Vojtěch Abraham

The origin of grasslands in the temperate forest zone of east-central Europe: long-term legacy of climate and human impact

The post-glacial fate of central European grasslands has stimulated palaeoecological debates for a century. Some argued for the continuous survival of open land, while others claimed that closed forest had developed during the Middle Holocene. The reasons behind stability or changes in the proportion of open land are also unclear. We aim to reconstruct regional vegetation openness and test the effects of climate and human impact on vegetation change throughout the Holocene. We present a newly dated pollen record from north-western fringes of the Pannonian Plain, east-central Europe, and reconstruct Holocene regional vegetation development by the REVEALS model for 27 pollen-equivalent taxa. Estimated vegetation is correlated in the same area with a human activity model based on all available archaeological information and a macrophysical climate model. The palaeovegetation record indicates the continuous presence of open land throughout the Holocene. Grasslands and open woodlands were probably maintained by local arid climatic conditions during the early Holocene delaying the spread of deciduous (oak) forests. Significantly detectable human-made landscape transformation started only after 2000 BC. Our analyses suggest that Neolithic people spread into a landscape that was already open. Humans probably contributed to the spread of oak, and influenced the dynamics of hazel and hornbeam.

Present-Day Vegetation Helps Quantifying Past Land Cover in Selected Regions of the Czech Republic

The REVEALS model is a tool for recalculating pollen data into vegetation abundances on a regional scale. We explored the general effect of selected parameters by performing simulations and ascertained the best model setting for the Czech Republic using the shallowest samples from 120 fossil sites and data on actual regional vegetation (60 km radius). Vegetation proportions of 17 taxa were obtained by combining the CORINE Land Cover map with forest inventories, agricultural statistics and habitat mapping data. Our simulation shows that changing the site radius for all taxa substantially affects REVEALS estimates of taxa with heavy or light pollen grains. Decreasing the site radius has a similar effect as increasing the wind speed parameter. However, adjusting the site radius to 1 m for local taxa only (even taxa with light pollen) yields lower, more correct estimates despite their high pollen signal. Increasing the background radius does not affect the estimates significantly. Our comparison of estimates with actual vegetation in seven regions shows that the most accurate relative pollen productivity estimates (PPEs) come from Central Europe and Southern Sweden. The initial simulation and pollen data yielded unrealistic estimates for Abies under the default setting of the wind speed parameter (3 m/s). We therefore propose the setting of 4 m/s, which corresponds to the spring average in most regions of the Czech Republic studied. Ad hoc adjustment of PPEs with this setting improves the match 3–4-fold. We consider these values (apart from four exceptions) to be appropriate, because they are within the ranges of standard errors, so they are related to original PPEs. Setting a 1 m radius for local taxa (Alnus, Salix, Poaceae) significantly improves the match between estimates and actual vegetation. However, further adjustments to PPEs exceed the ranges of original values, so their relevance is uncertain.

Middle- and upper-Holocene woodland history in central Moravia (Czech Republic) reveals biases of pollen and anthracological analysis

The aims of this article are, first, to investigate the middle- and upper-Holocene woodland history along the altitudinal gradient between the lowlands and uplands of Central Europe (190–550 m a.s.l.) and, second, to outline possible biases inherent in the charcoal record based on a comparison with the pollen record and its known biases. Our anthracological data set contains 42,547 determinations made in 120 charcoal samples taken at 69 sites. The lowest elevated part of the study region (below 200 m a.s.l.) is characterized by the long-term presence of a species-rich hardwood forest (mixed oak–elm–ash forest). Quercus charcoals dominated in the rest of the altitude zones during the Neolithic and Aeneolithic; however, shrub charcoals appearing in samples from areas with chernozem soils (generally up to 230 m a.s.l.) indicate open-canopy oak woodlands. The species composition differed along the altitudinal gradient during the Bronze Age period, when Carpinus, Fagus and Abies expanded to altitudes above 230 m a.s.l., while Fagus was more abundant above 290 m a.s.l. Broadleaved trees (Quercus, Fraxinus, Ulmus, Acer and Carpinus) and shrubs are generally more represented in charcoals than pollen. Since broadleaved trees are usually nutrient demanding and able to re-grow easily after being felled, we suppose that their charcoal record is influenced by two main factors: bias of the initial location of the archaeological site and bias caused by long-term human influence on forest vegetation in the vicinity of settlements. These results underline that combining charcoal and pollen analysis has great potential for studying phenomena in cultural landscapes, as each of the methods approaches nature from the opposite side of the human–nature gradient.

History of Czech Vegetation Since the Late Pleistocene

A long-term perspective is a crucial dimension for understanding the present-day composition and structure of the Czech flora and vegetation. We outline processes that were important for the development of the present-day diversity of flora and vegetation including extinctions of taxa and ecological mechanisms operating within glacial-interglacial cycles. Further, we present the history of vegetation during the key stages in the glacial and postglacial periods. First, we outline the pattern in the vegetation during the last glacial, including a discussion of the existence of refugia for trees. We further describe the changes in vegetation during the Late Glacial, which were mostly the results of abrupt climatic events. We also present a new synthesis of the Holocene regional development in vegetation based on a Landscape Reconstruction Algorithm, which results in different regional vegetation trajectories and three main phases in the development of vegetation. Finally, we give some examples of the histories of local vegetation at several sites mainly based on plant macrofossils.