The carbon sequestration potential of the Irish uplands

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Date
2022-09-01
Authors
Swan, Sophia
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University College Cork
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Abstract
The Irish uplands, which cover much of the western half of the country, have long been known as a bare, treeless landscape, used for grazing livestock. They are characterised by thin, peaty unproductive soils, and tend to provide poor economic returns to those farming them. A land use shift is currently occurring across the uplands, with many farmers ceasing actively to exploit the land and leaving the industry, a process exacerbated by isolation, poor incomes, and a lack of successors willing to continue farming the family landholdings. This comes at a time when Ireland is urgently seeking novel approaches to sequester carbon from the atmosphere, and offset GHG emissions from intensive agriculture. Expanding woodland cover onto degraded agricultural land is one of several potential methods being explored worldwide to increase terrestrial carbon sequestration and storage. This study aims to determine the future carbon sequestration potential of the Irish uplands, through the potential regeneration of native woodland, in the event that their land use shifts away from livestock grazing and the associated vegetation management of burning. We chose the Iveragh peninsular, Co. Kerry, SW Ireland as our study site. This is an area of extensive upland landscape, with a long history of extensive cattle and sheep grazing on the unenclosed land, including a considerable area of upland commonage. We used two approaches to estimate the potential carbon sequestration potential of regenerating woodland in the uplands. Firstly, we wished to determine the environmental and anthropogenic factors associated with woodland regeneration currently observed within the study site, so as to better predict the location and extent of any future woodland regrowth. This was achieved using a combination of online GIS mapping techniques, coupled with ground-truthing of the extent of tree regrowth. Secondly, we wished to establish the realistic nature of any potential future natural woodland cover, in terms of species composition, density and growth form of trees and in the soil composition underneath such woodland. We surveyed the woodland cover of a number of small, uninhabited and unexploited islands within lakes of the southwestern uplands. These islands were ascertained to have been ungrazed since at least the middle 19th century and likely for much longer, owing to their small size and inaccessibility to grazing animals. The vegetation and soil data were then used to calculate the potential carbon storage of any future woodland regeneration. GIS analysis revealed that slope, elevation, soil type, controlled burning practises and proximity to woodland seed source all influenced the current extent of tree regeneration in the study site. Significant differences were observed between the vegetative composition of the islands and adjacent mainland sites, with dense woodland cover consisting primarily of holly, rowan and birch observed across islands. This island vegetation sequestered ten times more carbon per hectare than adjacent mainland sites, which predominantly consisted of Molinia grassland, with no woodland growth noted. Soils in mainland sampling areas were consistently wetter and less carbon rich than those sampled on islands. Based on these factors, it was determined that within 40 years, 0.6% of the Irish uplands could show natural woodland regeneration, should barriers to re-growth (sheep grazing and vegetation burning) be removed. A higher percentage woodland regeneration could be achieved with additional proactive tree planting programme, which is likely necessary to establish woodland growth in areas remote from existing trees and which have been treeless for many centuries. Despite such a small, predicted increase in percentage tree cover via natural means, this still provides the potential to store over 600,000 tonnes of carbon, thus providing Ireland with valuable ways to offset carbon emissions, along with increasing biodiversity and reduce flood risk over the coming years.
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Carbon sequestration , Irish uplands , Woodland , Carbon storage
Citation
Swan, S. 2022. The carbon sequestration potential of the Irish uplands. MRes Thesis, University College Cork.