Dr. Ken Byrne:

I am very appreciative of the invitation from the committee to speak on the subject of sequestration, land management and nature restoration. The area of forest in Ireland is approximately 770,000 ha, which is 11% of the total land area. Most of these forests have been established during the past century. Coniferous species cover 71.2% of the forest area and broadleaves the remaining 28.8%. In addition to sequestering atmospheric carbon, Irish forests can contribute to climate change mitigation through the provision of wood products, which can displace energy-intensive materials in construction and energy generation. Due to Ireland's relatively high rainfall and moderate temperatures, our soils are very favourable to the accumulation of organic matter and, consequently, carbon.

Peatlands cover between 20% and 25% of the Irish landscape and contain two thirds of national soil carbon stocks. Pristine or undrained peatlands are long-term carbon sinks and sources of methane. This is altered dramatically by drainage and land use change, which lowers the water table and transforms a peatland from a carbon sink to a source. The amount of emissions from peat soils following drainage depends on several factors, including peat type, nutritional status, hydrology and previous land use. Afforestation has been a major driver of drainage and land use change in Irish peatlands and peat is the dominant soil type in Irish forests, accounting for 38.7% of the total area.

When assessing the role of these forests in carbon sequestration the key question is whether the losses of soil carbon from peatland drainage are compensated by carbon sequestration by the growing forest. Despite the prominence of peatland forests in out national forest estate, very few studies have investigated the carbon cycle in these forests. The first study of forests on blanket peatlands found that such soils emitted 0.59 tonnes of carbon per hectare per year. Recent research has concluded that forested blanket peatlands emit 1.68 tonnes of carbon per hectare per year. By tripling the estimated loss of soil carbon from forested peatlands this study has altered our understanding of the carbon sequestration potential of these forests. The losses of soil carbon may be partially or wholly compensated through carbon uptake by the growing trees. The compensatory capacity would be less for low-productivity compared with high-productivity forests.

In a recent study of Coillte forests the climate impact of rewetting 8,000 ha of low-productivity peatland forests over a 50-year period was assessed. This study found that such a rewetting programme would have little short-term benefit in terms of climate mitigation. Furthermore, when emissions due to deforestation are included, emissions from rewetting are two to five times greater than the reduction in soil emissions. These findings suggest that the short-term benefits of rewetting are negative. When considered in terms of global warming potential over the full time series of the study, 2021 to 2100, there is no climate mitigation benefit. This is due to the greater warming potential of methane which is the dominant greenhouse gas emitted from rewetted peatland. However, it should be emphasised that there have been very few studies of the effect of rewetting and greenhouse gas exchange in forested peatlands in Ireland. Furthermore, it may take several years for the emission reduction benefit of rewetting to occur. There are also likely to be forested peatland sites where rewetting is desirable form a climate perspective but technically difficult to achieve due to site-specific factors such as drainage, slope, hydrology or land use in adjacent areas. In such cases there is a need to develop alternative management systems such as semi-natural woodland. However, research and field-based assessment of such management systems is required.

The role of forests in mitigating climate change through sequestering carbon through changes in management and reduced harvest, on one hand, and providing renewable material and energy, on the other, are, at first consideration, competing aims that are frequently investigated separately. A focus on sequestration at the cost of wood use ignores the relationship between these interlinked roles. Focusing on the management of forests to produce long-term and large-scale carbon sinks ignores both the risk of some forests becoming unstable as they mature and becoming carbon sources and the post-harvest role of forests in climate mitigation. Sustainable forest management can balance both of these roles. As far back as 1730, Von Carlowitz defined sustainable forest management as "harvest should balance growth". This can be extended to include social and environmental roles and, with regard to carbon, management of forests so that harvest removals can be made while maintaining a net carbon sink. In Ireland, this is complicated further by so-called legacy issues such as: a low afforestation rate; uneven age-class distribution; and a large proportion of forests located on peat soils.

There is a need to address these and other issues by diversifying the forest estate through a range of measures, including: rewetting of peat soils; semi-natural woodland on peat soils; forest management mechanisms such as rotation length; diversifying species composition; and adopting new silvicultural systems such as continuous cover forestry. Such changes should, however, be informed by investigation of the carbon balance of Irish forests and interdisciplinary research that facilitates understanding of the impact of such changes on the economic, social and environmental services of our forests. This is essential if we are to harness the climate mitigation potential of our forests, not just in sequestering carbon in forest ecosystems but also in providing renewable material for construction and energy.