Late Holocene vegetation dynamics: degree and regional patterns of the Dark Ages woodland regeneration (ad 300–700) in the Netherlands

Vegetation History and Archaeobotany https://doi.org/10.1007/s00334-024-01000-z ORIGINAL ARTICLE Late Holocene vegetation dynamics: degree and regional patterns of the Dark Ages woodland regeneration (ad 300–700) in the Netherlands Marjolein T. I. J. Gouw‑Bouman1,2 Received: 20 March 2023 / Accepted: 4 July 2023 © The Author(s) 2024 Abstract During the Dark Ages, which include the Late Roman period (ad 270–450) and the Early Middle Ages (ad 450–1050), large-scale vegetation development in northwest Europe was characterised by widespread regeneration of woodlands. This regeneration phase represents a break from the extensive reduction in woodland from human activities in late Holocene vegetation history. In the Netherlands, possible causes for this reversal can be found in a decreased human impact on the landscape, a colder and possibly wetter climate, and geomorphological changes. This paper presents a synthesis from 38 pollen records from a range of sites across the Netherlands, from which regional differences in the degree of woodland regeneration and vegetation composition before and during the Dark Ages have been identified. Both original data as well as vegetation abundance modelled by REVEALS were used to assess the regrowth of the woodland cover. The observed trends were considered in terms of the landscape setting and population estimates in order to disentangle the relative importance of these forcing factors. The results indicate that landscape and human impact were the most important factors determining the vegetation structure and changes to it. The pollen data show that in the Netherlands, the clearance of woodland in the Roman period followed by its regrowth afterwards were greatest in the river area. This can be linked to a high population density there during the Roman period followed by a strong decrease of population in the Dark Ages and to increased flooding. Keywords Woodland regeneration · Roman period · Early middle ages · Palynology · Human impact · Subatlantic Introduction In northwest Europe, late Holocene vegetation composition and changes are considered to have been mainly controlled by human activities (Marquer et al. 2014). In general, this is shown by a decrease in woodland cover and an increase in cultural landscapes (Nielsen et al. 2012; Marquer et al. 2014; Githumbi et al. 2022a, b). In large parts of northwest Europe this decrease in woodland was temporarily reversed during the Late Roman period and Early Middle Ages (Teunissen 1990; Andersen and Berglund 1994; Bunnik 1999; Berglund Communicated by C. C. Bakels. * Marjolein T. I. J. Gouw‑Bouman 1 Department of Physical Geography, Utrecht University, Princetonlaan 8A, 3584 CB Utrecht, The Netherlands 2 Archeologisch Onderzoek Leiden BV (Archol), Leiden, The Netherlands 2003; Wick et al. 2003; Dreßler et al. 2006; Kalis et al. 2008; Rösch and Lechterbeck 2016). After this short phase of regeneration, there was a further rapid reduction of woodland as a result of medieval and modern clearances (Janssen 1974; Bunnik 1999; Litt et al. 2009; Whitehouse and Smith 2010; Nielsen et al. 2012; Fyfe et al. 2013; Marquer et al. 2014). In this paper, the phase of woodland regeneration or regrowth from the Late Roman period and Early Middle Ages is referred to as the Dark Ages (DA) woodland regeneration, in accordance with the overlapping Dark Ages Cold Period (DACP) of ad 250–700 (Helama et al. 2017; Riechelmann and Gouw-Bouman 2019) and the historical Dark Ages (James 1988). The Dark Ages are also referred to as the Migration Period in other parts of Europe, although this can cover a longer historical span (Halsall 2007). The DA woodland regeneration has been recognised in pollen studies from countries including Norway (Hjelle et al. 2022), Germany (Zolitschka et al. 2003; Dreßler et al. 2006; Rösch 2007; Litt et al. 2009; Rösch and Lechterbeck 2016; Gerlach et al. 2022; van der Knaap et al. 2020), Belgium Vol.:(0123456789) Vegetation History and Archaeobotany (Broothaerts et al. 2014a, b; Deforce et al. 2020), France (Etienne et al. 2013), Switzerland (Tinner et al. 2003; Wick et al. 2003), Poland (Gałka et al. 2014; Brown et al. 2019; Pędziszewska et al. 2020), Britain (Dark 2000; Forster 2010) and the Netherlands (Teunissen 1990; Bunnik 1999). In the Netherlands, this Dark Ages phase of expanding woodland is dated around ad 300–700, covering the Late Roman period (ad 270–450) and the first part of the Middle Ages (ad 450–1050) (Teunissen 1990; Bunnik 1996; Kalis et al. 2008). In spite of its widespread occurrence, little is known about the regional pattern and extent of this phase of woodland regeneration, or the role of climate, environmental and human changes as its primary causes (Fig. 1). The DA woodland regeneration directly followed a period of great change to human societies such as the collapse of the Roman Empire, which resulted in a population decline (van Es and Verwers 2010; van Beek and Groenewoudt 2011; Pierik and van Lanen 2019; Groenewoudt and van Lanen 2018; Pierik et al. 2018). Therefore, the cause of this regrowth phase is often considered to be the decreased human pressure on the landscape during this period. However, climate records also indicate a colder and wetter climate (Ljungqvist 2009; Büntgen et al. 2011, 2016; Helama et al. 2017; Gouw-Bouman et al. 2019; Riechelmann and Gouw-Bouman 2019), while geomorphological records point to a changing landscape (Vos 2015; Pierik et al. 2017a, b). How and to what extent these climatic and environmental factors contributed to the changes in the vegetation or even the decline of the Roman Empire is largely unknown. Since significant cultural, landscape and climate changes occurred simultaneously during the Late Roman period and Early Middle Ages, this period can be used to study the intricate relationship between vegetation and its influencing factors. The varied landscape and cultures of the Netherlands during the Late Roman period offer a good area to explore the influences of landscape setting and population dynamics on the DA woodland regeneration. Existing data from the Netherlands suggest that the degree of woodland regrowth and its timing varied spatially (Teunissen 1990; Bunnik 1999), which might be related either to variations in the abiotic (non living) landscape or human impact there. The aim of this study was to map the spatial pattern and differences in the degree of DA regeneration of woodland and to determine the main factors explaining these, using many Dutch pollen records from various landscape and environmental settings. Based on these available pollen records, an overview of the changes in the main vegetation structure from the Iron Age/Roman period (IA/ROM) to the Dark Ages (DA) is provided. In this study the increase in woodland in the DA and its regional patterns were investigated, using the changes in AP (Arboreal Pollen) percentages as an indication. The reconstructed changes in woodland and ov (...truncated)