A new Freestone Peach orchard intercropped with corn in Klickitat County, south central Washington.
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 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 494 million hectares of degraded and non-degraded cropland.[2] Current adoption[3] is allocated on the non-degraded cropland. To date, accurate and comprehensive datasets on the current adoption levels of different forms of tree intercropping do exist. A recent study by (Lal et al., 2018) estimates the total global extent of tree intercropping systems at approximately 600 million hectares. A more comprehensive study by (Zomer et al., 2014) uses global remote sensing data to estimate total global cropland with >10 percent, >20 percent and >30 percent tree cover. Given the resolution of satellite data used for the study, this data does not necessarily differentiate between tree intercropping systems and small areas with trees adjacent to cropland and should therefore be taken as a rough estimate. Moreover, 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.  Nevertheless, Drawdown models estimate a global area of 267.87 million hectares Mha under tree intercropping systems with 10-20% canopy cover, based on GAEZ cropland data and tree cover data derived from (Zomer et al., 2014).

Adoption Scenarios[4]

Drawdown’s future adoption were developed based on a) historical changes in the percent of agricultural land under 10-20% between 2000 – 2010, as determined by (Zomer et al., 2014); b) UK projections of future land-use change by 2050, as reported by (Thomson et al., 2018); and c) current estimates of tree intercropping adoption in the EU based on calculations in (den Herder, 2017).Seven custom adoption scenarios were made.

Impacts of increased adoption of tree intercropping 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 1: Analysis of this conservative scenario shows adoption of tree intercropping on 416.9 million hectares by 2050.
  • Scenario 1: Analysis of this more aggressive scenario shows adoption of tree intercropping on 490.4 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 tree intercropping is set at 1.7 tons of carbon per hectare per year, based on 15 data points from 9 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$988.12 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 calculated at US$639.02 per hectare per year for the solution (based on meta-analysis of 14 data points from 10 sources), compared to US$492.81 per year for the conventional practice (based on 67 data points from 35 sources). While the operational cost is calculated at US$1043.02 per hectare per year for the solution (based on 16 data points from 4 sources), compared to US$895.14 per year for the conventional practice (based on the 57 data points from 25 sources).

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 Scenario 1 is 416.9 million hectares in 2050, representing 84 percent of the total suitable land. Of this, 148.94 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 15.03 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$147.0 billion and lifetime operational cost is US$698.6 billion. Net savings is US$262.4 billion.

Total adoption in the Scenario 1 is 490.4 million hectares in 2050, representing 99 percent of the total suitable land. Of this, 222.44 million hectares are adopted from 2020-2050. The impact of this scenario is 24.4 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$227 billion and lifetime operational cost is US$1079.6 billion. Net savings is US$427.8 billion.

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. Still, a recent study by (Lal et al., 2018) estimates a range between 0.40 – 1.55 MgC/ha/year for all global tree intercropping systems, and a study by (Griscom et al., 2017) estimates the C sequestration potential of all tree intercropping systems at 0.37 MgC/ha/year. There is a scarcity of benchmarks specific to tree intercropping sub-types, although (Udawatta and Jose, 2011) estimate the total sequestration potential of alley cropping at 3.4 MgC/ha/year. Annual impact of tree intercropping in 2030 is 0.37-0.65 gigatons of carbon dioxide equivalent per year. Thus, though an imperfect benchmark, this study is generally on target.  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.