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Ohne Zusammenfassung     

Scaling Issues in Forest Succession Modelling

This paper reviews scaling issues in forest succession modelling, focusing on forest gap models. Two modes of scaling are distinguished: (1) implicit scaling, i.e. taking scale-dependent features into account while developing model equations, and (2) explicit scaling, i.e. using procedures that typically involve numerical simulation to scale up the response of a local model in space and/or time. Special attention is paid to spatial upscaling methods, and downscaling is covered with respect to deriving scenarios of climatic change to drive gap models in impact assessments. When examining the equations used to represent ecological processes in forest gap models, it becomes evident that implicit scaling is relevant, but has not always been fully taken into consideration. A categorization from the literature is used to distinguish four methods for explicit upscaling of ecological models in space: (1) Lumping, (2) Direct extrapolation, (3) Extrapolation by expected value, and (4) Explicit integration. Examples from gap model studies are used to elaborate the potential and limitations of these methods, showing that upscaling to areas as large as 3000 km² is possible, given that there are no significant disturbances such as fires or insect outbreaks at the landscape scale. Regarding temporal upscaling, we find that it is important to consider migrational lags, i.e. limited availability of propagules, if one wants to assess the transient behaviour of forests in a changing climate, specifically with respect to carbon storage and the associated feedbacks to the atmospheric CO₂ content. Regarding downscaling, the ecological effects of different climate scenarios for the year 2100 were compared at a range of sites in central Europe. The derivation of the scenarios is based on (1) imposing GCM grid-cell average changes of temperature and precipitation on the local weather records; (2) a qualitative downscaling technique applied by the IPCC for central and southern Europe; and (3) statistical downscaling relating large-scale circulation patterns to local weather records. Widely different forest compositions may be obtained depending on the local climate scenario, suggesting that the downscaling issue is quite important for assessments of the ecological impacts of climatic change on forests.     

Die primär gerichteten Sedimentstrukturen,insbesondere die Schrägschichtung im Koblenzquarzit am Mittelrhein

Zusammenfassung Die Schrägschichtung des Koblenzquarzits, eines typischen devonischen Geosynklinalsedimentes, ist durch Wanderung von Großrippeln entstanden. Eine methodische Gefügeanalyse ergibt, daß die bisher für Schrägschichtungs-Untersuchungen angewandte rein statistische Behandlung der meßbaren Einzelrichtungen zu erheblichen Fehlern führen kann. Es wird eine neue Auswertungsmethode vorgelegt, die auf der Erfassung homogener Bereiche beruht. Für Schrägschichtungs-Messungen im gefalteten Gestein wird ein einfaches Reduktionsverfahren vorgeschlagen.Anschließend an die Beschreibung der übrigen Gefügearten von gerichteten Strömungsmerkmalen werden die Richtungen der subaquatischen Rutschungen zur Ermittelung der primären Böschungsrichtungen des Meeresbodens während der Sedimentation herangezogen.Im paläogeographischen Gesamtbild ergibt sich die Notwendigkeit zur Annahme devonischer Gezeitenströme, deren zeitlich und regional wechselnder Richtungsverlauf ebenso wie die Abbildung im Sediment durch die Gliederung des Sedimentationsraumes in Becken und Schwellen bestimmt wurde. Eine mit Hilfe der Sedimentationsrichtungen nachweisbare embryonale synsedimentäre Faltung steht mit der zyklischen Schichtgliederung wahrscheinlich in engem ursächlichem Zusammenhang.     

Impacts of large-scale climatic disturbances on the terrestrial carbon cycle

Background

The amount of carbon dioxide in the atmosphere steadily increases as a consequence of anthropogenic emissions but with large interannual variability caused by the terrestrial biosphere. These variations in the CO₂ growth rate are caused by large-scale climate anomalies but the relative contributions of vegetation growth and soil decomposition is uncertain. We use a biogeochemical model of the terrestrial biosphere to differentiate the effects of temperature and precipitation on net primary production (NPP) and heterotrophic respiration (Rh) during the two largest anomalies in atmospheric CO₂ increase during the last 25 years. One of these, the smallest atmospheric year-to-year increase (largest land carbon uptake) in that period, was caused by global cooling in 1992/93 after the Pinatubo volcanic eruption. The other, the largest atmospheric increase on record (largest land carbon release), was caused by the strong El Niño event of 1997/98.

Results

We find that the LPJ model correctly simulates the magnitude of terrestrial modulation of atmospheric carbon anomalies for these two extreme disturbances. The response of soil respiration to changes in temperature and precipitation explains most of the modelled anomalous CO₂ flux.

Conclusion

Observed and modelled NEE anomalies are in good agreement, therefore we suggest that the temporal variability of heterotrophic respiration produced by our model is reasonably realistic. We therefore conclude that during the last 25 years the two largest disturbances of the global carbon cycle were strongly controlled by soil processes rather then the response of vegetation to these large-scale climatic events.     

On seismic activity

Summary Seismic activity at a point of the surface of the earth up to a given time has to be computed by the total energy per unit area at the point considered in consequence of the earthquakes up to that time. The definition of seismic activity of a region can be developed from that. Seismic activity in a given time-interval results from earthquakes up to the upper limit of that interval. In consequence of a suitable valuation seismic activity is always convergent. For sufficiently large time-intervals a formal relationship between seismic activity and seismicity can be constructed.Publication No. 27 of the Institut für Geodynamik, 69 Jena (GDR), Burgweg 11. Forschungsgemeinschaft der Deutschen Akademie der Wissenschaften zu Berlin.     

SS 433 — Again

The standard model for SS 433 encounters increasing difficulties, including geometrical and chemical irregularities, short-time correlations and the presence of circular polarization. It is argued that these difficulties disappear when one drops the assumption that the moving spectral lines are emitted by the (mapped) jets. All the spectral peculiarities can be blamed on (special) radiation from the inner accretion disk, at radius 10⁷ cm, around a young neutron star. The jets consist of relativistic pair plasma-like in all the other jet sources. A prediction is made for the center of the radio jets.