Greenhouse Gas Emmissions From Four California Wildfires: Opportunities to prevent and Reverse Environmental And Climate Impacts

פורסם: 4 בדצמ׳ 2010, 21:33 על ידי: Sustainability Org   [ עודכן 5 בדצמ׳ 2010, 4:30 ]
By Thomas M. Bonnicksen, Ph.D.
Published on: 11/8/2008
המרת מידות: 1 אייקר = 4,407 מ"ר = 4.047 דונם = 0.004 קמ"ר

Forests and forestry are playing an increasingly important role in sequestering carbon and reducing greenhouse gas emissions, especially during a period of rising concerns about global warming. The Forest Carbon and Emissions Model (FCEM) used in this study estimates forest carbon storage, sequestration, and greenhouse gas (GHG) emissions using equations from recognized scientific sources.

The purpose of this report is to provide estimates that illustrate the impact of wildfires on greenhouse gas emissions and the importance of thinning forests to protect forests and communities, and to prevent emissions from combustion and decay. It also focuses on the significance of removing dead trees and replanting to restore forests and recover greenhouse gases released by wildfire.

Climate Impacts of Wildfires

This report analyzes four catastrophic California wildfires using FCEM: the Angora, Fountain, Moonlight, and Star Fires. Together these wildfires burned over 144,825 acres of forestland.

Those who have not stood in the midst of flames 200-feet high, felt the overwhelming heat from a temperature more than 3,000 degrees Fahrenheit, and smelled the smoke and gases released, cannot fully appreciate a catastrophic wildfire. It is awesome and terrible, and firefighters who brave these conditions deserve our respect.

The four forests burned by these wildfires were overcrowded with trees — with trees of all sizes intermixed to form a uniform mass of fuel spreading over the landscape. They averaged 350 trees per acre when 50-60 trees per acre would be natural. They also contained unnaturally heavy surface fuels composed of litter, duff, down dead wood, shrubs, and small trees that ranged from an estimated 25 to 40 tons per acre. Tree density, especially young trees growing under larger trees as ladder fuel, and surface fuels are the two most important contributors to the size and severity of wildfires.

Consequently, when the massive amounts of fuel in these forests burned, they released an estimated 9.5 million tons of greenhouse gases into the atmosphere just from combustion. That is an average of about 63 tons per acre. However, combustion is only part of the story because dead trees also gradually release CO2 as they decay. CO2 emissions from decay are generally three times greater than emissions from combustion because large quantities of wood and other plant material remain unburned after a forest fire.

Combining combustion and decay emissions, FCEM estimates that these four fires will emit a staggering 38 million tons of greenhouse gases into the atmosphere. The fires released one fourth of the gases during combustion, and post-fire decay will release the remainder during the next 100 years, most of it during the next 50 years.

To put these emissions from combustion and decay into perspective, they are equivalent to adding an estimated 7 million more cars onto California’s highways for one year, each spewing tons of greenhouse gases out the tailpipe. Stated another way, this means 50 percent of all cars in California would have to be locked in a garage for one year to make up for the global warming impact of these four wildfires.

Opportunities for Action

One way to compensate for greenhouse gas emissions from wildfires is to lower the amount of biomass available for decay. Removing dead trees and storing the carbon they contain in the solid wood products consumers need can reduce total CO2 emissions by as much as 15 percent. Planting a young forest to replace one killed by wildfire and letting the growing trees absorb CO2 from the atmosphere through photosynthesis is another way. Doing both, especially with interim harvests for wood products after planting, effectively reverses the impact of wildfire emissions on global warming.

This report estimates accomplishments, planned and completed, to reduce and recover greenhouse gas emissions from four areas blackened by catastrophic wildfires in California. So far, FCEM estimates that these actions, in combination, will compensate for 42 to 114 percent of the actual and potential CO2 losses caused by three of the four wildfires.
Even so, opportunities still exist to do even more to restore two of the four forests burned and fight global warming. In particular, removing dead trees and planting national forest lands burned by the 2007 Angora and Moonlight Fires could recover an estimated 98 to more than 100 percent of the CO2 losses they caused. Equally important, these actions would help protect surrounding communities from a second wildfire or re-burn, which often occurs in forests that become dead-tree filled brush fields.

The immensity of greenhouse gas emissions from just these four wildfires is a warning. Clearly, we must make every effort to reduce the amount of excess biomass in forests to prevent catastrophic wildfires. That means decreasing the number of trees by thinning to make them more resistant to crown fires, which will also restore the natural health and diversity of our forests. Reducing the number and severity of wildfires may be the single most important action we can take in the short-term to lower greenhouse gas emissions and fight global warming.

Greenhouse Gas Emissions from Combustion

המרת מידות: 1 אייקר = 4,407 מ"ר = 4.047 דונם = 0.004 קמ"ר
Table 5 shows greenhouse gas emissions from combustion caused by the four wildfires analyzed in this report. The average is 62.8 tons of greenhouse gases emitted per acre. This is typical for California fires burning in today’s overcrowded forests. They exceed emissions that would have occurred in historic fires because the biomass available to burn is so much greater than it was in natural forests.

The emissions in Table 5 are large and difficult to interpret without comparisons. Therefore, Table 6 shows how many cars would be added to California’s highways for one year, each spewing tons of greenhouse gases out of the tailpipe, to equal combustion emissions. Seen another way, it shows how many cars in total and cars per acre burned that would have to be taken off the road and locked in a garage for one year to make up for the global warming impact of these four wildfires.


Greenhouse Gas Emissions from Combustion and Decay

Combustion emissions occur during a wildfire, but they are only part of the story because dead trees also gradually release CO2 as they decay. Dead trees generally decompose within about 100 years, most of the decay occurring in the first 50 years. As a conservative estimate, FCEM considers dead biomass left after a fire as carbon that will decay in 100 years and computes the amount of CO2 released accordingly.

Greenhouse gas emissions from decay (רקבון) are generally larger than combustion emissions. The reason is that 3.67 times the carbon content of biomass is released as CO2 during decomposition. Therefore, forests emit more CO2 when they decay than when they burn because large quantities of biomass remain in the forest after combustion. However, chaparral and brush fields burn more completely, so combustion emissions can exceed decay emissions.

Combining combustion and decay emissions provides a more complete picture of the impact of wildfires on global warming. In general, CO2 emissions from decay after a forest fire are three times the amount emitted during combustion. Table 7 shows the magnitude of CO2 emissions for the four forest fires analyzed, including passenger car equivalents.

The immensity of greenhouse gas emissions illustrated in Table 7 from just these four wildfires is a warning. Clearly, we must make every effort to reduce the amount of excess biomass in forests to prevent catastrophic wildfires. That means thinning trees to restore the natural health and diversity of forests and to make them more resistant to crown fires. Reducing wildfires maybe the single most important action we can take in the short-term to reduce greenhouse gas emissions and fight global warming.

Appendix A: The Forest Carbon and Emissions Model (FCEM)

Only recently has it been possible to estimate greenhouse gas emissions from wildfires and insect infestations. The Forest Carbon and Emissions Model (FCEM) used in this study is at the forefront of making these estimates (Bonnicksen 2008). The model is unique among available carbon models because of its simplicity and relevance to forest management. Even so, there is no accepted standard model for greenhouse gas emissions and carbon sequestration.

FCEM is a deterministic biomass-based model that uses an Excel spreadsheet to compute estimates. The model calculates estimates by systematically linking existing equations, ratios, and conversion and emission factors from a variety of recently published peer-reviewed scientific and other technical sources. The latter sources include non-peer-reviewed reports from universities, government agencies, and consulting firms.

In particular, FCEM computes above ground tree biomass using generalized allometric equations approved by the California Climate Action Registry (2007) as shown in FCEM Report 1 (Bonnicksen 2008) and reports cited by California Climate Action Registry (Brown et al. 2004a, 2004b, 2004c). FCEM computes estimates based on formulas and data from specific areas rather than relying on extrapolating results from case studies or generic forests and applying them to other places that may or may not be similar.

FCEM is a tool for conducting preliminary inventories of forest biomass, carbon, and CO2 stored in a particular forest, now or in the future, including tree stems, roots, foliage, branches, litter, duff, understory, down dead, standing dead, and soil. Other more comprehensive models should be used for scientific investigations and carbon accounting.

FCEM also includes four scenarios for estimating the impacts of fire and insect infestations, the benefits of removing dead trees and converting them into solid wood products, thinning, and planting. The model also estimates the relative impacts of wildfire and prescribed fire on emissions, before and after thinning, and thinning with and without prescribed fire. FCEM compares impacts and benefits in terms of greenhouse gas emissions and carbon sequestration and storage.

The goal behind the Forest Carbon and Emissions Model (FCEM) is to create an awareness of the impact of wildfire and insect infestations on greenhouse gas emissions and opportunities to prevent and recover from these disasters.

Source: rethinkforests.com

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