The important role that forests play in carbon sequestration and climate change mitigation is acknowledged internationally. Measuring actual sequestration poses a number of challenges especially when harvesting and management regimes, tree species, soil types, rotation lengths and biodiversity, are factored in. In addition, the afterlife of wood in areas such as displacement of fossil based material in construction needs to be considered.
A new Teagasc forest carbon tool (FCT) launched last month by Minister of State Pippa Hackett, is a first step in Ireland to measure the mean and cumulative CO2 sequestration of forests and woodlands by species, soil types and productivity.
“The FCT provides indicative information only and is not intended to provide definitive estimates on any particular forest,” she said.
“It is a user-friendly way for existing and potential forest owners to calculate how much carbon can be removed in woodlands and highlights the important role of harvested wood products.”
Tom Houlihan, of Teagasc, said the FCT is the first iteration which incorporates a range of assumptions and system boundaries for the data provided.
“There is an ongoing need to further develop our knowledge on the impact of a range of factors such as forest types, species choices, rotation lengths and management approaches on sequestration potential,” he said.
The tool covers 10 of the 12 grant and premium categories (GPCs) in Ireland. The annual sequestration for the various options “can range from one to nine tonnes of CO2 per hectare per annum”, said Minister Hackett.
CO2 cumulative removals/emissions, known as the “CAP” are measured in tonnes of CO2 per hectare (tCO2/ha). The total CAP is based on the mean annual sequestration rate comprising forest site sequestration , harvested wood products and energy substitution, measured over two crop rotations, which can vary from 60 to 70 years for fast-growing Sitka spruce to 300 years for slow-growing oak.
An example of the range of carbon sequestered can be illustrated by estimating the CAP and mean values for the following four GPCs: 3; 4; 6; and 11 based on one hectare of forest. All sites except GPC 11 carry 15% unplanted or biodiverse areas.
GPC 3: 70% Sitka spruce
This is the most popular GPC comprising 70% Sitka spruce, 15% broadleaves classed as highly productive forest. The site selected is a peaty mineral soil producing YC24 for Sitka and 10 for the selected broadleaves (yield class – YC – is the potential yield in m3/ha/annum). The stocking rate for the Sitka is 2,500/ha and 3,300 for the broadleaves.
The CAP value is 347.55 tCO2/ha covering two crop rotations up to 76 years. The CAP is based on a mean sequestration rate of 6.58 tCO2/ha, comprising 2.89 (forest site sequestration); 3.26 (harvested wood products); and 0.43 (energy substitution).
GPC 4: 85% diverse conifers
GPC 4 comprises 85% diverse conifers with two or more species such as Norway spruce; Douglas fir, Scot’s pine or other conifers on the Forest Service-approved species list. The site is mineral, producing YC16 with an initial stocking rate of 2,500/ha.
The CAP value is 298.65t CO2/ha covering two crop rotations approximately 90 years. The mean sequestration rate is 3.82t CO2/ha, comprising: 1.91 (forest site sequestration); 1.67 (harvested wood products); and 0.24 (energy substitution).
GPC 6: 85% oak
GPC 6 comprises a pure crop of oak on a good productive mineral site, capable of producing YC6 with an initial stocking rate of 3,300/ha.
The CAP value is 454.85t CO2/ha for two crop rotations in approximately 240 years. The mean sequestration rate is 1.96t CO2/ha/), comprising 0.68 (forest site sequestration); 0.68 (harvested wood products); and 0.6 (energy substitution).
GPC 11: agroforestry
The agroforestry scheme features relatively fast-growing broadleaves such as sycamore, alder or birch. The scheme is suitable for marginal grassland with potential for grazing by sheep and capable of producing a hay or silage crop. To allow ease of management, only 400 trees per hectare are planted at a 5x5m spacing.
The CAP value is 251.58t CO2/ha covering two crop rotations in approximately 150 years.
The mean sequestration rate is 1.68t CO2/ha, comprising 1.94 (forest site sequestration); 0.87 (harvested wood products); and 0.05 (energy substitution) less 1.18 (agriculture emissions).
On the above calculations, slow-growing broadleaves provide the highest CAP or cumulative CO2 over two rotations. The two rotations in these examples vary from 76 years for Sitka to 240 years for oak which results in a mean sequestration rate of 6.58t CO2/ha for Sitka compared with 1.96 for oak.
The carbon tool is an excellent indicator of the sequestration potential of different species and forests but it requires further modification as acknowledged by Tom Houlihan.
“It is designed to incorporate updates and enhancements in future iterations as new data and research become available,” he said. The project is supported by the Department of Agriculture, Food and the Marine and developed by Teagasc with specialist input from Forest Environmental Research & Services (FERS).
Brian Hussey, promoter of private forestry since the 1970s, died on 2 February. Co-founder of the Galway-based forestry company Woodland, he played a major role in the early years of private forestry in Ireland. The Dublin-born engineer farmed extensively in Wicklow and Clare in the 1960s and 1970s and was president of the Irish Grassland Association in 1976-77 before he set up Tree Farmers Ltd with Hal Sisk in 1978. He was also involved with the West Wicklow Development Association and was chair of the Irish Timber Growers Association (ITGA).
He had a central role in organising the seminal three-day national seminar, “The right trees in the right places”, in 1990. The event had a major influence on Irish forest policy, resulting in large-scale private – mainly farmer – afforestation programmes.
Brian had a visionary approach to Irish forestry which he outlined at national and EU level. I saw this at firsthand during my time as chair of the Irish Forest Industry Chain in Ibec, especially during presentations in Brussels. At the time, he was the ITGA representative in Ibec. He proved to be an insightful, feisty and combative debater when promoting forestry. After his retirement he began the successful ambitious four-year project of restoring the ruined Gregan Castle near Ballvaughan, Co Clare.
To his wife Anna, sons and daughters, brother and sister we extend our sincere condolences. Suaimhneas síoraí dá anam.