Tree Planting as Climate Policy?

The Trillion Tree Initiative and related congressional actions seek to expand the area of forest and the carbon mitigation benefits they can provide through sequestration of atmospheric carbon in standing forests and wood products. In the United States, forest area has increased over time as private sector investment has offset the loss of forests to urban growth with forest establishment on agricultural land.

Efforts to significantly expand the US forest carbon sink would benefit from a careful consideration of the nation’s history of tree planting and forest investment and the current structure of timber supply and demand. Establishing additional forests can be accomplished with direct funding of tree planting on private land, but the structure of land markets suggests a high potential for benefit leakage when planting expands timber supplies. Government investment in ecological and riparian restoration efforts, urban forestation, and in a forest carbon reserve may mitigate leakage effects but provide somewhat limited opportunities. The greatest potential for forest climate benefits at scale may arise through expanding the demand for wood products, thereby incentivizing further investment in forest growing and carbon storage benefits in products.

• Private-sector investment in forest management has enhanced the forest carbon sink in the United States. However, the aging of forests, loss of forests to urban uses, and dampened demand for wood products are expected to reduce carbon sequestration moving forward.
• Programs that would expand the area of forests (especially in the eastern United States) might stabilize the nation’s forest carbon sink, but program design is critical.
• Traditional tree-planting programs would grow timber supplies, thereby depressing timber prices and reducing private sector investment with leakage of program benefits.
• Tree planting focused where effects on timber supply are minimal could be one effective approach. This includes investment in ongoing ecosystem and riparian restoration initiatives, urban forests, and afforestation of rural lands with restrictions. A forest carbon reserve like the Conservation Reserve could expand the carbon sink, but at a high cost.
• The greatest potential for expanding the carbon sink is likely to be a sustained growth in the demand for wood products, resulting in a strong demand for forestland and, in effect, replicating the expansionary growth of the forest sector in the late twentieth century.

A broad consensus seems to have emerged regarding the use of forests to mitigate climate changes by drawing carbon dioxide (CO2) from the atmosphere and sequestering it in forest biomass and long-lived wood products. The Trillion Tree Initiative proposes to vastly expand the area of forests across the globe, and a bill in Congress proposes to grow additional forests by supporting private tree planting and refocusing public land management on carbon storage benefits. Instead of using forest offsets as part of an economy-wide cap-and-trade scheme, these initiatives aim to directly expand the forest carbon sink as a climate change mitigation measure.

Planting trees has long been viewed as a publicly acceptable and politically safe way to address environmental problems, largely because forests provide many cobenefits, including watershed protection, recreation, and wildlife habitat. But can tree-planting policies be an effective means of achieving climate change mitigation goals? Depending on policy design, publicly funded tree planting could cut both ways in the forest sector, defining winners and losers, and may or may not enhance the nation’s carbon sink.

Carbon cap-and-trade approaches rely on price signals to efficiently generate forest emissions offsets. Programs focused on tree planting or natural forest regeneration, or both, might achieve some of these benefits, but outcomes depend on a careful design of policy to account for the mechanics of the sector and its interactions with other parts of the economy. Efforts to significantly expand the US forest carbon sink would benefit from a careful consideration of the nation’s history of tree planting and forest investment and the structure of timber supply and demand. Publicly funded tree planting in a competitive marketplace for land and forests could lead to offsetting adjustments in private investments, so tree-planting subsidies alone are unlikely to grow forests’ climate benefits. This issue brief explores the potential effects and effectiveness of tree-planting programs for increasing the climate mitigation benefits of forests.

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