79 research outputs found

    Combining biodiversity resurveys across regions to advance global change research

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    More and more ecologists have started to resurvey communities sampled in earlier decades to determine long-term shifts in community composition and infer the likely drivers of the ecological changes observed. However, to assess the relative importance of and interactions among multiple drivers, joint analyses of resurvey data from many regions spanning large environmental gradients are needed. In this article, we illustrate how combining resurvey data from multiple regions can increase the likelihood of driver orthogonality within the design and show that repeatedly surveying across multiple regions provides higher representativeness and comprehensiveness, allowing us to answer more completely a broader range of questions. We provide general guidelines to aid the implementation of multiregion resurvey databases. In so doing, we aim to encourage resurvey database development across other community types and biomes to advance global environmental change research

    Evaluating structural and compositional canopy characteristics to predict the light‐demand signature of the forest understorey in mixed, semi‐natural temperate forests

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    Questions: Light availability at the forest floor affects many forest ecosystem processes, and is often quantified indirectly through easy‐to‐measure stand characteristics. We investigated how three such characteristics, basal area, canopy cover and canopy closure, were related to each other in structurally complex mixed forests. We also asked how well they can predict the light‐demand signature of the forest understorey (estimated as the mean Ellenberg indicator value for light [“EIVLIGHT”] and the proportion of “forest specialists” [“%FS”] within the plots). Furthermore, we asked whether accounting for the shade‐casting ability of individual canopy species could improve predictions of EIVLIGHT and %FS. Location: A total of 192 study plots from nineteen temperate forest regions across Europe. Methods: In each plot, we measured stand basal area (all stems >7.5 cm diameter), canopy closure (with a densiometer) and visually estimated the percentage cover of all plant species in the herb (7 m). We used linear mixed‐effect models to assess the relationships between basal area, canopy cover and canopy closure. We performed model comparisons, based on R2 and the Akaike Information Criterion (AIC), to assess which stand characteristics can predict EIVLIGHT and %FS best, and to assess whether canopy shade‐casting ability can significantly improve model fit. Results: Canopy closure and cover were weakly related to each other, but showed no relation with basal area. For both EIVLIGHT and %FS, canopy cover was the best predictor. Including the share of high‐shade‐casting species in both the basal‐area and cover models improved the model fit for EIVLIGHT, but not for %FS. Conclusions: The typically expected relationships between basal area, canopy cover and canopy closure were weak or even absent in structurally complex mixed forests. In these forests, easy‐to‐measure structural canopy characteristics were poor predictors of the understorey light‐demand signature, but accounting for compositional characteristics could improve predictions

    Die Stoffwechselwirkungen der Schilddrüsenhormone

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    Eine Methode zur Bestimmung des Volumens der körperlichen Elemente des Blutes

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    SHOVAV JÜL : ein eindimensionales Neutronenkinetikprogramm für Kugelhaufen Hochtemperaturreaktoren mit Temperatur- und Xenon- Rückkopplung

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    The present report describes the modelling basis and the structure of the neutron kinetics-code SHOVAV-Jlil. Information for users is given regarding the application of the code and the generation of the input data. SHOVAV-Jül is a one-dimensional space-time-code based on a multigroup diffusion approach for four energy groups and six groups of delayed neutrons It.has been developed for the analysis of the transient behaviour of high temperature reactors with pebble-bed core. The reactor core is modelled by horizontal segments to which different materials compositions can be assigned. The temperature dependence of the reactivity is taken into account by using temperature dependent neutron cross sections. For the simulation of transients in an extended time range the time dependence of the reactivity absorption by Xenon-135 is taken into account. The code starts always from a steady state as an initial condition for transient calculations. The steady state can be achieved by iterative adaptation of selected core parameters. Perturbations of the neutron balance can be inpressed by time dependent variation of the reactivity,the core composition and the control rod position or by time dependent boundary conditions such as coolant mass flow, coolant inlet temperature and steam content in the core. The code contains a one-dimensional thermohydraulic model for the core which calculates steady state and transient temperature distributions of the fuel, the moderator and the coolant. For the analysis of steam ingress accidents the coolant may be treated as a mixture of helium and water steam
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