The transformation of the forest steppe in the lower Danube Plain of southeastern Europe: 6000 years of vegetation and land use dynamics

Abstract

Abstract. Forest steppes are dynamic ecosystems, highly susceptible to changes in climate, disturbances and land use. Here we examine the Holocene history of the European forest steppe ecotone in the lower Danube Plain to better understand its sensitivity to climate fluctuations, fire and human impact, and the timing of its transition into a cultural forest steppe. We used multi-proxy analyses (pollen, n-alkanes, coprophilous fungi, charcoal and geochemistry) of a 6000-year sequence from Lake Oltina (southeastern Romania) combined with a REVEALS (Regional Estimates of Vegetation Abundance from Large Sites) model of quantitative vegetation cover. We found a greater tree cover, composed of xerothermic (Carpinus orientalis and Quercus) and temperate (Carpinus betulus, Tilia, Ulmus and Fraxinus) tree taxa, between 6000 and 2500 cal yr BP. Maximum tree cover ( ∼ 50 %), dominated by C. orientalis occurred between 4200 and 2500 cal yr BP at a time of wetter climatic conditions and moderate fire activity. Compared to other European forest steppe areas, the dominance of C. orientalis represents the most distinct feature of the woodland's composition at this time. Tree loss was underway by 2500 yr BP (Iron Age), with the REVEALS model indicating a fall to ∼ 20 % tree cover from the Late Holocene forest maximum, linked to clearance for agriculture, while climate conditions remained wet. Biomass burning increased markedly at 2500 cal yr BP, suggesting that fire was regularly used as a management tool until 1000 cal yr BP when woody vegetation became scarce. A sparse tree cover, with only weak signs of forest recovery, then became a permanent characteristic of the lower Danube Plain, highlighting more or less continuous anthropogenic pressure. The timing of anthropogenic ecosystem transformation here (2500 cal yr BP) falls between that in central-eastern (between 3700 and 3000 cal yr BP) and eastern (after 2000 cal yr BP) Europe. Our study is the first quantitative land cover estimate at the forest steppe ecotone in southeastern Europe spanning 6000 years. It provides critical empirical evidence that, at a broad spatial scale, the present-day forest steppe and woodlands reflect the potential natural vegetation in this region under current climate conditions. However, the extent of tree cover and its composition have been neither stable in time nor shaped solely by the climate. Consequently, vegetation change must be seen as dynamic and reflecting wider changes in environmental conditions including natural disturbances and human impact.

Millennial scale perspective on biodiversity conservation of the forest-steppe ecotone in Europe

“…Also, the forest-steppe ecotone was transformed by land use. While Neolithic to Iron age cultures reduced the forest cover of the ecotone somewhat, the transformation to a largely open agrarian landscape occurred only between 500 BCE in the Lower Danube region (Feurdean et al 2021) and the 17th century in the Kungur forest-steppe (Shumilovskikh et al 2019b(Shumilovskikh et al , 2021. In eastern Europe, this deforestation likely shifted the ecotone to the North and West so that areas that are currently mapped as forest-steppe were forest-covered before extensive land-use started (Shumilovskikh et al 2018).…”

Long-term ecology and conservation of the Kungur forest-steppe (pre-Urals, Russia): case study Spasskaya Gora

“…In comparison, the pollen record Chernaya from a peat bog Paltinskoe located in a hemiboreal forest around 100 km NW of Spasskaya Gora shows that NAP values vary between 1 and 27% during the late Holocene (Shumilovskikh et al 2020a). Pollen records from the East European forest -steppe (Shumilovskikh et al 2018;Feurdean et al 2021) show variation of AP values between 10 and 75% since the Middle Holocene, indicating that Spasskaya Gora was covered by forests rather than typical forest-steppe. Heterogenous local topography and presence of dry soil conditions due to underlying gypsum at Spasskaya Gora might have led to a formation of herb-rich deciduous forests on upland areas, suggested by presence of Greyzemic Phaeozems.…”

“…Although Cerealia-type includes a range of wild species producing large pollen grains (Beug 2004), values of ~ 1% together with increased charcoal likely indicate the presence of slash-and-burn agriculture in the vicinity of the lake. Applying low PPE of Cerealiatype estimated for forest-steppe regions (Grindean et al 2019) results in large cropland cover by REVEALS reconstructions (Feurdean et al 2021). In general, strong anthropogenic deforestation and transformation to cropland are known from the Central and East European forest-steppe in the Early Iron Age (Shumilovskikh et al 2018;Feurdean et al 2021).…”

“…Applying low PPE of Cerealiatype estimated for forest-steppe regions (Grindean et al 2019) results in large cropland cover by REVEALS reconstructions (Feurdean et al 2021). In general, strong anthropogenic deforestation and transformation to cropland are known from the Central and East European forest-steppe in the Early Iron Age (Shumilovskikh et al 2018;Feurdean et al 2021).…”

Holocene palaeoenvironmental conditions in NE Bulgaria uncovered by mineral magnetic and paleomagnetic records of an alluvial soil

“…The Balkans represent a central root for the Neolithic spread, which had started at about 9000 y BP from Anatolia to Southern Europe (Greece) towards central and western Europe (Bogucki, 1996;Weninger et al, 2009;Fort, 2015). On the other hand, anthropogenic forcing on the environment is evident in SE Europe since the beginning of forest clearance about 2500 y BP (Feurdean et al, 2021). This continuing humanenvironment interaction resulted in significant anthropogenically induced rise in greenhouse gas emissions and related warming (Ruddiman et al, 2016).…”