Carbon in Colorado’s Forests
Forests play a major role in atmospheric cycles. Carbon dioxide (CO₂) in the atmosphere, whether from human emissions or natural sources, traps heat from the Earth and radiates some of it back to the planet’s surface, leading to warming. Trees help mitigate this effect by absorbing CO₂ during photosynthesis and storing it as biomass in their trunks, branches, leaves and roots. Forests store large amounts of carbon, both in aboveground and belowground biomass, as well as in the soil. As forests grow and mature, they continue to sequester carbon, creating a significant carbon reservoir.
Colorado recognized the need for a detailed analysis of forest ecosystem and harvested wood product carbon, establishing a framework to continue monitoring these aspects in future years. This thorough characterization of statewide forest carbon stocks and fluxes serves as a foundation, informing efforts ranging from statewide policymaking to regional forest management planning, as well as local climate change adaptation and mitigation initiatives. Understanding these dynamics is crucial for scientists, policymakers and educators committed to achieving sustainable forest management and climate solutions in the state.
Contents
Report Breakdown
Background
The 2020 Colorado Forest Action Plan identified the need for more targeted and detailed analyses of forest carbon to better understand the specific roles and impacts of the state’s forested lands in climate mitigation, including their capacity for carbon sequestration and storage. Colorado lawmakers passed HB 22-1012, Wildfire Mitigation and Recovery, directing the Colorado State Forest Service to develop a statewide carbon accounting framework. This report addresses this directive and provides insights into the effects of changing environmental conditions and management activities on these forests, enabling more effective development and implementation of strategies for forest and carbon management.
The scope of this work includes Colorado’s forests and the associated harvested wood products derived from these forests. The framework, data sources, analysis and reporting leverage similar published reports from California, Oregon and Washington. It also enables future updates for monitoring and reporting and enhances transferability to other states in the intermountain region.
Forested lands can act as carbon sinks (absorbing more carbon than is released) or carbon sources (releasing more carbon than is captured after events like wildfires). Carbon pools, which are specific reservoirs where carbon is stored, include live and dead vegetation, soils and harvested wood products. This report summarizes carbon stocks and fluxes by pool, providing a comprehensive analysis of how carbon is stored and transferred.
Forest Ecosystem
The report adopts a carbon inventory framework developed by California, Oregon and Washington and focuses on forested land as defined by the USDA Forest Service’s Forest Inventory and Analysis (FIA) program. This approach tracks carbon stored in various components of the forest ecosystem, such as trees, roots and soil. Data is drawn from FIA’s extensive network of field plots, covering a wide range of forest types and ownerships. Colorado’s plots are remeasured every 10 years, with the initial installation beginning in 2002, so the first 10-year period is 2002 to 2011. The FIA program is a ground-based, permanent plot-remeasurement 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 national forest carbon inventory reporting.
Carbon stocks were calculated using the most recent ten years of available plot data (2010 to 2019) at the time of analysis. The average annual net carbon flux was calculated from plots initially measured between 2002 and2009 and remeasured from 2012 to2019. The change in forest carbon pools is calculated by tracking the growth, removals and mortality of trees re-measured ten years apart.
Colorado’s 22.8 million acres of forests held 1,552.6 ± 23.5 TgC between 2010 and 2019. The state’s forests were a net source of carbon, with forested land remaining forested emitting 0.9 TgC yr-1 based on plots first measured between 2002 to 2009 and remeasured from 2012 to 2019. Most of the forest carbon was in the live aboveground parts of the trees (20%) and in the soil (59%).
Widespread tree mortality during the reporting period (2002 to 2019) resulted in the largest carbon losses in the aboveground live carbon stocks, about 3.8 ± 0.5 TgC yr-1. Tree mortality removed 8.5 ± 0.6 TgC yr-1 from the aboveground live pool, which was much more than the carbon added by tree growth (5 TgC yr-1) and tree removal (0.4 TgC yr-1). This high tree mortality causes Colorado’s forests to become an overall carbon source.
As the live trees died, the amount of dead and downed woody material increased. Insects and diseases affected much more area (about 2.5 million hectares) than other disturbances, causing 85% of the total area impacted and 64% of the disturbance-related carbon losses.
National Forest System (NFS) lands had the largest forest area and carbon stock, followed by private lands, other federal lands, and state and local government lands. Forests on NFS lands had the greatest carbon loss (-0.608 TgC yr-1), followed by private lands (-0.138 TgC yr-1), state and local government lands (-0.046 TgC yr-1), and other federal lands (-0.030 TgC yr-1). Most forest types were net carbon sources, except for ponderosa pine and woodland hardwoods, which were weak carbon sinks. The aspen/birch forest group had the greatest net carbon loss (-0.586 TgC yr-1).
Nearly half of Colorado’s forest carbon was stored in two forest type groups: fir/spruce/mountain hemlock (29% of total stocks) and pinyon/juniper (20%). Carbon stocks and changes varied significantly across the four CSFS areas. Some forest types acted as carbon sinks in some regions but sources in others. The western CSFS regions had the most forest area and carbon stocks and experienced the greatest carbon losses.
Harvested Wood Products
Harvested wood product (HWP) carbon estimates for Colorado are based on an estimation tool developed by Groom Analytics LLC, CAL FIRE, and Oregon Department of Forestry. The HWP model follows annual harvest volumes through their timber product class allocation (i.e., sawlogs and pulpwood) and primary product allocation (i.e., lumber and panels). The model applies a 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.
The report utilized specific Colorado data sources for annual harvests and timber product ratios, categorized into four ownership groups to ensure consistency with the forest ecosystem model. Harvest data was compiled from various sources including the Western Wood Products Association yearbooks, USDA Four Corners reports, USFS Cut and Sold Reports, and Bureau of Land Management data, covering different years and ownership categories. While the HWP model captures the fate of harvested carbon, it uses separate data sources and is not linked to specific removal estimates as captured by FIA data. Only timber harvested within the state was used to assess carbon stocks in HWPs and imported wood was excluded. This method accounts solely for biogenic carbon emissions from harvested wood, omitting other carbon-containing greenhouse gases.
Carbon stocks were calculated using the most recent ten years of available plot data (2010 to 2019) at the time of analysis. The average annual net carbon flux was calculated from plots initially measured between 2002 and2009 and remeasured from 2012 to2019. The change in forest carbon pools is calculated by tracking the growth, removals and mortality of trees re-measured ten years apart.
The records of harvested wood products (HWP) show that from 1954 to 2019, Colorado harvested a total of 15.3 TgC (equivalent to 9.9 million thousand board feet of timber), averaging 0.2 TgC yr-1. The highest harvests were before 1979, after which they dropped by about half. Most of the timber (76%) came from the National Forest System lands, with the rest (22%) from private and Native American lands.
As of 2020, 5.8 TgC from harvested wood is still stored in products, with 46% in landfills and 54% in products still in use. The HWP sector acted as a carbon sink every year during the study period. The highest annual carbon capture was 0.2 TgC in 1969, and the lowest was 0.01 TgC in 2004.
Units
Units for carbon stocks are provided in teragrams of carbon (TgC), which is equivalent to million metric tons, or MMT C. Carbon flux values are provided in units of annual average teragrams of carbon per year (TgC yr-1) and carbon dioxide equivalent per year (TgCO2e yr-1). Carbon densities refer to the ecosystem’s carbon per unit area and are reported in megagrams per hectare.
Negative flux values represent a loss from that pool and positive fluxes represent growth in that pool. The negative net fluxes for Colorado forests represent overall loss of carbon from the forest ecosystem as carbon moves mainly to the atmosphere and harvested wood products and other mechanisms of export from the ecosystem.
Key Terms
Process of carbon entering a forest through photosynthesis, then stored in above or belowground pools, eventually released back to the atmosphere over time due to decomposition.
The amount of carbon stored within a specific carbon pool at a given point.
The change in carbon as it moves to another pool (e.g., transfer from the live aboveground pool to the dead aboveground pool), the atmosphere (e.g., decomposition of dead trees), or harvested wood products (i.e., cut trees).
The carbon dioxide (CO2) that is absorbed by trees during photosynthesis. It is stored within various biomass pools that may eventually return to the atmosphere through respiration, decomposition, or disturbance (i.e. fire or insect outbreak causing mortality).
Forests that have more carbon entering the system than leaving through decomposition or disturbance.
Forests that have more carbon leaving the system than being stored over time.
- Aboveground live tree – All live trees greater than or equal to 1.0 inch diameter at breast height (DBH) or 1.0 inch diameter at root collar (DRC) for woodland species.
- Aboveground standing dead tree – This pool includes standing dead trees that are greater than or equal to 5.0 inches DBH or DRC.
- Belowground live and dead – This pool includes belowground live and dead tree roots. This is disaggregated to belowground live and belowground dead in the report.
- Down woody material – Carbon pool of down woody material as defined in the FIA protocol.
- Aboveground and belowground understory vegetation – This pool is modeled from live tree carbon, geographic area, forest type and plot characteristics. It includes the aboveground and belowground components of woody shrubs and seedlings less than 1.0 inch DBH or DRC.
- Forest floor – Forest floor carbon includes duff and litter and was modeled as described in Domke et al. (2016).
- Soil – This pool includes soil organic carbon up to 1 meter in depth and is based on the model provided in Domke et al. (2017).
- Products in use – Wood products in active use.
- Solid waste disposal sites – Products that have been discarded.
Frequently Asked Questions
FIA plots are measured every 10 years, and this inventory assessed plots measured between 2002 and 2019, given data availability. Three of the largest state’s fires on record burned in 2020, but it can take time for the impact of these fire to be reflected in FIA plots and analyses. Given the 10-year remeasurement cycle, post-fire plots are being measured, but these conditions may not be captured fully until 2030.
We do capture fires that occurred prior to 2019, but at different capacities depending on when they burned. For example, the 2002 Hayman Fire is reflected in the carbon stocks, but since plots were not measured before and after this fire, the change in carbon (flux) is not captured. Other fires, like the 2012 High Park are captured in the stocks and fluxes since the first measurement period was before the fire. This report represents one snapshot in time that will be updated in the future.
Insects and disease outbreaks had the greatest impact of all disturbances. They impacted more forested areas than all other disturbances combined (wildfire, harvest, weather), accounting for 85% of the total disturbed area and 64% of the carbon loss due to disturbances. This varies by region within Colorado, with certain areas experiencing more severe effects depending on local tree species, climate, and management. For example, lodgepole pine forests in the NW portion of the state were severely impacted by mountain pine beetle outbreaks while the SW portion of the state was severely impacted by spruce beetles in recent decades. The associated forest type groups in these regions (spruce, fir, lodgepole pine) had large losses in forest ecosystem carbon. For more information on insect and disease outbreaks, check out CSFS’s annual forest health reports.
In forests with no disturbance within our study period, forests sequestered more carbon than they released, acting as a net sink.
This report is not meant to inform stand or project-scale forest management. However, the results of this project offer valuable insights for broader strategic planning, including statewide and landscape-level prioritization. For example, by identifying regions experiencing high forest carbon loss, it can help determine where targeted management is most needed. Further, it provides the state with a reference point, against which future changes, trends, and the effectiveness of forest management practices can be measured. Additionally, it serves as a useful tool for counties to shape strategic initiatives, such as climate action plans, by highlighting specific areas of concern and opportunity.
Not at this time. The forest ecosystem side of the report only reports on forested areas from the traditional, rural-focused FIA program. Although CSFS’s FIA field crews do collect urban data, a full panel (10-years of data covering the state) will not be complete until after 2025.
The statistic on our website is from Landfire EVT 2014, which estimates there are 24 million acres of forests and woodlands in Colorado. Our report utilized data from Forest Inventory and Analysis (FIA) to estimate the number of forested acres, which came to 22.8 million acres. This difference is because the two data sources use different methodologies and data collection criteria to estimate forested areas. More information on FIA’s methodology is found in section 3.1 of the report.
Explore the Data
Downloads
This spreadsheet contains input data for the Rocky Mountain region in Groom Analytics’ Harvested Wood Products Model, including Colorado specific inputs for annual harvests, conversions factors, and annual timber product ratios.
This spreadsheet contains the output data from Groom Analytics’ Harvested Wood Products Model, including annual harvests, carbon storage, emissions, and cumulative changes in timber product pools and emissions across ownerships, with results provided in units of TgC and TgCO2e.
Learn More
Since the late 1990’s, the USFS has collaborated with the Colorado State Forest Service to conduct and continuously update a comprehensive inventory and analysis of the forest and rangeland conditions in Colorado and Wyoming. Learn more about FIA.
Forest carbon markets are one natural solution to increasing carbon sequestration, which reduces the amount of greenhouse gases entering the atmosphere in the long term. Carbon markets exchange carbon credits and provide a way for forest landowners to derive long-term, non-consumptive value from well-managed forests. Explore the science & data byte to learn more.
The authors gratefully acknowledge everyone who contributed to the development of this report. Special thanks are extended to Nadia Tase of CALFIRE and Jeremy Groom of Groom Analytics for their significant contributions and engagement throughout the report’s development. Appreciation is also expressed to Sara Goeking, Kristen Pelz, Erin Berryman, Karin Kralicek and Erich Kyle Dodson of the USDA Forest Service Rocky Mountain Research Station Forest Inventory and Analysis (FIA) program, as well as Glenn Christensen of the USDA Forest Service Pacific Northwest Research Station. The authors recognize the invaluable support from the CSFS FIA program who collect critical data in Colorado’s forests. Expert advice and assistance from Keith Stockman and Todd Morgan are also acknowledged.