Teagasc’s Forest Carbon Tool (FCT) gives an indication of how much carbon can potentially be removed through various forest establishment options and other climate mitigation pathways, such as the use of harvested wood products (HWP).
Developed in conjunction with the Forest Environmental Research and Services (FERS) and the Department of Agriculture, the FCT supports forest establishment decision-making.
In addition to carbon sequestration, the long-term storage of carbon in HWPs and substitution of fossil fuels with wood energy represent important carbon pools and are incorporated in the FCT.
An important pathway that is not included in the current system is the substitution of energy-intensive building materials, such as concrete and steel, with wood products, which can have a high level of future impact.
For example, using 1.0t of wood instead of concrete can lead to an average reduction of over 2.0t of CO2 emissions over the life cycle of a product.
Using the FCT
Users can select from a dropdown list of current planting and soil type and forest tree species selection options. The FCT outputs provide indicative values for mean yearly CO2 sequestration, expressed as tonnes of CO2equivalent per hectare per year (tCO2eq/ha/yr) and mean cumulative sequestration values (tCO2eq/ha).
Both of these are normalised measures of sequestration that allow comparisons over different rotation ages.
Annual carbon sequestration rates do not stay constant, but change significantly over forest cycles.
Although growing forests capture and store CO2 during active growth, activities such as forest harvesting give rise to emissions, which the tool also takes into account (see examples below).
The following are examples of mean annual and crop rotation sequestration potential in tonnes of CO2 equivalent per hectare per annum (tCO2-eq/ha/yr). These take into account species mix, soils, yield class (YC: m3/ha/yr) and rotation.
Examples 1-3 provide summary outputs of mean annual carbon sequestration for planting grant and premium categories (GPCs) 8, 3 and 11, respectively, on suitable mineral soils. Examples provide an indication of the maximum potential sequestration (known as the CAP value) over two forest rotations. Productive conifer species (GPC 3) such as spruce can return high sequestration rates, especially when their HWPs are taken into account (Example 2).
While the net sequestration capacity from agroforestry is reduced when agricultural emissions are factored in, this category has the potential to assist mixed forest and livestock systems towards achieving carbon neutrality (Example 3).
Example 1: Birch forest (GPC 8).
Example 2: Diverse conifer/broadleaf (GPC 3). Comprises 70% Sitka spruce, 15% birch and 15% open area/retained habitat. Sitka achieves YC24 and is thinned over a 38-year rotation.
Example 3: Agroforestry (GPC 11) combining trees with livestock grazing.
Carbon balances are based on net emissions or removals from five pools (reservoirs of carbon), comprising trees above ground, roots, litter, deadwood and soil. Ongoing carbon transfers (termed fluxes) occur between these pools.
The rate of carbon uptake is determined by tree species, soil type, growth rate (yield class), forest management activities such as harvesting and previous land use.
Processes involved include long-term allocation of carbon into above- and below-ground forest biomass and turnover of biomass into soils and dead organic matter. There can also be carbon losses, such as those associated with decomposition from soils and dead organic matter. Where carbon uptake exceeds loss, the forest is a ‘sink’. Conversely, if loss exceeds uptake, the forest is a ‘source’.
The final output is the sum of all carbon stock changes.
A current area of further analysis is the effect soil type has on forest carbon balances.
Tom Houlihan is a forestry specialist with Teagasc