8000-Year Doubling of Midwestern Forest Biomass Driven by Population- and Biome-Scale Processes

Changes in woody biomass over centuries to millennia are poorly known, leaving unclear the magnitude of terrestrial carbon fluxes before industrial-era disturbance. Here, we statistically reconstructed changes in woody biomass across the upper Midwestern region of the United States over the past 10,000 years using a Bayesian model calibrated to preindustrial forest biomass estimates and fossil pollen records. After an initial postglacial decline, woody biomass nearly doubled during the past 8000 years, sequestering 1800 teragrams. This steady accumulation of carbon was driven by two separate ecological responses to regionally changing climate: the spread of forested biomes and the population expansion of high-biomass tree species within forests. What took millennia to accumulate took less than two centuries to remove: Industrial-era logging and agriculture have erased this carbon accumulation. , A preindustrial forest carbon sink Past changes in forest biomass can help to predict how forests—and their ability to sequester carbon—will change in the future. Raiho et al . modeled changes in biomass in the Midwestern United States over the past 10,000 years using data from preindustrial forest surveys combined with fossil pollen records. They found that forest biomass was not stable before industrialization, as many studies have assumed. Instead, biomass doubled over the past 8000 years due to increasing forest area after glaciers receded and changing tree species composition. The biomass accumulated over millennia has been lost in only 150 years of deforestation. —BEL , A model reconstructing preindustrial forests in the Midwestern United States shows a steady increase in forest biomass over millennia.