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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 125 (2000), S. 11-17 
    ISSN: 1432-1939
    Keywords: Key words Cotyledons ; Seedling establishment ; Seed mass ; Comparative ; Allocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Several experiments have shown that seedlings from larger-seeded species are better able to survive various hazards during establishment. Previous work has suggested a general mechanism might underpin this outcome. Larger-seeded species might tend to mobilize their metabolic resources over a longer period into the autotrophically functioning structures of the seedling. Consequently relatively more resources would remain uncommitted at any given time during the early period of the seedling’s growth, and available to support respiration during carbon deficit. An important aspect of this larger-seed-later-commitment mechanism would be that at a given time, larger-seeded species would hold more resources uncommitted not just absolutely, but relative to the functional seedling structures that needed to be supported. Here we quantify, across a wide range of phanerocotylar species, an allometric pattern that supports the generality of a larger-seed-later-commitment mechanism as an explanation for superior performance by larger-seeded species in face of the hazards of seedling establishment. Larger-seeded species allocate relatively less to cotyledon area, reflecting the initial functional size of the seedling, and relatively more to dry mass per unit area of cotyledon, reflecting stored metabolic reserves. The shift in relative allocation is progressive, rather than seedlings falling into discrete morphological types. The allometry is similar whether considered as correlated evolutionary divergences (phylogenetically independent contrasts) or as correlation across present-day species.
    Type of Medium: Electronic Resource
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  • 2
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    In:  Geological Society Special Publication 261: 141-153.
    Publication Date: 2007-10-08
    Description: Conventional Flood Frequency Analysis (FFA) has been criticized both for its questionable theoretical basis, and for its failure in extreme event prediction. An important research issue for FFA is the exploration of models that have theoretical/explanatory value as the first step towards more accurate predictive attempts. Self-similar approaches offer one such alternative, with a plausible theoretical basis in complexity theory that has demonstrable wide applicability across the geophysical sciences. This paper explores a simple self-similar approach to the prediction of extreme floods. Fifty river gauging records from the USA exhibiting an outlier event were studied. Fitting a simple power law (PL) relation to events with return period of 10 years or greater resulted in more accurate discharge and return period estimates for outlier events relative to the Log-Pearson III model. Similar success in predicting record events is reported for 12 long-term rainfall records from the UK. This empirical success is interpreted as evidence that self-similarity may well represent the underlying physical processes generating hydrological variables. These findings have important consequences for the prediction of extreme flood events; the PL model produces return period estimates that are far more conservative than conventional distributions.
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  • 3
    Publication Date: 2000-10-01
    Print ISSN: 0029-8549
    Electronic ISSN: 1432-1939
    Topics: Biology
    Published by Springer
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  • 4
    Publication Date: 2005-09-01
    Description: Flood frequency analysis (FFA) is a form of risk analysis, yet a risk analysis of the activity of FFA itself is rarely undertaken. The recent literature of FFA has been characterized by: (1) a proliferation of mathematical models, lacking theoretical hydrologic justification, but used to extrapolate the return periods of floods beyond the gauged record; (2) official mandating of particular models, which has resulted in (3) research focused on increasingly reductionist and statistically sophisticated procedures for parameter fitting to these models from the limited gauged data. These trends have evolved to such a refined state that FFA may be approaching the ‘limits of splitting’; at the very least, the emphasis was shifted early in the history of FFA from predicting and explaining extreme flood events to the more soluble issue of fitting distributions to the bulk of the data. However, recent evidence indicates that the very modelling basis itself may be ripe for revision. Self-similar (power law) models are not only analytically simpler than conventional models, but they also offer a plausible theoretical basis in complexity theory. Of most significance, however, is the empirical evidence for self-similarity in flood behaviour. Self-similarity is difficult to detect in gauged records of limited length; however, one positive aspect of the application of statistics to FFA has been the refinement of techniques for the incorporation of historical and palaeoflood data. It is these data types, even over modest timescales such as 100 years, which offer the best promise for testing alternative models of extreme flood behaviour across a wider range of basins. At stake is the accurate estimation of flood magnitude, used widely for design purposes: the power law model produces far more conservative estimates of return period of large floods compared to conventional models, and deserves closer study.
    Print ISSN: 0309-1333
    Electronic ISSN: 1477-0296
    Topics: Geography
    Published by Sage Publications
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  • 5
    Publication Date: 2006-01-01
    Description: Palaeoflood reconstructions based on stage evidence are typically conducted in data-poor field settings. Few opportunities exist to calibrate the hydraulic models used to estimate discharge from this evidence. Consequently, an important hydraulic model parameter, the roughness coefficient (e.g. Manning's n), is typically estimated by a range of approximate techniques, such as 'visual estimation' and semi-empirical equations. These techniques contribute uncertainty to resulting discharge estimates, especially where the study reach exhibits sensitivity in the discharge-Manning's n relation. We study this uncertainty within a hydraulic model for a large flood of known discharge on the Mae Chaem River, northern Thailand. Comparison of the 'calibrated' Manning's n with that obtained from semi-empirical equations indicates that these underestimate roughness. Substantial roughness elements in the extra-channel zone, inundated during large events, contribute significant additional sources of flow resistance that are captured neither by the semi-empirical equations, nor by existing models predicting stage-roughness variations. This bedrock channel exhibits a complex discharge-Manning's n relation, and reliable estimates of the former are dependent upon realistic assignment of the latter. Our study demonstrates that a large recent flood can provide a valuable opportunity to constrain this parameter, and this is illustrated when we model a palaeoflood event in the same reach, and subsequently examine the magnitude-return period consequences of discharge uncertainty within a flood frequency analysis, which contributes its own source of uncertainty. Copyright © 2005 John Wiley & Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 6
    Publication Date: 2006-01-01
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
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  • 7
    Publication Date: 2005-09-01
    Print ISSN: 0169-555X
    Electronic ISSN: 1872-695X
    Topics: Geography , Geosciences
    Published by Elsevier
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