The sustainable forest carbon cycle
Carbon is the basic building block of life. Trees absorb carbon dioxide (CO2) during the process of photosynthesis, oxygen is released and remaining carbon is stored in biomass. Some carbon is released back into the atmosphere from forest deadwood, litter and soils pool due to decomposition, but sustainably managed forests are a net absorber of carbon. Old, unmanaged and degrading forests eventually become a net emitter of carbon back into the atmosphere. The carbon in harvested wood products (HWPs) continue to store carbon, which can eventually be released back into the atmosphere unless it is recycled or used for bioenergy. Use of wood as bioenergy replaces fossil fuel used and reduces overall emissions.
Fossil fuel emission can also be reduced by substituting energy intensive materials with wood products (i.e. product substitution)
The substitution effect
In essence sustainable managed forests are carbon neutral after the first rotation. However, continued inflow of wood from harvest of successive rotations into the harvested wood product (HWP) pool, avoidance of emissions by substituting wood for energy intensive product with wood and by substituting bioenergy for fossil fuels use represents the largest carbon pool. This C pool increases after every harvest because the removal is permanent.
Compared to unmanaged forests (Perez-Garcia et al., 2005) and continuous cover forestry systems (Lundmark et al., 2014), high production plantation with optimized for long term HWP can store double the amount of carbon at 100years (see figure above, Black, unpublished).
Carbon storage in peatland forests
Maintaining the peatland forest carbon pool
Pristine, wetlands accumulate carbon, or may be carbon neutral, but the carbon balance changes when peats are drained and afforested (see figure above). Initially, methane (CH4) emissions are reduced due to the creation of aerobic conditions, but CO2 and N2O emissions increase due to peat oxidation and mineralisation. However, the forest becomes a net absorber of CO2 at canopy closure (4 to 12 years) due to accumulation of carbon in biomass, litter and deadwood pools. CO2 removal will be maintained as long as these forests remain productive and are managed in a sustainable manner. Maximization of the forest peatland carbon pool can be achieved by:
- Limiting or controlling deforestation, forest degradation and disturbance events (e.g. fires).
- Maintaining the productivity and stocking of afforested and reforested peatland sites.
- Ensuring crops do not go into nutritional check and remain well drained. This is challenging given the environmental constraints regarding fertilizer application and management of drains.
- Managing harvest and replanting operations to ensure an even age class distribution is achieved.
- Limiting afforestation to sites where peats are already degraded or exploited and where potential productivity is high enough to ensure both a sustained carbon removal and economic feasibility for timber or biomass production.
Deforestation and degradation
- Mature and subsequent rotation peatland forests have transitioned from a net removal of CO2 (-0.2Mt/yr) in 2006 to a net emission of 0.1 MtCO2/yr in 2015*. This may be due to:
- Age class shifts to younger less productive forests**
- Environmental constraints, which limit fertilizer application.
- Reduced stocking and poorer re-re-establishment on marginal land.
- Forest fires*.
- Deforestation of peatland forests to windfarms and EU life peatland restoration projects has resulted in an emission of about 0.5Mt CO2 since 2005*.
*excl. HWP (Source NFI, EPA and CARBWARE)
**Black et al., 2012
OUR mitigation strategy
Sustainable mitigation strategy
- Maintain productivity and stocking of managed forests.
- Limit emissions from deforestation, forest degradation and disturbance events (e.g. fires).
- Maximize carbon storage in long life HWP.
- Increase replacement of energy intensive products with wood, such as biomass for fossil fuel or material product substitution.
- Maintain high production plantations and sustainable harvest targeted for use as long term HWP and wood substitution of emission intensive products.
- Develop timber products and markets with high wood storage and product substitution value.
- Develop adaptive strategies to reduce the effect of negative impacts of climate change on forest growth and carbon mitigation potential.