Kenneth A. Byrne

Carbon dioxide dynamics of a restored maritime peatland

ABSTRACT The restoration of cutaway peatlands provides an opportunity to return the carbon (C) sink function and to examine the influence of climate on peat formation and C accumulation. We studied CO2 exchange dynamics in 2002 and 2003 at a rewetted cutaway peatland located within the temperate maritime climatic zone. Gross photosynthesis (PG), ecosystem respiration (RTOT), and net ecosystem exchange (NEE) were observed in a range of microsites representing a hydroseral succession gradient: Typha latifolia – Phalaris arundinacea, Eriophorum angustifolium – Carex rostrata, and Juncus effusus – Holcus lanatus vegetation communities and areas of bare (unvegetated) peat. Annual rainfall was 26% higher in 2002 and 4% lower in 2003 than the long-term average and influenced water table position at all microsites. Observed instantaneous CO2 fluxes varied temporally and spatially at all microsites. Modelled PG was strongly dependent on irradiation (Photosynthetically Active Radiation) and the Vascular Green Area index (VGA). RTOT was influenced by the soil temperature at 5 cm depth (T5cm) and the water table position. All microsites were net sources of CO2 in both years of the study, and higher losses (with the exception of Juncus / Holcus) were observed in 2003 at all microsites. In general, losses followed the trend Juncus / Holcus > Phalaris > Typha > bare peat > Eriophorum– Carex in 2002 and Phalaris > Juncus– Holcus > Typha > Eriophorum / Carex > bare peat in 2003. Losses ranged from −163 to −651 g CO2– C·m−2·y−1 in 2002 and −308 to −760 g CO2 – C·m−2·y−1 in 2003. Considerable wintertime losses were observed at all microsites. The results from this study suggest that these peatlands are vulnerable to interannual variations in climatic inputs and that future predictions of climatic change may make restoration of the C sink function in cutaway peatlands in the temperate maritime climatic zone a considerable challenge in the years ahead. Nomenclature: Moore, 1982.

Vegetation and environmental variation in an Atlantic blanket bog in South-western Ireland

A vegetation survey was carried out in a relatively intact Atlantic blanket bog in Southwest Ireland to study the vegetation patterns in relation to environmental variation, and to quantify the effect of artificial and natural borders on compositional variation. The data were analysed using canonical correspondence analysis. In terms of both vegetation and water chemistry, the study site can be categorized as typical of Atlantic blanket bogs in the maritime regions of North-western Europe. The distribution of plant species was explained mainly by depth of the water table. The distribution of bryophytes was secondarily explained by the pH of the bog water, while the distribution of vascular plants was secondarily explained by concentrations of ammonia. The vegetation distribution exhibited little variation between the central sector of the peatland and its disturbed edges (hill-grazing and restoration areas), but a substantial variation was observed between the area along a natural edge (stream) and the areas close to the other peatland borders or centre. Similarly, the internal variation within each sector (centre, hill-grazing edge and restoration area edge) was small, but substantial vegetation variation was observed within the area located along the stream. The area along the stream was associated with relatively deep water table, shallow peat depth, high water colour, pH and NH4+ concentrations, and low Cl− concentrations in the bog water. Our results suggest the existence of strong centre-natural margin gradients, as in raised bogs, and indicate that human or animal disturbance do not give rise to the marked transition zones that often characterize natural margins of mire systems. This indicates that even small areas and remnants of Atlantic blanket bogs are worthy of conservation and that their conservation value would benefit from the inclusion of sectors close to the natural peatland borders, which would increase the plant biodiversity of the conserved area.

Clay illuviation provides a long-term sink for C sequestration in subsoils

Soil plays a key role in the global carbon (C) cycle. Most current assessments of SOC stocks and the guidelines given by Intergovernmental Panel on Climate Change (IPCC) focus on the top 30 cm of soil. Our research shows that, when considering only total quantities, most of the SOC stocks are found in this top layer. However, not all forms of SOC are equally valuable as long-term stable stores of carbon: the majority of SOC is available for mineralisation and can potentially be re-emitted to the atmosphere. SOC associated with micro-aggregates and silt plus clay fractions is more stable and therefore represents a long-term carbon store. Our research shows that most of this stable carbon is located at depths below 30 cm (42% of subsoil SOC is located in microaggregates and silt and clay, compared to 16% in the topsoil), specifically in soils that are subject to clay illuviation. This has implications for land management decisions in temperate grassland regions, defining the trade-offs between primary productivity and C emissions in clay-illuviated soils, as a result of drainage. Therefore, climate smart land management should consider the balance between SOC stabilisation in topsoils for productivity versus sequestration in subsoils for climate mitigation.

Forestry in the Republic of Ireland: Government Policy, Grant Incentives and Carbon Sequestration Value

Recent decades have seen a rapid increase in the area of privately owned forest plantations in Ireland. This has been largely driven by grant aid from the government. These forests are significant carbon sinks and as such are delivering added benefit to the country by contributing to greenhouse gas reductions under the Kyoto Protocol. The direct impact of government subvention on the net present value (NPV) for a defined forestry plantation is investigated. The added value of carbon sequestration to forestry investment is also examined using the UK Forestry Commission carbon model. Extending the typical assumption of a constant carbon price for project appraisal purposes, this paper allows carbon prices to evolve randomly according to a flexible stochastic price process. The model chosen is an extended mean-reverting jump-diffusion, with the flexibility to capture the higher-order statistical features (i.e. skewness and kurtosis) of the carbon markets. This allows for an analysis of the risk and uncertainty around the NPV from exposure to stochastic carbon prices. It is shown that government funded grants for afforestation significantly improve the NPV on forestry investment. Carbon sequestration is shown to further add value.

The role of planted forests in the provision of habitat: an Irish perspective

The continued decline of natural forests globally has increased interest in the potential of planted forests to support biodiversity. Here, we examine the potential conservation benefits of plantation forests from an Irish perspective, a country where remaining natural forests are fragmented and degraded, and the majority of the forest area is comprised of non-native Sitka spruce (Picea sitchensis (Bong.) Carr.) and Norway spruce (Picea abies (L.) Karst.) plantations. We examine the true value of Irish plantation forests to native biodiversity, relative to remaining natural forest fragments, and to prior and alternative land use to afforestation. We find that plantation forests provide a suitable surrogate habitat primarily for generalist species, as well as providing habitat for certain species of conservation concern. However, we find that plantation forests provide poor habitat for native forest specialists, and examine potential management strategies which may be employed to improve habitat provision services for this group.

Carbon dioxide and methane fluxes in forested and virgin blanket peatland in the West of Ireland

Peadands in the boreal and temperate zone occupy some 3 50 million ha (LAINE et al. 1996). Their estimated carbon store is 355 Pg (l Pg = 10 g), approximately one-third of the world pool of soil carbon (GORHAM 1991). Some 15 million ha of these peatlands have been drained for forestry (LAINE et al. 1995). At least 90% of this area is found in Scandinavia and the former Soviet Union (PMVILAINEN & PÃIVÃNEN 1995). Most of these peadands have a natural tree layer, the productivity of which is increased by drainage and fertilisation. In maritime climates, sueh as lreland and the United Kingdom, peadands are naturally treeless and forestry development nor only involves drainage but also the use of exotie tree speeies and fertilisers (e.g. ZEHETMAYR 1954, FARRELL 1990). Peadands eover some 1.34 million ha, or 16.2% of the land area, of Ireland (HAMMOND 1981). While no aeeurate figures are available, in 1990 there were estimated to be at least 200,000 ha of forestry on peadand (FARRELL & Bovu 1990), the majority of i t on blanket peat. The earbon balanee in peadands may ehange dramatieally following forestry development sinee drainage lowers the water table and eonsequendy inereases aerobic deeomposition. Therefore, CO, emissions are inereased (e.g. SILVOLA et al. 1996). Lowering of the water table also reduees CH4 emissions. The reduetion of CH, emissions following drainage, with a net uptake in some eases, has been observed in a number of studies (e.g. GLENN et al. 1993, RouLET et al. 1993, MARTIKAINEN er al. 1995, RouLET & MooRE 1995, LAINE er al. 1996). The aim of this study was to investigate the ehanges in fluxes of CO, and CH, following forestry development by eomparing a virgin peadand sire with an adjaeent peatland site whieh was drained and subsequently afforested with Sitka spruee (Picea sitchensis (Bong.) Carr.) in 1958. The study sites were loeated in Cloosh Valley, Co. Galway, an extensive area of planration forestry on blanket peatland in the West of lreland. Material and methods

The influence of forestry on blanket peatland.

Abstract Blanket peatlands cover substantial areas of Great Britain and Ireland. The uses to which peatlands are put are governed by economic considerations without full regard for the ecological consequences. Peat has an important role in the carbon cycle. It absorbs (fixes) and releases CO2, and it releases methane. This review indicates how the physical and chemical properties of peats, the ecology, carbon cycling, and the surface water quality are influenced by afforestation. Attention is focused on the ways forests influence depositions of sulphates and nitrates in blanket peats, and how these peats affect the deposition of organic acids, and the depositions of neutral salts from wind blows in the reafforested areas of the west of Ireland. It is important to give careful consideration to the future role of blanket peats. This should involve the monitoring of various diagnostic features, including surface water quality, peat erosion, and the stability of ecosystems. Overall, the rehabilitation of forested blanket peats may be the most appropriate environmental option.

Wood waste decomposition in landfills: An assessment of current knowledge and implications for emissions reporting

Large quantities of wood products have historically been disposed of in landfills. The fate of this vast pool of carbon plays an important role in national carbon balances and accurate emission reporting. The Republic of Ireland, like many EU countries, utilises the 2006 Intergovernmental Panel on Climate Change (IPCC) guidelines for greenhouse gas reporting in the waste sector, which provides default factors for emissions estimation. For wood products, the release of carbon is directly proportional to the decomposition of the degradable organic carbon fraction of the product, for which the IPCC provides a value of 0.5 (50%). However, in situ analytic results of the decomposition rates of carbon in landfilled wood do not corroborate this figure; suggesting that carbon emissions are likely overestimated. To assess the impact of this overestimation on emission reporting, carbon decomposition values obtained from literature and the IPCC default factor were applied to the Irish wood fraction of landfilled waste for the years 1957-2016 and compared. Univariate analysis found a statistically significant difference between carbon (methane) emissions calculated using the IPCC default factor and decomposition factors from direct measurements for softwoods (F = 45.362, p = <.001), hardwoods (F = 20.691, p = <.001) and engineered wood products (U = 4.726, p = <.001). However, there was no significant difference between emissions calculated using only the in situ analytic decomposition factors, regardless of time in landfill, location or subsequently, climate. This suggests that methane emissions from the wood fraction of landfilled waste in Ireland could be drastically overestimated; potentially by a factor of 56. The results of this study highlight the implications of emission reporting at a lower tierand prompts further research into the decomposition of wood products in landfills at a national level.

Future change in carbon in harvested wood products from Irish forests established prior to 1990

Background: The Kyoto Protocol allows carbon in forests to contribute to emission-reduction targets. This has been extended to include carbon in harvested wood products (HWP). A projected baseline approach is proposed to identify business as usual and incentivize activities that reduce emissions or increase removals relative to reference level. In this article, we describe methods to calculate the projected reference level. Results: Wood product categories were derived using a top-down approach based on timber harvest data and sawmill statistics. The average of the overall projected forest management reference level for 2013–2020 was -206.81 Gg CO2-e including HWP and -72.72 Gg CO2-e excluding carbon stock change in HWP. Conclusion: These results highlight the potential of HWP to contribute to GHG mitigation strategies.

Soils and Carbon Storage

Soils act as both sources and sinks of atmospheric C and as such there is great interest in investigating the impact of land use and land use change on C stocks in soils. Peatlands occupy ~20% of the irish landscape and store 75% of all C stocks. While pristine peatlands are long term C sinks, drainage and land use may change these systems to sources of soil C. Forests are generally recognised to be C sinks although the role of soil differs between soil types. Studies to date suggest that afforested Gley soils are C sinks while afforested Brown Earths may lose C. Grassland is the dominant land use and site based studies suggest that it could be a C sink of 0.5 t C ha−1 year−1. Cropland is a net C source with cultivation being the principal driver of this loss. Options to maintain or enhance C stocks in tillage systems include the use of cover crops, straw and manure incorporation and a move to minimum tillage. Despite the progress that has been made in quantifying C stocks in Irish soils and in understanding the impact of land use on soil C stocks many information gaps remain.