Last reviewed on December 1, 2016

California Greenhouse Gas Inventory - Forests and Other Lands


Tree in a California forest
Growing trees remove CO2 from the air

The Air Resources Board's (ARB) natural and working lands inventory consists of forest and other natural lands, croplands, and urban forests. It is being developed using design principles established by the Intergovernmental Panel on Climate Change (IPCC), and estimates the carbon contained in ecosystems at points in time and the greenhouse gas (GHG) flux associated with changes in carbon stocks. The key GHGs of concern are carbon dioxide, methane, and nitrous oxide. The exchange of carbon dioxide between the atmosphere and land occurs through uptake by plant photosynthesis and release via respiration, and the decomposition and combustion of biomass. Methane is emitted during incomplete combustion of biomass and under anaerobic conditions in soils. Nitrous oxide is emitted from combustion of biomass.

For the past few years ARB has worked extensively with other state agencies, academic researchers and the public on inventory development. ARB worked with researchers from the University of California (UC) Berkeley to develop a methodology for assessing carbon stocks and changes for forest and other natural lands, and has completed the inventory quantification for the 2001-2010 time period, presented in the section below. Upcoming work includes incorporation of 2012 and 2014 data for forest and other natural lands, as well as estimation of carbon stocks, stock-change and GHG fluxes for urban forests, croplands, and soils in all land types. Development of inventory methods for croplands, urban forests, and soils for all land types are currently in progress.

Forest and Other Natural Lands Inventory

The forest and other natural lands inventory includes carbon uptake by vegetation, carbon losses associated with wild and prescribed fires, the decomposition and combustion of residues from harvest, and conversion to other land types. Previous inventory estimates for this category were based on a 2004 California Energy Commission study which quantified carbon stocks and change in forests and rangelands in the northern part of the State from 1994 to 2000. Results from the study were extrapolated to include the entire state and to other years, and the estimation approach afforded few options for updating. In 2015, researchers from UC Berkeley developed a data-driven methodology for assessing carbon stocks and changes for all land categories in California except agricultural and urban areas. The new methods use California specific land based data sets and satellite remote sensing data. The covered ecosystems include forests, woodlands, shrub lands, grasslands, wetlands and other natural lands. The method includes carbon contained in live and dead vegetation pools. Data sources for the new method include ground-based data from the Forest Inventory and Analysis (FIA) program of the USDA-Forest Service, remote sensing products from NASA's MODIS sensor, geospatial vegetation attributes and disturbance activity (fire, harvest etc.) data from the federal Landscape Fire and Resource Management Planning Tools Project (, and ancillary data on shrub lands and grasslands.

The method enables analysts to retrospectively assess ecosystem carbon stocks and to attribute stock-changes to fire and other processes. It enables statewide monitoring for changes on the land over time and for periodic quantification of carbon stocks and of GHG flux associated with changes in carbon stocks. Results of a recent analysis for a period spanning 2001 to 2010 are presented here.

Inventory tables for forest and other natural lands during the 2001-2010 period:

The presentation at the November 7, 2016 AB 32 Scoping Plan Workshop provides an overview of the IPCC inventory framework, inventory methodology (for all land types, including cropland and urban forest), and summary of inventory results:

Reports describing the development of the new methodology are available below.

Additional Work

ARB will continue to expand the scope of the natural and working lands inventory by incorporating the most recent data available. Additional work will be needed to quantify carbon stocks, stock-change and GHG fluxes associated with urban forests, croplands, and soils across all land categories. The sources and methods for quantifying ecosystem carbon and GHG flux in this sector are complex. Continued refinements will advance carbon quantification, attribution of GHG flux by disturbance process, and reduce uncertainty.


For general questions regarding the GHG inventory for forests and other lands, please contact: Anny Huang, Manager, Emission Inventory Analysis Section, Phone: (916) 323-8475