Importance of Forest Cover

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Synthesis
Synthesis: 

Preparers

Maria Janowiak, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.
Chris Swanston, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.
Todd Ontl, Northern Institute of Applied Climate Science, US Forest Service, Houghton, MI.

This topic page was developed using information from the report Considering Forest and Grassland Carbon in Land Management (WO-GTR-95).

Issues

Carbon storage is typically greater within forest ecosystems when compared to lands that are used for settlements or agriculture (1). Natural ecosystems themselves also have a great degree of variation in how much and for how long carbon is stored based on the interactions among climate, soils, vegetation, and past disturbance in a particular location (2). For this reason, actions to maintain the integrity of forest ecosystems or increase their extent will generally have positive benefits for greenhouse gas mitigation (3, 4).

Carbon stocks within different ecosystems in the eastern and western U.S. Major difference in the east storing significantly more carbon in wetlands.

Figure: Carbon stocks within different ecosystems in the eastern and western U.S. Data from Liu et al. (5and Liu et al. (6).

Management Options

Avoided Conversion of Forest to Non-Forest Use

Although the conversion of forest to non-forest use (i.e., deforestation) is often discussed as an international issue, a substantial amount of forested land within the United States is converted to other uses each year. Between 1982 and 2012, more than 1 million acres of U.S. forest land were converted each year to development, agriculture, or other purposes (7). Although this loss is more than accounted for by a gain of more than 1.3 million acres of non-forest area that is converted to or reverts back to forest each year (resulting in a net gain of forest acres) (8), converting land to a non-forest use removes a very large amount of carbon at one time. Because mature forest stands are more likely to be carbon rich from the high volume of tree biomass, recovery through afforestation takes a very long time (9). Forest harvesting can quickly remove much of that accumulated biomass carbon. Further, soil carbon generally declines after deforestation from accelerated decomposition of organic matter such as litter and tree roots (9). Efforts to maintain forest cover and prevent conversion to non-forest uses help to maintain the ability of that land to sequester carbon into the future, thereby preventing emissions and also increasing the potential for additional sequestration.

Afforestation of Non-Forest Lands

Just as avoiding forest losses through deforestation and conversion to other land uses helps maintain both carbon stored in forests and the capacity to continue sequestering additional carbon, afforestation increases the potential for land to store carbon by converting non-forest land to forest. For many decades, the trend in the United States has been toward increasing coverage of forest land as ecosystems recover from past clearing and disturbance and marginal agricultural lands are taken out of production (10). Afforestation can increase sequestration within the United States at an average of about 2.2 to 9.5 metric tons of carbon per acre per year for 120 years (11, 12). Afforestation may be more feasible on lower-value lands that are marginal for agriculture or other activities (13), with benefits for both biomass and soil carbon stocks (14).

Urban Forests Lands

While reductions in forestland conversion and increases in afforestation on previously converted lands play an important role in increasing carbon sequestration, we can also look to non-forested lands, such as urban areas, as a resource for not only sequestering carbon but also mitigating carbon outputs. Urban areas in the continental United States covered approximately 68 million acres in 2010, nearly 3.6 percent of the land area. Tree cover in urban areas averages 35 percent (15), making urban forests important stores of carbon in biomass. Between 597 and 690 million tons of carbon is stored within urban trees, with an annual sequestration rate of 18.9 million tons (16). Overall carbon sequestration of urban forests is proportional to existing canopy cover and tree density within a city (17). Although rural forests typically sequester twice as much CO2 as urban forests due to higher tree densities, urban trees can sequester more carbon per tree from higher growth rates (18). Enhanced carbon sequestration rates in urban trees may be explained by a combination of greater foliar biomass and reduced competition from lower tree densities, in addition to irrigation and fertilization. Urban forests also have additional benefits for carbon outside of sequestration. Trees in urban zones can have an important influence on carbon mitigation by reducing the energy requirements for building heating in winter due to wind protection and summer cooling from tree shading (19). For example, three mature trees spaced around an energy efficient home can reduce annual air conditioning demand by 25 to 43 percent (20).

Managing urban forests for carbon capture often focuses on allocating resources to tree species that are most effective at long-term carbon storage. While growth rate is important for carbon benefits, tree species that are long-lived, large in size, and have dense wood will store the greatest amounts of carbon, particularly relative to many short-lived, fast-growing species (21). Proper site selection for individual species is also important for maximizing the carbon benefits of urban trees. Trees that are well-adapted to their site will have higher growth rates and lower mortality rates, particularly in the initial years following establishment. Proper siting of trees in relation to buildings also optimizes the energy-saving benefits from derived from summer shading or wind protection. For example, trees typically provide the greatest summer cooling benefits when placed on the west side of buildings.

References: 

1. Pacala, S.; Birdsey, R.A.; Bridgham, S.D.; Conant, R.T.; Davis, K.; Hales, B.; Houghton, R.A.; Jenkins, J.C.; Johnston, M.; Marland, G. 2007. The North American carbon budget past and present. In: A. W. King, L. Dilling, G. Zimmerman, D. Fairman, R. Houghton, G. Marland, A. Rose, T. Wilbanks and (eds.), eds. The first state of the carbon cycle report (SOCCR): The North American carbon budget and implications for the global carbon cycle. 11.

2. Carvalhais, N.; Forkel, M.; Khomik, M.; Bellarby, J.; Jung, M.; Migliavacca, M.; Μu, M.; Saatchi, S.; Santoro, M.; Thurner, M. 2014. Global covariation of carbon turnover times with climate in terrestrial ecosystems. Nature. 514(7521): 213-217.

3. Birdsey, R.; Alig, R.; Adams, D. 2000. Chapter 8: Mitigation Activities in the Forest Sector to Reduce Emissions and Enhance Sinks of Greenhouse Gases. In: L. A. Joyce, R. Birdsey and (eds.), eds. The impact of climate change on America's forests: a technical document supporting the 2000 USDA Forest Service RPA Assessment. Fort Collins, CO: Rocky Mountain Research Station, USDA Forest Service.

4. Millar, C.I.; Skog, K.E.; McKinley, D.C.C.; Birdsey, R.A.; Swanston, C.W.; Hines, S.J.; Woodall, C.W.; Reinhardt, E.D.; Peterson, D.L.; Vose, J.M. 2012. Adaptation and mitigation. In: J. M. Vose, D. L. Peterson and T. Patel-Weynand, eds. Effects of climatic variability and change on forest ecosystems: a comprehensive science synthesis for the U.S. forest sector. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station: 125-192.

5. Liu, S.; Wu, Y.; Young, C.J.; Dahal, D.; Werner, J.; Liu, J. 2012. Projected future carbon storage and greenhouse-gas fluxes of terrestrial ecosystems in the western United States. In: Z. Zhu and B. C. Reed, eds. Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the western United States. USGS Prof. Pap. Reston, VA: U.S. Department of the Interior, U.S. Geological Survey.

6. Liu, S.; Liu, J.; Wu, Y.; Young, C.J.; Werner, J.; Dahal, D.; Oeding, J.; Schmidt, G.L. 2014. Chapter 7. Baseline and Projected Future Carbon Storage, Carbon Sequestration, and Greenhouse-Gas Fluxes in Terrestrial Ecosystems of the Eastern United States. In: Z. Zhu and B. C. Reed, eds. Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of the eastern United States. . Reston, VA: U.S. Department of the Interior, U.S. Geological Survey: 204.

7. U.S. Department of Agriculture. 2015. Summary Report: 2012 National Resources Inventory. and Center for Survey Statistics and Methodology, Iowa State University, Ames, Iowa.: Natural Resources Conservation Service, Washington DC,.

8. Birdsey, R. 2012. Forest Management Options for Carbon Sequestration: Considerations in the Eastern U.S. . In: C. Swanston, M. J. Furniss, K. Schmitt, J. Guntle, M. Janowiak, S. Hines and (eds.), eds. Forest and grassland carbon in North America: A short course for land managers. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: DVD.

9. Murray, B.; Sohngen, B.; Sommer, A.; Depro, B.; Jones, K.; McCarl, B.; Gillig, D.; DeAngelo, B.; Andrasko, K. 2005. Greenhouse gas mitigation potential in US forestry and agriculture. Washington, DC: Environmental Protection Agency. EPA.

10. Birdsey, R.; Pregitzer, K.; Lucier, A. 2006. Forest carbon management in the United States. Journal of environmental quality. 35(4): 1461-1469.

11. Birdsey, R.A. 1996. Regional estimates of timber volume and forest carbon for fully stocked timberland, average management after final clearcut harvest. In: R. Sampson, D. Hair and (eds.), eds. Forests and Global Change. Washington, DC: American Forests. 309-334.

12. Congressional Budget Office. 2007. The Potential for Carbon Sequestration in the United States.

13. Stanturf, J.A.; Schweitzer, C.J.; Gardiner, E.S. 1998. Afforestation of marginal agricultural land in the Lower Mississippi River Alluvial Valley, USA.

14. Chang, R.; Jin, T.; Lü, Y.; Liu, G.; Fu, B. 2014. Soil carbon and nitrogen changes following afforestation of marginal cropland across a precipitation gradient in Loess Plateau of China. PloS one. 9(1): e85426.

15. Nowak, D.J., E.J. Greenfield. 2012. Tree and impervious cover change in US cities. Urban Forestry & Urban Greening. 11(1): 21-30.

16. Nowak, D.J., E.J. Greenfield, R.E. Hoehn, E. Lapoint. 2013. Carbon storage and sequestration by trees in urban and community areas of the United States. Environmental Pollution. 178: 229-236.

17. McPherson, E.G. 1994. Using urban forests for energy efficiency and carbon storage. Journal of Forestry;(United States). 92(10).

18. Jo, H. K.; McPherson, E. G. 1995. Carbon storage and flux in urban residential greenspace. Journal of Environmental Management 45, 109–133

19. Nowak, D.J., S.M. Stein, P.B. Randler, E.J. Greenfield, S.J. Comas, M.A. Carr, R.J. Alig. 2010. Sustaining America's urban trees and forests: a Forests on the Edge report. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 27.

20. Huang, Y., H. Akbari, H. Taha, A.H. Rosenfeld. 1987. The potential of vegetation in reducing summer cooling loads in residential buildings. Journal of climate and Applied Meteorology. 26(9): 1103-1116.

21. McPherson, E.G.; Simpson, J.R. 1999. Carbon dioxide reduction through urban forestry– guidelines for professional and volunteer tree planters. Gen. Tech. Rep. PSW-GTR-171. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 237 p.

 

How to cite: 

Janowiak, M.; Swanston, C.; Ontl, T. 2017. Importance of Forest Cover. (June, 2017). U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. https://www.fs.usda.gov/ccrc/topics/forest-mgmt-carbon-benefits/forest-cover

Reading
Videos
Videos: 


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

Presenter : Louis Iverson

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

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