Chapter 6 of the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2016 report provides an assessment of the greenhouse gas fluxes resulting from land use and land-use change in the United States. The 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories recommends reporting fluxes according to changes within and conversions between certain land-use types termed: Forest Land, Cropland, Grassland, Wetlands, and Settlements (as well as Other Land).
The greenhouse gas flux from Forest Land Remaining Forest Land is reported for all forest ecosystem carbon (C) stocks (i.e., aboveground biomass, belowground biomass, dead wood, litter, and C stock changes from mineral and organic soils), harvested wood pools, and non-carbon dioxide (non-CO2) emissions from forest fires, the application of synthetic nitrogen fertilizers to forest soils, and the draining of organic soils. Fluxes from Land Converted to Forest Land are included for aboveground biomass, belowground biomass, dead wood, litter, and C stock changes from mineral soils.
- Approximately 33 percent of the U.S. land area is estimated to be forested in 2016, based on the U.S. definition of forest land.
- Since 1990, the conversion of grassland to forest land resulted in the largest source of C sequestration, accounting for approximately 67 percent of the sequestration in the Land Converted to Forest Land category in 2016.
- Timber harvests do not cause an immediate flux of all harvested biomass carbon to the atmosphere. Instead, a portion of the carbon stored in wood to a product pool, where the carbon is emitted over time, generally decades or even centuries.