Last reviewed on May 14, 2014

California Greenhouse Gas Inventory - Forests and Other Lands

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

Background

The ARB’s greenhouse gas (GHG) inventory for forests and other lands tracks the removal of CO2 from the atmosphere and emissions of GHGs to the atmosphere.  The inventory includes CO2 uptake by vegetation and GHG emissions from wild and prescribed fires, the decomposition and combustion of residues from harvest, conversion to other land types, and discarded wood products.  The key GHGs of concern are CO2, CH4 and N2O.  The exchange of CO2 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.

Current forest sector emission and sequestration estimates in the ARB’s GHG inventory are based on a 2004 California Energy Commission study which quantified carbon stock in forests and rangelands. The study focused on a time period from 1994 to 2000 and was geographically limited to the northern part of the State. Results from the study were extrapolated to include the entire state and to other years. The study was limited in geographic and temporal scope and afforded few options for updating.  Updated methods for regular periodic quantification of greenhouse gas fluxes on forest, range, and other natural lands are in development.

Research and Planned Improvements

In 2011, ARB contracted with researchers from University of California (UC) Berkeley to develop a new data-driven methodology for assessing carbon stock changes for all land 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, and wetlands. Data sources for the new method include Forest Inventory and Analysis (FIA) ground-based data (vegetation type, tree species and dimensions, percent canopy cover, etc.) from the USDA-Forest Service, remote sensing products from NASA’s MODIS sensor, geospatial vegetation data (vegetation community type, canopy height, percent canopy cover) from the federal Landscape Fire and Resource Management Planning Tools Project (Landfire), geospatial fire and harvest occurrence data from CalFIRE, and ancillary data on shrub lands and grasslands.

The method enables analysts to retrospectively assess ecosystem carbon stock changes resulting from fire, human activities, and other processes. It will enable monitoring of changes on the land over time and periodic quantification of the GHG flux associated with changes in ecosystem carbon stocks.  The research has generated a wealth of new data to support a planned update to the GHG inventory.

Additional work is needed to evaluate the data provided by the UC Berkeley research, to incorporate additional new data, and to identify further research needed to expand use of these tools.  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. 

The UC Berkeley research report describing the development of the new methodology is available below.

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

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