The Root of Vitality: Enhancing Soil Organic Carbon (SOC) through Reforestation Efforts

Carbon is one of the core building blocks of life on Earth. It exists in many forms (such as plant biomass, soil organic matter, and carbon dioxide gas) and connects the planet’s ecosystems through a complex, yet truly magical carbon cycle. While oceans represent the world’s largest carbon sink, soils play the first fiddle on land, serving as a reservoir for 75-80% of terrestrial carbon known as soil organic carbon (SOC). 

The primary SOC reservoirs on land are found in permafrost and peats in the Arctic region and Northern Eurasian and American boreal forests. Amidst the global warming crisis fueled by spiking CO2 and other greenhouse gas emissions primarily due to human activities, reforestation looks like a promising solution for replenishing soil organic carbon stocks not only to cool the planet but also to restore an ecological balance.  

Understanding SOC and Soil Carbon Storage

Widely considered a powerful antidote against intensifying climate change, soil organic carbon has garnered a lot of attention in both scientific and tech domains, which led to the emergence of various soil organic carbon (SOC) model solutions capable of simulating SOC dynamics under various land use scenarios, climates, and management practices. Given that carbon is constantly changing and moving from one pool to another (e.g. from oceans to the atmosphere and further to the soil), plotting a viable soil carbon-enhancing strategy requires a thorough understanding of how the carbon cycles in soil.

The cycling of carbon and soil carbon storage is governed by three key processes: photosynthesis, respiration, and decomposition. 

Plants pull out carbon dioxide gas from the atmosphere through photosynthesis, converting it into energy for vigorous growth – a process known as carbon sequestration. Some of the consumed carbon is then stored in the plant biomass, while some of it ultimately enters the soil either when plants die and start decaying or as excreta produced by grazing animals. These plant and animal byproducts are further broken down by soil microbiota. As a result, a small portion of the original carbon is fixed in the soil as stable soil organic matter, and the most part is released back into the atmosphere as CO2 through microbial respiration. 

Soil organic matter is home to billions of soil microorganisms and a continuum of plant, animal, and microbial residues at various decomposition stages, ranging from freshly fallen leaves to well-decomposed humus. Of all organic matter, humus is the least susceptible to decomposition, which makes it the largest pool of soil organic carbon with the longest residence time. Due to the direct correlation between SOC levels and the amount of organic matter, the latter is often determined by measuring soil carbon.

The Impact of Deforestation on SOC Stocks

Among terrestrial carbon sinks, forests retain the largest amount of carbon per surface area of land, wherein forest soils store twice as much carbon as tree biomass (60% vs 28%). All that carbon relentlessly cycles between trees, fertile dirt beneath the ground, soil fungi and microbes, and the atmosphere.

When trees are chopped down for timber, burned down by wildfires, killed by massive pest and disease outbreaks, or cleared to make space for cattle or crop production, the carbon they’ve stored above and under the ground leaks back into the air, increasing the amounts of GHGs acting as a blanket that heats the planet. Such manmade and natural disturbances also speed up natural carbon loss occurring during the decomposition of dead trees. Moreover, soils in deforested areas fall easy prey to erosion, accelerating degradation and dramatically affecting their capacity to sustain plant life and sequester carbon.

Reforestation: A Path to SOC Recovery

Increasing the quantities of carbon stored in forest soils has the potential to offset carbon dioxide emissions and mitigate the negative effects they have on the environment. First and foremost, it is vital to protect our old-growth forests for they are the major carbon sinks at our avail. All the more so since studies suggest their topsoils keep accumulating SOC when undisturbed. If destroyed, such forests may take centuries to get back to the original levels of their biomass and soil organic carbon pools. 

Second-growth and degraded forests, however, also are of great importance. By taking a proforestation approach to this dominating forest type, not only we can reduce carbon emissions caused by overlogging but also increase carbon sequestration rates through natural or encouraged regrowth.

Another climate-benefiting approach is reforestation – a process of replanting new trees in forests with largely shrunk populations. On top of the evident positive outcomes for biodiversity and wildlife habitats, it bears the potential to enhance forest’s SOC stocks through:

 Increased Biomass: 

During growth, replanted trees lose some of their branches and canopy that naturally replenishes soil organic matter and enriches the SOC pool upon decomposition.  

 Improved Soil Structure: 

Extensive root systems developed by trees hold the soil together, improving its structure and water-absorbing capacity, also acting as a shield against wind erosion. Carbon losses in healthy, solid-structured soils are minimal compared to bare or overly tilled soils.

 Enhanced Soil Biodiversity: 

Trees attract large populations of soil microorganisms that are indispensable in the decomposition and conversion of organic matter into humus having high stable soil organic carbon content. 

 Better Microclimate for Carbon Sequestration: 

Forests positively affect the water regimen in soils and moderate soil temperatures, creating a favorable environment for carbon sequestration and extending carbon residence time.  

 Agricultural Productivity: 

Trees integrated into agricultural lands can boost soil organic matter content by adding plant residue and boosting soil microbial activity. The resulting enhanced soil carbon storage entails a host of benefits, such as increased soil fertility, higher nutrient activation capacity, improved erosion resistance, and water-retaining capacity of soils, contributing to overall crop productivity and translating into more abundant yields.

Forest Carbon Projects

Roughly speaking, carbon offset projects encompass activities aimed at the generation of carbon offsets and their conversion into carbon credits for further trading or sale. A carbon offset is a reduction in CO2 emissions or equivalent capture of carbon dioxide from the atmosphere, which is measured in metric tons and achieved through specific activities. In the forestry domain, carbon projects typically imply techniques that enhance carbon sequestration, e.g. reforestation/afforestation, avoiding forest conversion, and improved forest management that improves SOC storage.    

To turn the carbon offsets into tradable carbon emission credits, such techniques and activities must undergo registration and verification by independent third parties and be approved by the entitled carbon registry. Basically, forest owners get paid for increases in carbon sequestration and storage that counterbalance emissions by other entities.

Challenges of Implementing Forest Carbon Projects

• In countries with weak law enforcement, forest territories under carbon offset projects are at risk of illegal logging that can wipe out the environmental benefits.
• Issues with land tenure and property rights, plus unequal involvement of local communities may disrupt the carbon-sequestering attempts.
• Carbon offset projects lower the cost of CO2 emissions for entities thereby discouraging them from investing in carbon sequestration technologies.
• Carbon measurement is fraught with uncertainties regarding the residence time of carbon: the captured carbon will eventually return to the atmosphere thus nullifying the offsets.

Technological Innovations in Monitoring

Technologies are central to the success of carbon forest projects. They enable real-time monitoring of major forest parameters: overseeing the dynamics of forest cover changes, assessing biomass levels, and measuring carbon sequestration rates. The democratization of space paved the way for widespread satellite imagery and remote sensing technology use. Today, they help track the progress of forest management activities aimed at carbon sequestration, enabling more accurate carbon measurements and more transparent reporting on the project results. 

One example is the remote sensing-powered SOC modeling method developed by EOS Data Analytics for measuring, estimating, and predicting SOC levels. The utilization of 140 predictors (including satellite imagery) allows for increased precision in soil organic carbon estimation and a tangible reduction in costly soil sampling at the verification stage (up to 90%). The company is gaining traction in the carbon market, building on its previous achievements, such as successful cooperation with a top-tier SOC project developer AgriProve that resulted in a grant-winning SOC model development.

The imperative role of SOC in mitigating climate change and alleviating the related challenges is no longer questioned. In this regard, carbon offset projects hold great promise as a means to encourage global incentivized efforts in replenishing SOC levels in one of the largest terrestrial carbon sinks – forests – through sustainable activities promoting carbon sequestration and longer soil carbon storage, such as reforestation and improved forest management. The integration of technologies into forest carbon projects holds the potential to facilitate the estimation and prediction of difficult-to-measure SOC through data-powered modeling based on satellite imagery and remote sensing technology, thus multiplying the benefits of carbon market stakeholders, not to mention the positive outcomes for the environment.

Autor:

Kateryna Sergieieva

Kateryna Sergieieva has a Ph.D. in information technologies and 15 years of experience in remote sensing. She is a scientist responsible for developing technologies for satellite monitoring and surface feature change detection. Kateryna is an author of over 60 scientific publications.