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Pollen-inferred quantitative reconstructions of Holocene land-cover in NW Europe for the evaluation of past climate-vegetation feedbacks. The Swedish LANDCLIM project and the NordForsk LANDCLIM network

Abstract : Reliable predictive models are needed to describe potential future climate changes and their impacts. Landsurface-atmosphere feedbacks and their impacts on climate are a current priority in the climate modelling commu-nity, but reliable records of long-term land use and vegetation change required for model evaluation are limited.Palaeoecological and palaeo-climatic data provide a unique record of the past changes in vegetation, land use andclimate on time scales relevant to vegetation processes and global change projections. The application of a newtechnique (the REVEALS model (Sugita 2007) to landscape reconstruction using fossil pollen data makes robustcomparisons with vegetation model output possible . The model corrects for biases caused by e.g. inter-taxonomicdifferences in pollen productivity and dispersal. Our results show that pollen percentages, a traditional indicator ofland cover changes, generally underestimate the unforested areas and certain broad-leaved trees such as Corylusand Tilia, while they often overestimate Betula and Pinus (see Cui et al. BG 6.2). Climate models use simplifiedland-surface classifications (plant functional types (PFTs)), such as grass (i.e. open land), deciduous trees, andconifers. Therefore, the observed large discrepancies in past land cover between the REVEALS estimates andpollen percentages are expected to influence model outcomes of the Holocene regional climate in NW Europe.The LANDCLIM project and research network (sponsored by the Swedish [VR] and Nordic [NordForsk]Research Councils) aim to quantify human-induced changes in regional vegetation/land-cover in NW Europeduring the Holocene, and to evaluate the effects of these changes on the regional climate through altered feedbacks.We use the REVEALS model, theoretically derived and empirically tested, to estimate the percentage cover oftaxa and groups of taxa (PFTs) from fossil pollen data for selected time windows of the Holocene, at a spatialresolution of ca. 1o x 1o. The REVEALS estimates of the past cover of PFTs will be 1) compared with theoutputs of the LPJ-GUESS (10 PFTs), a widely-used dynamic vegetation model and 2) used as an alternative tothe LPJ-GUESS-simulated vegetation (3 PFTs) to run for the past the regional climate model RCA3 developedat the Rossby Centre, Norrköping, Sweden. The study will evaluate and further refine these models (RCA3 andLPJ-GUESS) using a data-model comparison approach that incorporates new syntheses of palaeoclimatic data aswell. It will lead to new assessments of the possible effect of various factors on climate, such as deforestations andafforestations, and changes in vegetation composition and spatial patterns of land cover/land use. Refined climatemodels and empirical land-cover reconstructions will shed new light on controversial hypotheses of past climatechange and human impacts, such as the “Ruddiman hypothesis”.First maps of REVEALS estimates of plant functional types (PFTs) are now available for Sweden, Nor-way, Finland, Denmark, Estonia, Poland, Germany, The Czech Republic, Switzerland and Britain (see Mazier et al. C1.21 and Trondman et al. C1.22). Correlation tests show that the REVEALS estimates are robust in terms of ranking of the PFTs’ abundance (see Mazier et al, C1.21). The LANDCLIM project and network are a contribution to the IGBP-PAGES-Focus 4 PHAROS programme on human impact on environmental changes in the past. The following LANDCLIM members are acknowledged for providing pollen records, for help with pollen databases, and for providing results to the project: Mihkel Kangur and Tiiu Koff (Univ. Tallinn, Tallinn); Erik Kjellström (SMHI, Norrköping), Anna Broström, Lena Barnekow and Thomas Persson (GeoBiosphere Science Centre, Lund University); Anneli Poska (Physical Geography and Ecosystems Analysis, Lund University); Thomas Giesecke (Albrecht-von-Haller-Institute for Plant Sciences, University of Göttingen), Anne Bjune and John Birks (Dept. of Biology, University of Bergen); Pim van der Knaap (Institute of Plant Sciences, University of Bern); Malgorzata Latalowa (University of Gdansk); Michelle Leydet (IMEP CNRS 6116, University of Marseille III); Teija Alenius (Finnish Geological Survey, Espoo), Heather Almquist-Jacobson (Univ. Montana, USA), Jonas Bergman (Univ. Stockholm), Rixt de Jong (Univ. Bern), Jutta Lechterbeck (Hemmenhofen, Germany), Ann-Marie Robertsson (Univ. Stockholm), Ulf Segerström and Henrik von Stedingk (Univ. Umeå), Heikki Seppä (Univ. Helsinki).
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Submitted on : Friday, March 20, 2020 - 12:36:20 PM
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M.J. Gaillard, Shinya Sugita, Mats Rundgren, Benjamin Smith, Florence Mazier, et al.. Pollen-inferred quantitative reconstructions of Holocene land-cover in NW Europe for the evaluation of past climate-vegetation feedbacks. The Swedish LANDCLIM project and the NordForsk LANDCLIM network. European Geosciences Union General Assembly 2010, May 2010, Vienne, Austria. ⟨hal-02513213⟩

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