James E. Smith

Methods for calculating forest ecosystem and harvested carbon with standard estimates for forest types of the United States

This study presents techniques for calculating average net annual additions to carbon in forests and in forest products. Forest ecosystem carbon yield tables, representing stand-level merchantable volume and carbon pools as a function of stand age, were developed for 51 forest types within 10 regions of the United States. Separate tables were developed for afforestation and reforestation. Because carbon continues to be sequestered in harvested wood, approaches to calculate carbon sequestered in harvested forest products are included. Although these calculations are simple and inexpensive to use, the uncertainty of results obtained by using representative average values may be high relative to other techniques that use site- or project-specific data. The estimates and methods in this report are consistent with guidelines being updated for the U.S. Voluntary Reporting of Greenhouse Gases Program and with guidelines developed by the Intergovernmental Panel on Climate Change. The CD-ROM included with this publication contains a complete set of tables in spreadsheet format.

A model of forest floor carbon mass for United States forest types

Includes a large set of published values of forest floor mass and develop large-scale estimates of carbon mass according to region and forest type. Estimates of average forest floor carbon mass per hectare of forest applied to a 1997 summary forest inventory, sum to 4.5 Gt carbon stored in forests of the 48 contiguous United States.

An assessment of uncertainty in forest carbon budget projections

Estimates of uncertainty are presented for projections of forest carbon inventory and average annual net carbon flux on private timberland in the US using the model FORCARB. Uncertainty in carbon inventory was approximately 29% (2000 million metric tons) of the estimated median in the year 2000, rising to 11% (2800 million metric tons) in projection year 2040, with this range covering 95% of the distribution. Relative uncertainties about net flux were higher and more variable than relative uncertainty estimates of carbon inventory. Results indicated that relatively high correlations among projected carbon budgets for the regional forest types led to greater total uncertainty than under assumptions of independence among types, indicating that an accurate portrayal of correlations is important. Uncertainty in soil carbon, closely followed by uncertainty in tree carbon, were most influential in estimating uncertainty in carbon inventory, but uncertainties in projections of volume growth and volume removals were most important in estimating uncertainty in carbon flux. This implies the most eAective ways of reducing uncertainty in carbon flux are diAerent from those required to reduce uncertainties in carbon inventory. Analyses as presented here are necessary prerequisites to identify and reduce uncertainty in a systematic and iterative way. Published by Elsevier Science Ltd.

Forest volume-to-biomass models and estimates of mass for live and standing dead trees of U.S. forests.

Includes methods and equations for nationally consistent estimates of tree-mass density at the stand level (Mg/ha) as predicted by growing-stock volumes reported by the USDA Forest Service for forests of the conterminous United States. Developed for use in FORCARB, a carbon budget model for U.S. forests, the equations also are useful for converting plot-, stand- and regional-level forest merchantable volumes to estimates of total mass. Also includes separate equations for live, standing dead, aboveground only and full trees (including coarse roots), and for hardwood and softwood species. Example estimates are provided for regional tree-mass totals using summary forest statistics for the United States.

Carbon stocks on forestland of the United States, with emphasis on USDA Forest Service ownership

The U.S. Department of Agriculture Forest Service (USFS) manages one-fifth of the area of forestland in the United States. The Forest Service Roadmap for responding to climate change identified assessing and managing carbon stocks and change as a major element of its plan. This study presents methods and results of estimating current forest carbon stocks and change in the United States for public and private owners, consistent with the official 2010 U.S. greenhouse gas inventory, but with improved data sources for three states. Results are presented by National Forest System region, a major organizational management unit within the Forest Service, and by individual national forest. USFS forestland in the United States is estimated to contain an average of 192 Mg C/ha (mega grams carbon per hectare) on 60.4 million ha, for a total of 1 1,604 Tg C (teragrams C) in the year 2005. Privately-owned forestland averages 150 Mg C/ha on 173.8 million ha, with forestland of other public owners averaging 169 Mg C/ha on 43.1 million ha. In terms of change, private and USFS ownerships each sequester about a net 150 Tg C O2/yr, but an additional 92 Tg C O2/yr is stored in products from private harvests compared to about 3 Tg C O2/yr from harvest on USFS land. Emissions from other disturbances such as fires, as well as corresponding area estimates of disturbance are also important, but the needed datasets are not yet available. Recommendations are given for improving the estimates.

Greenhouse Gas and Carbon Profile of the U.S. Forest Products Industry Value Chain

A greenhouse gas and carbon accounting profile was developed for the U.S. forest products industry value chain for 1990 and 2004−2005 by examining net atmospheric fluxes of CO2 and other greenhouse gases (GHGs) using a variety of methods and data sources. Major GHG emission sources include direct and indirect (from purchased electricity generation) emissions from manufacturing and methane emissions from landfilled products. Forest carbon stocks in forests supplying wood to the industry were found to be stable or increasing. Increases in the annual amounts of carbon removed from the atmosphere and stored in forest products offset about half of the total value chain emissions. Overall net transfers to the atmosphere totaled 91.8 and 103.5 TgCO2-eq. in 1990 and 2005, respectively, although the difference between these net transfers may not be statistically significant. Net transfers were higher in 2005 primarily because additions to carbon stored in forest products were less in 2005. Over this same period, energy-related manufacturing emissions decreased by almost 9% even though forest products output increased by approximately 15%. Several types of avoided emissions were considered separately and were collectively found to be notable relative to net emissions.

Accounting for density reduction and structural loss in standing dead trees: Implications for forest biomass and carbon stock estimates in the United States

BackgroundStanding dead trees are one component of forest ecosystem dead wood carbon (C) pools, whose national stock is estimated by the U.S. as required by the United Nations Framework Convention on Climate Change. Historically, standing dead tree C has been estimated as a function of live tree growing stock volume in the U.S.s National Greenhouse Gas Inventory. Initiated in 1998, the USDA Forest Services Forest Inventory and Analysis program (responsible for compiling the Nations forest C estimates) began consistent nationwide sampling of standing dead trees, which may now supplant previous purely model-based approaches to standing dead biomass and C stock estimation. A substantial hurdle to estimating standing dead tree biomass and C attributes is that traditional estimation procedures are based on merchantability paradigms that may not reflect density reductions or structural loss due to decomposition common in standing dead trees. The goal of this study was to incorporate standing dead tree adjustments into the current estimation procedures and assess how biomass and C stocks change at multiple spatial scales.ResultsAccounting for decay and structural loss in standing dead trees significantly decreased tree- and plot-level C stock estimates (and subsequent C stocks) by decay class and tree component. At a regional scale, incorporating adjustment factors decreased standing dead quaking aspen biomass estimates by almost 50 percent in the Lake States and Douglas-fir estimates by more than 36 percent in the Pacific Northwest.ConclusionsSubstantial overestimates of standing dead tree biomass and C stocks occur when one does not account for density reductions or structural loss. Forest inventory estimation procedures that are descended from merchantability standards may need to be revised toward a more holistic approach to determining standing dead tree biomass and C attributes (i.e., attributes of tree biomass outside of sawlog portions). Incorporating density reductions and structural loss adjustments reduces uncertainty associated with standing dead tree biomass and C while improving consistency with field methods and documentation.

From Models to Measurements: Comparing Downed Dead Wood Carbon Stock Estimates in the U.S. Forest Inventory

The inventory and monitoring of coarse woody debris (CWD) carbon (C) stocks is an essential component of any comprehensive National Greenhouse Gas Inventory (NGHGI). Due to the expense and difficulty associated with conducting field inventories of CWD pools, CWD C stocks are often modeled as a function of more commonly measured stand attributes such as live tree C density. In order to assess potential benefits of adopting a field-based inventory of CWD C stocks in lieu of the current model-based approach, a national inventory of downed dead wood C across the U.S. was compared to estimates calculated from models associated with the U.S.’s NGHGI and used in the USDA Forest Service, Forest Inventory and Analysis program. The model-based population estimate of C stocks for CWD (i.e., pieces and slash piles) in the conterminous U.S. was 9 percent (145.1 Tg) greater than the field-based estimate. The relatively small absolute difference was driven by contrasting results for each CWD component. The model-based population estimate of C stocks from CWD pieces was 17 percent (230.3 Tg) greater than the field-based estimate, while the model-based estimate of C stocks from CWD slash piles was 27 percent (85.2 Tg) smaller than the field-based estimate. In general, models overestimated the C density per-unit-area from slash piles early in stand development and underestimated the C density from CWD pieces in young stands. This resulted in significant differences in CWD C stocks by region and ownership. The disparity in estimates across spatial scales illustrates the complexity in estimating CWD C in a NGHGI. Based on the results of this study, it is suggested that the U.S. adopt field-based estimates of CWD C stocks as a component of its NGHGI to both reduce the uncertainty within the inventory and improve the sensitivity to potential management and climate change events.

FORCARB2: An updated version of the U.S. Forest Carbon Budget Model

FORCARB2, an updated version of the U.S. FORest CARBon Budget Model (FORCARB), produces estimates of carbon stocks and stock changes for forest ecosystems and forest products at 5-year intervals. FORCARB2 includes a new methodology for carbon in harvested wood products, updated initial inventory data, a revised algorithm for dead wood, and now includes public forest land, reserved forest land, and forest land of low productivity. The model has been used to provide estimates and projections for policy-related needs, including the Resources Planning Act timber resource assessment and forest-related greenhouse gas inventories of the United States, and has provided the basis for an analysis of forest carbon for Ontario, Canada. The program is written in FORTRAN and is text based, though virtually every parameter is defined by input text-based files that can be modified or built by the user. We expect users who are fairly advanced in terms of knowledge about computers will be most capable in using this model. Step-by-step instructions for running the program, input and output files, and codes used are included, and input files for public forest lands of the United States are provided as an example. All electronic files for download, including the model source code, executable files, and input and output files are available at http://nrs.fs.fed.us/pubs/35613.

Estimating litter carbon stocks on forest land in the United States

Forest ecosystems are the largest terrestrial carbon sink on earth, with more than half of their net primary production moving to the soil via the decomposition of litter biomass. Therefore, changes in the litter carbon (C) pool have important implications for global carbon budgets and carbon emissions reduction targets and negotiations. Litter accounts for an estimated 5% of all forest ecosystem carbon stocks worldwide. Given the cost and time required to measure litter attributes, many of the signatory nations to the United Nations Framework Convention on Climate Change report estimates of litter carbon stocks and stock changes using default values from the Intergovernmental Panel on Climate Change or country-specific models. In the United States, the country-specific model used to predict litter C stocks is sensitive to attributes on each plot in the national forest inventory, but these predictions are not associated with the litter samples collected over the last decade in the national forest inventory. Here we present, for the first time, estimates of litter carbon obtained using more than 5000 field measurements from the national forest inventory of the United States. The field-based estimates mark a 44% reduction (2081±77Tg) in litter carbon stocks nationally when compared to country-specific model predictions reported in previous United Framework Convention on Climate Change submissions. Our work suggests that Intergovernmental Panel on Climate Change defaults and country-specific models used to estimate litter carbon in temperate forest ecosystems may grossly overestimate the contribution of this pool in national carbon budgets.