Silhouettes of tropical staple trees with glowing sunset on horizon.
Technical Summary

Perennial Staple Crops

Project Drawdown defines perennial staple crops as the production of trees and other perennial crops for staple protein, fats, and starch. This solution replaces conventional annual crop production in humid and semi-arid tropics in nondegraded grasslands and croplands.

Annual cropping systems are a major contributor of emissions from agriculture. The great majority of world cropland is used to produce annual staple crops like maize, wheat, potatoes, and soybeans. Annuals are not the only crops producing staple food, however; in the tropics, many perennial staple crops are already fully domesticated and widely grown, and yield as well or better than their annual staple crop competitors.

These perennial staple crops sequester impressive carbon in soils and above-ground biomass, like any tree. Their sequestration rates are much higher than any annual cropping system, though they present other trade-offs and challenges.

One critical assumption of this study is that all perennial staple crops adoption would be on nondegraded grassland and cropland, with no forest clearing, despite the current situation in which much forest is cleared for staple tree crops like avocado and oil palm. It is of great importance to note that if forest (particularly peatland) is cleared for tropical staple tree planting, the result is net emissions regardless of sequestration.

This solution has received very little attention in the climate change mitigation literature. Its high sequestration rate, high current adoption, and rapid growth rate indicate its impressive potential.

Methodology

Total Land Area[1]

Total available land for this solution is 330 million hectares. Current adoption[2] is 50 million hectares, according to the Food and Agriculture Organization Statistical Service (FAOSS). Current growth is very high for crops such as oil palm and avocado, but those are often planted on land cleared for the purpose. This solution assumes that the rate of growth will continue, but planting will exclusively be on degraded lands with no forest clearing.[3]

Adoption Scenarios[4]

Future adoption is based on a linear projection of regional data from 1962 to 2016 (FAOSS). Seven custom adoption scenarios were developed based on the low and high historic adoption rates, including some with early adoption of the solution (i.e., 70 percent adoption by 2030).

Impacts of increased adoption of perennial staple crops from 2020 to 2050 were generated based on two growth scenarios. These were assessed in comparison with a Reference Scenario, in which the solution’s market share was fixed at the current levels.

  • Scenario 1: In this scenario, perennial staple crops are adoped on 110.9 million hectares of degraded land.
  • Scenario 2: The high carbon sequestration potential of this solution leads to an aggressive adoption of 190.8 million hectares by 2050.

Emissions, Sequestration, and Yield Model

Carbon sequestration rates are set at 3.34 tons per hectare per year, based on six data points from four sources. It is assumed that all sequestered carbon is re-emitted at the end of an orchard or plantation’s useful life, which here is set at 37.5 years.

The weighted average yield of perennial staple crops is 2.4 times greater than that of annual staples, based on analysis of data from seven perennials and 15 annuals (FAOSS).

Financial Model

First costs are US$1298.4 per hectare, based on meta-analysis of 12 data points from six sources.[5] For all grazing solutions it is assumed that there is no conventional first cost because agriculture is already in place on the land. Net profit per hectare is calculated at US$1025.98 per year for the solution (based on meta-analysis of 22 data points from 13 sources), compared with US$154.12 per year for the conventional practice (based on 20 data points from 15 sources).[6] Annual operational cost per hectare is calculated at US$749.28 for the solution (based on meta-analysis of 19 data points from 12 sources), compared with US$328.42 for the conventional practice (based on nine data points from seven sources).[7]

Integration[8]

Project Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rainfed cropland, and irrigated cropland areas. Adoption of perennial staple crops was the second-highest priority for degraded grassland and the sixth-highest for degraded cropland.

Results

Total adoption in the Scenario 1 is 110.9 million hectares in 2050, representing 42.3 percent of the total suitable land. Of this, 60.9 million hectares are adopted from 2020 to 2050. The emissions impact of this scenario is 15.45 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$83.1 billion and lifetime operational cost is US$847.9 billion. Lifetime saving in net profit is US$1.4 trillion.

Total adoption in the Scenario 2 is 190.8 million hectares in 2050, representing 63.4 percent of the total suitable land. Of this, 140.8 million hectares are adopted from 2020 to 2050. The impact of this scenario is 31.26 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$190.2 billion and lifetime operational cost is US$1921.6 billion. Lifetime saving in net profit is US$3.3 trillion.

Discussion

Benchmarks

Benchmarks for this solution are unavailable, and mitigation benchmarks for tree crops of any kind are rare. This suggests a need for a new area of research. Projections for tree plantation can be used as a rough comparison. The Intergovernmental Panel on Climate Change estimates an impact of 4.0 gigatons of carbon dioxide-equivalent per year by 2030 from afforestation, given a carbon dioxide price of US$100 per ton (Metz, 2007). The perennial staple crops model shows 0.46–0.83 gigatons of carbon dioxide-equivalent per year by 2030, much lower. When combined with Project Drawdown's bamboo production and tree plantation solutions, however, emissions reductions increase to 1.33–2.45 gigatons of carbon dioxide-equivalent per year by 2030.

Limitations

Additional data on financials, sequestration rates, and yields would improve this study. The potential adoption area could be increased to include arid regions, as many perennial staple crops like mesquite are suited to arid conditions.

Conclusions

Perennial cropping solutions such as multistrata agroforestry and perennial staple crops can offer the high sequestration rates of afforestation and forest restoration while providing food. These somewhat neglected “edible afforestation” solutions are worthy of a place at the center of land-based mitigation efforts. It should also be noted that there are staple trees for cold climates, though their yields are not yet competitive with annual crops. Project Drawdown hopes to inspire further research and widespread adoption of this promising solution.


[1] 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.

[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 nondegraded status. In the second stage, land is allocated using the Project 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] All monetary values are presented in 2014 US$.

[4] 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.