Browsing by Subject "SOURCE AREA"

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  • Latalowa, Malgorzata; Swieta-Musznicka, Joanna; Slowinski, Michal; Pedziszewska, Anna; Noryskiewicz, Agnieszka M.; Zimny, Marcelina; Obremska, Milena; Ott, Florian; Stivrins, Normunds; Pasanen, Leena; Ilvonen, Liisa; Holmstrom, Lasse; Seppa, Heikki (2019)
    The study, based on the examination of 70 published and unpublished pollen profiles from Poland and supplementary data from the surrounding regions, shows that an abrupt, episodic Alnus population decline at the end of the first millennium CE was a much more widespread event than has been previously reported, spanning large areas of the temperate and boreal zones in Europe. The data from Poland suggest that the decline was roughly synchronous and most likely occurred between the 9th and 10th centuries, with strong indications for the 10th century. The pollen data indicate that human impacts were not a major factor in the event. Instead, we hypothesize that one or a series of abrupt climatic shifts that caused floods and droughts at the end of the first millennium CE could have initiated this ecological disturbance, leading to a higher vulnerability of the alder trees to a pathogen outbreak. Following current observations of the decline of alder stands in Europe due to a Phytophthora outbreak, we suggest that a similar process may have occurred in the past. This study provides insight into long-term alder (mainly Alnus glutinosa) dynamics in a condition of climate change and illustrates its great resilience, enabling the natural, successful regeneration of alder stands after critical diebacks if environmental conditions improve. Our finding that the Alnus pollen decline reflects a roughly synchronous event indicates that the decline could be used as an over-regional chronostratigraphic marker for 800-1000 CE in pollen diagrams from a large part of the European Lowland.
  • Seddon, Alistair W. R.; Festi, Daniela; Robson, T. Matthew; Zimmermann, Boris (2019)
    Ultraviolet-B radiation (UV-B, 280-315 nm) constitutes less than 1% of the total solar radiation that reaches the Earth's surface but has a disproportional impact on biological and ecological processes from the individual to the ecosystem level. Absorption of UV-B by ozone is also one of the primary heat sources to the stratosphere, so variations in UV-B have important relationships to the Earth's radiation budget. Yet despite its importance for understanding atmospheric and ecological processes, there is limited understanding about the changes in UV-B radiation in the geological past. This is because systematic measurements of total ozone and surface UV-B only exist since the 1970s, so biological or geochemical proxies from sediment archives are needed to reconstruct UV-B irradiance received at the Earth surface beyond the experimental record. Recent developments have shown that the quantification of UV-B-absorbing compounds in pollen and spores have the potential to provide a continuous record of the solar-ultraviolet radiation received by plants. There is increasing interest in developing this proxy in palaeoclimatic and palaeoecological research. However, differences in interpretation exist between palaeoecologists, who are beginning to apply the proxy under various geological settings, and UV-B ecologists, who question whether a causal dose-response relationship of pollen and spore chemistry to UV-B irradiance has really been established. Here, we use a proxy-system modelling approach to systematically assess components of the pollen-and spore-based UV-B-irradiance proxy to ask how these differences can be resolved. We identify key unknowns and uncertainties in making inferences about past UV-B irradiance, from the pollen sensor, the sedimentary archive, and through the laboratory and experimental procedures in order to target priority areas of future work. We argue that an interdisciplinary approach, modifying methods used by plant ecologists studying contemporary responses to solar-UV-B radiation specifically to suit the needs of palaeoecological analyses, provides a way forward in developing the most reliable reconstructions for the UV-B irradiance received by plants across a range of timescales.
  • Trondman, A. -K.; Gaillard, M. -J.; Mazier, F.; Sugita, S.; Fyfe, R.; Nielsen, A. B.; Twiddle, C.; Barratt, P.; Birks, H. J. B.; Bjune, A. E.; Bjorkman, L.; Brostrom, A.; Caseldine, C.; David, R.; Dodson, J.; Doerfler, W.; Fischer, E.; van Geel, B.; Giesecke, T.; Hultberg, T.; Kalnina, L.; Kangur, M.; van der Knaap, P.; Koff, T.; Kunes, P.; Lageras, P.; Latalowa, M.; Lechterbeck, J.; Leroyer, C.; Leydet, M.; Lindbladh, M.; Marquer, L.; Mitchell, F. J. G.; Odgaard, B. V.; Peglar, S. M.; Persson, T.; Poska, A.; Roesch, M.; Seppä, H.; Veski, S.; Wick, L. (2015)
    We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1 degrees x1 degrees spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.
  • Seddon, Alistair W. R.; Festi, Daniela; Nieuwkerk, Mayke; Gya, Ragnhild; Hamre, Borge; Kruger, Linn Cecilie; Ostman, Silje A. H.; Robson, T. Matthew (2021)
    Research indicates that phenolic compounds (e.g. para-coumaric acid) found within pollen grains may be useful as a proxy to reconstruct the UV-B radiation received at the Earth's surface in the geological past. However, application of this method to the plant-fossil record currently relies on a series of untested assumptions surrounding the ecological factors driving the response of pollen grains in the contemporary environment. Here, we investigate the relationship of Pinus spp. pollen to UV-B radiation using individuals of five populations sampled from three elevation gradients across Europe. We develop a novel radiation-modelling approach, which allows us to estimate the UV-B radiation dose of individual trees, weighted by different UV-B action spectra. We then use linear mixed-effects modelling to investigate: (a) whether the variations in UV-B-absorbing compounds in Pinus pollen are best described by models using coarser (subgenus) or finer (population) taxonomic levels; and (b) the duration of the period of accumulation of UV-B-absorbing compounds in pollen, ranging from 8 to 28 days. Our results demonstrate an overall positive relationship between para-coumaric acid and UV-B radiation, best described by applying a UV-B-accumulation period spanning 12-19 days. However, we also show clear evidence for population-level factors influencing this relationship across the study locations. Synthesis. Our multidisciplinary approach, which combines expertise from palaeoecology, plant physiology and atmospheric physics, provides clear evidence that pollen-grain chemistry is subject to population-level variations. We suggest that quantitative reconstructions of long-term changes in springtime UV-B radiation are still achievable using fossil reconstructions, but only with careful consideration of the factors leading to pollen representation in sediments. Future improvements are dependent on mechanistic understanding of the local factors which mediate the UV-B response across different populations, and on upscaling knowledge at the plant level to incorporate longer-term chemical variations represented within sediment samples.