diameter >18–31 cm) was observed, in which 50-75% of the total biomass is retained, significantly affecting biomass modeling and mean biomass estimation regardless of the model used.

Conclusions: This study confirms that humid tropical forests behave as an Extremistan environment. For biomass and carbon inventories, installing 10,000-m² sample units is recommended to mitigate the “tyranny” effect of the 5% heaviest trees, with a minimum size threshold of 4000 m².