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Credit: Michael Nichols

Land Use

Tropical Forests

Burning continues to be the preferred means of clearing land in the Amazon to make way for cattle. It is a delusional act because the thin acid soils quickly degrade and fail. This picture was taken in Rondonia State, just northeast of Bolivia.

In recent decades, tropical forests have suffered extensive clearing, fragmentation, degradation, and depletion of biodiversity. Once blanketing 12 percent of the world’s landmass, they now cover just 5 percent. While destruction continues in many places, tropical forest restoration is growing and may sequester as much as six gigatons of carbon dioxide per year.

As a forest ecosystem recovers, trees, soil, leaf litter, and other vegetation absorb and hold carbon. As flora and fauna return and interactions between organisms and species revive, the forest regains its multidimensional roles: supporting the water cycle, conserving soil, protecting habitat and pollinators, providing food, medicine, and fiber, and giving people places to live, adventure, and worship.

The specific mechanics of restoration vary. The simplest scenario is to release land from non-forest use, such as growing crops or damming a valley, and let a young forest rise up on its own. Protective measures can keep pressures such as fire, erosion, or grazing at bay.

Other techniques are more intensive, such as cultivating and planting native seedlings and removing invasives to accelerate natural ecological processes. Because forests and people rarely exist in isolation in today’s heavily populated world, local communities need to have a stake in what is growing, if restoration is to sustain.  

References

[coverage] of the world’s landmasses: Seymour, Frances, and Jonah Busch. Why Forests? Why Now? Washington: Center for Global Development, 2014.

“largest forest area…highest carbon uptake”: Pan, Yude, Richard A. Birdsey, Jingyun Fang, Richard Houghton, Pekka E. Kauppi, Werner A. Kurz, Oliver L. Phillips et al. “A Large and Persistent Carbon Sink in the World’s Forests.” Science 333, no. 6045 (2011): 988-993.

[sequestration] of carbon dioxide per year: Pan et al, “Carbon Sink.”

equivalent to 11 percent of…emissions: Seymour and Busch, Forests.

Tropical forest loss…emissions: Busch, Jonah, and Jens Engelmann. “Tropical Forests Offer up to 24–30 Percent of Potential Climate Mitigation.” Center for Global Development. November 4, 2014.

percent of…forestland…cleared…degraded: Minnemeyer, Susan, Lars Laestadius, Nigel Sizer, Carole Saint-Laurent, and Peter Potapov. A World of Opportunity. Global Partnership on Forest Landscape Restoration, 2011.

[sizing] “opportunities for restoration”: Minnemeyer et al, Opportunity.

“number of trunks…quality of the forest”: McKibben, Bill. “An Explosion of Green.” The Atlantic. April 1995.

[ability of] tropical forests [to] recover: Poorter, Lourens, Frans Bongers, T. Mitchell Aide, Angélica M. Almeyda Zambrano, Patricia Balvanera, Justin M. Becknell, Vanessa Boukili et al. “Biomass Resilience of Neotropical Secondary Forests.” Nature 530, no. 7589 (2016): 211-214.

forest landscape restoration: Laestadius, L., K. Buckingham, S. Maginnis, and C. Saint-Laurent. “Before Bonn and Beyond: The History and Future of Forest Landscape Restoration.” Unasylva 66, no. 245 (2015): 11-18.

“landscape as an integrated whole”: Lapstun, S. “Editorial.” Unasylva 66, no. 245 (2015): 2.

guiding principles for restoration: FAO. Forest Restoration and Rehabilitation. Module from the Sustainable Forest Management (SFM) Toolbox. Rome: Food and Agriculture Organization of the United Nations.

[potential impact of] Bonn Challenge…New York Declaration on Forests: Verdone, M., N. Olsen, P. Wylie, C. Saint Laurent, and M. Maginnis. Making the Case for Forest Landscape Restoration. White paper, initial working draft for future discussion. Post-Bonn Challenge 2.0 Ministerial Event, March 20–21, 2015. International Union for the Conservation of Nature; Laestadius et al, “Bonn.”

active forest restoration…[cost] per acre: Delgado, Christopher, Michael Wolosin, and Nigel Purvis. Restoring and Protecting Agricultural and Forest Landscapes and Increasing Agricultural Productivity. Working paper. London and Washington, D.C.: New Climate Economy, 2015.

estimates [of]…“net benefits…and carbon dioxide”: IUCN. “Bonn Challenge Approaches Target to Restore 150 million Hectares of Degraded Land.” International Union for the Conservation of Nature. September 4, 2016.

source of income…food security…energy…health…and safety: Seymour and Busch, Forests.

AFR100; Brazil: Pearce, Fred. “Paris COP 21—How ‘Landscape Carbon’ Can Be Part of a Solution on Climate.” Yale Environment 360. December 7, 2015.

view all book references

Errata

p. 116

Deletion: Only carbon stored in soil organic matter and aboveground biomass is accounted for; below-ground biomass is not included.

view all errata

Technical Summary

Tropical Forests

Project Drawdown defines tropical forests as: the restoration and protection of tropical-climate forests. This solution replaces degraded forest.

Tropical forest restoration is widely considered to offer substantial climate change mitigation opportunities, if conducted at large spatial scales. Despite this assertion, estimates of how much carbon could be sequestered from the atmosphere as a result of large-scale restoration are largely lacking. The international community has pledged to restore 350 million hectares of degraded forest land by 2030. Thus, efforts to quantify carbon storage over large spatial scales are timely.

Tropical forest regrowth is often rapid, and results in impressive rates of carbon sequestration. The tropical forests solution models natural regeneration of tropical forests on degraded lands. This has the benefit of being a low-cost strategy. It is assumed that forest regrowth will be legally protected so that it will not be cleared or degraded again.

Natural regeneration also offers co-benefits which make it an appealing option, including: biodiversity conservation, watershed protection, soil protection, and resilience to pests and disease.

Methodology

Total Land Area [1]

The total area allocated for tropical forests is 304 million hectares, representing degraded tropical forests. [2] Current adoption [3] is set at 0 hectares, as forests that have already been restored are accounted for as existing forest in the Drawdown Agro-Ecological Zone model.

Future restoration of tropical forests was calculated using the targets from the New York Declaration of Forests, which commits to reforesting 350 million hectares by 2030 (United National Framework Convention on Climate Change, 2014), and estimates from the World Resources Institute, which predict 304 million hectares of land are available for wide-scale restoration.

Adoption Scenarios [4]

Nine custom adoption scenarios were developed based on: (i) current restoration commitments to date; (ii) potential future commitments; (iii) the proportion of committed land restored to intact forest; and (iv) the year commitments are realized (2030, 2045 or 2060).

Impacts of increased adoption of tropical forests from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Plausible Scenario: Analysis of these scenarios under the most conservative approach yields the restoration of 128.42 million hectares of degraded land area by 2050.
  • Drawdown Scenario: Based on a more aggressive adoption approach with peak adoption by 2030 or later, this scenario yields the restoration of 238.8 million hectares of degraded tropical forest.
  • Optimum Scenario: Based on the most aggressive adoption approach with peak adoption by 2030 or later, this scenario yields the restoration of 255.26 million hectares of degraded tropical forest.

Sequestration Model

Sequestration rates are set at 4.1 tons of carbon per hectare per year, [5] based on meta-analysis of 7 data points from 6 sources. Note that data on soil carbon sequestration was unavailable.

Financial Model

It is assumed that any costs (e.g. carbon payments or payment for ecosystem services) are borne at a government or non-governmental organization (NGO) level. Drawdown land solutions only model costs that are incurred at the landowner or manager level.

Integration [6]

Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rainfed cropland, irrigated cropland, arid, and arctic areas. Tropical forest restoration is the highest-priority solution for degraded tropical forest land.

Results

Total adoption in the Plausible Scenario is 176.1 million hectares in 2050, representing 57.9 percent of the total suitable land. Of this, 176.1 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 61.2 gigatons of carbon dioxide-equivalent sequestered by 2050. Financial impacts are not modeled.

Total adoption in the Drawdown Scenario is 238.8 million hectares in 2050, representing 78.5 percent of the total suitable land. Of this, 238.8 million hectares are adopted from 2020-2050. The impact of this scenario is 89.0 gigatons of carbon dioxide-equivalent by 2050.

Total adoption in the Optimum Scenario is 255.3 million hectares in 2050, representing 83.9 percent of the total suitable land. Of this, 255.3 million hectares are adopted from 2020-2050. The impact of this scenario is 105.6 gigatons of carbon dioxide-equivalent by 2050.

Discussion

Benchmarks

A highly-cited article provides a benchmark for tropical forests, estimating 2.2 gigatons of carbon dioxide-equivalent per year from the afforestation of tropical degraded farmland (Arora and Montenegro, 2011). Though afforestation is not forest restoration, their sequestration rates are somewhat similar. The Drawdown model calculates 2.7 gigatons of carbon dioxide-equivalent per year for the tropical forests solution in the Plausible Scenario, with 3.6 and 3.9 gigatons of carbon dioxide-equivalent per year in the Drawdown and Optimum Scenarios, respectively.

As more data on soil carbon sequestration in tropical forest restoration becomes available, the sequestration rate of this solution, and thus its mitigation impact, will likely increase. Inclusion of economic impacts, e.g. costs to governments and NGOs, would be a valuable addition to future updates. As more benchmarks become available, they should be included in the study as well.

Conclusions

Drawdown considers tropical forest restoration to be an extremely high priority, given its massive sequestration potential and numerous co-benefits. It is assumed that these new forests will be legally protected, as in the forest protection solution. Reduction of land demand for food helps ease pressure on these new forests. Solutions like family planning, educating girls, plant-rich diet, and reduced food waste reduce demand. Agroecological intensification due to increased yields from solutions like conservation agriculture, silvopasture, and tropical staple trees also makes room for these new forests. Farmland restoration also helps make land available by bringing degraded farmland back in to production.


[1] To learn more about the Total Land Area for the Land Use Sector, click the Sector Summary: Land Use link below.

[2] Determining the total available land for a solution is a two-part process. The technical potential is based on the suitability of climate, soils, and slopes, and on degraded or non-degraded status. In the second stage, land is allocated using the Drawdown Agro-Ecological Zone model, based on priorities for each class of land. The total land allocated for each solution is capped at the solution’s maximum adoption in the Optimum Scenario. Thus, in most cases the total available land is less than the technical potential.

[3] Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.

[4] To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Land Use Sector-specific scenarios, click the Sector Summary: Land Use link.

[5] This includes above-ground biomass and roots, but not soil organic carbon.

[6] For more on Project Drawdown’s Land Use integration model, click the Sector Summary: Land Use link below.

Full models and technical reports coming in late 2017.

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