Sequestration vs Storage... What's the difference and why does it matter for forest C projects?
People commonly throw around words like carbon "storage" and "sequestration" when talking about the role of forests in mitigating climate change, but many struggle to understand the key differences and their implications for forest carbon projects. Here we provide some information and context to help clarify.
As of source of carbon dioxide (CO2), deforestation is responsible for at least 20% of total human-caused greenhouse gas emissions. However, when protected and well managed, forests can remove large amounts of carbon dioxide from the atmosphere through the process of photosynthesis. Trees convert the absorbed carbon into biomass where it is stored in the form of stems, roots, branches, foliage, litter, soil, etc. This process of carbon uptake and storage in biomass is known as sequestration, expressed as a rate per unit time. The carbon stock is the quantity of carbon in a specific forest pool – how much is stored. It is usually expressed per unit area, either explicitly (per ha, for example) or implicitly (within a geographical or politically defined boundary).
Storage then is a consequence of sequestration. In a ‘healthy’ forest, both show characteristic patterns that reflect the relative stages in stand development, as illustrated in the following figure.
When trees are small and before they become the dominant vegetation type, both storage and sequestration are low. The latter is simply because root and canopy biomass are not sufficiently developed to support high photosynthetic rates. As trees gain biomass, the capacity for photosynthesis increases during the middle stage. At this stage, carbon sequestration reaches its maximum, and though storage has increased substantially, trees still have a considerable capacity to continue accumulating carbon. If the stand survives long enough to enter late-stage development (often referred to as an “old growth” condition, if stands reach 100 years and older), senescence ensures a marked decline in the rate of carbon sequestration while storage approaches its maximum. It is worth noting that the relative length of each stage can be highly variable, depending on factors such as soil, climate, disturbance regime, and species composition.
When it comes to developing forest carbon projects, it is essential to understand the interaction between these two processes and their implications for the flow of carbon offsets. Both can be important and their impacts may change over time as a project matures. For example, it's important to protect carbon stored in mature forest biomass from being released into the atmosphere when forests are disturbed (harvested or degraded). However, it's also effective to promote conditions where forest sequestration (removing CO2 from the atmosphere) can be enhanced. At 3GreenTree, we are focused on helping clients better understand these differences towards developing effective and marketable forest carbon projects.