The evolution of heathlands during the Holocene has been registered in various soil records. Paleoecological analyses of these records enable reconstruction of the changing economic and cultural management of heaths and the consequences for landscape and soils.
Heaths are characteristic components of cultural landscape mosaics on sandy soils in the Netherlands. The natural habitat of heather species was moorland. At first, natural events like forest fires and storms caused small-scale forest degradation; in addition on that, the forest degradation accelerated due to cultural activities like forest grazing, wood cutting, and shifting cultivation. Heather plants invaded degraded forest soils, and heaths developed. People learned to use the heaths for economic and cultural purposes. The impact of the heath management on landscape and soils was registered in soil records of barrows, drift sand sequences, and plaggic Anthrosols. Based on pollen diagrams of such records we could reconstruct that heaths were developed and used for cattle grazing before the Bronze Age. During the late Neolithic, the Bronze Age, and Iron Age, people created the barrow landscape on the ancestral heaths. After the Iron Age, people probably continued with cattle grazing on the heaths and plaggic agriculture until the early Middle Ages. Severe forest degradation by the production of charcoal for melting iron during the Iron Age till the 6th–7th century and during the 11th–13th century for the trade of wood resulted in extensive sand drifting, a threat to the valuable heaths. The introduction of the deep, stable economy and heath sods digging in the course of the 18th century resulted in acceleration of the rise of plaggic horizons, severe heath degradation, and again extension of sand drifting. At the end of the 19th century heath lost its economic value due to the introduction of chemical fertilizers. The heaths were transformed into “new” arable fields and forests, and due to deep ploughing most soil archives were destroyed. Since AD 1980, the remaining relicts of the ancestral heaths are preserved and restored in the frame of the programs to improve the regional and national geo-biodiversity. Despite the realization of many heath restoration projects during the last decades, the area of the present heaths is just a fraction of the heath areal in AD 1900.
Heaths are characteristic biotopes in northwestern Europe. Most
of the heaths in the study area occur on Late Glacial cover sand and Holocene
drift sand deposits. The current biodiversity management regards dry and
moist heaths as region-specific ecotopes that need to be preserved and
protected (LNV, 2001, 2006).
Two factors are crucial for the survival of heaths on chemical poor sandy
substrates (Weeda et al., 1988).
Heath plants live in symbiosis with ericoid mycorrhiza. These
organisms provide the heath plants with nitrogen that is hardly available for
other plants, which live without this form of symbiosis. Heath plants have specific adaptations to drought stress. Leaves will
stop evaporation of water under dry or warm air conditions but can evaporate
large amounts of water under humid air conditions. These adaptations enable
heath plants to enhance nutrient uptake from soil water with low nutrient
concentrations. In this way heath plants are able to concentrate the
sufficient amount of nutrients necessary for plant growth from soil water
that contains low nutrient concentrations.
Moors on poorly drained soils formed the natural habitats for heath plants.
The Holocene vegetation development and soil formation on cover sands started
without significant human interference. At that time, the soilscape was in
accordance with the geomorphological structure: xeromorphic podzols on cover
sand ridges, gleyic podzols on cover sand planes, and histic podzols in brook
valleys. During the early Holocene, natural events such as forest fires and
storms caused small-scale forest degradation and created habitats outside the
bogs where heath could develop. It was long thought that this situation
continued until the late Neolithic, but now there are reasons to believe that
the activities of pre-agricultural communities from before
Several other comprehensive studies, based on soil archives, have been
performed to explore the causes of Holocene sand drifting in the areas
Drenthe (Riksen et al., 2006; Castel, 1991), Veluwe (Koster, 1978), and the
SE Netherlands (van Mourik et al., 2012a, b). In the pollen diagrams
presented in these studies,
From the late Neolithic onwards, the effect of human land use on soil and landscape increased. The deciduous forest gradually degraded by some woodcutting, forest grazing, and shifting cultivation (van Mourik et al., 2012a, b), and the heaths that were already present in the area could expand. Most probably, the valuable common heaths on aeolian sandy soils were sustainably managed by the community (de Keyzer, 2014). However, periods of severe forest degradation and sand drifting threatened the survival of the heaths. Since the early Iron Age, forest degradation was triggered by the use of oak trees for the production of charcoal to melt iron from bog iron ore, rattle stones, and plaggic horizons (Laban et al., 1988). The production of iron resulted in extensive sand drifting in the Veluwe region from the Iron Age until the 6th–7th century (Beukenkamp and Sevink, 2005). During the 11th–13th century the clear cutting of forests for the sale of wood resulted in extensive sand drifting in the SE Netherlands (van Mourik et al., 2012a, b; Vera, 2011). In the course of the 18th century, the deep, stable economy and digging of heath sods were introduced. On the one hand, this accelerated the rise of plaggic horizons; on the other hand, heaths degraded severely and sand drifting extended again.
Nowadays, many moist and dry heath areas in the Netherlands are protected, as they form part of national and (pan-)European ecological networks (LNV, 2001, 2006; Jongman et al., 2011). In order to preserve the heath areas, future sustainable heath management must be based on knowledge on the origin of heath biotopes and the role of heaths in historical land use systems (Smits and Noordijk, 2013).
Information about historical land management on cover sands can be unlocked from soil archives. In the course of the 20th century, the majority of the heaths were transformed into arable land and forest plantations. Soils were deeply ploughed, and soil archives were severely damaged or even destroyed (Fig. 1).
As a consequence the total heath area in the Netherlands decreased from
600 000 to 30 000
Destruction of soil archives on the Maashorst (North Brabant) during the transition of (former) heaths into modern arable fields. Left: undisturbed gleyic podzol; right: deeply ploughed podzol.
The aim of this paper is to reconstruct the impact of ancestral heath
management on the development of soils (podzols, Arenosols, and plaggic
Anthrosols) and landforms (barrows, drift sand covers, and dunes) based on
previously published research cases. Key sites that were used for this paper
include recently investigated barrow paleosols (Doorenbosch, 2013) and a
cross section through an inland dune ridge (van Mourik et al., 2012a). These
sites will be described and discussed in detail in the following sections.
The soil records from the barrow landscapes cover the period between
Barrows, mounds underneath or in which prehistoric humans buried the dead,
were built from
Heath area in the Netherlands around AD 1850 and the diminution of heaths between 1833 and 2008. The locations of the four research sites are indicated: VN – Vaassen–Niersen; R – Renkum stream valley; E – Echoput; BB – Bedafse Bergen.
Many of these burial mounds have been excavated and sampled for pollen analysis to reconstruct the barrow environment (Fig. 3). To reconstruct environmental development, pollen spectra of samples from the mounds are less valuable, but spectra of samples of the buried podzols underneath a barrow, with the pre-barrow land surface on top, are opportune with the restriction of the regular complications of soil pollen spectra (van Mourik, 2001). Pollen grains precipitate onto the land surface and infiltrate by bioturbation into the soil profile and reach the A, E, B, and even the C horizons. Soil acidification, a regular development during the Holocene in sandy substrates, caused retrogressive activity during acidic soil formation. Hence, older pollen assemblages will be preserved in the lower parts of the soil (van Mourik, 1999, 2001). When the soil was buried during the construction of the barrow, the active soil processes stopped and the soil record was conserved. The pollen grains incorporated into the paleosol before and during the time that barrow was built are in many cases still present today.
Soil record of a barrow showing a paleosol buried by a barrow, built with sods, dug in heathlands in the surroundings. Photograph by Q. Bourgeois.
A barrow is usually constructed of sods. These sods were taken from the upper part of the soil in the surroundings and placed upside down when building the barrow. Sods contain parts of the soil record from the place where they were taken, including pollen grains. Pollen spectra of the constructing materials and the paleosol have been used to reconstruct the morphology of the barrow landscape (Waterbolk, 1954; Groenman-van Waateringe, 1988; Bloemers, 1988; Doorenbosch, 2013). These investigations have revealed that all studied barrows were built in heath vegetation that has been kept in existence mainly by human activities for several millennia, before, during, and after the barrows were constructed. The management of heath will be further specified in the following paragraphs of this article.
For this paper we used the cases of the Renkum stream valley, Vaassen–Niersen, and
Echoput, previously published in Doorenbosch (2013), to demonstrate heath
management of the barrow landscape between
Pollen records of paleosols in barrow landscapes, buried podzols, and Anthrosols provide paleoecological information on plant species present on site and in the region during the formation of the barrows, drift sand deposits, and plaggic horizons. Previous research has shown that pollen grains that infiltrated soils and were incorporated into plaggic deposits are well preserved in the anaerobic and acidic microenvironment of excremental aggregates (van Mourik, 1999, 2001).
Samples for pollen extraction were collected in 10 mL tubes in profile pits.
Pollen extractions were carried out using 10 % potassium hydroxide (KOH),
10 % hydrochloric acid (HCl), bromoform–ethanol (specific
gravity
In a stream valley near Renkum (for the location see Fig. 2) an alignment of
barrows is situated with a length of at least 4.5
Pollen spectra from the samples taken from the barrows of the Renkum alignment.
Figure 4 shows the pollen spectra from the barrows of the alignment in the
Renkum stream valley. In the Neolithic A period Ericales pollen form a
considerable part of the pollen spectra. Heath pollen tends to spread mostly
within a few meters from the place where the heath is growing and pollen is
produced (de Kort, 2002). This implies that the considerable percentage of
heath pollen indicates that all investigated barrows in the area were
constructed in an open space with vegetation where heath was an important
component. In addition to heath, grasses also formed part of the vegetation in
the open places. Arboreal pollen percentages fluctuate between barrows from
around 45 to around 75 %, indicating varying sizes of the open spaces the
barrows were situated in. Based on research that was performed in recent
heath areas with varying distances to the forest, such arboreal pollen
percentages indicate that the open spaces had an average distance to the
forest of 30–250
Barrow alignments of Renkum, situated in a (hypothetical)
long-stretched heath area surrounded by forest. The vegetation reconstruction
is based on palynological data from barrows. An exact reconstruction of the
forest area is therefore not possible (indicated by the question mark), since
barrows are not present in those areas. The figure is based on the digital
elevation model of the AHN
(©
Besides the barrows that have been palynologically investigated in this area,
palynological data from many other barrows in the Pleistocene cover sand
areas in the Netherlands are known (see Sects. 3.2, 3.3; see also
Doorenbosch, 2013). These data show that these barrows were also built in
heaths. Only a fraction of the barrows have been preserved to present
(Bourgeois, 2013, p. 40); originally the number of barrows was much higher in
the Netherlands, and only a part of these preserved barrows have been
palynologically analyzed. Considering that all investigated barrows were
built in heath vegetation, it is probable that the non-investigated barrows
in these areas were also built in open spaces where heath vegetation was
dominant. The barrows of Renkum were built in an alignment, and the distance
between the barrows is mostly less than a few hundred meters. Since the
A second example is given in Fig. 6, showing the results for several barrows
that are situated in the northeastern part of the Veluwe (for the location
see Fig. 2). In this area several barrow alignments and solitary barrows are
present. Palynological data are available for five burrows in this area. Data
were obtained from the old surfaces underneath the barrows, from sods from
several periods in which the barrows were constructed (in several cases barrows
were constructed in multiple phases: the barrow was reused for secondary
burials and new sods were added to the original barrow to cover these burials),
as well as from ditches associated with the barrows. These barrows were dated
from the late Neolithic A to the Middle Bronze Age
period (
The pollen spectra show that the barrows in this area, like the barrows in
the Renkum stream valley, were built in open places with heath vegetation,
surrounded by oak forest and alder carr in the lower parts of the area. The
open spaces were probably larger than in the Renkum stream valley, with an
ADF of around 100
Pollen spectra from samples taken from the barrows at Vaassen, the barrows at Niersen barrows, and the Celtic field at Vaassen.
Barrow alignments of Vaassen–Niersen, situated in a (hypothetical)
long-stretched heath area surrounded by forest. The vegetation reconstruction
is based on palynological data from barrows. An exact reconstruction of the
forest area is therefore not possible (indicated by the question mark), since
barrows are not present in those areas. The figure is based on the digital
elevation model of the AHN (©
The vegetation of the open space seems stable, since the barrow spectra from all represented periods show similar vegetation patterns: an open place with species-poor grassy heathland surrounded by oak forest with an alder carr nearby. Figure 7 shows the visual impact on the landscape in the area of Vaassen–Niersen, assuming all barrows were built in heath.
A third example concerns the twin barrows of the Echoput (site indicated in Fig. 2), which date to the middle or earlier late Iron Age (Bourgeois and Fontijn, 2011, p. 87; Doorenbosch, 2013; van der Linde and Fontijn, 2011, p. 62). These barrows were excavated and sampled for pollen analyses by the Faculty of Archaeology of the University of Leiden (Doorenbosch, 2011). The pollen analyses were performed by the first author of this article as part of her PhD research (Doorenbosch, 2013). From both burial mounds samples were taken from the old surface and several sods. In addition, the soil profiles underneath both barrows were sampled. Results are shown in Figs. 8, 9, and 10.
Pollen spectra from the sod and old surface samples taken from Echoput barrow 1 and 2.
Pollen diagrams derived from the series of samples taken from underneath Echoput barrow 1.
Pollen diagrams derived from the series of samples taken from underneath Echoput barrow 2.
Sequence of development phases of the Bedafse Bergen and its soil archives.
The soil archives of the Bedafse Bergen (left: Rakt; right: Bedafse
Bergen). The sample locations for OSL are indicated with rings, and for
The pollen spectra from the old surfaces and sods consist mainly of
herbaceous pollen, dominated by heather (
The “Bedafse Bergen” is a biogenic land dune ridge west of Rakt, a
historical complex of a hamlet and arable fields, surrounded by coppice. West
of the hamlet, cattle heathland was present. A plaggic Anthrosol developed on
the arable fields (Fig. 11, phase A). After AD 1000 the heaths in this
region were threatened by sand drifting due to severe forest degradation. The
degradation was caused by complete deforestation during the 11th–13th
century (Vera, 2011; van Mourik et al., 2012a, b). This deforestation
triggered the first regional extension of (older) sand drifting; aeolian
eroded sand was transported by the southwesterly winds from the heaths to
Rakt. The coppice hedge around the hamlet served as a protecting screen and
initiated the building of a ridge of inland dunes, the Bedafse Bergen
(Fig. 11, phase B). The introduction of the deep, stable economy in the 18th
century (Vera, 2011) initiated the second extension of (younger) sand
drifting (Fig. 11, phase C). At the east side of the ridge, the western edge
of the plaggic Anthrosol was buried by (younger) drift sand; at the west side
of the ridge we could excavate the podzol in cover sand, buried by older
drift sand. Both profiles were sampled for pollen analysis and OSL dating
(Tables 1, 2). The Ah of the buried podzol in the Bedafse Bergen profile was
also sampled for radiocarbon (
The pollen diagram of Rakt is shown in Fig. 13, and the pollen diagram of the Bedafse Bergen in Fig. 14.
Pollen diagram of Rakt.
Pollen diagram of the Bedafse Bergen.
OSL datings of the Rakt profile (Fig. 10, left).
Absolute dating of the Bedafse Bergen profile (Fig. 10, right).
During the transformation of heaths into new arable land and forests in the
20th century, the majority of the soil archives were destroyed. For this
reason, the soil archives of the Bedafse Bergen have a high scientific value.
The position of the sampled profile is indicated in Fig. 11c. The oldest
formation is cover sand. The post-sedimentary infiltrated pollen spectra of
the 3Ap in cover sand demonstrate that arable land was created on
The buried podzols of the Bedafse Bergen and Rakt profiles developed
originally at the same stratigraphic level in cover sand. The position of the
sampled profiles is indicated in Fig. 11c. The Bedafse Bergen podzol is
buried below 12 m high dune sand deposits. Only the basic layers of the
drift sands and the top horizons of the podzol have been sampled for pollen
analysis and dating of the basis of the older drift sand deposits. The pollen
spectra of the horizons of the buried podzol contain high percentages of
Ericaceae, pointing to the presence of heath. The relatively high percentages
of
Based on the examples given above and many other palynologically investigated
barrows (Doorenbosch, 2013), it can be concluded that barrows were built in
open spaces that varied in size from small, with an average distance to the
forest (ADF) of
The open spaces covered with heath vegetation must have been kept open until the barrows were built, and in most cases they were kept open long after the barrows had been built. To maintain the heath, the landscape must have been managed. When heath is not managed, other plant species will replace the heath vegetation. Management activities like grazing, sod cutting, and burning could have been carried out to maintain the heath vegetation. Although for the earliest heathland areas (e.g. the Laarderwasmeer area) no clear indications for heath management, such as grazing, have been found, it is assumed that the heath vegetation was maintained by anthropogenic influences.
For the late Neolithic, when the first barrows were built, indications for
heath management are clearer. Sod cutting must have taken place for the
purpose of the barrow building, but the amount of sods needed to build a
barrow is not sufficient to explain the size of the heath areas. Burning
might have been part of the heath management activities. Indications for
burning have only been found in a few cases by the recording of charcoal that
was probably not just related to the burial itself. Indications for
large-scale burning of the heath areas have not been found, however. Grazing
indicators such as grasses (Poaceae),
Archeozoological evidence from several excavations suggests that prehistoric
farming communities kept mainly sheep and cattle (Brinkkemper and
van Wijngaarden-Bakker, 2005, p. 493). In present times both sheep and cows
are used to maintain heathland areas by grazing. Young
Unfortunately, not much is known about heath and the maintenance of heath during the Roman period. The practice of barrow building was no longer continued and no soil records have been investigated that could give information on the use of heathland in the period thereafter. Some studies have been conducted, however, suggesting that heathland areas continuously existed throughout the Roman period, indicating that some form of heath management must have taken place during that time, for example at the Echoput (see Sect. 3.3). At the Echoput heath was present at and prior to the period in which the barrows were built (the late Iron Age). This heath area must have been managed for some time in order to have been maintained. At the same site several post holes have been discovered close to the barrows. The infill of these post holes, which probably date to the late Medieval Period, has been analyzed for pollen as well (Doorenbosch 2013, chap. 8.1). It was shown that at the time the posts were placed the heath had expanded compared to when the barrows were built. It cannot be said with certainty that the heath was present and maintained in the period in between the barrow building and the post placing, but it is likely that this is the case. The presence of heath during the Roman period was also shown in pollen diagrams from several paleosols, for example Venloop (Maashorst, North Brabant; van Mourik et al., 2012a) and Defensiedijk (Weert, central Limburg; van Mourik et al., 2010). In addition, the presence of heath during the Roman period is mentioned in several other studies (Bakels, 2014; Kooijstra, 2008; Kooijstra and Groot, 2015). With the continuous presence of heath vegetation it is most probable that the local population continued with extensive grazing management on the heaths until the early Middle Ages. In Twente and Drenthe (eastern Netherlands) the sustainable management of the common heaths was controlled by the so-called Marke administrative system (Spek, 2004); in the Campina (southern Netherlands) the stability of the common heaths was the common denominator of sustainable agricultural production of the smallholders and the elites (de Keyzer, 2013). Small-scale events such as storms and fires could destabilize the ecosystems for a relatively short time, but commercial interventions caused more permanent destabilization and sand drifting: the iron industry from the Iron Age till the 7th century (Beukenkamp and Sevink, 2005), the deforestations from the 11th–13th century, and the introduction of the deep, stable economy in the course of the 18th century (Vera, 2011).
In the early Middle Ages people learned to produce manure by using organic
materials such as the ectorganic horizon of deciduous forests and grass sods
from the brook valleys as stable fillings (van Mourik et al., 2016). Serious
degradation of heaths during this time is not recorded in the soil archives.
Heath management was most probably restricted to burning and mowing of older
During the 11th–13th century, landowners cut the last forests, because the prices of wood were going up (Vera, 2011). These deforestations resulted in regional extension of sand drifting (van Mourik et al., 2012a, b). To acquire fuel, farmers dug sods of the ectorganic horizon of the moist heaths (Burny, 1999), but after the removal of the ectorganic sods, the moist heaths will recover in 2–4 years, and sand drifting was not an issue. From archived documents it is known that the farmers protected the dry heaths carefully against sand drifting (Vera, 2011). But in the course of the 18th century the combination of population growth and the increase in food demand resulted in the extension of arable fields and the increase of the production of stable manure. The lack of stable fillings was compensated by the use of humic sods from the dry heaths (Vera, 2011; Burny, 1999). Mowing and burning were sustainable management rules, but sod digging caused degradation and initiated the next wave of sand drifting (van Mourik et al., 2012a, b).
At the end of the 19th century, the plaggic agriculture came to an end. Due
to the combination of the falling prices of wool and the introduction of
chemical fertilizers and urban compost, the heaths lost their economic value
and the government started with the reclamation of the heaths into new arable
fields. After the introduction of hybrid maize in AD 1950, these fields
became the base of the bio-industry (chicken,
beef, and pork). The heathlands that were damaged by sand drifting were
turned into forests, mainly Scotch pine plantations. Figure 2 shows how the
heath surface diminished from
Due to the presently increased nitrogen concentrations in rain and groundwater, heaths cannot survive without management measures to prevent an accelerated succession to brushwood and forest. Applied measures are, like in the 19th century, intensive grazing, mowing, burning and sod digging (Smits and Noordijk, 2013).
The invasion of heaths into the cover sand landscape of the
Netherlands is associated with forest degradation – first on a small scale in
open places in the original forest, which existed due to natural causes,
followed by larger-scale anthropogenic deforestations.
People created and maintained the barrow landscape on ancestral heaths
from the late Neolithic until the late Iron Age. For these people, heath was not only economically but also
culturally valuable. During and after the Roman period, people continued with heath management,
mainly by cattle grazing; the heaths maintained their economic but lost
their cultural value. Introduction of the plaggic agriculture system around AD 500 resulted in
further soil acidification of the heaths and the development of plaggic
horizons on arable fields. Deforestations during the 11th–13th century caused extension of sand
drifting, and the introduction of the deep, stable economy in the 18th century
resulted in extensions of the drift sand landscape and heath degradation. At the end of the 19th century the heaths lost their economical functions
and were transformed into modern production fields. The loss of the heath area was accompanied by the loss of soil archives. Preservation of the remaining soil archives is crucial for the geological
heritage and future research.
The study of the barrows resulted from the project “Ancestral Mounds at the
Leiden University, funded by NWO, Netherlands Organization for Scientific
Research”. We are grateful
to Jakob Wallinga (NCL, Wageningen University) for the performance of the OSL
datings of the Rakt and Bedafse Bergen profiles. For the
We thank the reviewers Bas van Geel, Jan Sevink, Martina Glocke, and Sjoerd Kluiving for their valuable advice on how to improve the quality of this paper. Edited by: S. Kluiving