AB 1504 Process

The purpose of the committee is to provide recommendations and technical information to assist the Board in achieving the Board’s goals and objectives as outlined in the Board’s report to the Air Resources Board on AB32 and in relation to the climate adaptation strategies as referenced in EO-13-08. The IFWG will establish, for Board consideration, a clear list of priorities for policy development by March 31, 2009.


Assembly Bill 1504 California Forest Ecosystem and Harvested Wood Product Carbon Accounting


The Fire and Resource Assessment Program (FRAP) develops an annual Forest Ecosystem and Harvested Wood Product Carbon inventory (Forest Carbon Inventory) through collaboration with the U.S. Department of Agriculture (USDA) Forest Service (FS) Forest Inventory and Analysis Program (FIA), USDA FS Pacific Northwest Research Station (PNW) and the University of Montana Bureau of Business and Economic Research (BBER).

This annual Forest Carbon Inventory report assists the Board of Forestry and Fire Protection in assessing whether the goal of sequestering 5 million metric ton C02e of forest carbon as established by Assembly Bill 32 and 1504 are being met. This report also informs the goals identified in the California Forest Carbon Plan (released in 2018). 


The Global Warming Solutions Act (Assembly Bill 32, Chapter 488, Statutes of 2006) requires California to reduce greenhouse gas (GHG) emissions to 1990 levels by 2020. The initial AB 32 Scoping Plan established by the California Air Resources Board (CARB) in 2008 included a forest sector target with a goal of maintaining the forest carbon sink with a net annual sequestration rate of 5 million metric tons of carbon dioxide equivalent (MMT CO2e).

The responsibility for setting forest carbon policy to ensure the AB 32 forest sector goals are met lies with the California Board of Forestry and Fire Protection (i.e., the Board). The Board of Forestry and Fire Protection’s responsibility in meeting or exceeding the AB 32 forest sector targets was formalized in Assembly Bill 1504 (AB 1504, Chapter 534, Statutes of 2010).

AB 1504 emphasizes the critical and unique role California’s forests play in the state’s carbon balance by sequestering carbon dioxide from the atmosphere and storing it long-term as carbon. It also emphasizes the goal of maximum sustained production of high-quality timber products in serving the public while also providing other benefits and ecosystem services such sequestration of carbon dioxide, recreation, watershed, wildlife, range and forage, fisheries, regional economic vitality, employment, and aesthetic enjoyment. The bill requires the Board to ensure the rules and regulations governing the harvest of commercial tree species consider the capacity of forests to sequester 5 Million Metric Tons (MMT) of CO2e annually by 2020.

California Forest Ecosystem Carbon

These forest ecosystem carbon estimates for California are based on the current USDA FS Forest Inventory and Analysis (FIA) program data. The FIA program is a ground-based, permanent plot re-measurement system of the same trees over time, which captures and quantifies growth, removals and mortality well. It is repeatable, provides low errors, and is consistent with forest carbon inventory data and reporting nationally.

The FIA program switched from a periodic to an annual inventory of forest land in California in 2001 by installing a complete sample of the state each year using 10% of the full set of plots. This equates to a complete sample of all inventory in California every 10 years, with completion of the first full annualized inventory of California forests in 2010. In 2011, FIA began re-measuring the same plot locations as established in 2001 with full re-measurement expected in 2020. Following Intergovernmental Panel on Climate Change (IPCC) Tier 3 methods, stock and flux estimates for standing live and dead trees (including foliage and roots), understory vegetation (including roots), down dead trees, forest floor litter, and soil organic carbon are provided in the report. Changes from forest land-use conversions and non-CO2 emissions are also included.



Figure 1: Flows of carbon in a forest from the atmosphere to the forest and back. Carbon is stored mostly in live and dead wood as forests grow. Does not include C removed from harvest, or soil C removed in groundwater or erosion (Ryan et al. 2010).

California Harvested Wood Product Carbon

Harvested wood product (HWP) carbon estimates for California are based on a model created by BBER and the USDA FS.

The HWP C model follows annual harvest volumes through their timber product class allocation (i.e., softwood sawlogs, softwood pulpwood, etc.) and primary product allocation (i.e, softwood lumber, softwood plywood, etc.). The model uses a complex series of calculations based on a variety of parameters such as product half-lives and discarded product disposition ratios to determine how much carbon remains stored in harvested wood products in use and at solid waste disposal sites.

Estimates follow the IPCC Tier 3 Production approach and therefore include all California-origin timber, but exclude imported wood. Estimates also include carbon stored in HWP from historic harvests dating back to 1952. Harvested wood product carbon emissions associated with and without energy production are also provided for informational purposes, but are not included in the IPCC forest sector carbon accounting.



Figure 2: A schematic of calculations to quantify HWP storage and emissions. These calculations quantify HWP products in use, products in SWDS, emissions with energy capture, and emissions without energy capture using the IPCC approach (in AB 1504 2017 Reporting Period FINAL REPORT).


Assembly Bill 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory Annual Reports

  1. AB 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory: 2006 – 2015
  2. AB 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory: 2006 – 2015 ERRATUM/ SHEET
  3. AB 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory: 2007-2016 DATA UPDATE
  4. AB 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory: 2017 Reporting period
  5. AB 1504 California Forest Ecosystem and Harvested Wood Product Carbon Inventory: 2017 Reporting period, Appendix 3: HWP C Model inputs; calculations

Harvested Wood Product Carbon Workshop April 2018

In April of 2018, the Board and CAL FIRE hosted a workshop to share the proposed HWP C accounting methodology, model input parameters and data sources. Click here to view the recorded webinar and workshop materials.

AB 1504 Supporting information

Prior to implementing annual California forest carbon inventory reports, a variety of presentations were made to the Board for consideration in how to develop the AB 1504 program. Click here to view these presentations and the final AB 1504 implementation plan determined by the Board.



For more information please contact:

Nadia Tase

Climate Change and Forest Inventory Specialist

Fire and Resource Assessment Program

California Department of Forestry and Fire Protection

(530) 573-2320




Ryan, M.G.; Harmon, M.E.; Birdsey, R.A.; Giardina, C.P.; Heath, L.S.; Houghton, R.A.; Jackson, R.B.; McKinley, D.C.; Morrison, J.F.; Murray, B.C.; Pataki, D.E.; Skog, K.E. 2010. A synthesis of the science on forests and carbon for U.S. forests. Issues in Ecology 13: 17.  https://www.fs.fed.us/rm/pubs_other/rmrs_2010_ryan_m002.pdf (accessed: November 2, 2017).