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. They are 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 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 316 million hectares, and consists of degraded grassland. [2]
Current adoption [3] is estimated at 100 million hectares (Nair, 2012). Future adoption was based on low (5 percent), medium (10 percent), and high (15 percent) targets for agroforestry-based restoration of degraded land through the Bonn Challenge and New York Declaration in Forests (Summit, 2014).
Adoption Scenarios [4]
Six custom adoption scenarios were generated, with some estimating an early adoption (i.e. 70 percent adoption on allocated land by 2030).
Impacts of increased adoption of multistrata agroforestry 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: The most conservative adoption scenarios were considered for this scenario, yielding adoption of multistrata agroforestry on 118.6 million hectares of the total allocated area.
- Drawdown Scenario: This scenario yields adoption of the solution on 131.6 million hectares.
- Optimum Scenario: This scenario yields adoption of the solution on 144.5 million hectares.
Emissions, Sequestration, and Yield Model
Sequestration rates are set at 7.0 tons of carbon per hectare per year, based on meta-analysis of 19 data points from 10 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$1,431.71 per hectare, [5] based on meta-analysis of 11 data points from 7 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 from multistrata agroforestry is US$2,059.50 per year (14 data points from 8 sources); there is no conventional net profit per hectare, as new adoption is on degraded grassland.
Integration [6]
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 third priority for non-degraded grassland, the top priority for degraded grasslands, and the fourth priority for non-degraded croplands, particularly those with steep slopes.
Results
Total adoption in the Plausible Scenario is 118.7 million hectares in 2050, representing 37.5 percent of the total suitable land. Of this, 18.7 million hectares are adopted from 2020-2050. The sequestration impact of this scenario is 9.2 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$26.8 billion. Net savings is US$709.7 billion.
Total adoption in the Drawdown Scenario is 131.6 million hectares in 2050, representing 41.6 percent of the total suitable land. Of this, 31.6 million hectares are adopted from 2020-2050. The impact of this scenario is 16.3 gigatons of carbon dioxide-equivalent by 2050.
Total adoption in the Optimum Scenario is 144.5 million hectares in 2050, representing 45.7 percent of the total suitable land. Of this, 44.5 million hectares are adopted from 2020-2050. The impact of this scenario is 23.3 gigatons of carbon dioxide-equivalent by 2050.
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 3.7-4.3 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 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: Food link.
[5] All monetary values are presented in US2014$.
[6] For more on Project Drawdown’s Food Sector integration model, click the Sector Summary: Food link below.
