Does site elevation determine the start and intensity of human impact? Pollen evidence from southern Germany

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-020-00780-4 ORIGINAL ARTICLE Does site elevation determine the start and intensity of human impact? Pollen evidence from southern Germany Manfred Rösch1 · Philipp Stojakowits2 · Arne Friedmann2 Received: 28 January 2019 / Accepted: 19 November 2019 © The Author(s) 2020 Abstract We investigated lake sediments from Großer Ursee, Landkreis Ravensburg, Allgäu, Baden-Württemberg, to explore whether human activity was delayed and less intense at higher sites compared to those in the adjacent lower area around Bodensee (Lake Constance). A 11.1 m high resolution pollen profile from the centre of the lake was analysed, which covers the late Würm and complete Holocene sequence, providing a continuous pollen record of 1,092 samples. Human and climate induced vegetation and landscape change is discussed. The history of human impact indicated in this profile at around 700 m in the western Allgäu, with a precipitation above 1,000 mm/year and with a less favourable climate is compared with human impact in adjacent lower landscapes, with a more favourable climate for agriculture such as the Bodensee region. Since the Neolithic period, differences in vegetation development between the regions were mainly caused by a varying intensity of human impact which itself was strongly influenced by climatic differences. In the lowlands with a warm and dry climate, human impact started earlier and was stronger than in less favourable areas. Finally, the regular occurrence of Trapa natans at Großer Ursee, much more frequent there than in the adjacent warmer landscape to the west, is discussed in terms of various ecological factors. Keywords High-resolution pollen analysis · Human impact · Climatic impact · Alpine foreland · Allgäu · Bodensee (Lake Constance) · Trapa natans Introduction The success of agriculture depends on soil quality and climatic conditions. The present day climatic range of crop cultivation is broader than in the past, a consequence of progress in agricultural technology and plant breeding (Flint 2015). The climatic range of agriculture in the past is estimated to have been within a mean annual ground Communicated by T. Giesecke. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00334-020-00780-4) contains supplementary material, which is available to authorized users. * Manfred Rösch 1 Institut für Ur‑ und Frühgeschichte Und Vorderasiatische Archäologie, Universität Heidelberg, Sandgasse 7, 69117 Heidelberg, Germany 2 Institut für Geographie, Universität Augsburg, Alter Postweg 118, 86135 Augsburg, Germany surface temperature range of 7–20 °C and a total annual precipitation of 400–1,000 mm. The required precipitation depends on the temperature, the higher the temperature, the higher the required precipitation. Agriculture has its optimal conditions when the precipitation is totally consumed by evaporation and plant transpiration, and there is no runoff, because runoff means loss of plant nutrients (Wright 1977). Focusing on temperate Europe, the landscapes best suited for agriculture are the loess-covered plain in the lowlands with mean annual ground surface temperatures between 7 and 10 °C and a total annual precipitation between 450 and 650 mm. These are the landscapes which were settled since the early Neolithic and with strong human impact in all periods (Preuß 2008). The low mountain ranges of central Europe, the lowlands of northern central Europe, as well as the pre-alpine lowlands have a wetter and cooler climate than the lowlands of the loess belt. The question is, if this last area was settled later and also less intensely for most of the time as the archaeological record suggests (for example, Engelhardt 2006; Nadler 2006), what were the climatic limits for agriculture in the past? For this, high resolution 13 Vol.:(0123456789) Vegetation History and Archaeobotany pollen evidence can be more meaningful than archaeological evidence, which is restricted by the state of the art. We focus on a site where there is hardly any archaeological evidence older than the medieval period, where its suitability for agriculture is questionable, and which is not cultivated now. Because no prehistoric lake shore settlements were known in the eastern part of the Rhine glacier region with an annual precipitation above 1,000 mm, it was thought that prehistoric farmers were not able to colonize and cultivate these regions of eastern Oberschwaben and Allgäu, which today have no arable farming, but only animal husbandry. A high-resolution lake pollen profile from Großer Ursee, Landkreis Ravensburg, situated in this wet climatic region, should, in comparison with profiles from the dryer landscapes, answer this question. The aim was to provide a high resolution standard pollen record of the vegetation history and human impact in the western part of the Allgäu where such data have been scarce up to now, compared to adjacent areas to the east and west. Another aim was to compare this site and its evidence for human impact with the nearby region to the west, which is better suited for agriculture and where archaeological evidence for strong human occupation goes back to the later Neolithic (ca. 4300–3500 bc), the western Bodensee area. To the east part of the Allgäu, in Bayern (Bavaria), close to the Alps is also discussed (Fig. 1). Geographical setting The Rhine glacier covered an area of about 10,000 km2 outside the Alps at the time of its maximum extension in the Würm period (Keller and Krayss 1993, 2005), which is today represented by the regions Ostschweizer Mittelland in eastern Switzerland and Oberschwaben in southwestern Germany, with Bodensee (Lake Constance) in the centre. The glacier formed its terminal moraines close to the Adelegg hills, which consist of molasse conglomerate, and close to the Iller glacier in the east. This area is also part of the European main watershed between the rivers Rhine and Danube (Scholz 2016) and there is a group of lakes and bogs here, the south-easternmost of which is Großer Ursee (10° 01′32″ E, 47° 45′ 10″ N). It covers 20 ha, with a maximum water depth of 10 m (Fig. 1). Its watershed is at 695 m a.s.l., but in contrast, the sites around Bodensee are at between 395 and 450 m. Seven km to the southeast of Großer Ursee, the Adelegg hills reach an altitude of more than 1,100 m. The temperatures in the Allgäu are not only lower than at Bodensee, but the precipitation is also much higher, as the Allgäuer Alpen and Bregenzer Wald cause increasing precipitation to the east. Because of the unfavourable climatic conditions of the Allgäu, the only form of farming there today is stock grazing. The potential natural vegetation there is considered 13 to be Fagus (beech) woods with Abies (fir) and some Picea (spruce), but the woodlands would mainly consist of Abies in some places (Müller et al. 1974). For soils, eutric cambisols cover (...truncated)