A model analysis reconstructing the growth of preindustrial forests in the upper Midwest United States shows a steady increase in forest biomass over thousands of years, driven by forest expansion and changing species composition as climate in the region changed following deglaciation. The findings challenge previous conclusions that forest biomass in this region and, by extension, the accumulated carbon, remained relatively static in the millennia before industrialization. Strikingly, the model results also show that what took nearly 8,000 years to accumulate was lost in only 150 years of post-industrial logging and agriculture. Forests represent one of the largest pools of terrestrial carbon. However, the strength and pacing of forest biomass carbon accumulation over centuries to millennia aren’t well understood. As such, estimations of terrestrial carbon fluxes before industrial-era disturbance are uncertain, as is their role in future long-term projections of the carbon climate system. By combining historical data from preindustrial forest surveys and fossil pollen records, Ann Raiho and colleagues developed ReFAB (Reconstructing Forest Aboveground Biomass), a Bayesian statistical model, and used it to reconstruct changes in biomass in the Midwest U.S. over the last 10,000 years. Raiho et al . found that forest biomass in this region was not stable before industrialization, as has been previously believed. Instead, after an initial decline due to postglacial climate change, woody biomass increased slowly yet consistently, nearly doubling over the subsequent 8,000 years and storing as much as 1,800 teragrams of carbon. According to the authors, this steady biomass accumulation was made possible by spatial expansion of forest area following deglaciation and ecological succession to high-biomass tree species. Raiho et al. suggest that the findings could inform forest management strategies that seek to emulate the natural processes that enhanced carbon sequestration throughout the preindustrial Holocene to buffer climate change well into the Anthropocene.
Science
8,000 year doubling of Midwestern forest biomass driven by population- and biome-scale processes
24-Jun-2022