Tree plantation in Umatilla, Oregon
Technical Summary

Tree Plantations (on Degraded Land)

Project Drawdown defines tree plantation on degraded land as: the cultivation of trees for timber or other biomass uses on degraded land. Climate mitigation is achieved through biosequestration in soils, biomass, and timber. This practice replaces annual cropping on active cropland, and other uses on degraded grassland and forest. Tree plantation on degraded land also aims to reduce emissions from deforestation by providing an alternative source of timber, though this impact is not modeled here.

Tree plantation on degraded land has been widely promoted as a land-based mitigation strategy due in part to its high sequestration rates. Drawdown's tree plantation on degraded land scenarios are more modest than many. This is because other tree-focused solutions with high sequestration rates are given higher priority, including tree intercropping, silvopasture, multistrata agroforestry, perennial staples crops, tropical forests restoration, and temperate forests restoration. Nonetheless, tree plantation on degraded land is of critical importance for mitigation, building material, and restoration of degraded lands.

Methodology

Total Land Area[1]

The total area allocated for tree plantation on degraded land is 718 million hectares, and is comprised of degraded grassland and forest. The degraded forest represents only the current adoption of the solution, while all new adoption of the solution is allocated on the degraded grassland area. Current adoption[2] is estimated at 294 million hectares, based on data from the Food and Agriculture Organization (FAO, 2015).[3]

Adoption Scenarios[4]

Projected adoption of tree plantation on degraded land is based on historic country-level growth rates from FAO (2015), aggregated by region and based on the model projection from recent literature (Evans, 2009; Kreidenweis et al., 2016). Eight custom scenarios are developed.

Impacts of increased adoption of tree plantation on degraded land 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: Scenario analysis shows tree plantation on degraded land adoption on 406.62 million hectares of degraded land.
  • Scenario 2: Aggressive adoption yields adoption of tree plantation on degraded land on 467.85 million hectares of the allocated degraded land area.

Emissions, Sequestration, and Yield Model

The sequestration rate is 3.3 tons of carbon per hectare per year, based on 29 data points from 13sources. This is in line with Intergovernmental Panel on Climate Change (IPCC) estimates (Watson, 2007). It is assumed that all sequestered carbon is re-emitted at harvest, except for carbon stored in timber. Average timber yield per hectare per year was based on meta-analysis. An average lifespan of 26 years was considered for an tree plantation on degraded land plantation, based on the meta-analysis of 36 data points from 5 sources .

Financial Model

First cost of tree plantation on degraded land is US$668.57 per hectare,[5] based on meta-analysis of 22 data points from 9 sources. It is assumed that first costs for the land use that tree plantation on degraded land is replacing have already been paid, as the land is already in production. Net profit per hectare is calculated at US$593.96 per year for the solution (based on meta-analysis of 16 data points from 13 sources), compared to US$37.84 per year for the conventional practice (based on 20 data points from 15 sources).[6]  Annual operational cost per hectare is calculated at US$123.37 for the solution (based on meta-analysis of 18 data points from 12 sources), compared to US$80.64 for the conventional practice (based on 9 data points from 7 sources).[7] The financial variables for conventional practice are weighted by the percent degraded grassland area to the total land area, as it is assumed that not all degraded grassland area is under conventional practice.

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 tree plantation on degraded land was constrained by Drawdown's higher prioritization of food production and forest restoration. In degraded grassland, tree plantation on degraded land was the second-highest priority.

Results

Total adoption in the Scenario 1 is 406.62 million hectares in 2050, representing 57 percent of the total available land. Of this, 112.52million hectares are adopted from 2020-2050. The sequestration impact of this scenario is 22.2 gigatons of carbon dioxide-equivalent greenhouse gases by 2050. Net cost is US$17 billion and lifetime operational cost is US$164.8 billion. Lifetime saving in net profit is US$2.1 trillion

Total adoption in the Scenario 2 is 467.85 million hectares in 2050, representing 65 percent of the total available land. Of this, 173.75 million hectares are adopted from 2020-2050. The impact of this scenario is 35.9 gigatons of carbon dioxide-equivalent by 2050. Net cost is US$72 billion and lifetime operational cost is US$259.5 billion. Lifetime saving in net profit is US$3.3 trillion.

Discussion

Benchmarks

The IPCC provides a benchmark of 4.0 gigatons of carbon dioxide-equivalent per year in 2030 from afforestation, given a price of $100 per ton of carbon dioxide (Metz, 2007). The Drawdown model shows 0.67-1.09 gigatons of carbon dioxide-equivalent per year in 2030. These impact are substantially lower, as this study has much lower adoption than most studies due both to higher prioritization of other land uses and to not modeling a price on carbon dioxide. When combined with the bamboo production and perennial staple crops solutions, however, emissions reduction in 2030 increased to 1.33-2.45 gigatons of carbon dioxide-equivalent per year in 2030.

Limitations

The study has several limitations. One limitation is the use of a single sequestration rate across all climates. The current version of the model does not account for albedo impacts at temperate and boreal latitudes. This will be addressed in future versions. It would also be desirable to model the impacts of timber replacing carbon and steel in construction, as these materials are emissions-intensive.

Conclusions

Tree plantation on degraded land is already practiced on a wide scale, and represents an important high-carbon land use. It produces products of critical importance, and can help reduce pressure on intact forests. Though not a "silver bullet," it is an essential component of land-based mitigation efforts.

 

[1] To learn more about the Total Land Area for the Land Use Sector, click the Sector Summary: Land Use link below.

[2] 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.

[3] 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.

[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: Land Use 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 Land Use integration model, click the Sector Summary: Land Use link below.