Carbon Science
Carbon Sequestration Revealed: The Hidden Science Behind Irish Forest Measurements
Irish forests removed an average of 3.8 million tonnes of carbon dioxide equivalent yearly from the atmosphere between 2007 and 2016. Carbon sequestration in forests stands as one of our most powerful natural tools against climate change.
Carbon sequestration describes how forests act as a carbon sink by capturing atmospheric CO2 and storing it throughout the forest ecosystem. The national forest estate in Ireland serves as an important and expanding carbon sink, with current estimates exceeding 312 million tonnes. Ireland has pledged to reduce greenhouse gas emissions through several measures that include expanding climate-resilient forests to 18% of total land area.
The science behind this carbon capture and sequestration reveals fascinating details. Research shows that forest land in Ireland sequestered an average of 2.45 Mt CO2-eq yearly between 1990 and 2022. Harvested wood products added another 0.83 Mt CO2-eq per year. Forest types vary by a lot in their carbon sequestration and storage potential, with annual rates ranging from one to nine tonnes of CO2 per hectare per year.
In this piece, we'll get into how experts measure carbon in Irish forests and learn about the sequestration potential of different forest types. We'll also explore the challenges of carbon accounting in forestry. Understanding these processes helps us appreciate our forests' vital role in climate strategy.
Carbon Pools in Irish Forests: What Gets Measured
The forest ecosystem works as a vital carbon reservoir through five main carbon pools. Trees might die and release carbon individually. However, the forest system never stops capturing and storing carbon dioxide through these connected pools.
Aboveground Biomass: Trunks, Branches, Leaves
You can see carbon storage happening in the aboveground biomass - trunks, branches and foliage. This pool stands as the second largest carbon store in Irish forests. It holds 16% (52.574 million tonnes) of the total carbon stock measured in 2022. Trees turn atmospheric CO₂ into organic matter through photosynthesis and store it as biomass. Scientists track diameter and height growth rates of different species under various conditions to measure this pool.
Belowground Biomass and Root Carbon Storage
Living tree roots create a hidden carbon storage network beneath the soil surface. This often-overlooked pool has 3.8% (12.259 million tonnes) of Ireland's forest carbon stock. Living trees store about 20% (64.833 million tonnes) of the total forest carbon when you combine above and below ground components.
Deadwood and Litter Contributions to Carbon Sink
Dead organic matter creates another major carbon pool. Each forest type stores different amounts of carbon in its litter. Research shows average carbon values of 4.1 tonnes/ha in broadleaf, 4.8 tonnes/ha in coniferous, and 2.7 tonnes/ha in mixed forests. Deadwood and decomposing material slowly move carbon into soil organic matter, building a long-term carbon reservoir.
Soil Organic Carbon in Mineral vs Peat Soils
Soil emerges as the largest carbon pool in Irish forests. It holds 78% (252 million tonnes) of the total carbon stock. Different soil types store varying amounts of carbon. Histosols (peat soils) store about 645 tonnes C/ha. This is a big deal as it means that peat soils store more carbon than mineral soils, which hold between 162-416 tonnes C/ha. Irish forests grow on deep peats (>40cm depth) 38% of the time, adding greatly to the national carbon store.
Harvested Wood Products as Long-Term Storage
Harvested wood products (HWPs) create an important extended carbon pool beyond the forest. These products held 236,109 tonnes of carbon in 2022. This carbon was captured during tree growth but now lives outside forest boundaries. HWPs store carbon for long periods, especially in durable items like furniture and building materials.
How Irish Forests Are Measured for Carbon Sequestration
Ireland uses multiple scientific methods to measure forest carbon sequestration with greater precision. These measurements are the foundations of national carbon accounting and climate policy development.
Ground-Based Tree Measurements: Diameter and Height
Forest inventories help estimate biomass carbon stocks through direct field measurements. Technicians measure tree circumference at about 1.4 metres above ground. They calculate diameter and apply biomass expansion factors (BEFs). BEFs help convert merchantable timber volume into total biomass carbon estimates. These factors change based on soil type, species, yield class, and stocking density. Scientists use triangulation methods or reference objects to calculate tree dimensions without touching them.
Remote Sensing via Satellite and Aerial Imaging
Satellite imagery has improved forest carbon measurement over the last several years. Scientists first used it for forest mapping. Now, remote sensing merges with field data to estimate carbon parameters. Advanced Light Detection And Ranging (LiDAR) technology helps characterise woody biomass and timber volumes effectively. Ireland has created specialised products like the Thematic Hedgerow Map with 1m pixel resolution. This map shows mature hedgerows with estimated 80% accuracy. These tools provide a full picture of carbon stocks in areas of all sizes.
Eddy Covariance Towers for CO2 Flux Monitoring
Eddy covariance systems measure forest-atmosphere carbon exchange directly. These towers sample vertical velocity and gas concentrations 20 times per second. They calculate net CO2 movement between forests and atmosphere. The Department of Agriculture funds the National Agricultural Soil Carbon Observatory (NASCO). NASCO has installed 28 flux towers across Ireland. This reliable system monitors live greenhouse gas fluxes and measures carbon movement through agricultural ecosystems. Measurements from Dripsey forest site showed carbon sequestration of -2.12 t C ha-1 yr-1 in 2011.
Inventory Modelling using CFS-CBM Framework
Ireland uses the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) to combine field measurements with predictive modelling. Scientists fine-tuned this model using Irish National Forest Inventory data from 2006-2017. Ireland became one of two countries besides Canada to use detailed plot-level NFI data for this purpose. Recent adjustments with 2022 NFI data have improved the accuracy of biomass stock and carbon change estimates. The model handles different forest categories separately and distinguishes afforested areas since 1990 from existing forestland.
Forest Types and Their Sequestration Potential in Ireland
Different forest types in Ireland show remarkable variations in their ability to capture carbon. Species, soil type, site conditions, and management practises affect how forests capture carbon. Young forests store less carbon than their mature counterparts.
Sitka Spruce (GPC 3): 6.58 tCO2/ha Mean Rate
Sitka spruce leads Irish forestry with over 300,000 hectares of coverage. These trees store about 2.5 million tonnes of CO2 equivalent (75% of total carbon stored in Irish forests). This conifer runs on Ireland's wet maritime climate and achieves exceptional growth rates up to 34 tonnes per hectare each year. The standard plantation (GPC 3) has 70% Sitka spruce with 15% broadleaves. It delivers a Carbon Accumulation Potential (CAP) value of 347.55 tCO2/ha over two rotations (76 years). The mean sequestration rate of 6.58 tCO2/ha has 2.89 (forest site), 3.26 (harvested wood products), and 0.43 (energy substitution).
Diverse Conifers (GPC 4): 3.82 tCO2/ha Mean Rate
Plantations with 85% diverse conifers (Norway spruce, Douglas fir, Scots pine) show moderate sequestration rates. GPC 4 forests deliver a CAP value of 298.65 tCO2/ha over about 90 years. The mean sequestration rate of 3.82 tCO2/ha includes 1.91 (forest site), 1.67 (harvested wood products), and 0.24 (energy substitution).
Oak Forests (GPC 6): 1.96 tCO2/ha Mean Rate
Oak forests capture carbon at 1.96 tCO2/ha, but their longevity creates impressive long-term storage. Oak plantations (GPC 6) reach a CAP value of 454.85 tCO2/ha over two rotations lasting 240 years. Broadleaved trees in the UK capture around 1.8 t C ha-1yr-1 on Yield-Class-4 sites.
Agroforestry (GPC 11): 1.68 tCO2/ha with Emission Offset
Agroforestry systems combine trees with agriculture to create multifunctional landscapes. Research in Northern Ireland showed that 24-year-old agroforestry with wide-spaced ash can capture up to 3.2 t C ha-1 yr-1. Standard agroforestry schemes (GPC 11) with fast-growing broadleaves at 400 trees per hectare show a mean sequestration rate of 1.68 tCO2/ha. This rate could support carbon-neutral beef production when combined with hedgerows.
Native Woodlands vs Mixed High Forests: CAP Comparison
Native woodlands grow slower than commercial plantations but store carbon over longer periods. Mixed high forests (mainly fast-growing conifers with 20% broadleaves) reach CAP in 60-100 years. Native woodlands need 100 years. Notwithstanding that, native woodlands are a great way to get biodiversity benefits alongside carbon storage. Ireland's native woodlands capture an estimated 30,000 t C yr-1.
Challenges in Carbon Accounting and Future Research Needs
Carbon accounting has made great strides, but measuring forest carbon sequestration accurately remains challenging. Scientists have started to question many of their long-held models and practises based on new evidence.
Revised Emission Factors for Peat Soils: 1.68 tC/ha/year
New research from 2021 shows drained forest peat soils emit 1.68 tC/ha each year—almost three times more than previous calculations. This finding has cut forestland sequestration estimates by half, forcing Ireland to completely revise its carbon accounts.
Impact of Forest Age Class Shifts on Sequestration
The carbon profile of Irish forests will change dramatically as forests get older. Forests over 30 years old ("Managed Forest Land") will become a small net carbon source, releasing about 0.1 million tonnes CO2 yearly. Scientists believe extending rotation ages could remove up to 9Mt CO2 by 2030.
Species-Specific Carbon Dynamics and Soil Interactions
Scientists continue to study how various tree species affect soil carbon. We lack enough data about how forest management methods—thinning, clear-cutting, continuous cover forestry—affect long-term carbon storage. Soil holds about half of all forest carbon stocks, making these interactions crucial to understand.
Climate Change Risks: Drought, Pests, and Wildfire
Climate change poses growing threats to Irish forests. Trees face changes in growth patterns, wind damage, water stress, and dangerous pathogens. The ash dieback crisis shows how diseases and pests can seriously harm carbon storage capacity.
Improving Public Engagement and Landowner Incentives
Ireland aims to add 8,000 hectares of new forests yearly. This goal requires better community participation and stronger incentives for landowners to overcome social barriers.
Conclusion
Our exploration of carbon sequestration in Irish forests reveals their remarkable ability to curb climate change. Irish forests remove about 3.8 million tonnes of carbon dioxide equivalent each year and serve as vital carbon sinks in our national climate strategy.
Carbon storage works through five distinct pools - aboveground biomass, belowground biomass, deadwood, soil, and harvested wood products. These pools create a complex storage system. Soil emerges as the largest carbon reservoir and holds an impressive 78% of the total forest carbon stock. Scientists need to understand soil dynamics well, especially in peat soils that store much more carbon than mineral soils. This knowledge helps them maintain accurate carbon accounting.
Forest measurement techniques have evolved a lot over time. Ground-based measurements give us essential baseline data. Remote sensing and eddy covariance towers provide broader and more dynamic insights. The CFS-CBM framework has improved our ability to model carbon dynamics precisely.
Each forest type shows different potential to store carbon. Sitka spruce leads with the highest rate at 6.58 tCO2/ha. Oak forests store carbon more slowly but continue this process much longer. This means we must balance immediate carbon capture with long-term storage goals when selecting forest types.
Scientists have made substantial progress, yet challenges remain. New research has led to revised emission factors for peat soils, which changes previous carbon accounting dramatically. Older forests will temporarily become carbon sources instead of sinks as forest age classes change. Climate change brings more threats - drought, pests, and wildfire pose serious risks to forest carbon stocks.
Moving forward requires more research into species-specific carbon dynamics and their relationship with soils. Ireland's ambitious afforestation targets need better community engagement and landowner incentives to overcome social barriers. Without doubt, deeper understanding will help us use Irish forests' potential as natural climate solutions while balancing carbon storage with biodiversity and other ecosystem services.
