Annals of Botany 91: 402-403, 2003
© 2003 Annals of Botany Company
Schulze, E.-D. (ed.) Carbon and nitrogen cycling in European forest ecosystems. Ecological studies, volume 142
Carbon and nitrogen cycling in European forest ecosystems. Ecological studies, volume 142.
Ernst-Detlef Schulze, ed.
Berlin, Heidelberg, New York: Springer-Verlag, 2000.
£34 (softback). 500 pp. plus CD-ROM.
The storage of carbon in forests is a contentious issue of ecological, policy and business concern, both nationally and internationally. Carbon dioxide in the global atmosphere is quantitatively the most significant greenhouse gas so the main concern of the protocol delivered at Kyoto in 1997 is to stabilize and then to reduce the amount of carbon dioxide in the atmosphere. The most obvious and effective way of making this reduction is to decrease inputs to the atmosphere from the burning of fossil fuels. The alternative strategy to reducing the inputs is to enhance the outputs, and that is where forests and the associated controversy come in. At Kyoto, provision was made for removal of carbon dioxide from the atmosphere by forests and its subsequent storage within forests, the so-called carbon sequestration by forests. This was a brave—some would say foolish—step by the Parties who, with their advisers, did not know a great deal about the rates of transfer of carbon dioxide between the atmosphere and forests, the rates of turnover of carbon and its residence time within forests and, particularly, the dynamics of the processes that determine the contribution that forests might make. They were, of course, aware that growing trees accumulate carbon, and the common perception at the time was that atmospheric carbon sequestered by forests was largely stored in the wood of the growing trees; that much of the carbon in forests is in the soil (about three-quarters of it globally) rather than in the trees was not a current idea in vogue. Thus, at Kyoto, the Parties played safe and restricted the role of vegetation to forests that were the result of afforestation and reforestation since 1990, i.e. to new, young forests, planted onto land that had not recently had forest growing on it, on which young trees could be expected to grow fast and accumulate carbon. Nonetheless, they left the door open for possible inclusion, at a later date, of carbon sequestration into both trees and soil in much older, natural and semi-natural forests. This has been the basis of the controversy at subsequent annual conferences of the Parties, some Parties wishing all forests and their soils to be included willy-nilly and, at the other extreme, others not wanting any forests to be included because mitigation by forests directs commitment away from the more important task of reducing emissions. In between, there are yet other Parties who would like to see the contribution that forests can make acknowledged and taken into the account, but have genuine concerns because of major gaps in our knowledge about the turnover of carbon in forest soils and anxieties regarding the vulnerability and permanence of the current forest carbon sinks. This book comprises the results of two experimental projects designed to address these issues, funded by the European Union.
The projects have the acronymns NIPHYS (NItrogen PHYsiology of forest plants and Soils) and CANIF (CArbon and Nitrogen cycling In Forest ecosystems), and they took place more or less sequentially between 1993 and 1999. The projects were experimental investigations of the processes involved in the contributions of carbon and nitrogen, together with the functional significance of biodiversity, in the overall biogeochemical cycles in forest ecosystems across Europe. A number of forest sites were selected along a north–south transect through Europe, starting in northern Sweden, passing through the nitrogen deposition maximum in central Europe, and ending in Italy. There were 13 main sites along this transect where the major programmes of measurements were made, supplemented by 12 additional complementary sites for less comprehensive, more particular purposes.
This volume describes in great detail the conduct and results of these investigations. The information contained is huge and will appeal to people with many different interests in ecosystem functioning. I cannot possibly summarize the wealth of material presented or do justice to the extensive results in a short review. I will try to indicate what is to be found, give the overall flavour and pick out just a very few points that are of particular interest to me and maybe to others.
The book is made up of 21 chapters divided into the following five parts: (1) ‘Introduction to the European transect’ (two chapters), covering the basic objectives, the concepts of the projects, the experimental design and basic data about the experimental sites. (2) ‘Plant-related processes’ (seven chapters), covering biomass, nutrient pools and growth (including roots and mycorrhizas), nutrient fluxes above- and below-ground (utilizing a wide range of techniques, including stable isotopes and isotopic labelling), and controls over ecosystem cycling. (3) ‘Heterotrophic processes’ (six chapters), covering soil respiration, carbon and nitrogen fluxes in the soils, decomposition and mineralization (including nitrification and denitrification), embracing studies both in the field and in the laboratory by controlled incubation. (4) ‘Diversity-related processes’ (three chapters), covering the biodiversity of mycorrhizas, other fungi and microorganisms. And (5) ‘Integration’ (three chapters), covering some catchment–scale studies, a large synthesis chapter (48 pages) in which a model is used to bring it ‘all’ together, and a final chapter in which the coordinator, Detlef Schulze, picks out a few plums that are of broad, fundamental significance.
I found the different approaches to the processes of mineralization and decomposition described in the section on heterotrophic processes to be particularly rewarding. The contrasting methods used were detritus production, in situ CO2 efflux, 14C isotope analysis, laboratory incubation and in situ litter bags. These are all methods that are frequently used but usually only one or perhaps two are used in any investigation. They all measure aspects of the same processes but in different ways and are focused on different components of the processes. Should they all lead to the same conclusions or do the artefacts implicit in each of the methods dictate the conclusions? If one accepts the validity of each approach and draws comparisons amongst them then one may arrive at the conclusion, as Schulze does, that the C and N cycles of European forests are not in balance and that resource supply exceeds resource use. If one adds in the work on biodiversity, it seems that soil communities are not the limitation to use of the extra resources.
Although the sites are all aligned more or less along the north–south transect and were almost all either Norway spruce or European beech sites, limitations of the transect approach were clearly apparent. The sites differed sufficiently in factors other than climate, such as soil type, age and stocking of trees, previous history, etc. that it was necessary to compare them very much on the basis of individual properties. Nonetheless, this did not detract seriously from the investigation but did limit some of the across-site comparisons because of lack of site replication. Out of this came the conclusion that there is huge variability amongst forest sites in Europe, and that to sample these sites adequately for carbon sequestration is not a trivial problem. The answer cannot be simply to increase the number of sites, the requirement would be for an impractically large number to sample adequately the range of age, species, management, etc. The solution has to lie in further enhancing our understanding of the dynamics of the processes to improve and generalize models, and to utilize the new remote-sensing technologies to characterize and classify sites, if we are to obtain a reasonably accurate estimate of the carbon sequestration capacity of our forests.
Like almost all of the projects funded by the EU over the last 15 or so years, these two projects contained partners from a number (eight) of countries across the EU, and from one of the countries seeking accession, the Czech Republic. From my own experience over 9 years with ECOCRAFT, such projects have been remarkably successful through the 1990s in generating exchanges of ideas and technology that today gives us a vibrant European Science Community. Ecological science, soil and forest science, physiological ecology, forest meteorology and hydrology, ecological and forest modelling, and applications of remote sensing have all benefited through EU-funding support. How this legacy will now continue to develop in Framework 6 is a question currently under much discussion. The direct successor to these two projects has been the FORCAST project, one of nine projects in the CARBONEUROPE ‘cluster’ of projects. Will such clusters continue or be completely replaced by fully ‘integrated projects’; will future funding come through a European Funding Council; and will there be closer integration with national funding councils? The fundamental truth that emerges from these projects is that continuity is all important in ecological research. Within ecological systems, observations and, particularly, experiments that are designed to provide answers that both enhance science and inform policy must be carried through over periods of more than 3 years. The continuity provided by successive funding tranches in these and other programmes has enabled this. Long may this continue!
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