Expanding the Carbon Horizon: Should Shrubs, Grass, Deadwood, and Soil be Counted in Carbon Markets?

The inclusion of shrubs, grass, deadwood, and soil in international carbon markets remains a complex and nuanced issue. These components undeniably contribute to carbon sequestration, but whether they should be part of carbon projects depends on various factors, including project type, ecosystem considerations, and the challenges associated with measurement and permanence. This article will present arguments both for and against their inclusion, with examples and data-driven insights. It will also focus on how these components fit into different types of carbon projects, including Afforestation, Reforestation, and Deforestation (ARD) projects and mangrove/wetland restoration efforts.

The Carbon Sequestration Role of Shrubs, Grass, Deadwood, and Soil

For Inclusion

Shrubs, grasses, deadwood, and soil play essential roles in carbon sequestration, especially in ecosystems where tree cover is sparse or absent. Globally, soil holds more carbon than the atmosphere and all vegetation combined, at an estimated 2,500 gigatons (Gt) (IPCC, 2019). In ARD and land restoration projects, these non-tree components significantly enhance a project's carbon sequestration potential.

For example, in semi-arid regions or degraded lands, where trees struggle to thrive, shrubs and grasses can act as primary carbon sinks. The Great Green Wall initiative across Africa, aimed at restoring 100 million hectares of land, relies heavily on shrubs and grasses to stabilize soils and capture carbon, making them vital for carbon accounting in these projects (FAO, 2020).

Deadwood, often overlooked, is also a substantial carbon reservoir. The FAO's Global Forest Resources Assessment (2020) states that deadwood contains about 8% of global forest carbon stock, a figure that rises in ecosystems like boreal forests. Including deadwood in carbon markets could provide a more holistic view of forest carbon dynamics.

Against Inclusion

However, opponents argue that including these carbon pools could overcomplicate carbon project methodologies. Shrubs and grasses are often fast-growing and ephemeral, cycling carbon quickly between the atmosphere and land. This temporary storage raises concerns about the permanence of carbon credits based on these components. For instance, a drought season could lead to dying off, releasing the stored carbon and making it difficult to guarantee long-term sequestration.

Deadwood, similarly, decomposes over time, releasing carbon back into the atmosphere. Including deadwood in carbon accounting could overestimate a project’s sequestration potential, especially if project timelines extend beyond its decay period.

Soil Carbon: Not Always Included, But Vital in Some Projects

While soil holds a vast carbon reserve, it is not universally included in all carbon projects. This is due to the difficulty of measuring soil carbon with precision across diverse landscapes. Soil carbon levels can vary dramatically with depth, moisture, and land use, complicating the establishment of reliable baselines.

However, some projects, especially those focused on wetland and mangrove restoration, do include soil carbon due to its significant contribution to overall sequestration. Wetland soils can store 3 to 5 times more carbon than terrestrial forests, with global wetland ecosystems holding up to 500 gigatons of carbon (IPCC, 2019). For example, the Indus Delta Mangrove Restoration Project in Pakistan, covering over 300,000 hectares, derives the majority of its carbon credits from soil carbon, which sequesters more than the mangrove biomass itself (Alongi, 2012).

However, including soil carbon requires robust monitoring and verification, raising project costs and logistical complexities. Some project developers may avoid including soil carbon due to these challenges, particularly in regions where monitoring infrastructure is underdeveloped.

Afforestation, Reforestation, and Revegetation(ARR) Projects: Expanding Carbon Pools

Afforestation, Reforestation, and Revegetation (ARR) projects are central to carbon markets, focusing mainly on tree biomass as the primary carbon pool. However, expanding ARR projects to include carbon stored in shrubs, grasses, and soils could provide additional benefits, particularly in ecosystems where trees are not the dominant vegetation.

For instance, in afforestation projects in degraded savanna regions, where trees grow slowly, shrubs and grasses often dominate. Including these in the carbon accounting could improve project outcomes and generate more carbon credits in the short term while trees are still maturing.

On the other hand, some reforestation projects in tropical ecosystems may find it challenging to include non-tree carbon pools. Shrubs and grasses in these areas often experience rapid dieback and regrowth, making it difficult to ensure long-term sequestration. Moreover, while these pools contribute to carbon storage, their inclusion could inflate project costs by necessitating additional monitoring and verification processes.

Mangrove and Wetland Restoration: The Case for Including Soil and Deadwood Carbon

Mangrove and wetland ecosystems are some of the most carbon-rich environments on Earth, with a significant portion of their carbon stored in soil and dead organic matter. In particular, mangrove soils sequester up to four times more carbon than tropical forests (Alongi, 2012). The inclusion of soil carbon in these projects can drastically increase the number of carbon credits generated.

For example, a mangrove restoration project in Kenya’s Gazi Bay estimated that 85% of its carbon credits came from soil carbon, highlighting the critical importance of including this pool in carbon accounting. Without soil carbon, the project’s carbon credit generation would be significantly lower, making it less viable in the carbon market (FAO, 2020).

However, concerns about the permanence of soil carbon in these ecosystems remain. Changes in water table levels, salinity, and human-induced modifications like drainage can lead to the rapid release of stored soil carbon. Thus, including soil carbon in these projects requires careful management and robust methodologies to ensure its long-term sequestration.

Conclusion

The debate on whether shrubs, grass, deadwood, and soil should be included in international carbon markets remains ongoing. Proponents argue that these components significantly enhance carbon sequestration potential, particularly in ecosystems where tree growth is limited. Including these carbon pools can also provide more holistic ecosystem restoration benefits, such as biodiversity conservation and soil stabilization.

Opponents, however, caution that including these pools introduces complexities in measurement, permanence, and verification, potentially leading to overestimated sequestration figures. Soil, in particular, plays a pivotal role in some projects, especially mangrove and wetland restoration efforts, but its inclusion must be managed carefully.

As technologies improve and carbon markets evolve, the inclusion of these carbon pools will likely become more standardized. However, project developers must weigh the pros and cons carefully, ensuring that any credits generated from these components are based on robust scientific methodologies and long-term monitoring.

References:

- Alongi, D. M. (2012). Carbon sequestration in mangrove forests. Carbon Management, 3(3), 313-322.

- FAO (2020). Global Forest Resources Assessment 2020. FAO, Rome.

- IPCC (2019). Climate Change and Land: An IPCC Special Report. Intergovernmental Panel on Climate Change.