The structure, distribution, and biomass of the world's forests

Authors: Pan Y, RA Birdsey, OL Phillips, RB Jackson

Forests are the dominant terrestrial ecosystem on Earth. We review the environmental factors controlling their structure and distribution globally, and evaluate their current and future trajectory. Adaptations of trees to climate and resource gradients, coupled with disturbances and forest dynamics, create complex geographical patterns in forest assemblages and structures. These patterns are increasingly discernible through new satellite and airborne observation systems, improved forest inventories, and global ecosystem models. Forest biomass has emerged as a complex property affected by forest distribution, structure, and ecological processes, including productivity and mortality dynamics. Since at least 1990, there have been consistent increases in biomass density in global established forests, despite increasing mortality in some regions. This trend suggests that a global driver such as elevated CO2 may be enhancing biomass gains. Global forests have also apparently become more dynamic. Advanced remote sensing technologies, an expanding measurement base, and improved ecosystem modeling provide critical ecological insights and support for enhancing forest conservation and ecosystem services.