Jiří Sádlo

Mid-Holocene bottleneck for central European dry grasslands: Did steppe survive the forest optimum in northern Bohemia, Czech Republic?

Revisiting the classical Gradmann’s ‘steppe theory’ for central Europe, we examine whether the early Holocene steppe habitats survived the critical period of maximum Holocene afforestation: the mid-Holocene bottleneck. Despite the undisputable fact that afforestation was a dominant ecological factor in this period, our parallel analyses of pollen and molluscs from sedimentary sequences discovered in the dry lowland area of northern Bohemia, Czech Republic (Zahájí and Suchý potok sites, lower Ohře area) provide strong evidence for uninterrupted local occurrence of steppe grasslands throughout the Holocene. At the onset of the Neolithic agriculture, this area was covered by forest-steppe. Analogously to the present forest-steppe landscapes of eastern Europe and south-western Siberia, dry areas of northern Bohemia were dominated by open-canopy pine–birch forests that enabled continuous survival of many light-demanding plant species from the late Glacial and early Holocene to the Neolithic. Later on, anthropogenic deforestation and livestock grazing created a semi-natural steppe. Our data suggest that this secondary steppe can be viewed as a direct continuation of the late Pleistocene and early Holocene natural steppe rather than a purely cultural steppe developed only after deforestation of a continuously forested mid-Holocene landscape by humans. At the same time, we provide evidence supporting Gradmann’s ‘steppe theory’, assuming that in central Europe, Neolithic farming started in those areas that were not completely forested but contained remnants of natural steppes. This finding has important implications for the interpretation of present biodiversity patterns in central Europe.

Unusual vegetation stability in a lowland pine forest area (Doksy region, Czech Republic)

Although the Holocene is characterized by prominent vegetation changes, some vegetation types can reveal surprising stability. We studied Holocene woodland history in a sandstone pseudokarst area (Doksy region, Northern Bohemia, Czech Republic). Twelve soil profiles collected under native or semi-cultural pine forests were analyzed using anthracological methods. In seven of them, the age of profile bases was established using radiocarbon dating. All analyzed samples show a high degree of mutual similarity of species composition regardless of the site or the depth of the sampled soil layer, as well as a good concordance between the composition of fossil and contemporary vegetation. Forest vegetation dominated by Pinus sylvestris with a low but regular occurrence of Picea abies, Quercus sp. and Vaccinium sp. has prevailed since late Boreal up to the present. No considerable vegetation changes were detected during this period, except for succession after fire events. A high content of charcoal within soil profiles indicates that the study area has been affected by forest fires through a substantial part of the Holocene. Recurrent wildfires probably represented a crucial factor sustaining pine forests by cyclic succession, although the relative contribution of human versus natural causes of fire cannot be assessed. In earlier phases of the Holocene, the prevalence of pine in the local vegetation was revealed using palynological data, so that we can conclude that the pine-dominated forests ecosystem existed during the entire Holocene in the study area. This pronounced vegetation stability contrasts sharply with the changeable historical vegetation of Central European lowlands.

Plant Invasions in the Czech Republic

At present there are 1454 alien taxa (species, subspecies, varieties, hybrids and cultivars) of vascular plants recorded in the Czech Republic, among them 350 archaeophytes, introduced since the beginning of the Neolithic until the end of the Middle Ages, and 1104 neophytes, introduced in the Modern Period. Of the total number, 985 (67.7%) taxa are classified as casual, 408 (28.1%) as naturalized but non-invasive and 61 (4.2%) as invasive. Aliens make up 33.1% of the total plant diversity recorded in this country, or 14.4% of the permanently present flora. The highest levels of invasion of plant communities are recorded in cities and villages and their surroundings, floodplains of large rivers, disturbed landscapes in the north, and agricultural landscapes and forest plantations in the warm lowlands, especially in southern, central and eastern Bohemia. The habitats and vegetation types harbouring the highest percentages of alien species in the Czech Republic are generally those with a high level of disturbance or with a fluctuating input of nutrients.