The Howland Research Forest is located in commercial softwood timberlands in central Maine. It was established in 1984 as part of a Forest Service funded Spruce-Fir Cooperative with then landowner, International Paper, to monitor the impact of pollutant deposition on forest health. Present research at Howland is focused on understanding the carbon cycle. As a forest grows, it removes carbon dioxide (CO₂) from the atmosphere and stores it in woody biomass and soils (carbon sequestration). Carbon sequestration in forest growth is widely believed to be limiting the rate of CO₂ rise in the atmosphere today, slowing the pace of greenhouse gas increase.

In 1995, researchers from the Forest Service Northern Research Station, University of Maine, and Woods Hole Research Center, (later joined by colleagues from Cornell, the University of New Hampshire, University of Georgia, University of Utah, Harvard University, and University of Colorado) began directly measuring forest CO₂ uptake and loss at Howland to learn how forest carbon sequestration is affected by short and long-term climate variation and other factors. Funding support came from the Northern Global Change Program and later the National Science Foundation, National Institute for Global Environmental Change, and Department of Energy.

Howland was one of the original locations in the international AmeriFlux and Fluxnet networks of carbon flux measurement sites and thus has one of the longest records of measurement anywhere. Measurements of carbon flux are made from 100-ft-tall research towers located in different stands at Howland. The main Howland tower has been operating since 1995 in mature spruce-hemlock forest. This is an unusually old forest for the northeastern US, with most canopy trees dating from around the Civil War and some in excess of 300 years old, yet the forest is still taking up and storing almost 2 tons of carbon per hectare each year (similar to much younger forests elsewhere). This surprising result shows the potential for old-growth forests to continue to sequester carbon. Forest carbon uptake was found to vary considerably between years and our research has revealed a complex interaction between climate and carbon uptake (e.g. warmer than average spring conditions lead to enhanced C uptake and storage but warmer than average summers lead to decreased carbon storage). A unique aspect of Howland is the location of addition carbon measurement towers in similar forest that has then been experimentally manipulated to test our understanding of the factors that regulate carbon sequestration. The main tower acts as a "control" for these experimental treatments; the first was begun in 1999 and is a study of how nitrogen deposition influences forest C cycling and storage, and the second begun in 2001 investigates the consequences of commercial forestry activities (shelterwood harvest) on forest carbon. These towers are located 0.8 and 1.2 km from the original site. Results from the harvested area show that forest carbon uptake was reduced for only several years and that the efficiency of uptake has increased. Other important scientific discoveries from Howland were the first characterization of flux measurement uncertainty and the development of several models of forest C uptake driven by remote sensing (satellite) data. Howland is a NASA core EOS land validation site for the MODIS and AERONET programs, and served as a focus of a regional carbon budget program ("COBRA" run by Harvard). The present Howland program is vigorous and productive with external funding for Howland researchers averaging over $500,000/yr for the last 7 years and research results published in more than 30 scientific papers.

The Howland site was part of the 1.1 million acres sold by International Paper Company in 2005 to GMO Renewable Resources, LLC, (GMORR), a private forest investment management company.

For more information about USDA Forest Service Howland research, contact Dr. David Hollinger (dhollinger@fs.fed.us).