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COST 639 - WG 1
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COST 639 - WG 1
WG 1 - Hot spots for effects of climate change on soil C and N

Research will focus on ecosystem and/or site state factors that are expected to respond strongly to climate change in a manner that is likely to turn these ecosystems into sources of GHGs. Landforms with a particular relevance for different regions in Europe have been selected. In addition, forms of ecosystem disturbances that are believed to be of wide spread importance are chosen.

Landform peatland: In these ecosystems the biological activity of soil microorganisms is affected by anaerobic conditions. Peatlands are a frequent landform in Nordic countries and Western Europe. As a soil type, they have unique properties. From the knowledge of processes and responses of upland (mineral) soils to global warming only limited predictions can be deduced for peatlands. Even their definition and delineation on soil maps is uncertain. There is growing concern about peatland degradation in response to climate change or land management and the deleterious effects of such degradation on GHG release, hydrology, water quality and ecosystem biodiversity. Virgin peatlands (mires) accumulate atmospheric C and N, but emit methane. Nitrogen oxide emissions from natural mires are insignificant. However, peatlands are a heterogenous group of soils with different emissions. Drainage can have a dramatic effect on GHG emissions. In the Nordic countries, approximately 15 million ha of peatland are used as managed forest land and have to a certain extent been drained. Following drainage the methane emissions decrease and the net primary production and N2O and CO2 emissions increase. An integrated assessment of research needs to include an understanding of the links between vegetation cover, hydrological processes, biogeochemistry, soil ecology, water flow paths, and the interactions between peatland and climate change. Peatland is at some places exploited as a source for fuel but understood as a partly or slowly renewable source of energy. Therefore,the use of peat as fuel is a controversial topic. The impact of land-use change of peatlands (e.g. afforestation, see WG 2) and the natural aggradation of peatlands as a consequence of global warming requires a rigorous evaluation. A GHG budget of the entire ecosystem is required in order to establish the net response (i.e. sink of C and N in higher biomass production vs. source of GHGs from soils). The loss of peatland also affects the richness of the landscape and needs to be treated in the context of biodiversity issues. The GHG emissions from peatland ask for a close cooperation between forest soil scientists and biologists. We want to stimulate discussion on appropriate methods for coupling small-scale peatland studies with global or regional scale studies. Available soil inventories in e.g. Austria, Finland and Sweden may be used for upscaling.

High elevation/latitude ecosystems: In these ecosystems the biological activity of soil microorganisms is constrained by low temperatures and a short growing season. However, the loss of GHGs from soils can occasionally be rapid, because large amounts of C and N occur in chemically labile forms that are rapidly mineralised, provided temperature increases. Thawing of permafrost may in some areas have a profound impact of emissions of CO2, N2O and CH4. The extent to which increased plant productivity will compensate for soil GHG emissions is unknown. Budgeting the overall effect of soil warming is impossible, as long as the mechanisms of stabilization and the stock of readily decomposable soil C are unknown. We will collate soil C data from case studies where total C has been fractionated into a labile and a recalcitrant pool and will establish pedotransfer functions for the estimating of the labile C pool from easily accessible site factors. - High elevation ecosystems are also undergoing a change because the land-use is changing. Societal changes lead to the abandonment of pastures and the subsequent reforestation. The consequences for GHG emissions are not yet quantified.

Mediterranean ecosystems: Simulation models predict a low C sequestration potential for Mediterranean forest soils, mainly because the productivity of sites with a prolonged summer drought is slow. More important than adapted forest management may be the effect of land use change (afforestation), because it may reverse the effects of earlier soil degradation. Afforestations in the Mediterranean region have been shown to lead to considerable increases in soil C and N stocks. It needs to be shown how representative these results are for the entire region and how land-use changes can be communicated to land owners. An obstacle is that land use and soil data are scattered over institutions and are not yet harmonized. The Action is an incentive to exploit these data sets.
Experts for these landforms will identify the governing soil processes for each ecosystem and will identify similarities between ecosystem processes and responses that help to extrapolate results to a wider area. They will collect information on the spatial extent of these landform types and establish quantitative limits for the potential release of GHGs under future site conditions. The Action will deliver a set of default values of GHG emissions for several classes of landforms that we consider to be hotspots. These default values will be delivered with an estimate of their accuracies and are suggested for use in GHG emission reports where regionally valid data are unavailable. The focus of the Action is to derive such default values, but not the specification of different land-use forms. The approach of default values for different situations of interest has been brought forward by Miko Kirschbaum (IPCC expert) during the IUFRO World Congress 2005 and has been received with great interest. Eventually (not objective of the Action), the results of the Action can be incorporated in a Geographic Soil Information Systems such as the CORINE soil map. The knowledge of ecosystems that may emit large quantities of GHGs may also enable stratification of soil inventories to optimise the use of resources in order to detect sources of GHGs. [LINK]
Natural and human induced disturbances: Forest ecosystems are subject to wind throw and fire with a certain region-specific periodicity. Within a short time, large quantities of soil C and N are converted to GHGs (‘slow in / rapid out’). In Central and Northern Europe, secondary Norway spruce forests are common. This forest type is highly productive and is the backbone of forestry in several regions. The production risk of spruce monocultures is considerable and storm events regularly destroy vast areas of spruce forests and forests with other species. Second important aspects are insect infestations that often follow storm damages. As long as merely the economic value of timber production is compared, this forest type is superior to mixed-species forests. An extra-value is created in continuous-cover forestry due to the maintenance of high stocks of C and N in the ecosystems these forests have a higher value due to their types need to be re-evaluated. This assessment is to be the basis for scientifically funded incentives for the establishment of mixed-species forests, if they prove to have low GHG emissions. – The main reason for GHG emissions from agricultural soils is tillage and adapted forms of agriculture have a large potential for the reduction of emissions. However, agricultural soils are also responsive to climatic change. A major problem is erosion, especially when soils are bare during a part of the year. Case studies will help to quantify, how adapted land management can reduce erosion and how much erosion contributes to GHG emissions form soils.

Drought impacts and rewetting: Soils emit GHGs especially during drying/re-wetting cycles. These pulse emissions are contributing a lot to the annual N oxide fluxes into the atmosphere. This knowledge has been soundly established on the basis of laboratory experiments and single case studies. The relevance for a national GHG budget is not clear. Preliminary results show that discontinuous monitoring of N oxide emissions can underestimate the annual emissions substantially, when the short drying/re-wetting cycles are missed. We want to link this process-level-knowledge with the current land use in order to quantify their potential contribution to annual GHG emissions.

We will cover the effects of forest fires and their importance on GHG emissions from forests in the context of disturbances. An in-depth assessment will not be achieved, because the topic is very complex and is, to our knowledge, the subject of an individual COST proposal.

Expertise on emissions of CO2 and nitrogen oxides from different types of ecosystems and differently treated/disturbed ecosystems has been established in sectorial approaches, i.e. separately for agricultural and forest ecosystems and wetlands, and either with emphasis on C or N. We aim at fostering the interfaces between these findings by means of joint data evaluations and by consultation of experts in these fields.

The data supporting WG 1 are derived from already existing databases that exist at various research institutes. A preliminary screening has shown that the required data are available from case studies that have been pursued in another context, but have not yet been utilized from the perspective of potential hotspots of GHG emissions. Moreover, the researchers of the Action are currently pursuing or have recently finished projects, where the required data have been collected. These data sources are not yet published, but are available for the Action.

Preier, P.

Bundesamt für Wald


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