Part of the Answer to Climate Change May Be America’s Trees and Dirt, Scientists Say

Farming/Growing, Feedstocks, Field/Orchard/Plantation Crops/Residues, Infrastructure, Opinions, Oregon, Policy, R & D Focus, Sustainability

November 19, 2018

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by Brad Plumer (New York Times) … A new study published on Wednesday, however, found that better management of forests, grasslands and soils in the United States could offset as much as 21 percent of the country’s annual greenhouse gas emissions.

At the high end of the projections, that would be roughly equivalent to taking every single car and truck in the country off the road.

The paper, published in the journal Science Advances, identified a number of promising strategies, like replanting trees on degraded lands, changing logging practices to better protect existing forests and sequestering more carbon in farmland soils through new agricultural techniques.

“We’re not saying these strategies are a substitute for getting to zero-carbon energy; we still need to do that too,” said Joseph E. Fargione, a scientist at the Nature Conservancy and lead author of the study. “But we think that natural climate solutions generally get overlooked. And we found a lot of opportunities here to help mitigate climate change.”

Other scientists agreed that storing more carbon in forests and soils could be a potent tool, though some were more cautious about how much was feasible in practice. For instance, the authors of the study used remote-sensing data to identify more than 100 million acres of land in the United States that is not currently being used for crops or pasture but that could be suitable for planting more trees, which absorb carbon from the air.

“I’m intrigued and hopeful but also a little skeptical,” said Timothy D. Searchinger, a researcher at Princeton University and the World Resources Institute. “They’ve provided a very rough map of these lands, and it would be a good idea to go out and examine this land more closely to see if they’re right and if so, more closely determine what it would take to reforest it.”

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The study looked at nearly two dozen possible approaches. For instance, policymakers could encourage more farmers to plant cover crops between their main harvests rather than leaving their fields bare, which would help pull more carbon from the air into the soil. While cover crops are becoming increasingly common in the United States, the practice often requires extra labor or equipment, so financial incentives may be needed to speed adoption.

Other steps could prove more contentious. The study noted that large swaths of forests in the South and Pacific Northwest are being cleared as cities expand. But restricting urban sprawl, as cities in Oregon have tried to do, can be tricky in practice.

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Another huge obstacle to conserving more of these ecosystems is the growing global demand for farmland, as the world adds billions more people. Reducing that pressure will most likely require difficult steps like significantly improving crop yields, curtailing food waste and perhaps moderating global meat consumption. READ MORE

Natural climate solutions for the United States (Science Advances)

Years-long biomass study shows promising results (Biomass Magazine/Humboldt State University)

Natural solutions can reduce global warming: US forests, wetlands, and agricultural lands could absorb a fifth of greenhouse gas pollution — equivalent to emissions from all US vehicles (Science Daily)

Excerpt from Science Advances: To avoid conflicts with other important societal goals for land use, we constrain our maximum estimate to be compatible with human needs for food and fiber (Supplementary Materials). Within these constraints, 5.1 Mha of cropland can be restored to grasslands, forests, and wetlands, equal to the area that has left the Conservation Reserve Program (CRP) since 2007 (8) and less than half the land currently dedicated to corn ethanol. We also estimate that 1.3 Mha of pasture could be reforested without affecting livestock production, assuming recent improvements in efficiency continue (see the Supplementary Materials). We assume that timber production can temporarily decrease by 10%, which maintains timber production levels within the historic range of variation and enables managed forests and plantations to transition to longer harvest rotations (see the Supplementary Materials). We assume that extensive natural forests on private lands can all undergo harvest extension, with the temporary loss of timber supply replaced by reforestation and thinning for fire risk reduction (12) or with thinning or select harvest practices that still provide timber but maintain carbon levels (Supplementary Materials) (13, 14). We further constrain our analysis to avoid impacts on biodiversity. This biodiversity constraint precludes both the conversion of natural habitat to energy crops and the afforestation of native grasslands.

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Higher estimates than ours can be obtained by reforesting or afforesting areas that we excluded (e.g., productive crop and pasture lands and natural grasslands) and/or by using rates of carbon sequestration from plantation systems rather than from natural regenerating forests ….

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A growing body of literature suggests that future global food demand can be met via investments in yield increases, closing yield gaps, diet shifts, aquaculture, and biofuel policy, without the need to further expand cropland into natural areas (35, 36). In the United States, marginal cropland, much of which is unprofitable (37), could be restored to grassland or forests with net societal benefits (38). Similarly, NCS may compete with bioenergy production. However, this conflict can be reduced or avoided depending on the form of bioenergy production or NCS. Some forms of biomass production, such as residues and wastes, or high-yielding methods, such as algae, do not require productive land (39). Our grassland restoration pathway could produce a limited amount of additional biomass while maintaining carbon sequestration in soils if low-productivity croplands are converted to perennial energy grasses (40). Further, NCS based on improved management of existing land uses do not create land use conflict and can even increase productivity within that land use (e.g., fire management or cover crops). However, aggressive expansion of dedicated bioenergy crops, given the large land requirement of both first- and second-generation bioenergy crops (41), would be likely to reduce the mitigation potential available through NCS, notably via reforestation, avoided grassland conversion, and natural forest management. READ MORE

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