Fire and carbon cycling in boreal forests

Last updated January 29, 2024

Terrestrial ecosystems found in the boreal (or taiga) regions of North America and Eurasia cover 17% of the Earth's land surface, and contain more than 30% of all carbon present in the terrestrial biome.^[1] In terms of carbon storage, the boreal region consists of three ecosystems: boreal forest, peatland, and tundra. Vast areas of the globe and are contributing greatly to atmospheric carbon release due to increased temperature and fire hazard. High northern latitudes will experience the most significant increase in warming on the planet as a result of increased atmospheric greenhouse gases thus placing in jeopardy the carbon sink in these areas. In addition to the release of carbon through the melting of permafrost, high intensity wildfires will become more common and thus contribute to the release of stored carbon. This means that the boreal forest and its fire regime is becoming an increasingly more significant factor in determining the global carbon budget.

Boreal forests are also important economic factors in Russia and Canada specifically, and the uncertainty of fire patterns in the future as a result of climate change is a major consideration in forest management plans. A decrease in allowed timber harvest could be a solution to long term uncertainty of fire cycles.^[2]

Carbon cycling in boreal forests

Although temperate and tropical forests in total cover twice as much land as boreal forest, boreal forest contains 20% more carbon than the other two combined.^[1] Boreal forests are susceptible to global warming because the ice/snow–albedo feedback is significantly influenced by surface temperature, so fire induced changes in surface albedo and infrared emissivity are more significant than in the tropics.^[3]

Boreal forest fires contribute greatly to greenhouse gas presence in the atmosphere. Large boreal fires produce enough energy to produce convective smoke columns that can break into the troposphere and occasionally penetrate across the tropopause. In addition, the cold temperature in boreal regions result in low levels of water vapor. This low level of water vapor combined with low solar radiation results in very low photochemical production of the OH radical, which is a chemical that controls the atmospheric lifetime of most tropospheric gases. Therefore, the greenhouse gas emission in boreal forest fires will have prolonged lifetimes over the forest.^[3]

Fire regime

The fire regimes of boreal forest in Canada and in Russia are distinct. In Russia, the climate is drier and the majority of fires are human caused. This means that there are more frequent fires of lower intensity than in Canada and that most carbon output as a result of fire is in Russia.^{[ citation needed ]} Forestry practices in Russia involve the use of heavy machinery and large-scale clear-cuts, leading to the alteration of fuel complexes. This practice is reportedly causing areas to degrade into grass steppes, rather that regenerate as new forest. This may result in the shorting of fire return intervals. Industrial practices in Russia also create additional fire hazards (severe damages in the Russian Federation affect about 9 million ha). Radioactive contamination on an area of about 7 million ha creates a fire hazard because fire can redistribute radionuclides.^[4]

The majority of boreal forest fires in Canada are started by lightning. Subsequently, there are fewer fires on average in Canada but a much higher frequency of high intensity crown fire than Russia with a crown fire rate of 57% in Canada as opposed to 6% in Russia.^[5] Natural fire rotation across Canadian and Alaskan boreal forests is one to several centuries.

Peatland and tundra

Fire indirectly plays a role in the exchange of carbon between terrestrial surface and the atmosphere by regulating soil and moisture regimes, including plant succession, photosynthesis, and soil microbial processes. Soil in boreal regions is a significant global carbon sink; boreal forest soil holds 200 Gt of carbon while boreal peatlands hold 400 Gt of carbon. Northernmost permafrost regions contain 10,355 ± 150 Pg of soil organic carbon (SOC) in the top 0-3 m and 21% of this carbon is in the soil organic layer (SOL) pool found in the top 30 cm of the ground layer.^[7]

The depth of the organic soil layer is one of the controls on permafrost, leading to a generalization of two domains in boreal forest: thick soil layer and thin soil layer. Thick organic soil insulates the subsoil from warmer summer temperatures and allows for permafrost to develop. Although permafrost keeps ground moist during winter, during summer months upper organic soil horizons will become desiccated. As average temperatures increase, Permafrost is melting at a faster rate and, correspondingly, the length of the fire season is increasing. When the fire-free interval (FFI) is decreased, the loss of the SOL may result in a domain change to a thin soil layer, leading to less carbon storage in the soil, greater fire vulnerability, and decreased permafrost. In black spruce forests, decreased FFI can ruin successional trajectories by opening the door for deciduous trees and shrubs to invade, which also further increases fire vulnerability.^[7]

Data regarding carbon storage in the permafrost region as well as fire activity in boreal forests is sparse, which is a significant barrier in determining an accurate carbon budget. An expert assessment indicates that the permafrost region will become a net carbon source by 2100.^[8]

A 5 - 10 degree C rise in forest floor temperature after a fire will significantly increase the rate of decomposition for years after the fire occurs, which temporarily turns the soil into a net carbon source (not sink) locally.^[1]

Fire enhances the biogenic emissions of NO and N20 from soil.^[3]

Related Research Articles

A carbon sink is anything, natural or otherwise, that accumulates and stores some carbon-containing chemical compound for an indefinite period and thereby removes carbon dioxide from the atmosphere. These sinks form an important part of the natural carbon cycle. An overarching term is carbon pool, which is all the places where carbon can be. A carbon sink is a type of carbon pool that has the capability to take up more carbon from the atmosphere than it releases.

In physical geography, tundra is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. The term comes from the Finnish word tunturia, meaning "treeless plain". There are three regions and associated types of tundra: Arctic tundra, alpine tundra, and Antarctic tundra.

Taiga, generally referred to in North America as a boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches.

Permafrost is soil or underwater sediment which continuously remains below 0 °C (32 °F) for two years or more: the oldest permafrost had been continuously frozen for around 700,000 years. While the shallowest permafrost has a vertical extent of below a meter, the deepest is greater than 1,500 m (4,900 ft). Similarly, the area of individual permafrost zones may be limited to narrow mountain summits or extend across vast Arctic regions. The ground beneath glaciers and ice sheets is not usually defined as permafrost, so on land, permafrost is generally located beneath a so-called active layer of soil which freezes and thaws depending on the season.

In environments containing permafrost, the active layer is the top layer of soil that thaws during the summer and freezes again during the autumn. In all climates, whether they contain permafrost or not, the temperature in the lower levels of the soil will remain more stable than that at the surface, where the influence of the ambient temperature is greatest. This means that, over many years, the influence of cooling in winter and heating in summer will decrease as depth increases.

A boreal ecosystem is an ecosystem with a subarctic climate located in the Northern Hemisphere, approximately between 50° and 70°N latitude. These ecosystems are commonly known as taiga and are located in parts of North America, Europe, and Asia. The ecosystems that lie immediately to the south of boreal zones are often called hemiboreal. There are a variety of processes and species that occur in these areas as well.

Major environmental issues caused by contemporary climate change in the Arctic region range from the well-known, such as the loss of sea ice or melting of the Greenland ice sheet, to more obscure, but deeply significant issues, such as permafrost thaw, as well as related social consequences for locals and the geopolitical ramifications of these changes. The Arctic is likely to be especially affected by climate change because of the high projected rate of regional warming and associated impacts. Temperature projections for the Arctic region were assessed in 2007: These suggested already averaged warming of about 2 °C to 9 °C by the year 2100. The range reflects different projections made by different climate models, run with different forcing scenarios. Radiative forcing is a measure of the effect of natural and human activities on the climate. Different forcing scenarios reflect things such as different projections of future human greenhouse gas emissions.

Climate change has serious effects on Russia's climate, including average temperatures and precipitation, as well as permafrost melting, more frequent wildfires, flooding and heatwaves. Changes may affect inland flash floods, more frequent coastal flooding and increased erosion reduced snow cover and glacier melting, and may ultimately lead to species losses and changes in ecosystem functioning.

<span class="mw-page-title-main">Arctic methane emissions</span> Release of methane from seas and soils in permafrost regions of the Arctic

Arctic methane release is the release of methane from seas and soils in permafrost regions of the Arctic. While it is a long-term natural process, methane release is exacerbated by global warming. This results in a positive feedback cycle, as methane is itself a powerful greenhouse gas.

The 2004 Alaska fire season was the worst wildfire season on record in the U.S. state of Alaska in terms of area burned. Though the 1989 fire season recorded more fires, nearly 1,000, the 2004 season burned more than 6,600,000 acres in just 701 fires. The largest of these fires was the Taylor Complex Fire. This fire consumed over 1,700,000 acres and was the deemed to be the largest fire in the United States from at least 1997 to 2019. Out of all 701 fires, 426 fires were started by humans and 215 by lightning.

Climate change feedbacks are effects of global warming that amplify or diminish the effect of forces that initially cause the warming. Positive feedbacks enhance global warming while negative feedbacks weaken it. Feedbacks are important in the understanding of climate change because they play an important part in determining the sensitivity of the climate to warming forces. Climate forcings and feedbacks together determine how much and how fast the climate changes. Large positive feedbacks can lead to tipping points—abrupt or irreversible changes in the climate system—depending upon the rate and magnitude of the climate change.

The permafrost carbon cycle or Arctic carbon cycle is a sub-cycle of the larger global carbon cycle. Permafrost is defined as subsurface material that remains below 0^o C for at least two consecutive years. Because permafrost soils remain frozen for long periods of time, they store large amounts of carbon and other nutrients within their frozen framework during that time. Permafrost represents a large carbon reservoir, one which was often neglected in the initial research determining global terrestrial carbon reservoirs. Since the start of the 2000s, however, far more attention has been paid to the subject, with an enormous growth both in general attention and in the scientific research output.

The carbon cycle is an essential part of life on Earth. About half the dry weight of most living organisms is carbon. It plays an important role in the structure, biochemistry, and nutrition of all living cells. Living biomass holds about 550 gigatons of carbon, most of which is made of terrestrial plants (wood), while some 1,200 gigatons of carbon are stored in the terrestrial biosphere as dead biomass.

A peatland is a type of wetland whose soils consist of organic matter from decaying plants, forming layers of peat. Peatlands arise because of incomplete decomposition of organic matter, usually litter from vegetation, due to water-logging and subsequent anoxia. Like coral reefs, peatlands are unusual landforms that derive mostly from biological rather than physical processes, and can take on characteristic shapes and surface patterning.

<span class="mw-page-title-main">Deforestation and climate change</span> Relationship between deforestation and global warming

Deforestation is a primary contributor to climate change, and climate change affects forests. Land use changes, especially in the form of deforestation, are the second largest anthropogenic source of atmospheric carbon dioxide emissions, after fossil fuel combustion. Greenhouse gases are emitted during combustion of forest biomass and decomposition of remaining plant material and soil carbon. Global models and national greenhouse gas inventories give similar results for deforestation emissions. As of 2019, deforestation is responsible for about 11% of global greenhouse gas emissions. Carbon emissions from tropical deforestation are accelerating. Growing forests are a carbon sink with additional potential to mitigate the effects of climate change. Some of the effects of climate change, such as more wildfires, insect outbreaks, invasive species, and storms are factors that increase deforestation.

Changing climate conditions are amplified in polar regions and northern high-latitude areas are projected to warm at twice the rate of the global average. These modifications result in ecosystem interactions and feedbacks that can augment or mitigate climatic changes. These interactions may have been important through the large climate fluctuations since the glacial period. Therefore it is useful to review the past dynamics of vegetation and climate to place recent observed changes in the Arctic into context. This article focuses on northern Alaska where there has been much research on this theme.

Susan M. Natali is an American ecologist. She is the Arctic program director and senior scientist at the Woodwell Climate Research Center, where her research focuses on the impact of climate change on terrestrial ecosystems, primarily on Arctic permafrost. She is also the project lead for Permafrost Pathways, a new initiative launched in 2022 with funding from TED's Audacious Project. On Monday, April 11, 2022, Dr. Natali gave a TED Talk introducing the Permafrost Pathways project at the TED2022 conference in Vancouver, BC.

Jennifer Harden is geologist known for her research on soils, particularly tracking changes in soil profiles over time and the role of soil systems in carbon and nitrogen cycling.

Merritt Turetsky is an American ecosystem ecologist and a professor at the University of Colorado Boulder. She currently serves as the Director of Arctic Security for the University of Colorado. She served as the first woman Director of the Institute for Arctic and Alpine Research (INSTAAR) from 2019-2023. Her research considers fire regimes, climate change and biogeochemical cycling in Arctic wetlands. Turetsky is a member of the Permafrost Action Team (SEARCH), a group of scientists who translate and deliver science to decision-makers.

The Taiga of North America is a Level I ecoregion of North America designated by the Commission for Environmental Cooperation (CEC) in its North American Environmental Atlas.

References

1 2 3 Kasischke, Eric S. (2000). "Boreal Ecosystems in the Global Carbon Cycle". Fire, Climate Change, and Carbon Cycling in the Boreal Forest. Ecological Studies. Vol. 138. pp. 19–30. doi:10.1007/978-0-387-21629-4_2. ISBN 978-1-4684-9532-4.
↑ Daniel, Colin J.; Ter-Mikaelian, Michael T.; Wotton, Mike B.; Rayfield, Bronwyn; Fortin, Marie-Josée (2017). "Incorporating uncertainty into forest management planning: Timber harvest, wildfire and climate change in the boreal forest". Forest Ecology and Management. Elsevier B.V. 400: 542–554. doi: 10.1016/j.foreco.2017.06.039 .
1 2 3 Levine, Joel S.; Cofer III, Wesley R. (2000). "Boreal Forest Fire Emissions and the Chemistry of the Atmosphere". Ecological Studies. 138: 44–45.
↑ Goldammer, Johann G.; Stocks, Brian J. (2000). "Eurasian Perspective of Fire: Dimension, Management, Policies, and Scientific Requirements". Ecological Studies. 138: 53.
↑ de Groot, William J.; Cantin, Alan S.; Flannigan, Michael D.; Soja, Amber J.; Gowman, Lynn M.; Newbery, Alison (2013-04-15). "A comparison of Canadian and Russian boreal forest fire regimes". Forest Ecology and Management. The Mega-fire reality. 294 (Supplement C): 23–34. doi:10.1016/j.foreco.2012.07.033.
↑ "GISS Surface Temperature Analysis (v4)". NASA. Retrieved 12 January 2024.
1 2 Hoy, Elizabeth E.; Turetsky, Merritt R.; Kasischke, Eric S. (2016). "More frequent burning increases vulnerability of Alaskan boreal black spruce forests". Environmental Research Letters. 11 (9): 095001. Bibcode:2016ERL....11i5001H. doi: 10.1088/1748-9326/11/9/095001 . ISSN 1748-9326.
↑ Abbott, Benjamin W.; Jones, Jeremy B.; Schuur, Edward A. G.; III, F. Stuart Chapin; Bowden, William B.; Bret-Harte, M. Syndonia; Epstein, Howard E.; Flannigan, Michael D.; Harms, Tamara K. (2016). "Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment". Environmental Research Letters. 11 (3): 034014. Bibcode:2016ERL....11c4014A. doi: 10.1088/1748-9326/11/3/034014 . hdl: 1912/8229 . ISSN 1748-9326.

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[:0-1] 1 2 3 Kasischke, Eric S. (2000). "Boreal Ecosystems in the Global Carbon Cycle". Fire, Climate Change, and Carbon Cycling in the Boreal Forest. Ecological Studies. Vol. 138. pp. 19–30. doi:10.1007/978-0-387-21629-4_2. ISBN 978-1-4684-9532-4.

[2] Daniel, Colin J.; Ter-Mikaelian, Michael T.; Wotton, Mike B.; Rayfield, Bronwyn; Fortin, Marie-Josée (2017). "Incorporating uncertainty into forest management planning: Timber harvest, wildfire and climate change in the boreal forest". Forest Ecology and Management. Elsevier B.V. 400: 542–554. doi: 10.1016/j.foreco.2017.06.039 .

[:1-3] 1 2 3 Levine, Joel S.; Cofer III, Wesley R. (2000). "Boreal Forest Fire Emissions and the Chemistry of the Atmosphere". Ecological Studies. 138: 44–45.

[4] Goldammer, Johann G.; Stocks, Brian J. (2000). "Eurasian Perspective of Fire: Dimension, Management, Policies, and Scientific Requirements". Ecological Studies. 138: 53.

[5] Groot, William J.; Cantin, Alan S.; Flannigan, Michael D.; Soja, Amber J.; Gowman, Lynn M.; Newbery, Alison (2013-04-15). "A comparison of Canadian and Russian boreal forest fire regimes". Forest Ecology and Management. The Mega-fire reality. 294 (Supplement C): 23–34. doi:10.1016/j.foreco.2012.07.033.

[6] "GISS Surface Temperature Analysis (v4)". NASA. Retrieved 12 January 2024.

[:2-7] 1 2 Hoy, Elizabeth E.; Turetsky, Merritt R.; Kasischke, Eric S. (2016). "More frequent burning increases vulnerability of Alaskan boreal black spruce forests". Environmental Research Letters. 11 (9): 095001. Bibcode:2016ERL....11i5001H. doi: 10.1088/1748-9326/11/9/095001 . ISSN 1748-9326.

[8] Abbott, Benjamin W.; Jones, Jeremy B.; Schuur, Edward A. G.; III, F. Stuart Chapin; Bowden, William B.; Bret-Harte, M. Syndonia; Epstein, Howard E.; Flannigan, Michael D.; Harms, Tamara K. (2016). "Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment". Environmental Research Letters. 11 (3): 034014. Bibcode:2016ERL....11c4014A. doi: 10.1088/1748-9326/11/3/034014 . hdl: 1912/8229 . ISSN 1748-9326.

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