Long-term Carbon Studies at the Harvard and Howland Forests of New England

Cover image of Ecological Monographs, Volume 90, Number 4

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).

Summary of the Howland Forest carbon cycle processes.  Carbon stocks and fluxes across different ecosystem components are averaged over multi-decadal measurements of eddy covariance fluxes, soil chamber fluxes, and biometric inventories.