A seminal publication in Ecological Monographs (Finzi et al. 90(4), 2020, e01423) on long-term studies of carbon cycling at the Harvard Forest of western Massachusetts presents a comprehensive carbon budget and evidence that this 80-120 year old hardwood forest is gaining carbon at an average rate of about 3 Mg ha^-1 yr^-1. My former research associate, Kathleen Savage, and I contributed two decades of soil respiration measurements to this study. Working with Susan Trumbore and Julia Gaudinski, we also provided radiocarbon evidence of a small (0.2 Mg ha^-1 yr^-1) soil sink for carbon.

During the same period, we also conducted studies on carbon cycling at the 160 year old spruce-hemlock forest of Howland Maine. A summary of the Howland carbon budget synthesis is the subject of the Davidson et al. oral presentation for the 2020 annual meeting of the American Geophysical Union. A peer-reviewed paper has since been published with additional analyses and updates: Hollinger et al. 2021. JGR-Biogeosciences, 126, e2021JG006276. https://doi.org/10.1029/2021JG006276. Like its Harvard Forest neighbor to the south, the Howland Forest is also gaining carbon, with a 3-decade average rate of about 2 Mg ha^-1 yr^-1. Most was found in accumulating live tree biomass, with a small fraction possibly accumulating in the soil or as dead wood (see figure below).