Description: Differences between pollen-based reconstructions and dynamic vegetation simulations of past vegetation change in Europe over the last seven millennia are interpreted as being due primarily to land-use change. Incorporating land use in climate and dynamic vegetation models requires new approaches.

Description: Differences between pollen-based reconstructions and dynamic vegetation simulations of past vegetation change in Europe over the last seven millennia are interpreted as being due primarily to land-use change. Incorporating land use in climate and dynamic vegetation models requires new approaches.

Description: We compare Holocene tree-cover changes in Europe derived from a transient MPI-ESM1.2 simulation with high spatial resolution LPJ-GUESS time-slice simulations and pollen-based quantitative reconstructions of tree cover based on the REVEALS model. The dynamic vegetation models and REVEALS agree with respect to the general temporal trends in tree cover for most parts of Europe, with a large tree cover during the mid-Holocene and a substantially smaller tree cover closer to the present time. However, the decrease in tree cover in REVEALS starts much earlier than in the models indicating much earlier anthropogenic deforestation than the prescribed land-use in the models. While LPJ-GUESS generally overestimates tree cover compared to the reconstructions, MPI-ESM indicates lower percentages of tree cover than REVEALS, particularly in Central Europe and the British Isles. A comparison of the simulated climate with chironomid-based climate reconstructions reveals that model-data mismatches in tree cover are in most cases not driven by biases in the climate. Instead, sensitivity experiments indicate that the model results strongly depend on the tuning of the models regarding natural disturbance regimes (e.g. fire and wind throw). The frequency and strength of disturbances are – like most of the parameters in the vegetation models – static and calibrated to modern conditions. However, these parameter values may not be valid during climate and vegetation states totally different from todays. In particular, the mid-Holocene natural forests were probably more stable and less sensitive to disturbances than present day forests that are heavily altered by human interventions. Our analysis highlights the fact that such model settings are inappropriate for palaeo-simulations and complicate model-data comparisons with additional challenges. Moreover, our study suggests that land-use is the main driver of forest decline in Europe during the mid- and late-Holocene.

Description: Characterization of land cover change in the past is fundamental for understanding the evolution and present state of the earth system, the amount of carbon and nutrient stocks in terrestrial ecosystems, and the role played by land-atmosphere interactions in influencing climate. The estimation of land cover changes using palynology is a mature field, as thousands of sites in Europe have been investigated over the last century. Nonetheless, a quantitative land cover reconstruction at continental scale has been largely missing. Here we present a series of maps detailing the evolution of European forest cover during last 12000 years. Our reconstructions are based on the Modern Analogue Technique (MAT): a calibration dataset is built by coupling modern pollen samples with the corresponding satellite-based forest cover data. Fossil reconstructions are then performed by assigning to every fossil sample the average forest cover of its closest modern analogues. The occurrence of fossil pollen assemblages with no counterparts in modern vegetation represents a known limit of analogue-based methods. To lessen the influence of no-analogue situations, pollen taxa were converted into Plant Functional Types prior to running the MAT algorithm. We then interpolate site-specific reconstructions for each timeslice using a four-dimensional gridding procedure to create continuous gridded maps at continental scale. The performance of the MAT is compared against methodologically independent forest cover reconstructions produced using the REVEALS method; MAT and REVEALS estimates are most of the time in good agreement at a trend level, yet MAT regularly underestimates the occurrence of densely forested situations, requiring the application of a bias correction procedure The calibrated MAT-based maps draw a coherent picture of the establishment of forests in Europe in the early Holocene with the greatest forest cover fractions reconstructed between ~8500 and 6000 cal. yr. BP. This forest maximum is followed by a general decline in all parts of the continent, likely as a result of anthropogenic deforestation. The continuous spatial and temporal nature of our reconstruction, its continental coverage and gridded format make it suitable for climate, hydrological, and biogeochemical modelling, among other uses.

Description: This dataset corresponds to the pollen-based REVEALS estimates of 25 plant taxa for Europe and associated standard errors, published in Marquer et al. (2017). This is part of the results from the Swedish project LandClim I (Gaillard et al., 2010; Trondman et al., 2015; Marquer et al., 2014, 2017). The study area includes a large part of northern and Central Europe, i.e. Ireland, Great Britain and a latitudinal transect from the Alps in the south to northernmost Norway. These REVEALS estimates are based on 151 pollen records (small/large, lakes/bogs/mires) that were selected from the European Pollen Database (Fyfe et al., 2009; Giesecke et al., 2014), the Alpine Palynological Data-Base (University of Bern, Switzerland), or were provided directly by individual data contributors. The selected pollen records are grouped into 36 1° x 1° grid-cells. Twenty-five consecutive time windows over the last 11,700 years BP are used: 0-100, 100-350, 350-700 BP for the three first time windows, and 500 calendar years each from 700 to 11,700 BP. For details about the REVEALS model, see Sugita (2007). In the excel file, the folder "Metadata" contains the explanation of abbreviations in the data folders and information about the pollen records used for the REVEALS reconstructions. All REVEALS estimates and their SEs are given in proportions of the grid cell (the total of all REVEALS estimates sum up to 1). The codes of the 25 consecutive time windows are given in the folder "Code time windows". The results of the 36 grid cells are in the folder "REVEALS 36GCs" and the related standard errors in the folder "SE_REVEALS 36GCs". Note that in the folder "Metadata", the GPS coordinates correspond to the upper left (NW) corners of each grid cell.