Alarming Trend: Colorado’s Forests Are Releasing More Carbon Than They Absorb

Due to tree mortality from insects, disease, and wildfires, Colorado’s forests now emit more carbon than they absorb. A new Forest Carbon Inventory tracks these changes, providing valuable data for policymakers and forest managers.

Colorado’s forests store vast amounts of carbon, but in recent years, they have released more carbon than they absorbed, primarily due to tree deaths caused by insects and disease, according to a Colorado State Forest Service report.

Trees naturally absorb carbon dioxide, helping to reduce the amount of this heat-trapping gas in the atmosphere. However, when trees die and decompose, they gradually release stored carbon back into the environment.

The report’s findings are valuable as policymakers consider options for drawing down carbon to reduce climate change and forest managers develop long-term strategies for forest and carbon management.

“People are looking to our natural ecosystems to mitigate climate change,” said Tony Vorster, lead author of the report and a research scientist with the Natural Resource Ecology Laboratory. “We shouldn’t necessarily look to our forests to offset emissions because they’re currently a net carbon source across the state as a whole, and that trend is probably going to continue with ongoing droughts and wildfires.”

Vorster said that future reports will show Colorado’s forests are an even greater source of carbon because of recent severe wildfires that were not accounted for in the report released Jan. 9, which covers 2002-2019.

A Comprehensive Forest Carbon Inventory

The state-mandated Forest Carbon Inventory provides the most detailed and comprehensive assessment to date of how much carbon is stored in Colorado’s forests and harvested wood products and how that amount is changing over time.

“It’s natural for forests to cycle through times where they are carbon sinks and then carbon sources. We’re interested in long-term trends,” Vorster said.

Researchers from the Colorado State Forest Service and the Natural Resource Ecology Laboratory, both part of Colorado State University’s Warner College of Natural Resources, developed a statewide carbon accounting framework to produce the ongoing inventory. The inventory establishes a baseline for measuring future changes, so managers and policymakers can gauge the long-term effectiveness of decisions. It will be updated every few years.

“While other reports have provided estimates for forest carbon, this report stands out as the first to focus solely on the state’s forest sector,” said Ashley Prentice, a CSFS forest carbon specialist and co-author of the report. “It delivers a detailed, in-depth analysis of how much carbon is stored, how it is changing, and the factors driving these changes.”

Researchers estimated that Colorado’s 22.8 million acres of forests and harvested wood products stored 1,558 teragrams of carbon between 2010 and 2019. (A teragram is one trillion grams or a million metric tons.) To put that into perspective, Prentice said if all that carbon were released, it would be roughly equivalent to annual carbon dioxide emissions from 1.3 billion gas-powered vehicles.

Compared to their total carbon stock, the state’s forests emit a relatively small 0.9 teragrams of carbon annually, Prentice calculated, which is roughly equivalent to the annual carbon dioxide emissions from 770,000 vehicles.

Patchwork of carbon gains and losses

Trees are half carbon. They absorb carbon dioxide through photosynthesis and store it as biomass in their trunks, branches, leaves, roots, and in the soil.

This inventory is the first for Colorado to include harvested wood products, like lumber or furniture, which continue to store carbon until they decompose or are burned. Harvested wood contributed only a small fraction of carbon to the state’s overall stock, 0.4%; however, Prentice said, “These products represent an opportunity for long-term carbon storage while also supporting local economies.”

Changes in carbon stocks varied greatly across forest types and locations, in line with disturbances by wildfire, weather, insects, disease, and timber harvest.

Insects and disease – most notably, bark beetle outbreaks – affected more forests than wildfire, harvest, and weather combined during the study period. Insects and disease were responsible for 85% of the total area impacted by disturbances and 64% of disturbance-related carbon losses.

Undisturbed forests sequestered more carbon than they emitted.

So, can we just plant more trees to make up the difference?

“We’re not going to plant our way out of this, but reforestation is a strategy that can be used to reduce the loss of forest and to mitigate some of these carbon losses,” Vorster said.

He stressed that while the inventory is focused on carbon, it is only one of a host of factors forest managers consider, including wildlife, recreation, economics, and wildfire risk. He also noted that it’s important to take the long view in carbon management. For example, forest thinning to limit wildfire severity might cost carbon stocks in the short term but could retain more carbon in the long run.

Tree-level tracking

The inventory calculated higher carbon stocks and lower emissions than past estimates, probably due to differences in methodology, Vorster said.

In developing a new inventory framework, CSFS and NREL adapted estimation methods used by West Coast states for the Rocky Mountain region, creating a template that can be used by other states.

The inventory tracks tree-level growth, removal, and mortality trends through federal data from the U.S. Forest Service’s Forest Inventory and Analysis program. CSFS surveys Colorado’s FIA plots every 10 years, beginning in 2002, for consistent, long-term data on individual trees. The plots are representative of the state’s overall forested area, on both public and private land, but do not include urban trees. Timber harvest data going back to 1954 was used to determine carbon stock and changes in harvested wood products.

Reference: Carbon in Colorado’s Forests

The research was funded by the State of Colorado.

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