Forests and Carbon Storage

M. Janowiak

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Overview

Overview

U.S. forests currently serve as a carbon 'sink', offsetting approximately 13% of U.S. emissions from burning fossil fuels in 2011, and from 10 to 20% of U.S. emissions each year. Climate change may affect the ability of U.S. forests to continue to store and sequester carbon.

The synthesis discusses the role of forests in carbon sequestration, and management options for helping forests maintain or increase their capacity to store carbon, even under future conditions.

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Synthesis

Synthesis

Preparers

Mike Ryan, Rocky Mountain Research Station; Richard Birdsey, Northern Research Station; Sarah Hines, Rocky Mountain Research Station.

An archived version of this topic paper is available

Introduction

Climate change increases the uncertainty of U.S. forests' ability to serve as a "sink" for carbon storage, but management options exist that could buffer the impacts of climate change on forests, and even lead to increased forest carbon storage potential.
Trees take up carbon dioxide (CO2) and release oxygen (O2) through photosynthesis, transferring the carbon (C) to their trunks, limbs, roots, and leaves as they grow. When leaves or branches fall and decompose, or trees die, the stored C will be released by respiration and/or combustion back to the atmosphere or transferred to the soil. Because of these processes, forests and forested landscapes can store considerable carbon and their growth can provide a carbon sink; landscapes that have been recently converted or reconverted to forests (from another land cover) can provide a carbon sink that is considerably larger than other land cover types.

Approximately 33% (303 million hectares) of the U.S. land base is forested (1). This represents roughly 7.5% of the world’s total forestland (2). In 2010, U.S. forests and long-lived wood products accounted for a net sink of 251 million metric tons of carbon (922 million metric tons CO2) (3). Forest growth and afforestation currently offset approximately 16% of U.S. emissions from burning fossil fuels (4). This is an enormous ecosystem service; Jackson and Schlesinger (5) estimated that offsetting another 10 percent of emissions would require the conversion of one-third of our current U.S. cropland to forest plantations.
While individual trees or tracts release some or all of their carbon if harvested, burned, or otherwise disturbed, subsequent forest regrowth will sequester carbon from the atmosphere. Forested landscapes tend to include a mix of disturbed and regrowing forest stands, and have a carbon balance of near zero over the medium and longer term (6,7) (Figure 1).

Our large carbon sink today is a legacy of harvesting and forest conversion that took place in the past. These disturbances released much carbon dioxide (CO2) into the atmosphere decades ago, and the regrowing forest is recovering some of that released CO2 on land that has not been permanently converted to non-forest cover (8) (Figure 2).

  • Graph of carbon storage over years

    Management results should be examined for large areas and over long time periods. Carbon stores change when larger areas and more stands are included in an analysis. As the number of stands increases, the gains in one stand tend to be offset by losses in another, and the flatter the carbon stores curve becomes (From McKinley et al, 2010).

  • Graph of carbon balance of the U.S. forest sector

    Carbon balance of the U.S. forest sector in millions of metric tons of carbon per year. The large flux of carbon from forests to the atmosphere (from logging and deforestation) peaked in 1915 at 760 million metric tons of carbon per year. Currently forests take up about 250 million metric tons of carbon per year (From Birdsey et al, 2006).

 The persistence of the current U.S. forest carbon sink is uncertain because the effects of historic land use should taper off, while projected increases in the rates of natural disturbances such as fire may liberate current carbon stocks (4). Atmospheric factors may change forest growth rates, since increased nitrogen deposition and atmospheric CO2 concentrations from fossil fuel emissions can enhance tree growth. These factors may also augment current rates of carbon sequestration by forests (9). However, other global change factors, such as increased transpiration rates and atmospheric pollutants and the likelihood of increased drought, may offset potential increased sequestration rates (10).

While much about the forest carbon cycle is well understood, several key unknowns remain. The scientific community, including foresters, understands the carbon value of keeping forests as forests, planting forests where none existed historically (afforestation), replanting forests where they were located historically (reforestation), using forest biomass as fuel in place of fossil fuel, and storing carbon in long-lived products (which may continue to store carbon for years or decades). However, further research on several topics could improve our ability to design good forest management practices with respect to carbon:

  1. Understand the biophysical limits on storage over landscapes and over time, and how these limits may change in the future.
  2. Improve capabilities to predict the frequency and severity of forest disturbances.
  3. Implement a system of complete accounting of the global warming effects of forest management, which would include their albedo or reflectance (forests are dark and absorb solar energy) and the release of other greenhouse gases such as nitrogen oxides.
  4. Improve data and accounting of storage in all forest carbon pools and the displacement of carbon loss to other areas.

Expected Changes

Over the next 50 years, the United States is expected to become warmer and wetter, which may enhance forest growth in some regions. However, forest carbon stocks are likely to be more vulnerable to disturbances that are exacerbated by climate change, such as insect outbreaks, fire, drought, and storms. This may in turn lower the productivity and storage capacity of some forests while threatening the ability of some forests to remain forests. Because of more frequent/repeat burning, some forests may convert to shrubland. (11,12,13,7). The effects of climate change are likely to affect forested landscapes in the eastern and western U.S. differently. The following are examples of what may occur, but does not represent a comprehensive list:

  • In the eastern U.S., elevated temperature and atmospheric CO2 concentrations will likely continue to enhance sequestration by forests, but this sequestration may be offset by forest fragmentation and disturbances by invasive insects.
  • In the Southeast, warmer temperatures may increase the rate of decomposition of soil organic matter, thereby increasing CO2 emissions and reducing the potential for sequestration in soils (4, p.12).
  • In the western U.S., elevated temperatures and decreased precipitation is expected to lead to drought conditions that will exacerbate stress complexes that include fire and insect disturbance. Insect infestations are expected to affect more land than wildfire on an annual basis (4). Higher tree mortality, slower regeneration, and changes in the mix of tree species may result from these disturbances. While short-term effects will depend upon the amount of area affected, the cumulative impact of disturbances may turn western forests from a carbon sink into a source of atmospheric carbon.

In the decade since 2002, forest fires annually burned 0.9 percent of forested land in the United States, with the largest fire year (2006), burning 1.3 percent of forested land. This corresponds to an overall average return interval of 100 years for U.S. forest fires. Models run with downscaled climate data for the Greater Yellowstone Ecosystem predict substantial increases in fire in this region by mid-century, with fire rotation reduced to less than 30 years from the current 100-300 year return interval (14). If fires become more severe, especially where ecosystems are not adapted to severe fire, the likelihood that fire will change forest to shrublands or grasslands may increase (15). Annual carbon emissions related to fire vary considerably depending upon the year. Circumstances that directly affect fire activity include atmospheric circulation, temperature, and moisture patterns (16). Estimates of fire-related emissions range from 22.6 million metric tons/year (2010) to 84.4 million metric tons (2006), compared to net forest sequestration of 251 million metric tons/year (3).

Options for Management

The most defensible options for managing forests for their carbon storage are (7):

  • Keep forests as forests (avoid deforestation), including active regeneration of frequent fire forests subjected to crown fires where natural regeneration may take centuries.
  • Manage forests sustainably for a variety of ecosystem services (maximizing carbon stores on a landscape in the near-term may ultimately lead to more uncertain carbon outcomes, due to an increased risk of fire or disturbance in the mid to long-term).
  • Reforest areas where forests historically occurred.
  • Substitute forest biomass for fossil-fuel use, especially forest biomass generated in normal operations, fuels treatment and forest restoration activities.
  • Promote long-lived forest products such as wood-framed buildings. Long-lived forest products continue to act as carbon stores whereas substitute materials, such as concrete, result in significant carbon emissions. (7).

Harvesting old-growth forests for their forest products is not an effective carbon conservation strategy because the carbon remaining in the wood products plus the regrowth are not enough to compensate for the loss of large carbon stocks in the intact forests (17). Harvest and regeneration of young to middle-aged forests for long-lived forest products can help with carbon storage. In forests with an ecological history of surface and mixed-severity fires, managing for maximum carbon storage will lead to an increase in stand density and the probability of more severe fires. In contrast, managing to reduce fuels and the risk of crown fire will reduce the carbon stored in the forest and will likely be a source of atmospheric carbon unless the thinnings are used for biomass fuel.

Selling carbon or other ecosystem service credits may provide a supplementary revenue stream to help reduce costs of forest management in the future, especially if carbon reductions become more valuable in the United States. However, because carbon trading markets typically require long-term encumbrances on the land, participation in these markets may not be a viable option for all landowners. In addition, the specific accounting rules related to carbon offset must recognize that forest carbon stores are reversible and can be affected by economic drivers. Protocols that ensure that any carbon offsets generated will be real, permanent, additional, verifiable, and enforceable are critical to the integrity of any market-based solution. Another option would simply be to pay landowners for maintaining forest biomass, as the current Conservation Reserve Program pays landowners to maintain a certain land use. While perhaps more expensive, it would be much simpler to understand and administrate.

Forest managers must recognize that carbon is only one of many ecosystem services that forests provide and that focusing solely on carbon could lead to non-optimal management decisions. Fuels treatments and forest restoration activities in frequent-fire forests will promote a more adaptable, sustainable forest that tends to experience low intensity fires instead of crown fires. Yet such treatments may move carbon from the forest to the atmosphere. Intensive biomass use could also move carbon from the forest to the atmosphere, at least in the short term. Carbon should be only one of the many factors considered when making forest management decisions.

References

  1. Smith, W.B.; Miles, P.D.; Perry, C.H.; Pugh, S.A. 2009. Forest resources of the United States, 2007.
    General Technical Report WO-78. Washington, DC: USDA Forest Service, Washington Office.
  2. Food and Agricultural Organization (FAO) of the United Nations. 2011. State of the World's Forests 2011. Rome, Italy.
  3. US Environmental Protection Agency. 2012. Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2010. Washington D.C.
  4. Vose, J. M.; Peterson, D. L.; Patel-Weynand, T., eds. 2012. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Gen. Tech. Rep. PNW-GTR-870. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 265 p.
  5. Jackson, R.B.; Schlesinger, W.H.. 2004. Curbing the U.S. carbon deficit. Proceedings of the National Academy of Sciences. USA 101: 15827-15829.
  6. Kashian, D. M.; Romme, W. H.; Tinker, D. B.; Turner, M. G.; Ryan, M. G. 2006. Carbon storage on landscapes with stand-replacing fires. BioScience. 56: 598-606.
  7. McKinley, D.C.; Ryan, M.G.; Birdsey, R.A.; Giardina, C.P.; Harmon, M.E.; Heath, L.S.; Houghton, R.A.; Jackson, R.B.; Morrison, J.F.; Murray, B.C.; Pataki, D.E.; Skog, K.E. 2011. A synthesis of current knowledge on forests and carbon storage in the United States. Ecological Applications 21(6): 1902-1924.
  8. Birdsey, R.; Pregitzer, K.; Lucier, A. 2006. Forest carbon management in the United States 1600-2100. Journal of Environmental Quality. 35: 1461-1469.
  9. Canadell, J. G.; Pataki, D. E.; Gifford, R.; Houghton, R. A.; Lou, Y.; Raupach, M. R.; Smith, P.; Steffen, W. 2007. Saturation of the terrestrial carbon sink. In: Canadell, J.G.; Pataki, D. E.; Pitelka, L., eds. Terrestrial ecosystems in a changing world. Berlin Heidelberg, Germany: The IGBP Series , SpringerVerlag: 59-78.
  10. Felzer, B.; Reilly, J.; Melillo, J.; Kicklighter, D.; Sarofim, M.; Wang, C.; Prinn, R.; Zhuang, Q. 2005. Future effects of ozone on carbon sequestration and climate change policy using a global biogeochemical model. Climatic Change (73): 345-373.
  11. Dale, V. H.; Joyce, L. A. ; McNulty, S.; Neilson, R. P. 2000. The interplay between climate change, forests, and disturbances. Science of the Total Environment. 262: 201-204.
  12. Westerling, A. L.; Gershunov, A.; Brown, T.J.; Cayan, D. R.; Dettinger, M.D. 2003. Climate and wildfire in the western United States. Bulletin of the American Meteorological Society 84: 595-604.
  13. Running, S.W. 2006. Is global warming causing more, larger wildfires? Science 313: 927-928.
  14. Westerling, A.L.; Turner, M.G.; Smithwick, E.A.H.; Romme, W.H.; Ryan, M.G. 2011. Continued warming could transform Greater Yellowstone fire regimes by mid-21st century. Proceedings of the National Academy of Sciences. 108(32): 13165-13170.
  15. Smithwick, E. A. H.; Harmon, M. E.; Domingo, J.B. 2007. Changing temporal patterns of forest carbon stores and net ecosystem carbon balance: the stand to landscape transformation. Landscape Ecology 22: 77-94.
  16. McKenzie, D.; Heinsch, F.A.; Heilman, W.E. 2011. Wildland Fire and Climate Change. U.S. Department of Agriculture, Forest Service, Climate Change Resource Center.
  17. Harmon, M.E.; Ferrell, W.K.; Franklin, J.F. 1990. Effects on carbon storage of conversion of old-growth forests to young forests. Science. 247: 699-702.
  18. McKinley, D.C.; Ryan, M.G.; Birdsey, R.A.; Giardina, C.P.; Harmon, M.E.; Heath, L.S.; Houghton, R.A.; Jackson, R.B.; Morrison, J.F.; Murray, B.C.; Pataki, D.E.; Skog, K.E. 2011. A synthesis of current knowledge on forests and carbon storage in the United States. Ecological Applications. 21(6): 1902-1924.

How to cite

Ryan, M.G.; Birdsey, R.A.; Hines, S.J. (October 2012). Forests and Carbon Storage. U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. www.fs.usda.gov/ccrc/topics/forests-carbon

Reading
Research

Research

There is extensive Forest Service research on carbon storage in forests - some examples are available below via the CCRC Research Roundup.

Effects of warming on a Puerto Rican subtropical forest
International Institute of Tropical Forestry

This project is working to (1) evaluate the vulnerability of Puerto Rico’s forests to projected increases in temperature; (2) improve our understanding of global warming effects on tropical forest carbon (C) and nutrient cycling; and (3) provide valuable forest response information to land managers, policy makers, and global climate modeling efforts.

Contact:
The effect of rising mean annual temperature on tropical montane forests
Pacific Southwest Research Station

This project uses a temperature gradient spanning 5 degrees Celsius to perform studies on responses to warming in a tropical system, including: soil carbon response, soil microbial community response, and carbon stock and flux responses for above and below ground carbon pools and fluxes. These studies take place in the Hawaii Experimental Tropical Forest and Hakalau Forest National Wildlife Refuge, across an area where canopy vegetation, soil type, soil moisture, and successional history are all relatively constant.

Contact:
Watering the Forests for the Trees: an emerging priority for managing water in forest landscapes
Pacific Northwest Research Station

Water stress represents a common mechanism for many of the primary disturbances affecting forests, and forest management needs to explicitly address the very large physiological demands that vegetation has for water. This study demonstrates how state-of-science ecohydrologic models can be used to explore how different management strategies might improve forest health.

Contact:
Evaluating land use planning effects on carbon storage to address climate change
Pacific Northwest Research Station

Research and policy discussions highlight the role of forests in reducing greenhouse gases by storing carbon. An important factor regarding forests and carbon is simply maintaining the amount of land that is retained in forest cover. Since 1973, Oregon’s statewide land-use planning program has sought to maintain forest and agricultural lands in the face of increasing development by maintaining forest and agricultural zones and to limit growth to within urban growth boundaries. We combine projections of forest and agricultural land development with estimates of average carbon stocks for different land uses to examine what effect land-use planning has had in maintaining forest carbon in western Oregon. In addition to other benefits arising from the conservation of forestland, results indicate that Oregon’s land-use planning system in western Oregon yields significant gains in carbon storage equivalent to a reduction of 1.7 million metric tons of carbon dioxide (CO2) emissions per year.

Contact:
Updated US National Carbon Storage and Sequestration Estimates
Northern Research Station

The latest research on urban forests in the United States reveals that urban whole tree carbon storage densities average 7.69 kg C per m2 of tree cover and sequestration densities average 0.28 kg C per m2 of tree cover per year. Total tree carbon storage in U.S. urban areas (c. 2005) is estimated at 643 million metric tons ($50.5 billion value; 95% CI = 597 million and 690 million metric tons) and annual sequestration is estimated at 25.6 million metric tons ($2.0 billion value; 95% CI = 23.7 million to 27.4 million metric tons). Estimates are presented by state and include the latest urban tree cover data and field data from urban areas across the United States.

Contact:
Effects of urban tree management and species selection on atmospheric carbon dioxide
Northern Research Station

Trees sequester and store carbon in their tissue at differing rates and amounts based on such factors as tree size at maturity, life span, and growth rate. Concurrently, tree care practices release carbon back to the atmosphere based on fossil-fuel emissions from maintenance equipment (e.g., chain saws, trucks, chippers). Management choices such as tree locations for energy conservation and tree disposal methods after removal also affect the net carbon effect of the urban forest. Different species, decomposition, energy conservation, and maintenance scenarios were evaluated to determine how these factors influence the net carbon impact of urban forests and their management. If carbon (via fossil-fuel combustion) is used to maintain vegetation structure and health, urban forest ecosystems eventually will become net emitters of carbon unless secondary carbon reductions (e.g., energy conservation) or limiting decomposition via long-term carbon storage (e.g., wood products, landfills) can be accomplished to offset the maintenance carbon emissions. Management practices to maximize the net benefits of urban forests on atmospheric carbon dioxide are discussed.

Contact:
Assessing Local Urban Forest Carbon Storage, Sequestration and Effects on Emissions from Building Energy Use
Northern Research Station

The i-Tree suite of models is designed to link research with local data on tree populations to assess the services and values provide by trees. The model is constantly being updated with new features and is being used globally. The model estimates numerous ecosystem services, disservices, and values, and includes estimates of tree carbon storage and annual sequestration, and their effects on building energy and consequent emissions from power plants. For more, please see the i-Tree tools page.

Contact:
Soil carbon dynamics in peatlands: PEATcosm
Northern Research Station

Peatland ecosystems represent 3-5% of earth's land surface, but store 12-30% of soil organic carbon. However, this very large pool of carbon is vulnerable to loss to the atmosphere as CO2 because of climate change. Lowered water tables caused by climate change or human-caused drainage can shift peatlands from being net carbon sinks to net carbon sources. The PEATcosm experiment was initiated to study the relationships between water tables, plant communities, and carbon and nutrient cycling in peatlands in a controlled setting. Read more on the experiment here [pdf].

Contact:
PINEMAP: Mapping the future of southern pine management in a changing world
Southern Research Station, Eastern Forest Environmental Threat Assessment Center
Project website: http://pinemap.org/

The PINEMAP project integrates research, extension, and education to enable southern pine landowners to manage forests to increase carbon sequestration; increase efficiency of nitrogen and other fertilizer inputs; and adapt forest managment approaches to increase forest resilience and sustainability under variable climates.

Contact:
International collaboration research with China: the U.S.-China Carbon Consortium
Southern Research Station, Eastern Forest Environmental Threat Assessment Center

The U.S.-China Carbon Consortium is a collaborative effort between American and Chinese institutions interested in studying the role of managed ecosystems in global carbon and water cycles. The overall goal is to develop a network of study sites so that data and results can be shared and synthesized at broad spatial scales in order to assess the importance of human influences on carbon and water fluxes in a changing climate.

Contact:

Pages

 

Tools

Tools

COLE (Carbon OnLine Estimator)

COLEv2.0 enables the user to examine forest carbon characteristics of any area of the continental United States.

ecoSmart Landscapes

The ecoSmart Landscapes tool can be used to calculate carbon dioxide sequestration and building energy savings provided by individual trees in California.

First Order Fire Effects Model (FOFEM)

FOFEM is a model that predicts first-order fire effects including tree mortality, fuel consumption, emissions (smoke) production, and soil heating caused by prescribed burning or wildfire.

Forest Inventory Data Online (FIDO) and EVALIDator

These tools draw from US Forest Service Forest Inventory and Analysis (FIA) Data to produce estimates for selected forest attributes for an area of interest, including carbon stocks.

Forest Planner

The Forest Planner enables landowners to visualize alternative forest management scenarios for their properties and their effect on variables including timber stocking and yields, carbon storage, and fire and pest hazard ratings.

Forest Vegetation Simulator (FVS)

The Forest Vegetation Simulator (FVS) is a family of forest growth simulation models that allow a user to explore how silvicultural treatments may affect growth and yield and, therefore, carbon stocks.

Fuel and Fire Tools (FFT)

This suite of tools uses fuels data to let users perform a variety of calculations related to fire behavior and emissions. These include predicting surface and crown fire behavior, fuel consumption, and carbon emissions. The FFT integrates several tools that were previously stand-alone, including the FCCS.

Global Carbon Atlas

The Global Carbon Atlas lets users explore, visualize and interpret national to global carbon emissions from both human activities and natural processes.

i-Tree

i-Tree is a peer-reviewed software suite that allows users to assess the benefits provided by urban trees. Some applications give estimates of the benefits that trees provide related to greenhouse gas mitigation and building energy savings

NASA - CASA Global CQUEST - Carbon Query and Evaluation Support Tools

The CASA Global CQUEST application provides datasets and a geographical data viewer that support large-scale carbon inventory. Users can display global data on net primary productivity, net ecosystem productivity, and other variables interactively as a map and obtain data values in tabular format.

Pages

Videos

Videos

Get started with the CCRC's short course, or dive into the video collection on Forests and Carbon: 


 

An overview of a set of tools that assess how climate change might influence tree distributions in the eastern U.S.

Presenter : Louis Iverson

The Alder Spring project in the Mendocino National Forest is a case study in climate change mitigation.

Presenter : Mark Nechodom

Forest management options for reducing carbon emissions and enhancing carbon sequestration in forests.

Presenter : Maria Janowiak

What is a carbon neutrality number and how can we ensure that wood used to produce energy makes sense from a carbon offset standpoint?

Presenter : Ken Skog

The effect of disturbances, such as increased fires and insect attacks, will drive ecosystem change as much or more than warmer temperatures from climate change.

Presenter : Dave Peterson

See how climate change and increased disturbances from fire, insects and other sources will affect the forest carbon cycle. Carbon losses can be fully recovered, if the forest regenerates after the disturbance and if given enough time.

Presenter : Mike Ryan

Learn about gross primary production, photosynthesis, respiration and senescence, and the effect of elevated atmospheric CO2 and ozone on forest stand productivity.

Presenter : Christian Giardina

Wondering about carbon offsets, credits, baselines, permanence and leakage? Get the carbon basics here and find out why forest offsets could be a bridge to the future.

Presenter : Sarah Hines

Andrea Tuttle takes a look at forest carbon markets and how these can be used to capture and hold carbon on the landscape.

Presenter : Andrea Tuttle

Presents a western U.S. perspective on forest management for carbon sequestration, and the above and below- ground carbon consequences of different management strategies.

Presenter : Bernard Bormann

The Eastern U.S. forest perspective on carbon sequestration and examples of forest carbon management projects.

Presenter : Richard Birdsey

Get the scoop on forestland carbon storage in the United States, which helps offset approximately 12% of US carbon emissions from fossil fuels.

Presenter : Christopher Woodall

Grasslands, which make up 30% of the U.S. land surface, store significant amounts of carbon belowground in roots and soils. Learn how disturbances such as drought, grazing, fire and tillage can significantly impact the grassland carbon balance.

Presenter : Rebecca McCulley

Climate drives insect outbreaks in forests; insect outbreaks can then influence climate through the carbon cycle.

Presenter : Jeffrey Hicke

Andrea Tuttle discusses the drivers of deforestation, current international approaches to reducing emissions and lessons learned from REDD pilot programs.

Presenter : Andrea Tuttle

Introduction to how carbon is distributed globally in soils, vegetation, the atmosphere and the ocean, and how carbon moves between these pools.

Presenter : Chris Swanston

The largest terrestrial carbon pool is contained in soils. Carbon stored in soils plays a number of important roles, including keeping carbon out of the atmosphere and improving moisture and nutrient retention.

Presenter : Luke Nave

Trees in cities provide important ecosystem services and help to reduce the urban heat island effect and lower building energy use.

Presenter : David Nowak

Find about the many tools that are available from the US Forest Service for forest carbon estimation, as well as their strengths and limitations.

Presenter : Coeli Hoover

Tropical forests are critical ecosystems affecting the Earth's climate and hydrological cycles, and human cultures. Learn more about how they may be affected by climate change.

Presenter : J Boone Kauffman

U.S. forests play a large role in offsetting carbon emissions, about 20 % of the U.S. fossil fuel carbon output. If a forest replaces itself after a disturbance like fire, then there is no long-term loss of carbon.

Presenter : Mike Ryan