Publications
NIBIOs employees contribute to several hundred scientific articles and research reports every year. You can browse or search in our collection which contains references and links to these publications as well as other research and dissemination activities. The collection is continously updated with new and historical material.
2003
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Authors
Holger LangeAbstract
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Abstract
Living organisms in ecosystems are conceptualized as autonomous agents with a spectrum for their behavior. Ecosystems are described here as interacting multi-agent systems. Implementing such a system is a challenge for current hardware and software technology both technically and conceptually, in particular if one of the agents is human, either virtually within the system or as external participant and user (real human).Interfering with and manipulating the system occurs at arbitrary times during simulation, with a collection of choices to do that, rendering the details of the particular simulation fundamentally unpredictable.As a result, we have an open interactive system with tight feedback loops, for which new computer models (beyond the Universal Turing Machine) are required. We discuss some of the theoretical concepts for the appropriate software technology and shortly present one example of such a system, a forest simulator used by forest administrators.
Authors
Holger LangeAbstract
High resolution digital elevation maps (DEMs) offer the investigation of multifractal properties of the spatial characteristics of river basins like the width function, and the determination of the relation between average slope and basin area.There have been a number of universality claims in this respect; the range of the scaling exponent for the slope-area relation seems to be narrow, and the multifractal spectrum of the width function is characterized by a single site-specific Lipschitz-Hlder exponent alpha, the spectrum having an envelope given by that of Peanos basin.Comparing 17 river basins covering two orders of magnitude in basin area, our findings do not confirm this universal character. In particular, the Lipschitz-Hlder exponent crucially depends on the resolution of the width function extraction; we show that it is easy to produce almost identical spectra for completely different basins when varying the resolution.The problem of interior points is also encountered. We adopt Venezianos modified calculation of f(alpha) in this case. The slope-area exponent covers a wide range of values which also include the pure random case. We thus question the usability of these measures as a classification tool for river basins. http://www.cosis.net/abstracts/EAE03/05246/EAE03-J-05246.pdf
Authors
Holger LangeAbstract
For the intepretation of multifractal properties of experimental time series, two prominent procedures used are the double trace method (DTM) and the universal multifractal (UM) approach. We calculated multifractal spectra for a collection of long-term precipitation, air temperature and river discharge records, covering a wide range of spatial scales.Considering K(q) in this framework leads to an effective classification of dynamical behavior. Comparison of the DTM and UM methodologies, however, reveals substantial differences which make them difficult to reconcile. This is in particular true for the discharge case.The scaling exponent is generally larger in magnitude for the DTM and in some cases even extends into the non-analytical regime. Part of previous work thus could not be confirmed. Whether the description of river flow as multifractal process is feasible remains an open question. http://www.cosis.net/abstracts/EAE03/05092/EAE03-J-05092.pdf
Abstract
An individual-based agent model is presented which resembles aspects of natural evolution in ecosystems under selective pressure due to limited resources. The environmental conditions are determined by spatial and temporal variability of resource abundances.The agents have to choose between three different types of resources; the one consumed most during lifetime solely counts for the fitness of the individual agent. Simulation runs show that populations specialized in different resource types are mutually influencing each other under temporal variation of a single resource type.Mobility of agents in a locally heterogenous world enables recolonization after a population has starved to death. Wavelet analysis of the population time series reveals that some observed population dynamics show phenomena such as localized periodicities which cannot be explained by linear dependencies on the resource input dynamics.
Abstract
Modern information technology allows the investigation of the characteristic properties of living systems from a new perspective. Which of the ecosystem features are necessary conditions resulting from their constraints, which are accidental, constituting contingent facts of their respective histories?As long as we know of a single phylogenetic tree in nature, the difference is hard to tell, rendering the reconstruction and realisation of artificial ecologies a major challenge. It has been taken up by the high technology of the time since decades; since two decades, IT is leading in this respect.Are there life forms that can be created in contemporary computers, and which ones? Successes and failures of a number of virtualizations are forming de facto constraints for theoretical ecosystem research. Artificial Life (AL) research appears to be not just another attempt towards realistic models for ecological systems, but undermines the basic assumptions of most of conventional modeling in this area: in AL, behavior is in general irreducible to internal mechanisms; behavior results rather from interactive and intentional usage of the simulation.We try to elucidate and demonstrate the crucial role of interaction in these simulations, drawing from current developments in theoretical computer science as well as a number of examples. We propose a new classification of ecosystem models according to its degree of interactivity.
2002
Abstract
Concentrations and fluxes of dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), together with pools of carbon and nitrogen in the soil and biomass, were determined along north-south and east-west transects across Norway, Sweden and Finland. The data were analysed statistically and modelled using the mechanistic model DyDOC.Concentrations of DOC and DON were greatest in the O horizon and decreased downwards in the soil. The highest production of dissolved organic matter appears to take place in the O horizon and any contribution from thoroughfall is probably small. A pronounced seasonal effect with peak DOC concentrations in late summer/early autumn may be due to a seasonal (largely temperature) effect on DOC production.The effect of acidic precipitation upon DOC concentrations and fluxes was unclear. DOC in the O horizon was mostly of recent origin, while DOC in the B horizon appeared to include some older material, possibly desorbed from the soil. A positive correlation was found with electrical conductivity and a negative correlation with pH in DOC concentrations from the O horizon.A lack of correlation between DOC concentrations and temperature is probably due to a time lag between peak temperatures and peak DOC concentrations. Modelling of DOC concentrations and fluxes using DyDOC gave rasonable results, suggesting that it might be possible to use DyDOC as a general tool for modelling and forecasting DOC concentrations and fluxes in Nordic forest ecosytems.Scenario analysis using DyDOC suggested that increased temperature without increased litter input might result in increased production of CO2 rather than DOC. An increase in both temperature and litter input would lead to increased DOC concentrations, with possible implications for drinking water quality. Increased precipitation will lead to increased fluxes of DOC.