Showing papers by "Ernst Detlef Schulze published in 2000"

Respiration as the main determinant of carbon balance in European forests

Abstract: Carbon exchange between the terrestrial biosphere and the atmosphere is one of the key processes that need to be assessed in the context of the Kyoto Protocol1. Several studies suggest that the terrestrial biosphere is gaining carbon2,3,4,5,6,7,8, but these estimates are obtained primarily by indirect methods, and the factors that control terrestrial carbon exchange, its magnitude and primary locations, are under debate. Here we present data of net ecosystem carbon exchange, collected between 1996 and 1998 from 15 European forests, which confirm that many European forest ecosystems act as carbon sinks. The annual carbon balances range from an uptake of 6.6 tonnes of carbon per hectare per year to a release of nearly 1 t C ha-1 yr-1, with a large variability between forests. The data show a significant increase of carbon uptake with decreasing latitude, whereas the gross primary production seems to be largely independent of latitude. Our observations indicate that, in general, ecosystem respiration determines net ecosystem carbon exchange. Also, for an accurate assessment of the carbon balance in a particular forest ecosystem, remote sensing of the normalized difference vegetation index or estimates based on forest inventories may not be sufficient.

Managing forests after Kyoto

Abstract: The Kyoto protocol aims to reduce carbon emissions into the atmosphere. Part of the strategy is the active management of terrestrial carbon sinks, principally through afforestation and reforestation. In their Perspective, Schulze et al. argue that the preservation of old-growth forests may have a larger positive effect on the carbon cycle than promotion of regrowth.

Carbon and nitrogen cycling in European forest ecosystems

Abstract: A Introduction to the European Transect.- 1 The Carbon and Nitrogen Cycle of Forest Ecosystems.- 1.1 Introduction.- 1.2 The Carbon and Nitrogen Cycles.- 1.3 The NIPHYS/CANIF Project.- 1.4 Experimental Design.- 1.5 Conclusions.- References.- 2 Experimental Sites in the NIPHYS/CANIF Project.- 2.1 Site Description. The NIPHYS/CANIF Transect.- 2.2 Soil Characteristics.- 2.3 Ecosystem C and N Pools.- 2.4 Database.- 2.5 Conclusions.- References.- B Plant-Related Processes.- 3 Tree Biomass, Growth and Nutrient Pools.- 3.1 Introduction.- 3.2 Experimental Background.- 3.3 Biomass.- 3.4 Forest Productivity.- 3.5 Carbon and Nutrient Pools.- 3.6 Allometric and Functional Relations.- 3.7 Conclusion.- References.- 4 Linking Plant Nutrition and Ecosystem Processes.- 4.1 Introduction.- 4.2 Experimental Approach.- 4.3 Nutrient Concentrations.- 4.4 Nutrient Contents.- 4.5 Nitrogen Partitioning in Different Tree Compartments.- 4.6 Ecosystem C and N Pools.- 4.7 Conclusions.- References.- 5 Root Growth and Response to Nitrogen.- 5.1 Introduction.- 5.2 Approaches to the Study of Root Growth.- 5.3 Root Growth Measurements Obtained by Soil Coring.- 5.4 Root Growth Measurements Obtained by Root Windows.- 5.5 Root Growth Measurements Obtained by In-Growth Cores.- 5.6 Root Growth at Different European Forest Sites.- 5.7 Conclusion.- References.- 6 Nitrogen Uptake Processes in Roots and Mycorrhizas.- 6.1 Introduction.- 6.2 Approaches to Study Different Aspects of the N Uptake Process.- 6.3 Studies with Excised Roots and Mycorrhizas.- 6.4 Field-Based Experiments.- 6.5 Conclusions.- References.- 7 The Fate of 15N-Labelled Nitrogen Inputs to Coniferous and Broadleaf Forests.- 7.1 Introduction.- 7.2 Sites of Investigation.- 7.3 Approaches to Study the Fate of 15N-Labelled Nitrogen Inputs.- 7.4 N Release and Tree Uptake from 15N-Labelled Decomposing Litter in a Beech Forest in Aubure.- 7.5 Ecosystem Partitioning of 15N-Labelled Ammonium and Nitrate on the Sites in the Fichtelgebirge and Steigerwald.- 7.6 Conclusion.- References.- 8 Canopy Uptake and Utilization of Atmospheric Pollutant Nitrogen.- 8.1 Introduction.- 8.2 Atmospheric Nitrogen Pollutants.- 8.3 Pathways for Canopy Uptake of Nitrogen.- 8.4 Approaches to the Determination of Canopy Uptake of Nitrogen.- 8.5 Review of Research.- 8.6 Role in the Critical Load.- 8.7 Ecophysiological Consequences of Canopy N Uptake.- 8.8 Conclusions.- 8.9 Way Forward.- 8.10 Policy Implications.- References.- 9 Biotic and Abiotic Controls Over Ecosystem Cycling of Stable Natural Nitrogen, Carbon and Sulphur Isotopes.- 9.1 Introduction.- 9.2 Approaches to the Study of Stable Isotopes in the Field.- 9.3 ?15N of Ammonium and Nitrate in Wet Deposition.- 9.4 Stable Isotope Signatures in Different Ecosystem Compartments.- 9.5 ?15N Signatures as Indicators of N Saturation in Forest Ecosystems.- 9.6 Conclusion.- References.- C Heterotrophic Processes.- 10 Soil Respiration in Beech and Spruce Forests in Europe: Trends, Controlling Factors, Annual Budgets and Implications for the Ecosystem Carbon Balance.- 10.1 Introduction.- 10.2 Approaches to Measuring Soil Respiration.- 10.3 Daily and Seasonal Trends in Soil Respiration and Climatic Variables.- 10.4 Factors Controlling Soil Respiration.- 10.5 Comparison of Chamber Measurements with the Eddy Covariance Measurements Below the Canopy.- 10.6 Annual Budgets of Soil Respiration.- 10.7 Conclusion.- References.- 11 Annual Carbon and Nitrogen Fluxes in Soils Along the European Forest Transect, Determined Using the 14C-Bomb.- 11.1 Introduction.- 11.2 Forests, Sampling Procedure and Analysis.- 11.3 Model Description.- 11.4 Estimations of C and N Pools and Fluxes.- 11.5 Pools and Distribution of Carbon and Nitrogen in Soil Profiles.- 11.6 Variations in the Carbon Age and Mean Residence Times (MRTs).- 11.7 Annual Carbon and Nitrogen Fluxes.- 11.8 General Discussion.- 11.9 Conclusion.- References.- 12 Carbon Mineralisation in European Forest Soils.- 12.1 Introduction.- 12.2 Experimental Background.- 12.3 C Mineralisation in the North-South Transect.- 12.4 Long-Term Fertilisation Experiments.- 12.5 Mean Residence Time.- 12.6 Comparison of Intact and Sieved Soil Cores.- 12.7 Conclusion.- References.- 13 Litter Decomposition.- 13.1 Introduction.- 13.2 Factors Affecting the Decomposition Process.- 13.3 Enzymatic Activity.- 13.4 Nitrogen Dynamics in Decomposing Litter.- 13.5 Decomposition Studies in Europe: from DECO, VAMOS, MICS to CANIF.- 13.6 Decomposition Studies Within a Latitudinal Transect of European Beech Forests.- 13.7 Conclusion.- References.- 14 Soil Nitrogen Turnover - Mineralisation, Nitrification and Denitrification in European Forest Soils.- 14.1 Background and Aim of the Study.- 14.2 Methods Used to Study N Turnover.- 14.3 Net N Mineralisation Based on Laboratory Studies.- 14.4 Net Nitrification Based on Laboratory Studies.- 14.5 Manipulation of pH, N Availability and Nitrifier Density in the Laboratory.- 14.6 Autotrophic Versus Heterotrophic Nitrification.- 14.7 Net N Mineralisation and Nitrification in N-Fertilisation Experiments.- 14.8 Comparison of N Turnover in Similar Soils at Different Climate.- 14.9 Comparison of N Turnover in Sieved and Intact Soil Cores.- 14.10 In Situ Mineralisation Studies at Aubure.- 14.11 Comparison of in Situ and Laboratory-Based Mineralisation Studies.- 14.12 Denitrification.- 14.13 Final Discussion.- 14.14 Conclusions.- References.- 15 Nitrogen and Carbon Interactions of Forest Soil Water.- 15.1 Introduction.- 15.2 Approaches to Studying the Forest Soil Waters.- 15.3 Soil Water Concentrations of Nitrogen and Carbon.- 15.4 Correlation Between Dissolved Organic Nitrogen and Carbon.- 15.5 Conclusions.- References.- D Diversity-Related Processes.- 16 Fungal Diversity in Ectomyccorhizal Communities of Norway Spruce [Picea abies (L.) Karst.] and Beech (Fagus sylvatica L.) Along North-South Transects in Europe.- 16.1 Introduction.- 16.2 Analysis of Ectomycorrhizal Community Structure and Diversity.- 16.3 ECM Communities of Spruce Forests.- 16.4 ECM Communities of Beech Forests.- 16.5 Genetic Diversity Within a Population of Laccarina amethystina.- 16.6 Isolation and Growth of ECM Fungal Isolates on an Organic N Source.- 16.7 Comparative Evaluation of Ectomycorrhizal Diversity.- 16.8 Conclusion.- References.- 17 Diversity and Role of the Decomposer Food Web.- 17.1 Introduction.- 17.2 Approaches to Investigating Decomposer Communities.- 17.3 The Microflora.- 17.4 The Soil Fauna.- 17.5 Contribution of the Decomposer Food Web to C and N Flows.- 17.6 Conclusions.- References.- 18 Diversity and Role of Microorganisms.- 18.1 Introduction and Background.- 18.2 Experimental Background.- 18.3 Community of Microfungi in Beech Forests.- 18.4 Functional Diversity of Bacteria in the Litter of Coniferous Forests.- 18.5 Conclusion.- References.- E Integration.- 19 Spatial Variability and Long-Term Trends in Mass Balance of Nand S in Central European Forested Catchments.- 19.1 Introduction.- 19.2 Approaches to Studying Long-Term Changes in Watersheds.- 19.3 Temporal Variations and Trends.- 19.4 Budgets.- 19.5 Biological Cycling of Sulphur.- 19.6 Conclusion.- References.- 20 Model Analysis of Carbon and Nitrogen Cycling in Picea and Fagus Forests.- 20.1 Introduction.- 20.2 Model Description.- 20.3 Input Data and Parameter Values.- 20.4 Model Calibration and Comparison with Measured Data.- 20.5 Model Analysis.- 20.6 Conclusions.- References.- 21 Interactions Between the Carbon and Nitrogen Cycle and the Role of Biodiversity: A Synopsis of a Study Along a North-South Transect Through Europe.- 21.1 Introduction.- 21.2 Change of Ecosystem Processes Along the European Transect.- 21.3 What Limits the C and N Fluxes in These Forest Ecosystems?.- 21.4 What Are Net Ecosystem Productivity (NEP) and Net Biome Productivity (NBP) and How Do They Relate to Ecosystem Parameters?.- 21.5 Are There Thresholds and Non-Linearities?.- 21.6 What Role Does Biodiversity Play in Ecosystem Processes?.- 21.7 Conclusions.- References.- Species Index.

Carbon stocks and soil respiration rates during deforestation, grassland use and subsequent Norway spruce afforestation in the Southern Alps, Italy

Abstract: Changes in carbon stocks during deforestation, reforestation and afforestation play an important role in the global carbon cycle. Cultivation of forest lands leads to substantial losses in both biomass and soil carbon, whereas forest regrowth is considered to be a significant carbon sink. We examined below- and aboveground carbon stocks along a chronosequence of Norway spruce (Picea abies (L.) Karst.) stands (0-62 years old) regenerating on abandoned meadows in the Southern Alps. A 130-year-old mixed coniferous Norway spruce-white fir (Abies alba Mill.) forest, managed by selection cutting, was used as an undisturbed control. Deforestation about 260 years ago led to carbon losses of 53 Mg C ha(-1) from the organic layer and 12 Mg C ha(-1) from the upper mineral horizons (Ah, E). During the next 200 years of grassland use, the new Ah horizon sequestered 29 Mg C ha(-1). After the abandonment of these meadows, carbon stocks in tree stems increased exponentially during natural forest succession, levelling off at about 190 Mg C ha(-1) in the 62-year-old Norway spruce and the 130-year-old Norway spruce-white fir stands. In contrast, carbon stocks in the organic soil layer increased linearly with stand age. During the first 62 years, carbon accumulated at a rate of 0.36 Mg C ha(-1) year(-1) in the organic soil layer. No clear trend with stand age was observed for the carbon stocks in the Ah horizon. Soil respiration rates were similar for all forest stands independently of organic layer thickness or carbon stocks, but the highest rates were observed in the cultivated meadow. Thus, increasing litter inputs by forest vegetation compared with the meadow, and constantly low decomposition rates of coniferous litter were probably responsible for continuous soil carbon sequestration during forest succession. Carbon accumulation in woody biomass seemed to slow down after 60 to 80 years, but continued in the organic soil layer. We conclude that, under present climatic conditions, forest soils act as more persistent carbon sinks than vegetation that will be harvested, releasing the carbon sequestered during tree growth.

Canopy transpiration in a chronosequence of Central Siberian pine forests

Abstract: Tree transpiration was measured in 28, 67, 204 and 383 - year old uniform stands and in a multi-cohort stand (140 t0 430) of Pinus sylvestris ssp. sibirica Lebed. in Central Siberia during August of 1995.

Canopy Uptake and Utilization of Atmospheric Pollutant Nitrogen

Abstract: Research on effects of air pollutants on forests concentrated initially on quantifying wet deposition into ecosystems, because of its significance in acidifying soils (Ulrich 1987; Last and Watling 1991) and because it can be easily monitored. By contrast, the deposition of pollutant gases has not received an equivalent amount of attention, even though the ecological importance of this process has long been recognised (Nilgard 1985; Roelofs et al. 1985). Understanding of gas interactions with canopies has led to a general explanation of the processes leading to forest decline (Schulze 1989). The processes involved in deposition and canopy uptake of pollutant N have remained difficult to quantify due to their complexity (e.g. Duyzer et al. 1992; Hanson and Lindberg 1991; Joslin et al. 1990) and a lack of adequate techniques to measure uptake fluxes directly under field conditions. Thus, estimates of the amounts of nitrogen entering into the ecosystem directly via the canopy, bypassing soils and roots, and the induced physiological responses in the trees and ground flora, have been assessed only by indirect methods (Pearson and Stewart 1993; Sutton et al. 1993).

Interactions between the carbon and nitrogen cycles and the role of biodiversity: A synopsis of a study along a north-south transect through Europe

Abstract: The NIPHYS/CANIF project of the EEC has provided the unique opportunity to examine forest ecosystem processes and diversity along a transect through Europe ranging from north Sweden to central Italy. The main objectives of this study were (1) to identify and quantify effects of N deposition on ecosystem processes, particularly the C cycle, by extending the range of observations across a deposition maximum in central Europe, and (2) to study feedback effects between ecosystem processes and biodiversity. The study resulted in a very comprehensive and consistent set of data on ecosystem processes over a 5-year period. However, in contrast to earlier large-scale ecosystem studies (IBP: Reichle 1981; Acid Rain Programme: Last and Watling 1991), the samples were collected and data generated by the same scientists at all sites. This assured comparisons of results on a broad geographic scale. In addition, key parameters were assessed by different methods, and integrating parameters were collected for different processes, in order to test and verify predictions made at higher and lower scales, ranging from physiological responses to ecosystem level processes.

The carbon and nitrogen cycle of forest ecosystems

Abstract: Our understanding of the biology of major biogeochemical cycles came initially from, and is still based upon, field observations (Bolin et al. 1979; Clark and Rosswall 1981; Apps and Price 1996). This is in contrast to very advanced models, which explore the physics of the climate system and are based on laws of physics or chemistry with a mechanistic understanding of the underlying processes (Houghton et al. 1996; Bengtsson 1999). For the biologist, the responses of organisms reach far beyond physicochemical reactions, and they include genetically regulated changes in physiological pathways or activation of enzyme systems as part of acclimations and adaptations that are coupled with climate and species composition changes. Generic predictions thus remain elusive because there are too many species and pathways. Although climate greatly influences the biogeochemical cycles, models that include biology thus remain at a correlative level. Moreover, the cycling of elements like carbon (C) cannot readily be separated from the abundance, state and cycles of other elements, especially nitrogen (N) (Schulze et al. 1994) which, in turn, is tied to the cycling of other elements (Ulrich 1987). Nevertheless, detailed knowledge of the biology of C cycling and that of other major and minor elements is urgently needed because the Kyoto Protocol demands strategies to balance industrial emissions by biological C fixation (WBGU 1998; IGBP 1998). By this protocol, mankind is taking a first step to deliberately engineer the biology of the global C cycle; but without full understanding of the underlying processes, there is a risk of serious deleterious side effects (Schellnhuber and Wenzel 1998; Schellnhuber 1999).

Experimental sites in the NIPHYS/CANIF project

Abstract: The NIPHYS/CANIF sites Fig. 2.1 were chosen to represent a latitudinal, climatic and deposition transect through Europe containing conifer and broadleaf stands. The main species are Norway spruce, Picea abies L. (Karst.) and European beech, Fagus sylvatica L. In southern France, Picea and Fagus are lacking at suitable sites and were replaced by maritime pine, Pinus pinaster Ait. (P. maritima Lam.), Aleppo pine, P. halepensis Mill. and white oak, Quercus pubescens Willd. for some of the studies. F. sylvatica has its most northern distribution in southern Scandinavia. Therefore, in northern Sweden, F. sylvatica was replaced with birch, Betula pubescens Ehrh.

Carbon and water exchanges of two contrasting central Siberia landscape types: regenerating forest and bog

Abstract: 1 In central Siberia Pinus sylvestris forests and bogs are common elements of the landscape and they show different functional behaviour in terms of energy and carbon exchanges 2 The two ecosystems show a remarkable difference in energy dissipation, with average Bowen ratios of 0·6 and 2·9, respectively 3 The alternation of bogs and forests with different energy partition at the surface could affect rainfall distribution and the disturbance regimes (lightening and fires) and drive the ecology of such a complex landscape 4 During summer, water shortage and poor nutrient conditions in the soil heavily affect carbon exchange rates of the regenerating forest (− 7·7 mmol m−2 day−1) Consequently the bog becomes a significant dominant carbon sequestration element of this particular landscape with higher rates of carbon uptake (− 104·2 mmol m−2 day−1)

Linking plant nutrition and ecosystem processes

Abstract: Mineral nutrients are a major part of all the physiological and biogeochemical processes in forest ecosystems. This is especially true for forests across Europe, which were deprived of nutrients due to intensive wood and litter use, and which experienced deposition of acids, nitrogen and sulphur over the second half of this century, resulting in significant nutrient imbalances for growth (Schulze 1989). Decreased nutrient availability can lead to a reduction of leaf size (Linder 1987), resulting in an almost instantaneous decrease in current year growth. In this way, the nutrient status of long-lived conifer needles might influence net primary production (NPP) long after a transient nutrient shortage, caused, e.g. by one dry season, has occurred. In natural forest ecosystems nutrient uptake from soil solution and nutrient release through litterfall and fine root turnover should balance each other such that the turnover time of nutrients within the system meets the requirements for stand growth (Gorham et al. 1979; Miller 1986; Attiwill and Adams 1993) and keeps the ecosystem nutrient cycle tight. Any deviation from this cycle due to anthropogenic influence (e.g. Vitousek et al. 1997) or natural disturbance (e.g. Foster et al. 1997) could alter one or more processes within the nutrient cycle with long-lasting effects on forest functioning.

Biotic and abiotic controls over ecosystem cycling of stable natural nitrogen, carbon and sulphur isotopes

Abstract: In forest ecosystems, physical, chemical and biological processes which regulate the uptake and flow of matter cause differences in the isotopic signatures of N, C and S compounds due to fractionation. Thus, tracing processes of isotopic fractionations in forest ecosystems can help identify transfer pathways and capacities. Atmospheric nitrogen pollution has been recognised as the cause for formerly N-limited forests to approach N saturation (Aber et al. 1989, 1998). The increase in N availability in forest ecosystems may have consequences for net ecosystem productivity on a local scale, but also for the carbon budget of terrestrial ecosystems on a global scale (Schulze 1994; Schimel 1995). Clearly, knowledge about the amount of N being deposited and cycling through forest ecosystems is of paramount importance for the carbon assimilation of the terrestrial biosphere (Lloyd and Farquhar 1996). In a similar manner, information on stable sulphur isotopes is of importance regarding pollution inputs and their effect on ecosystem health (Krouse 1989; Gebauer et al. 1994).

The Fate of 15N-Labelled Nitrogen Inputs to Coniferous and Broadleaf Forests

Abstract: Nitrogen in forest soils is mainly composed of organic N compounds originating from litterfall. During leaf senescence of the forest vegetation, N compounds are either allocated to perennial tissues or remain in the leaf litter, mainly as polyphenol-protein condensates. For example, senescent beech leaves are composed of 45% cellulose and hemicellulose, 5 to 10% lignin and 25 to 35% brown polyphenol condensates which contain about 70% of the litter N (Berthelin et al. 1994). Beech litter has a C/N mass ratio of 50–70 and evolves into soil organic matter with a C/N ratio ranging from 10 to 30 depending on the humus type. These organic N compounds in forest soils are highly protected from major N losses due to their high chemical stability and low mobility.

Model Analysis of Carbon and Nitrogen Cycling in Picea and Fagus Forests

Abstract: The CANIF project experimentally investigates the carbon and nitrogen flows in Picea abies and Fagus sylvatica forest stands. The experimental subprojects encompass a large diversity of research subjects ranging from root studies for uptake of nutrients, root turnover, the diversity and the role of mycorrhizae, soil fauna and microorganisms, soil organic matter dynamics, tree growth and nutrient relations to measurements of leaching fluxes. Only by putting all these different aspects together is an overview of the functioning of the ecosystem possible. Process-based models that incorporate the carbon, nutrients and water flows of the ecosystem are very appropriate to use for this integrative function. Their great advantage is that such models with site-specific input data for climate and deposition levels can highlight the major differences between sites.