A Place for the Heathlands

The vegetation development in Thy appears to be unique both in the Danish and the northwest European context. As early as the middle of the Neolithic, large, open, grass-dominated landscapes began to form. By the transition to the Bronze Age, forests and trees were sparse.^{1 ( 1 )}
Bech et al. 2018; Søgaard et al. 2018 This stands in contrast to most other regions in Denmark, where open cultural landscapes only emerged during the second half of the Bronze Age.^{2 ( 2 )}
Allentoft et al. 2022 In contrast, the heathland landscape in western Jutland developed earlier and more synchronously with the cultural landscape in Thy. Archaeological evidence suggests that wood was a limited resource in Thy. For instance, the numerous barrows in the region rarely contained oak coffins; instead, stone cists were common. Peat was widely used as fuel for cremation, heating, and cooking, while driftwood, bog oak, alder, and willow were occasionally used in house construction.^{3 ( 3 )}
Olsen et al. 1996, Malmros 2018

Pollen analysis has thoroughly documented the vegetation development in Thy. Long pollen sequences from lakes and bogs,^{4 ( 4 )}
Liversage and Robinson 1995, Andersen 1992 and 1993ab, Søgaard et al. 2018 burial monuments and cultural layers,^{5 ( 5 )}
Andersen 1997, 2018, Liversage and Robinson 1995 and smaller wetland deposits near settlements^{6 ( 6 )}
Søgaard et al. 2018, Mortensen et al. 2019 have all contributed to this knowledge. Furthermore, pollen data can now be used in quantitative landscape analyses through the application of landscape reconstruction algorithms (LRA).^{7 ( 7 )}
Sugita 2007 A new reconstruction based on pollen data from Lake Ove (Ovesø, Fig. 1) reveals the land coverage of the most common plant species and vegetation types within a 20–25 km radius (Fig. 2).^{8 ( 8 )}
Kristiansen et al. 2020 This provides a robust foundation for understanding vegetation development both on a regional scale and in more localized contexts, such as settlements, fields, or barrows. The following sections explore this development throughout prehistory, with a particular focus on the formation of the Bronze Age grazing landscape in Thy.

The vegetation development during the Mesolithic in Thy broadly mirrors trends seen across the rest of Denmark.^{9 ( 9 )}
Jessen et al. 2014, Rasmussen and Bradshaw 2005 However, compared to eastern Denmark, where forests developed dense, shaded canopies, the forests in sandier regions such as west Jutland and Thy were notably more open.^{10 ( 10 )}
Nielsen and Buchwald 2010 In these areas, the forest’s open character allowed an undergrowth of grasses, heather, and herbs to thrive.^{11 ( 11 )}
Fritzbøger and Odgaard 2010

The early agricultural practices of the Funnel Beaker culture had a pronounced impact on forest composition in eastern Denmark. Continuous clearing and burning of forests created arable land and, crucially, grazing areas for cattle.^{12 ( 12 )}
Allentoft et al. 2022 In Thy, there are also signs of burning and the formation of coppiced or grazing forests;^{13 ( 13 )}
Andersen 1993a however, this agricultural strategy is less apparent compared to eastern Denmark. One possible explanation is that Thy was already relatively open, providing ample natural grazing opportunities for the incoming farmers’ cattle.

A significant shift occurred during the Single Grave culture around 2800 BCE, when a new population with a subsistence economy heavily reliant on cattle farming migrated into the region.^{14 ( 14 )}
Allentoft et al. 2022 Grazing pressure and deforestation intensified, leading to the reduction of forest cover from approximately 60% to just 30% within a few centuries. This included deforestation both on dry soils and alder forests in wetter areas, resulting in the creation of extensive open grassland and meadows.^{15 ( 15 )}
Kristiansen et al. 2020 The newcomers, who originated from the steppe regions north of the Black Sea, appear to have recreated the open steppe environment familiar to them.^{16 ( 16 )}
Kristiansen et al. 2017

This transformation in vegetation parallels the development of the heathlands in southwest Jutland, which also emerged during this period due to extensive deforestation.^{17 ( 17 )}
Odgaard 1994, Haak et al. 2023 However, while nutrient-poor and leached soils in southwest Jutland gave rise to heathland landscapes, Thy’s more fertile soils allowed for the establishment of grass-dominated landscapes. Despite the intensity of deforestation during the Single Grave culture, forests did not vanish entirely. Both natural and coppiced woodlands persisted throughout the Late Neolithic, although they eventually disappeared during the Bronze Age.

The regional reconstruction reveals that extensive deforestation persisted throughout the Bronze Age. Landscape modelling based on pollen data from Lake Ove indicates that Thy had become significantly forest-poor by the Early Bronze Age, with only 10% forest cover remaining. The oldest barrows (Bronze Age Period II)^{18 ( 18 )}
Visby and Bjergene 1&2 were situated in coppiced forests with moderate grazing pressure. In contrast, younger barrows (Period III) were primarily located in more open, treeless landscapes subjected to higher grazing pressure.^{19 ( 19 )}
Andersen 1997 This period also marks the maximum spread of grassland and grazing indicators, as shown in the pollen record from Ovesø (Fig. 2).

The densely populated Bronze Age settlements in Thy, illustrated in Fig. 3, align with this grassland expansion. The peak settlement intensity coincides directly with the peak spread of grassland.^{20 ( 20 )}
Bech 2018a, Bech et al. 2018 However, during Period III, a significant transformation begins: the heathland that had gradually emerged earlier in the Bronze Age becomes a much more pronounced landscape feature, replacing much of the grassland. This shift is likely the result of intense grazing pressure and ongoing nutrient leaching. Evidence of this development can be seen in regional pollen diagrams from Hassinghuse Mose, Ovesø, and Bjerre Sø, as well as several local reconstructions.

Interestingly, the large-scale construction of Bronze Age barrows may have played a central role in this ecological shift. The construction of these barrows, made using turf stripped from dryland soils, required vast amounts of grass turf. Thy is notable for having one of the highest densities of Bronze Age barrows in Europe, with at least 4,000 registered.^{21 ( 21 )}
Kristiansen 2018 Most were built or expanded between 1500 and 1100 BCE, and their construction likely affected an area of 90–100 km².

The combination of heavy grazing, increased population pressure, and large-scale turf removal for barrow construction created dramatic landscape changes. These cumulative impacts have been described as a self-inflicted ecological disaster, fundamentally altering Thy’s natural environment.^{22 ( 22 )}
Kristiansen 2018, Bech and Kristiansen 2018

Evidence of soil depletion, podsolization, and heathland formation during the Bronze Age is to be found not only in vegetation reconstructions, but also in archaeological excavations. In 2008, Museum Thy excavated a barrow in South Thy (FF 110605–58), constructed during Early Bronze Age Period III (1300–1100 BCE),^{23 ( 23 )}
Reiter et al. 2021 corresponding to the peak grassland spread in Thy. The barrow was built on yellowish sandy moraine clay soil that showed no initial podsolization. Pollen analysis indicated that the turf used to construct the barrow was taken from a semi-dry grazing meadow.^{24 ( 24 )}
Enevold 2010

Analysis of the old topsoil beneath the barrow revealed just 0.2% heather pollen, suggesting it was built in an area of scrub forest that had previously been cultivated. Later, during Bronze Age Period IV or V (1100–700 BCE), two ritual sites with associated stone structures were established outside the barrow, a pattern seen at other barrows in Thy.^{25 ( 25 )}
Nielsen & Bech 2004 Figures 4a and 4b illustrate one of these ritual sites, showing clear evidence of podsolization caused by soil leaching and that the formation of heathland postdated the barrow’s construction and the establishment of the ritual sites.

From the Early Bronze Age, sandy and coastal lowland soils were gradually incorporated into cultivation, likely due to a shortage of arable land in the moraine areas.^{26 ( 26 )}
Liversage and Robinson 1995, Bech 2018 Although nutrient-poor, these fields were easy to work, and the high groundwater table supported crops during dry periods.^{27 ( 27 )}
Henriksen et al. 2018 However, this advantage became a challenge after 800 BCE, as the climate became wetter and colder. The high groundwater levels rendered the lowland fields waterlogged, leading to their eventual abandonment as arable land.

The local vegetation development after the Bronze Age is less well documented compared to earlier periods. However, certain studies, such as those conducted in Østerild in North Thy, provide valuable insights. These studies show how the landscape on the raised seabed evolved following a rise in groundwater levels.^{28 ( 28 )}
Mortensen et al. 2019 In this area, fields became overgrown with peat formations, yet pollen analyses indicate that the land was not abandoned but instead repurposed for grazing. Interestingly, grass – not heath – became the dominant landscape element.

The open grazing landscapes that still define parts of Thy today have a remarkably long continuity, tracing back to the Stone Age. It was only with the establishment of extensive plantations to combat sand drift – an issue that particularly affected Thy during the sixteenth to eighteenth centuries – that forests were reintroduced to the region.

The development of Thy’s landscapes reflects a complex interplay between human activity and environmental change, creating a regionally unique history of vegetation and land use. From the open grazing landscapes of the Neolithic to the grass-dominated expanses of the Bronze Age and the subsequent formation of heathlands, Thy’s environment was shaped by intensive deforestation, grazing pressures, and cultural practices like barrow building. These changes were driven by population growth, evolving agricultural strategies, and ecological challenges that included soil depletion and climatic shifts. Despite these transformations, the open landscapes of Thy, which have roots in the early prehistoric periods, endured through the Iron Age and Viking Age, leaving a legacy that persists in the region’s character today. This long-term perspective on human–environment interaction highlights the delicate balance between cultural innovation and ecological sustainability, offering valuable insights for understanding past and present land-use strategies.