Hillside of a farm employing regenerative farming and agroforestry practices.
Technical Summary

Multistrata Agroforestry

Project Drawdown defines multistrata agroforestry as: a perennial cropping system featuring multiple layers of trees and other perennial crops, with high biosequestration impacts. The system is characterized by having an overstory of taller trees, and an understory of one or multiple layers of crops growing in some degree of shade. Their structure and function are similar to those of natural forests, though some are much more simplified. This solution replaces grazing on non-degraded tropical humid grassland.

Carbon sequestration rates of multistrata agroforestry are very high, particularly for a food production system. The practice also offers impressive co-benefits, notably ecosystem services like habitat, erosion control, and water quality. In fact, tropical home gardens, a multistrata system, have been described as “the epitome of sustainability” (Kumar and Nair, 2004).

Climate mitigation literature often lumps multistrata agroforestry in an undifferentiated "agroforestry" category with silvopasture and tree intercropping. Its high sequestration rates and forest-like ecosystem services make multistrata agroforestry worthy of consideration on its own. Though their adoption potential is modest, multistrata systems can have a disproportionately high mitigation impact.

Methodology

Total Land Area[1]

The maximum area allocated to multistrata agroforestry is 330 million hectares, and consists of non-degraded grassland.[2] Current adoption is allocated on non-degraded forest land.

Current adoption[3] is estimated at 100 million hectares (Nair, 2012).

Adoption Scenarios[4]

Six custom adoption scenarios were generated to model i) projected adoption rates of 10%, 20%, or 30% of the land allocated to multistrata agroforestry; and ii) early adoption rates, with 70% of all adoption occurring by 2030). These scenarios are not unreasonable in light of the Bonn Challenge and New York Declaration of Forests which propose to complete all restoration by 2030.Impacts of increased adoption of multistrata agroforestry from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Scenario 2: The most conservative adoption scenarios were considered for this scenario, yielding adoption of multistrata agroforestry on 139.06 million hectares of the total allocated area.
  • Scenario 2: This scenario yields adoption of the solution on 166.01 million hectares.

Emissions, Sequestration, and Yield Model

Sequestration rates are set at 4.45 tons of carbon per hectare per year, based on meta-analysis of 16 data points from 8 sources. Unlike some other Drawdown perennial crop solutions, multistrata agroforestry does not address the emissions and financial impacts of replacement, as plantings last many decades or even centuries, even as individual trees may be replaced.

Yields are assumed to be equal to business-as-usual annual cropping, due to the great variation in crops and cropping systems in multistrata agroforestry.

Financial Model

First costs of multistrata agroforestry are estimated at US$1,335.7 per hectare,[5] based on meta-analysis of 15 data points from 11 sources. For all agricultural solutions, it is assumed that there is no conventional first cost, as agriculture is already in place on the land. Net profit per hectare is calculated at US$1,799.4 per year for the solution (based on meta-analysis of 21 data points from 12 sources), compared to US$154.12per year for the conventional practice (based on 20 data points from 15 sources).[6] Annual operational cost per hectare is calculated at US$442.17 for the solution (based on meta-analysis of 8 data points from 7 sources), compared to US$328.42 for the conventional practice (based on 9 data points from 7 sources).[7]

Integration[8]

Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rainfed cropland, and irrigated cropland. This solution is limited to humid tropical climates. Adoption of multistrata agroforestry was the fifth priority for non-degraded grassland.

Results

Total adoption in the Scenario 2 is 139.06 million hectares in 2050, representing 56 percent of the total suitable land. Of this, 39.06 million hectares are adopted from 2020-2050. The sequestration impact of this scenario is 911.3 gigatons of carbon dioxide-equivalent by 2050. Marginal first cost is US$54.06 billion and lifetime operational cost is US$142.9 billion. Net savings is US$1.7 trillion.

Total adoption in the Scenario 2 is 166.01 million hectares in 2050, representing 62 percent of the total suitable land. Of this, 66.01 million hectares are adopted from 2020-2050. The impact of this scenario is 20.4 gigatons of carbon dioxide-equivalent by 2050. Marginal first cost is US$92.12 billion and lifetime operational cost is US$245.4 billion. Net savings is US$3.0 trillion.

Discussion

Benchmarks

Benchmarks for the climate change mitigation impact of multistrata agroforestry as such are unavailable, as it is typically considered part of an undifferentiated “agroforestry” solution if it is considered at all. A highly-cited study estimated sequestration of 4.0-8.0 gigatons of carbon dioxide-equivalent per year for all tropical agroforestry by 2050 (Albrecht and Kandji, 2003). The combined impacts of Drawdown’s three agroforestry solutions (multistrata agroforestry along with silvopasture and tree intercropping) is 3.19-4.56 gigatons of carbon dioxide-equivalent per year in 2050, though this includes some temperate silvopasture and tree intercropping.

Limitations

Little climate mitigation data is available that breaks out multistrata systems as a subset of agroforestry. Access to such data would improve this study, as would additional financial data.

Conclusions

Perennial cropping solutions like multistrata agroforestry can offer the high sequestration rates of afforestation and forest restoration while providing food. These somewhat neglected "edible afforestation" solutions are in fact worthy of a place at the center of land-based mitigation efforts. In tropical humid climates, efforts to protect and scale up multistrata agroforestry should be a high priority.

 

[1] To learn more about the Total Land Area for the Food Sector, click the Sector Summary: Food 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 2018 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: Food link.

[5] All monetary values are presented in US2014$.

[6] Tropical staple trees are not as labor-efficient as annual crops, in a mechanized context. However, 175 million hectares of the world’s farms are smallholders with little mechanization. The net profit per hectare figure shows that these crops are economically viable despite higher labor costs.

[7] Tropical staple trees are not as labor-efficient as annual crops, in a mechanized context. However, 175 million hectares of the world’s farms are smallholders with little mechanization. The net profit per hectare figure shows that these crops are economically viable despite higher labor costs.

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