Cows on a hillside between trees.
Technical Summary

Silvopasture

Project Drawdown defines silvopasture as: the addition of trees to pastures for increased productivity and biosequestration. This solution replaces conventional livestock grazing on pasture and rangeland.

Research suggests that silvopasture systems can store significant amounts of carbon in both soils and tree biomass, while maintaining or increasing productivity and providing a suite of additional benefits. Traditional silvopasture systems, such as the dehesa in Spain and forest pastures in Scotland, have existed for centuries. More recently, research efforts have demonstrated the high suitability of this system for Latin American grasslands, and several organizations and governments have been working to promote its adoption.

Under silvopasture, emissions of the greenhouse gases methane and nitrous oxide continue, but are more than offset by carbon sequestration, at least until soil carbon saturation is achieved. Drawdown takes the conservative assumption that emissions do not change with conversion from conventional to managed grazing.

Climate mitigation literature often lumps silvopasture into an undifferentiated "agroforestry" category with multistrata agroforestry and tree intercropping. Silvopasture's high sequestration rates and increased meat and dairy yields make it worthy of consideration on its own. Though managed grazing has been the focus on much attention for its climate mitigation potential, this study demonstrates that silvopasture is also worthy of attention. In fact, it is shown to have a substantially higher mitigation impact than managed grazing itself.

Methodology

Total Land Area[1]

Total available land is calculated at 823 million hectares, and consists of non-degraded grassland with minimal or moderate slopes in humid climates.[2] Current adoption[3] of silvopasture is estimated at 550 million hectares, based on  Lal (2018) estimates[1].

Adoption Scenarios[4]

In the absence of limited data available either on historical growth rates of silvopasture or of any future projections, Drawdown’s future adoption is based on linear projections of current global data on documenting areas under silvopasture and grazing and pasture. Seven custom adoption scenarios were developed based on a) regional areas under >30 percent tree-cover as determined by (Zomer et al., 2014), b) estimates of historic adoption rates reported in (Nair, 2012) and (Lal et al., 2018), c) a meta-analysis of current area of grazing or pasture land already under silvopasture practice, and d) a meta-analysis of current area of grazing or pasture land under improved pasture. Impacts of increased adoption of silvopasture 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: This conservative scenario results in the adoption of 720.5 million hectares by 2050.
  • Scenario 2: This more aggressive adoption scenario results in the adoption of 772.3 million hectares by 2050.

Emissions, Sequestration, and Yield Model

Sequestration rates of silvopasture are set at 2.7 tons of carbon per hectare per year. This is the result of meta-analysis of 14 data points from 8 sources. Yield gains compared to business-as-usual annual grazing were set at 11.1 percent, based on meta-analysis of 6 data points from 2 sources.

Financial Model

First costs are estimated at US$1180.65 per hectare.[5] For all grazing solutions, it is assumed that there is no conventional first cost, as conventional grazing (in this case) is already in place on the land. Results are based on meta-analysis of 20 data points from 10 sources. Net profit per hectare is calculated at US$840.25 per year for the solution (based on meta-analysis of 17 data points from 11 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$761.57 for the solution (based on meta-analysis of 17 data points from 12 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 areas. Adoption of silvopasture was limited to non-degraded grassland with minimal or moderate slopes, and was the highest priority for these lands. The majority of grassland is likely too dry to support tree growth, thus this study is somewhat conservative in its adoption projections.

Results

Total adoption in the Scenario 1 is 720.5 million hectares in 2050, representing 88 percent of the total suitable land. Of this, 170.5 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 26.58 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$206.7 billion and lifetime operational cost of US$2.3 trillion. Net savings is US$1.7 trillion. Increase in global livestock yield is 0.75 million metric tons from 20205-2050.

Total adoption in the Scenario 2 is 772.3 million hectares in 2050, representing 94 percent of the total suitable land. Of this, 222.3 million hectares are adopted from 2020-2050. The impact of this scenario is 42.31 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$272.9 billion and lifetime operational cost of US$3.1 trillion. Net savings is US$2.3 trillion. Increase in global livestock yield is 1.2 million metric tons from 2020-2050.

Discussion

Benchmarks

A recent study by (Lal et al., 2018) estimates a range between 0.55 – 1.90 for the technical potential of C sequestration by silvopastures. Annual impact of silvopasture in 2030 is 0.55-1.07 gigatons of carbon dioxide equivalent per year is closely in line with Lal 2018 benchmark.

Limitations

The Drawdown study could be improved with additional data points on financials. Better data on current and projected adoption would be of use as well, as would projections of mitigation impact. More research on the suitable area of global grassland, with sufficient rainfall to permit tree growth, is also essential to precisely determine the potential impact of this solution.

Conclusions

Silvopasture is the highest ranked of all of Drawdown's agricultural solutions in terms of mitigation impact, though it has received little attention. It should be a priority for scaling up wherever grasslands are humid enough to permit tree growth. This is particularly important given the need to produce climate-friendly livestock products to meet global demand for meat and dairy, even given plant-based diet and reduced food waste projections. Thus, silvopasture is an essential supply-side food solution in any mitigation program.

 

[1] Lal 2018; Lal, R., Smith, P., Jungkunst, H. F., Mitsch, W. J., Lehmann, J., Nair, P. R., ... & Skorupa, A. L. (2018). The carbon sequestration potential of terrestrial ecosystems. Journal of Soil and Water Conservation, 73(6), 145A-152A.

[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] 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.