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Credit: Inga Spence

Food

Tree Intercropping

A new Freestone Peach orchard intercropped with corn in Klickitat County, south central Washington.

Like all regenerative land-use practices, tree intercropping—intermingling trees and crops—increases the carbon content of the soil and productivity of the land. The arrangement of trees and crops varies with topography, culture, climate, and crop value, but there are common benefits:

  • Windbreaks reduce erosion and create habitat for birds and pollinators.
  • Fast-growing annuals, susceptible to being flattened by wind and rain, can be protected.
  • Deep-rooted plants can draw up minerals and nutrients for shallow-rooted ones.
  • Light-sensitive crops can be protected from excess sunlight.

Tree intercropping has many variations. Alley cropping is a system in which trees or hedges are planted in closely spaced rows to fertilize the crops grown between. Parkland systems are a discontinuous cover of scattered trees. There are many others, and most are beautiful—chili peppers and coffee, coconut and marigolds, walnuts and corn, citrus and eggplant, olives and barley, teak and taro, oak and lavender. The possible combinations are endless.

Plowed under during the twentieth century to make room for industrialized methods of farming, tree intercropping is one of dozens of techniques that can create an agricultural renaissance—a transformation of food-growing practices that bring people, regeneration, and abundance back to the land.

References

Tree intercropping has many variations: Toensmeier, Eric. The Carbon Farming Solution. White River Junction, VT: Chelsea Green Publishing, 2016.

Malawi…Alley-cropped maize: Akinnifesi, F. K., W. Makumba, and F. R. Kwesiga. “Sustainable Maize Production Using Gliricidia/Maize Intercropping in Southern Malawi.” Experimental Agriculture 42, no. 04 (2006): 441-457.

concept known as kaizen in Japan: “Kaizen.” The Economist. April 14, 2009.

view all book references

Technical Summary

Tree Intercropping

Project Drawdown defines tree intercropping as: a suite of agroforestry systems that deliberately grow trees together with annual crops in a given area at the same time. This solution replaces conventional annual crop production on temperate and tropical degraded cropland.

The main purpose of growing trees varies across different types of tree intercropping. Some systems use trees to support annual crop production (e.g. intercropping with nitrogen-fixing trees, as in evergreen agriculture) or as protective systems against erosion, flooding, or wind damage (e.g. hedgerows, riparian buffers, and windbreaks). In other systems, the trees are crops themselves (e.g. strip intercropping of annual crops with timber or fruit trees).

Tree intercropping is an important strategy for producing annual crops while sequestering carbon in soils and aboveground biomass. It provides important co-benefits, including erosion control, riparian stabilization, soil fertility improvements, and, in many cases, increased yields. Tree intercropping systems are widely adopted by tropical smallholders, but are also practiced on millions of hectares of cropland in highly mechanized regions of China and Europe.

Methodology

Total Land Area [1]

The total available land for tree intercropping is 242.0 million hectares for temperate and 148.0 million hectares for tropical, totaling 390.0 million hectares of degraded cropland. [2] Current adoption [3] is based on a study of agricultural areas with more than 10 percent tree cover (Zomer, 2014). These areas were divided into temperate/boreal (27.1 million hectares) and tropical (36.2 million hectares). Combined current adoption is 63.3 million hectares.

Many available estimates show a higher area under tree intercropping; however, to avoid double-counting, our estimates only consider areas dedicated to tree intercropping, excluding annual cropping areas with sparse trees. These areas are part of our conservation agriculture, regenerative agriculture, improved rice cultivation, and System of Rice Intensification solutions.

Adoption Scenarios [4]

In the absence of any robust adoption projections for the future adoption of tree intercropping, aggressive adoption assumptions were made (50-100 percent of the total allocated area) to maximize adoption of tree intercropping in the degraded tropical and temperate/boreal cropland area. Three custom adoption scenarios were made, some of which included early adoption (i.e. 70 percent of allocated area by 2030). The modeling was done separately for the tropical and temperate regions.

Impacts of increased adoption of tree intercropping 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 this conservative scenario shows adoption of tree intercropping on 213.2 million hectares by 2050.
  • Drawdown Scenario: Analysis of this more aggressive scenario shows adoption of tree intercropping on 293.0 million hectares by 2050.
  • Optimum Scenario: Analysis of this most aggressive scenario shows adoption of tree intercropping on 372.7 million hectares by 2050.

As data for financial inputs was limited, the same data was used for all three Drawdown forest models (protective, tropical, and temperate).

Emissions, Sequestration, and Yield Model

The sequestration rate for temperate/boreal tree intercropping is set at 1.3 tons of carbon per hectare per year, based on 9 data points from 7 sources. The rate for tropical systems is 2.7 tons of carbon per hectare per year, based on 21 data points from 15 sources. Protective systems show a rate of 0.9 tons of carbon per hectare per year, based on 7 data points from 4 sources.

Note: these rates assume tree intercropping with tillage-based annual cropping. Combining tree intercropping with climate-friendly practices like conservation agriculture may well result in sequestration rates higher than either practice alone. This is an important area for future research.

Financial Model

First costs are estimated at US$980.26 per hectare, based on meta-analysis of 11 data points from 3 sources. [5] 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 is US$385.61 per hectare per year, compared to US$376.99 for the conventional practice.

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 areas. Adoption of tree intercropping was the top priority for degraded cropland.

Results

Total adoption in the Plausible Scenario is 213.3 million hectares in 2050, representing 54.2 percent of the total suitable land. Of this, 139.0 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 17.2 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$147.0 billion. Net savings is US$22.1 billion.

Total adoption in the Drawdown Scenario is 293.0 million hectares in 2050, representing 74.5 percent of the total suitable land. Of this, 218.7 million hectares are adopted from 2020-2050. The impact of this scenario is 26.9 gigatons of carbon dioxide-equivalent by 2050.

Total adoption in the Optimal Scenario is 372.7 million hectares in 2050, representing 94.8 percent of the total suitable land. Of this, 298.4 million hectares are adopted from 2020-2050. The impact of this scenario is 36.6 gigatons of carbon dioxide-equivalent by 2050.

Discussion

Benchmarks

Benchmarks for the climate change mitigation impact of tree intercropping are rare, as it is typically considered part of an undifferentiated “agroforestry” solution, if at all. A highly-cited study estimated 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, silvopasture, and tree intercropping) is 3.7-4.3 gigatons of carbon dioxide-equivalent per year by 2050, though this includes some temperate silvopasture and tree intercropping. The Intergovernmental Panel on Climate Change (IPCC, 2014) has a much more conservative view of the potential of agroforestry, showing less than 0.02 gigatons of carbon dioxide-equivalent per year by 2030, even at a carbon price of US$100 per ton of carbon dioxide-equivalent. Drawdown's three agroforestry models combined show 0.7-0.9 gigatons of carbon dioxide-equivalent per year by 2030.

Limitations

Additional financial data would increase the utility of the financials of this solution. It would also be valuable to calculate yield impacts.

Conclusions

There is much potential to scale up tree intercropping, for example in the mechanized regions of North and South America. On cropland with moderate to steep slopes, poor or degraded soils, or facing other challenges, tree intercropping is an important tool for slope stabilization and restoration and improvement of degraded and infertile soils. Tree intercropping combines the sequestration power of trees with the ability to continue producing the annual crops that humanity depends upon. This solution surely has a major role to play in agricultural mitigation efforts.


[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.

Full models and technical reports coming in late 2017.

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