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 1,076 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 142.0 million hectares, based on the area of grazing land with at least 30 percent tree cover (Zomer, 2014).
Adoption Scenarios [4]
Regional data from Zomer (2014), including growth in global agroforestry from 2000-2010, was used to develop three custom adoption scenarios. The conservative adoption scenarios consider only the agricultural areas with over 30 percent tree cover, while the aggressive adoption scenarios also considers the partial (50 percent) or full (100 percent) conversion of agricultural areas with over 20 percent tree cover to over 30 percent tree cover, in order to increase the adoption area available to silvopasture.
Impacts of increased adoption of silvopasture 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: This conservative scenario estimates an increase in silvopasture area from 142.0 million hectares in 2014 to 215.0 million hectares by 2050.
- Drawdown Scenario: This more aggressive adoption scenario results in the adoption of 246.5 million hectares by 2050.
- Optimum Scenario: The most aggressive adoption scenario results in the adoption of 278.0 million hectares by 2050.
The lower future adoption of this solution, despite having significant allocated area, can be attributed to the low adoption rates reported in the historical data (2000-2010), which was used to project future adoption.
Emissions, Sequestration, and Yield Model
Sequestration rates of silvopasture are set at 4.8 tons of carbon per hectare per year. This is the result of meta-analysis of 26 data points from 8 sources. Yield gains compared to business-as-usual annual grazing were set at 10.0 percent, based on meta-analysis of 13 data points from 4 sources.
Financial Model
First costs are estimated at US$568.18 per hectare. [5] For all agricultural 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 6 data points from 4 sources. Net profit per hectare is US$552.83 per year (13 data points from 5 sources), compared to US$145.97 per year for the conventional practice (10 data points from 8 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 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 Plausible Scenario is 215 million hectares in 2050, representing 19.9 percent of the total suitable land. Of this, 73 million hectares are adopted from 2020-2050. The emissions impact of this scenario is 31.2 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$41.6 billion. Net savings is US$699.4 billion. Increase in global livestock yield is 0.8 million metric tons from 2015-2050.
Total adoption in the Drawdown Scenario is 246.5 million hectares in 2050, representing 22.9 percent of the total suitable land. Of this, 104.5 million hectares are adopted from 2020-2050. The impact of this scenario is 47.5 gigatons of carbon dioxide-equivalent by 2050.
Total adoption in the Optimum Scenario is 278.0 million hectares in 2050, representing 25.8 percent of the total suitable land. Of this, 136.0 million hectares are adopted from 2020-2050. The impact of this scenario is 63.8 gigatons of carbon dioxide-equivalent by 2050.
Discussion
Benchmarks
It appears that estimates of the global mitigation potential of silvopasture have not been attempted previously. In the absence of benchmarks specific to silvopasture, this study refers to a highly-cited study which 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 in 2050, though this includes some temperate silvopasture and tree intercropping. Thus, though an imperfect benchmark, this study is generally on target.
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] 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.
