Aim Understanding the driving forces and mechanisms of changes in past plant distribution and abundance will help assess the biological consequences of future climate change scenarios. The aim of this paper is to investigate whether modelled patterns of climate parameters 6000 years ago can account for the European distribution of Fagus sylvatica at that time. Consideration is also given to the role of non-climatic parameters as driving forces of the Holocene spread and population expansion of F. sylvatica. Location Europe.Methods European distributions were simulated using a physiologically-based bioclimatic model (STASH) driven by three different atmospheric general circulation model (AGCM) outputs for 6000 years ago. ResultsThe three simulations generally showed F. sylvatica to have potentially been as widespread 6000 years ago as it is today, which gives a profound mismatch with pollen-based reconstructions of the F. sylvatica distribution at that time. The results indicate that drier conditions during the growing season 6000 years ago could have caused a restriction of the range in the south. Poorer growth conditions with consequently reduced competitive ability were modelled for large parts of France.Main conclusions Consideration of the entire European range of F. sylvatica showed that no single driving force could account for the observed distributional limits 6000 years ago, or the pattern of spread during the Holocene. Climatic factors, particularly drought during the growing season, are the likely major determinants of the potential range. Climatic factors are regionally moderated by competition, disturbance effects and the intrinsically slow rate of population increase of F. sylvatica. Dynamic vegetation modelling is needed to account for potentially important competitive interactions and their relationship with changing climate. We identify uncertainties in the climate and pollen data, as well as the bioclimatic model, which suggest that the current study does not identify whether or not climate determined the distribution of F. sylvatica 6000 years ago. Pollen data are better suited for comparison with relative abundance gradients rather than absolute distributional limits. These uncertainties from a study of the past, where we have information about plant distribution and abundance, argue for extreme caution in making forecasts for the future using equilibrium models.
Managing the appearance of images across different display environments is a difficult problem, exacerbated by the proliferation of high dynamic range imaging technologies. Tone reproduction is often limited to luminance adjustment and is rarely calibrated against psychophysical data, while color appearance modeling addresses color reproduction in a calibrated manner, albeit over a limited luminance range. Only a few image appearance models bridge the gap, borrowing ideas from both areas. Our take on scene reproduction reduces computational complexity with respect to the state-of-the-art, and adds a spatially varying model of lightness perception. The predictive capabilities of the model are validated against all psychophysical data known to us, and visual comparisons show accurate and robust reproduction for challenging high dynamic range scenes.
Once HDR displays were developed, a constant question persisted about how much dynamic range is needed for display. If one uses physical scene luminances or human visual system threshold detections to answer this question, the needed ranges are unachievable at exorbitant cost, and likely to remain so for decades. Therefore we designed studies to find the range that is preferred by human observers, and for suprathreshold appearances. Two studies address the diffuse reflective regions, and a third study tested preferences of highlight regions. Test images were specifically designed to test these limits without the perceptual conflicts that usually occur in these types of studies. For the diffuse range, we found displays capable of a dynamic range between 0.1 and 650 cd/m2 match the average preferences. However, to satisfy 90% of the population, a dynamic range from 0.005 to ∼3,000 cd/m2 is needed. Since a display should be able to produce values brighter than the diffuse white maximum, as in specular highlights and emissive sources, the highlight study concludes that the average preferred maximum luminance for highlight reproduction satisfying 50% of viewers is ∼2,500 cd/m2. This value increases to marginally over 20,000 cd/m2 when catering to 90%. Though there is some variability in preferred brightness between certain demographics, the call for a more capable display is still evident, as preferred luminances found in this study exceed even the best of consumer displays today.
The dynamic range of the human visual system should be an important parameter in the design of high dynamic range (HDR) display devices. A good display should at least approximate this range. However, the literature reports a simultaneous dynamic range between 2 and 4 log units of luminance, leaving ambiguity as to what dynamic range HDR display devices should cater for. In this paper we present a sequence of psychophysical experiments, carried out with the aid of a high dynamic range display device, to determine the simultaneous dynamic range of the human visual system under full adaptation to a given background luminance. Our findings show that the human visual system is capable of distinguishing contrasts over a range of 3.7 log units under specific viewing conditions. Further, we show how the dynamic range is affected by stimulus duration, contrast of the stimulus as well as background illumination, thereby accounting for the differences reported in the literature and providing guidance for display design.
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