Biological Sequestration: Forestry and Agriculture
Biological sequestration absorbs CO2 emissions through the growth of vegetation and the continued storage of some of the carbon in plant tissues and organic materials derived from plant tissues (e.g. stored in the soil). There are two broad types of biological sequestration projects:
Those that avoid emissions via conservation of existing carbon stocks, including:
- Avoiding deforestation, and
- Avoiding degradation of existing forests.
Those that increase carbon storage, including:
- Converting land from non-forest cover to forest (afforestation and reforestation)
- Increasing carbon stocks in forest land remaining forest (forest management), and
- Increasing soil carbon stocks through soil management techniques (e.g. no-till agriculture).
“Tree projects” have a natural appeal, since they conjure up images of pristine and healthy ecosystems. Yet the reality of forest carbon sequestration projects is far more complex. The amount of carbon sequestered by forests depends upon a number of factors including tree age, growth rate, local climate, and soil quality. Although we can reliably quantify the amount of carbon in a forest, we have to make educated guesses about how much carbon there would have been if no sequestration project had been implemented. It is possible that trees would have grown even without a sequestration project.
Another complication is the impact of climate change on forests. Climate change impacts on forest health and the trees’ ability to store carbon as a result of increased temperatures, altered precipitation patterns, and changes in disturbance regimes (fire, insects, disease) are still largely unknown across the globe. Although forests typically recover from natural disturbance, continued disturbance (by people or as a result of climate change) can keep forests from recovering.
Understanding the true effect of forest management requires looking at the net effect over many years. Some people argue for converting mature and old forests into stands of young, fast growing trees. Despite the fact that young forests have the greatest gross rate of carbon uptake, if an old growth forest is cut down and replaced with young fast-growing trees, it will take years to decades before the new forest will constitute a net carbon sink. This is because most of the carbon in an old forest is emitted within a few years of clearing, from wood waste from converting logs to wood products, logging waste left on the land, decomposition of stumps and roots, and loss of carbon caused by disturbance of the forest floor and soil.
Leakage is of particular concern in biological sequestration projects. Leakage is the unanticipated loss of carbon reductions outside the project boundary. For example, the reforestation of pastureland may drive local farmers to clear forests elsewhere for new pastures. Leakage can best be addressed through careful project design (e.g., incorporating project activities that avoid increasing pressure on other lands). Leakage must be accounted for and subtracted if project calculations are to be credible and accurate.
Permanence is another issue that carbon sequestration projects must contend with. Permanence—or rather, impermanence—refers to the fact that sequestration can be reversed and the carbon re-emitted to the atmosphere. Often people think of fire and illegal logging as causes of loss of forest carbon, but planned, legal logging probably removes more carbon from forests each year. When emissions are greater than growth and sequestration, then carbon stocks go down and sequestration is reversed. Because of this potential for reversal, forest carbon sequestration must be monitored and if sequestered carbon is lost the reversal must be counted as an emission.
Forest carbon sequestration projects are attractive because forests provide a wide range of ecosystem services. Forests provide clean water, and moderate water flow rates. Forests provide habitat for many plant and animal species, and provide livelihoods for millions of people.
Protecting Existing Forests
Projects that protect existing old growth forests are expected to provide the greatest carbon mitigation benefits. Emissions from forest degradation and deforestation are currently estimated to be causing about 20% of total global anthropogenic greenhouse warming. Currently, emissions from deforestation are so great that stopping this source of emissions would have the greatest net impact on forest-related emissions. Despite the importance of protecting existing forests – usually referred to as REDD: ‘Reducing Emissions from Deforestation and Degradation’ – very few such projects have been implemented in the voluntary market, and CDM does not currently allow for REDD projects.
Creating REDD credits has many great challenges: Quantifying baseline emissions, preventing displacement of emissions, solving conflicts about who controls forests, getting countries to agree to continuing to protect forests, and continuing to provide crops and forest products. It can be argued that deforestation is a demand-side problem, and that as long as the demand for biomass (fuel and timber) and land cannot be shifted and decreased, forestry offset projects in one area will only cause a change in the supply source rather than lower demand on the whole. This problem is also a kind of ‘leakage’ because the demand shifts from one place to another.
In other words, none of the forestry standards are able to account for international leakage and market shifting. This argument holds true for certain sectors (e.g. timber demand) but may not for others, where good project design is able to affect supply and demand (e.g. by providing local livelihoods through sustainable harvesting, more sustainable and productive agriculture, increasing energy efficiency and providing alternatives to wood fuel and serving demands for wood products with new, highly productive plantations that take harvesting pressure off natural forests).
Most beneficial are projects that maximize both carbon storage and carbon uptake by protecting carbon-rich old growth forests but allowing selective, well-managed harvesting to increase carbon uptake of young trees, to create local economic opportunities, and to protect biodiversity.
Without doubt, exemplary bio-sequestration projects can address several global problems: they can sequester and store carbon, protect watersheds, offer economic opportunities for the local population, and conserve or restore biodiversity. Conversely, poor-quality projects may result in a loss of biodiversity, displacement of the local populations, and even net loss of carbon stocks.
Ways to address these challenges of biological sequestration projects include:
- Limiting offset projects to afforestation and reforestation, where we can have more confidence in baselines.
- Developing REDD quantification and liability at the national scale, to account for leakage.
- Imposing rules for biological sequestration projects that specifically focus on maximizing biodiversity and social benefits.
- Addressing permanence by requiring that sequestration be monitored for as long as it is used as the basis for emission credits and counting credits as emitted if monitoring ceases or shows the underlying carbon sequestration to be reversed.
The currently available offset standards deal with the challenges of bio-sequestration projects in the following ways:
- Either excluding or strictly limiting bio-sequestration projects (Gold Standard, CDM)
- Imposing rules for bio-sequestration projects that specifically focus on maximizing biodiversity and social benefits (CCB Standards, Plan Vivo).
- Addressing issues of permanence by either issuing temporary offset credits (CDM) or establishing carbon buffer zones which retain a portion of the project carbon credits and sales in case of forest loss and provide funding for reestablishment (VCS, Plan Vivo).