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COST 639
COST 639 - Background
A. Background

Previous knowledge
Carbon (C) stored in soils represents the largest terrestrial organic carbon (C) pool. The biogeochemical cycles of C and nitrogen (N) are closely interwoven. Although the discussion on climate change focuses on CO2, the coupled cycling of C and N deserves equally much attention. As a result of mineralization processes, both elements are liberated from soil organic matter and can be lost from the soil via the aqueous or the gaseous phase. Both C and N occur in terrestrial ecosystems in several chemical forms and are potentially emitted as greenhouse gases (GHG). On the contrary, soils can act as a strong sink for GHGs. Considerable uncertainty exists regarding the sink strength of soils under different forms of land-use, especially under future climate conditions and in regimes of ecosystem disturbances, that are typical for particular regions. Due to the significance of the GHG exchange between the atmosphere and soils, C changes in terrestrial ecosystem pools are included in international treaties (Kyoto Protocol, UNFCCC).

The issue of soils acting as a GHG sink is controversial. Cultivated soils have lost a substantial part of their original C and N as a consequence of anthropogenic use. GHG emissions due to land use change include those by deforestation, biomass burning, conversion to agricultural use of natural ecosystems, drainage of wetlands and soil cultivation. The current sink strength of soils for the retention of C and N is bound to decline, if no specific incentives for adapted forms of land-use are provided. Crucial topics are the maintenance of the current sink activity of forests soils, agricultural forms of management that turn arable soils into GHG sinks, and the protection of pristine landscapes such as wetlands and old forests, that are currently large reservoirs of C and N.

Biogeochemical models indicate that forest soils will act as a slow and continuous sink for C and N. Agricultural soils are most likely a continuous source of GHGs. Modelling results are difficult to verify by field experiments, because the spatial variability often exceeds the temporal trend. Only a few long-term research projects exist and the temporal trend of C and N pools in field experiments is less clear than in simulation models. Stock changes in soils are difficult to detect because the spatial variability of soil chemical properties is large and blurs the signal of a temporal trend. Soil inventory methods that allow the efficient detection of temporal changes in the C and N stocks are still to be developed.

Recognizing that the required soil monitoring for a complete periodic assessment of soil C and N stocks throughout Europe is prohibitively expensive, we will focus on the identification of sites, where stock changes are most likely, according to expert judgement. We will investigate (i) the probability of C and N stock changes within a certain type of land use, (ii) the extent of stock changes as a consequence to land-use change, and (iii) the impact of ecosystem disturbances on stock changes. Our target is to identify site types and land management practices, where the stock changes are most likely to happen, because these are the areas where monitoring efforts need to be concentrated. We will focus on the interfaces of different land uses (agriculture, forestry, unmanaged land), that are often treated separately by researchers in different fields of environmental sciences. Among the consequences of the lack of communication is that the effects of modification of land management within a certain type of land-use are better understood than the effect of land-use changes. This is unfortunate, because land-use change (e.g. afforestation of agricultural land), is expected to have a large effect on the GHG sink strength of soils. The diversification among different scientific approaches is accentuated, when Good Practice Guidelines for GHG Reporting (IPCC Good Practice Guidance 2000) takes care of direct N2O emission from soils while GPG LULUCF takes care of N2O emissions from management (including disturbances) and carbon emissions from management and disturbances however, not all processes have been covered by the default methodologies due to lack of data.

Disturbance of ecosystems often leads to the release of GHGs into the atmosphere. The term ‘slow in / fast out’ has been coined for the fact, that the increase of C and N stock in terrestrial ecosystems is a slow process (time scale of decades) that can be optimised by ingenious land management, but that disturbances as instantaneous events can lead to immediate losses of C and N (time scale of hours). In this context we focus on disturbances that are typical for specific regions. In the Nordic countries and Western Europe, peatlands currently retain large quantities of C and N, because the decomposition of soil organic matter is slow under wet and cold conditions. Global warming and drainage of these wetlands could release large quantities of GHGs into the atmosphere. Drying of peatlands therefore is a slow, but potentially extremely effective ecosystem disturbance and peatlands are therefore assumed to be hotspots of a future GHG release. - In the temperate region forests are presently a sink of GHGs and will continue to work as sinks for the foreseeable future (decades), but the future development of disturbances (wind throw, pest infestations) is difficult to predict. Secondary spruce plantations have been shown to be particularly vulnerable to disturbance. This forest type is quite common in regions where forestry has already a long history. The GHG sink strength of Mediterranean ecosystem is currently under-exploited, because degraded landscapes are wide-spread. Reversing the effect of past land disturbances is on the political agenda. This land-use change is believed to have a great potential for the sequestration of GHGs.

Existing projects
Numerous projects have dealt and are dealing with the quantification and thorough mechanistic understanding of C and N fixation in terrestrial ecosystems. The IP CarboEurope (6th Framework Programme [FP], building on a project cluster in the FP 5) and the recently approved IP NitroEurope (FP 6) are investigating greenhouse gas fluxes and inventory methods at various scales. The core of CarboEurope was built around a network of flux towers that enable the measurement of the CO2-exchange between the biosphere and the atmosphere at the ecosystem level. The IPs are supported by a plethora of national research projects. The COST Action E21 dealt with the greenhouse gas mitigation potential of forests, Action E43 currently deals with the harmonization of forest inventories. An identified gap in these Actions is that soils could not be dealt with in the required detail. COST Action 627 improves the understanding of the C-N interactions in soils of grassland ecosystems and the impacts of land-use in a changing environment on C and N emissions.

Reporting of GHG fluxes in and out of terrestrial ecosystem is a global issue. The legally binding reduction of GHG-emissions require substantial efforts by the member countries of the EU and non-compliance with the negotiated national emission reductions will lead to substantial penalty payments at the end of the first commitment period of the Kyoto Protocol (2012). The storage of C and N in terrestrial ecosystems has therefore both an economic and an ecological component. In the first commitment period of the Kyoto Protocol, land management includes afforestation, reforestation, deforestation (Article 3.3), whereas Article 3.4, dealing with further land management options, is optional. For future commitment periods, a more comprehensive treatment of land management is expected. It is therefore necessary to obtain a complete picture on GHG emissions early on. To take this important step the Action will build on the knowledge from CarboEurope and NitroEurope and focus on ‘hot spots’ of GHG emissions from soils (types of ecosystems, types of land management). The diversity of landscapes and forms of land-use within the EU is large and calls for an international platform of interaction. This will involve an interdisciplinary approach in the collaboration of people with expertise in forest ecology, agriculture, biology, geography and socio-economy. A meaningful proposal for the evaluation of GHG emissions from terrestrial ecosystems is a vital contribution to guidelines for future reporting rules. The challenge is to establish a dialogue between stakeholders in the scientific, administrative, and political arena. To take these important steps, the Action builds on the outcome of EU projects and the Guidelines of the IPCC for GHG Reporting. The COST Action as an international cooperation will give momentum to national research in this area.

The Action network here described will include (i) experts in specific types of land use, (ii) experts in inventory methods, (iii) modellers, (iv) experts who are involved in the political negotiations, (v) authors of already finalized guidelines, (vi) graduate students and early stage researchers.
18.12.06 | Preier, P.
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