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Iron Age wood usage at an enclosure in northern Germany
Quaternary International xxx (2017) 1e9
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Iron Age wood usage at an enclosure in northern Germany Insa Alice Lorenz a, *, Volker Arnold b, Doris Jansen c, Mareike Grootes d, Oliver Nelle a €sidium Stuttgart, Fischersteig 9, 78343 GaienhofenDendrochronologisches Labor, Landesamt für Denkmalpflege Baden-Württemberg im Regierungspra Hemmenhofen, Germany b Berliner Str. 61, 25746 Heide, Germany c Institute for Ecosystem Research, Christian-Albrechts-University Kiel, Olshausenstr. 75, 24098 Kiel, Germany d Cornelis Dopperlaan 9, 2343 ME Oegstgeest, The Netherlands a
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2016 Accepted 15 February 2017 Available online xxx
The first known Iron Age enclosure in the northern German state of Schleswig-Holstein was discovered in 2010. Archaeological excavation revealed a trench, a palisade and an occupation layer. The function of the wall and trench system remains unknown but there are several possibilities: It could have been used for protection, as a type of symbolic separation or to demarcate a cult site. The enclosure was constructed around the year zero. Charcoal samples were taken in a spatially detailed manner during excavation, as well as a new pollen core from a small spring mire directly next to the site. Anthracological analysis showed that Quercus (oak) was the main type of wood used in the construction of this enclosure. Thirteen additional wood taxa were identified, of which the next best represented is Corylus (hazel) and surprisingly a significant amount of Ilex (holly) was found. The samples did not contain Fagus (beech) or Carpinus (hornbeam), which are both common in the area today. According to pollen data, Fagus had begun to establish in the local woodland during the time of the enclosure, but did not gain importance before the migration period. By diameter analysis of the charcoals the size of the used wood (branch or trunk) was reconstructed. In addition, mean annual tree ring widths of the used wood e especially Quercus e show that the wood comes from young stems and/or branches of older trees and probably not from coppiced wood. The study shows that even small-scale archaeological excavations can yield important new data on wood utilization with a high spatial precision, which contributes to the reconstruction of local woodland composition. © 2017 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Iron Age Environmental archaeology Anthracology Landscape history Paleoecology Pollen analysis
1. Introduction The analysis of charcoal from archaeological sites provides information on ancient wood use, the composition of forests, and human influence on the landscape (e.g. Asouti and Austin, 2005; Jansen and Nelle, 2014). In the cooperation between anthracology, being a paleoecological discipline, and archaeology (also named “archaeoanthracology”, e.g. Vernet, 2002) research strategies have to be developed adjusted to the individual excavation. Depending on resources and archaeological management samples of different quantities are taken for charcoal analysis and subsequently analysed. While a wealth of archaeoanthracological studies exists in the Mediterranean part of Europe, there are still only few examples for detailed charcoal studies in the more northern parts
* Corresponding author. E-mail address: [email protected] (I.A. Lorenz).
of the continent. Given several layers over a longer time period, archaeoanthracology can show the wood usage and even the vegetation changes over a certain time, in a way comparable to pollen diagrams (e.g. from Neolithic until Bronze Age: Badal et al., 1994; for Mesolithic and Neolithic: Heinz, 1991; Heinz and Barbaza, 1998). Badal et al. (1994) differentiate between diachronous and synchronous paleoecological interpretations, the latter being relevant for the study presented here, where charcoal from an Iron Age site was obtained during a small-scale excavation. Due to limited resources or monument protection reasons, excavation areas may be small and are exploratory or exemplary. In archaeological care and preservation of monuments, invasive and destructive action at sites which are not endangered is usually kept to the minimum necessary. That said if small excavation areas are sampled in detail for natural sciences investigations, and each archaeological layer is considered, the knowledge acquired can be important even in relation to the small size of intervention. In this paper, we explore the potential as well as the limitation of
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a detailed analysis of charcoal from an Iron Age enclosure, which we complement with pollen evidence from a spring fen directly next to the site. Enclosures are circular ramparts which were built from the Neolithic till the Middle Ages. They were used either as €hn fortifications, as religious separation or as a meeting place (Da € ller-Wiering, 1999). Another famous Iron Age enclosure is and Mo Biskupin in Poland dated to 747-722 B.C.E. (Grenz and Rajewski, 1978). The Riesewohld site was discovered in 2010 by the use of Lidardata and is located in the Riesewohld forest in northern Germany as the first known of its type for the Iron Age period. An enclosure similar in size and time of construction is the structure formed by the inner wall of the ‘Heidenschanze von Sievern‘ (Niedersachsen, € rfler, 2013; see also Scho € n, 2000; Jo €ns, Germany; Arnold and Do 2010). The forest shows features of a natural, broad-leaved Central European forest with potentially ancient continuous woodland. We complement the archaeoanthracological data set with pollen data from neighbouring small spring mires to discuss the evidence for local woodland composition and change (Nelle et al., 2010). Though small in area, the charcoal sampling was very detailed, with the aim of relating samples to the enclosure structures. Our intention was (i) to identify the kind of wood (taxa and diameter) which was used by the Iron Age people, (ii) to characterize the construction of the fort by charcoal data, and (iii) to give a possible woodland scenario for the time of construction by means of combining charcoal and pollen data. The study also contributes to increase the general knowledge of prehistoric wood usage in a region where archaeoanthracological studies are still rare. Exceptions are e.g. the analysis of charcoal from an iron smelting site of the €rfler, 2000; Do €rfler and Wiethold, 2000) or a Roman Iron Age (Do diachronic study of wood utilization in burial contexts from the Neolithic until the Iron Age (Jansen et al., 2013).
2. Regional setting and study site 2.1. The archaeological site The enclosure is the first one discovered dating to the Iron Age in Schleswig-Holstein (Northern Germany) and was found by the use of Lidar-data on the area of the Riesewohld Forest, at 55e64 m a.s.l. €st’ and the Infostation It lies between the ‘Landweg Osterwohld-Ro Riesewohld (Fig. 1). A shallow trench and low wall (height
difference of maximum 0.9 m) surround the inner part, which is shaped as an irregular ellipse, 240 m long and 100 m wide, covering € rfler, 2013). In 2004, a small a total area of 1.8 ha (Arnold and Do archaeological excavation took place inside the enclosure. Ceramics findings placed the construction in the Pre-Roman Iron Age. New sections excavated in 2011e2015 revealed more ceramics, pointing to a settlement character of the structure. Dendrochronological analyses by Karl-Uwe Heußner (DAI Berlin, opinion of 30.10.2015, lab number C 81742-81768) date four Quercus, four Fraxinus and one Fagus wood samples from a well e all with a wane edge e between 11 and 31 B.C.E. This well is located in a sink at the inner rim of the east wall and near to the 2011 excavation. The AMSdating of one isolated post hole to 976-816 cal. B.C.E. shows that some activities preceded the main building phase which is placed € rfler, 2013) and the dendroaccording to ceramics (Arnold and Do evidence to around the beginning of the Common Area. Back then the wall with a surrounding rudimentary trench and a palisade between wall and trench was built. This palisade was replaced in patches over time. Later a major fire destroyed the wooden construction and produced the majority of the charcoal. The palisade seems to have been replaced after the fire on top of the remains of the levelled wall. Similar to the Riesewohld structure the early construction phase of the ‘Heidenschanze von Sievern‘ had a palisade with a sand rampart on the inside and a trench on the € n, 2000). outside (Scho
2.2. Riesewohld forest The forest covers an area of about 7 km2 (Fig. 1, Coordinates: 54 000 N, 9 120 4000 O). A moraine ridge stretches from the north to the south which originated from a later Saalian Stage. The climate is temperate, with an average annual temperature of 8.6 C and an annual precipitation of about 1000 mm (DWD, 2013). For watersaturated clouds moving eastwards and inland from the North Sea, the moraine ridge and therefore the area of the Riesewohld is the first obstacle, with its height rising from 7 m up to 64 m above sea level. In this way orographic rainfall causes higher humidity. Consequently, many springs, small spring mires and small forest streams characterize the woodland and make the area less attractive for agriculture. The humid parts of the wood especially seem to have a long woodland continuity despite their use by local people, for wood gathering or woodland grazing. The woodland is close to 90
€st’, i ¼ Infostation Riesewohld (Edupics.com Fig. 1. The Riesewohld forest is located in Schleswig-Holstein (Germany), in the district of Dithmarschen. P ¼ ‘Landweg Osterwohld-Ro and Landesamt für Vermessung and Geoinformation Schleswig-Holstein).
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the condition of a natural Central European primeval forest (Thiessen, 2011). Nowadays, besides some conifer plantations, most of the woodland is dominated by (oak-)beech woodland with numerous spots of birch-common oak or alder-ash woods in areas near groundwater and waterlogging (Dierßen, 2004; Arnold and €rfler, 2008). During the last centuries Denker, 2007; Nelle and Do this forest was a communal forest subdivided into small extensively used parcels.
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diameter for each taxon is shown by histograms (Fig. 2). The mean tree ring width per fragment is calculated by dividing the fragments’ radial width by the ring number (Marguerie and Hunot, 2007). Marguerie and Hunot (2007) propose using only wood pieces from the outer parts of a large tree. In this study, however, we applied the approach also to fragments of smaller diameter, to take into account the possibility of coppicing. Coppiced trees show a fast growth in the first years, thus charcoals would give higher width values than those of branches.
3. Material and methods 3.3. Pollen analysis 3.1. Charcoal sampling Charcoal samples were obtained during an archaeological excavation directed by Volker Arnold in 2011. The excavation included the trench, the rampart and the inner part of the enclosure. The section is divided in a raster (partly in 1 1 m and partly in 1 0.5 m). These square and half square meters are summarized as categories “trench”, “palisade”, “rampart” and “cultural layer” for subsequent interpretation of charcoal collections. Artificial layers comprising 10e15 cm were sampled in each square and half square meter and were numbered from top (3) to bottom (12; Table 1). Samples were dry-sieved with a mesh size of 5.5 mm. In a few cases e if the soil contained too much clay e the mesh size had to be 12 mm.
A 50 cm deep peat profile “RWI” was cut out from a ca. 100 m2 large spring mire ca. 25 m south of the enclosure. Ten 2 cm3; samples (sample vertical depth 1 cm) were treated with standard procedures, including KOH digestion, HF treatment and acetylation (Faegri and Iversen, 1989; Moore et al., 1991). Pollen grains were counted with microscope magnifications of x 400 to x 1000. Pollen percentages are based on the terrestrial pollen sum, which does not include Alnus and Betula, both being treated here as local wetland pollen. The pollen diagram was made using Tilia 1.7.16 (Eric Grimm, Illinois State Museum). 4. Results 4.1. Charcoal analysis
3.2. Charcoal analysis From samples containing sufficient charcoal usually 20 fragments were analysed for every grid square and layer in this section (Table 1). For every piece the number of annual rings, the radial width of the piece, presence/absence of wane edge and the diameter class were recorded (Jansen, 2013). A total number of 1074 charcoal pieces was analysed in this way. Taxonomic identification is based on the wood anatomical atlas by Schweingruber (1990) and the charcoal reference collection of the Paleoecology Research group of the Institute for Ecosystem Research at the University of Kiel. The freshly broken pieces were analysed in their transversal, tangential and radial orientation using a stereoscope with a magnification from x 7.5e112.5 (Nikon SMZ 1500) and an incident-light microscope with a magnification from x 50-500 (Nikon ME 600 Eclipse). The small size of fragments made identification of the taxa difficult at times. Very small pieces down to 1 mm showing uniseriate rays and bigger vessels, but not multiseriate rays, could be both Quercus and Castanea (chestnut), but Castanea did not exist in this area during the time period of the enclosure. The separation of Sorbus and Pyrus/Malus/Crataegus within the subfamily Maloideae is challenging as well because the main anatomical difference e the distinct spiral thickenings of Sorbus e is hard to see on very small fragments. Pyrus pyraster, Malus sylvestris, Crataegus laevigata and Crataegus monogyna cannot be differentiated and are listed together as Pyrus/Malus/ Crataegus. The minimum diameter of the wood was analysed by using a diameter stencil (Ludemann, 1996; Nelle, 2002). The visible curvature of annual rings and the angles of wood rays were used to classify the pieces in one of the five diameter classes (up to 2 cm, >2e3 cm, >3e5 cm, >5e10 cm and >10 cm) as proposed by Ludemann and Nelle (2002). The mean diameter (mD; Formula 1) was calculated for the sum of all pieces from one taxon. It is used as an indicator for the wood diameter. Other studies employing this approach can be compared easily to each other (Jansen et al., 2013). As a reference, experiments resulted in a mean diameter for firewood of 3e4 cm, stump-shoots ca. 8 cm and construction timber 10e13 cm (Nelle et al., 2013). The percentage distribution in
An overall number of 1074 charcoals from 70 samples of the excavation 2011 were taxonomically identified. One single piece remains unidentified. Deciduous Quercus (oak) is by far the most common wood type, constituting 81% of the pieces, followed by 5% Ilex (holly), 4% Corylus (hazel), 3% Acer (maple), 2% Fraxinus (ash), 1% Tilia (lime), and with less than 1% Ulmus (elm), Prunus (stone fruit), Pyrus (pear)/Malus (apple)/Crataegus (whitethorn), Betula (birch), Alnus (alder), Populus (poplar), Sambucus (elder), Sorbus, Salix (willow) and Pinus (pine; Table 2). The charcoal from the 2011 excavation is analysed per grid square and a complete profile analysis is established in Fig. 3 and Table 1. The palisade and the rampart grid squares contained the highest charcoal concentrations. The lower layers of the palisade showed signs of four main poles. Thus more grid squares were analysed in that area. In this section a large proportion of all rampart parts is composed of Quercus (Fig. 4). The lowest number of pieces was found in the trench (52 pieces, all Quercus). Outside the palisade there were one piece each of Corylus, Fraxinus and Prunus and some Ilex pieces. In the middle of the palisade and in the rampart section there was one piece of Populus, respectively. On the inside of the palisade, which is next to the rampart, were two pieces of Ilex, Pyrus/Malus/Crataegus and Corylus. The last two taxa were also present in the middle of the rampart. There were nearly as many Ilex pieces (31) as Quercus pieces (48) at the boundary of the ‘cultural layer’. The cultural layer showed the highest taxa diversity: Apart from Quercus a lot of Corylus, Acer, Fraxinus, some Ilex, Tilia, Ulmus and few Prunus, Betula, Sambucus, Sorbus, Alnus, Salix and Pinus. The charcoal density decreases in the cultural layer with the distance from the enclosure as does the ceramic density. The diameter class distribution and the mean annual ring width provide information whether the used wood comes from older or younger trunks or branches. It was possible to attribute 987 pieces to one of the five diameter classes (1074 pieces total). The overall mean diameter is 7 cm. Most of the charcoal pieces are within the >5e10 cm diameter class, followed by class >3e5 cm and >10 cm. Quercus, Corylus, Ilex, Acer and Tilia are present in all diameter classes. Quercus is most present in the diameter classes 3e5 cm and 5e10 cm (Fig. 2). Ilex shows a very similar distribution as Quercus.
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Fig. 2. Percentage values and distribution of the diameter classes, with the mean diameter (md) value below the taxa and the total number of analysed charcoal (n). Proportion of diameter classes from Quercus, Ilex, Corylus and Acer.
Fig. 3. Classification of the section in a grid square e with designation numbers: grey Fields: analysed, black fields: no charcoal pieces available, white fields: no analysis performed.
The distribution of Corylus however is exceptional because its share is similar in each diameter class, even >10 cm. Acer has a distribution shifted to the higher classes. The total mean diameter ranges from 5.2 cm (Corylus) to 9.7 cm (Acer). Nearly half of the fragments (498 of 1074) had less than five year rings. The number of annual year rings ranges from 0 (not measurable) to 60 (Ilex). Quercus nearly covers all annual ring numbers. Ilex also has a wide spectrum of growth rings. Corylus and Acer have up to 17 rings and all other taxa e except Prunus (one piece with 27 rings) e have less than ten annual rings. The range of the mean width of annual rings varies from 0.07 mm (Corylus) to 8.5 mm (Betula) (Fig. 5).
decline is typical for the Iron Age and can be dated for around 500 € rfler et al., 2012; Arnold and Do €rfler, B.C.E. (Wiethold, 1998; Do 2013) and thus places the diagram in a period before and contemporary to the enclosure. Alnus gains higher values again in zone 3, with a slight decrease of Betula and considerable values of Rosaceae in sample 22 cm. Fagus and Carpinus do not reach values more than 2%, respectively. Quercus shows percentages between 20 and 25%.
4.2. Pollen analysis
Charcoal data are used here to interpret the structure of the circular enclosure. Sampling of charcoal was based on the grid squares. The grid borders do not match the borders of the enclosure parts (trench on the outside, followed by the palisade, the rampart and the ‘cultural layer’) in position and orientation as they have been designed prior to the identification of the (different) structures. Thus single samples might contain charcoals from different structures. Due to this problem, for example the grid squares 2451/ 52 could be included in both the palisade and the rampart (Fig. 3). A vertical evaluation is not considered, because the enclosure is
The pollen diagram includes 10 samples from 16 to 46 cm below surface (Fig. 6). Alnus and Betula were excluded from the terrestrial pollen sum, since they both grow today on the spring mire. The diagram was divided into three local pollen zones (RWI 1e3). Zone RWI 1 is characterised by high Tilia values, as well as considerable amounts of Cyperaceae grains and fern spores. In zone 2, Alnus shows a minimum, paralleled by an increase of Betula, a decrease of Tilia and Cyperaceae and the onset of the Rosaceae curve. The Tilia
5. Discussion 5.1. Enclosure: wood resource usage, construction and function
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Fig. 4. Number of analysed charcoal pieces for each square field part per taxon. The * highlights small values.
supposed to have one construction phase, and charcoal spectra are dominated by Quercus in all vertical samples. The high percentage of Quercus in the charcoal assemblage points to its use as construction timber. The high proportions in the diameter classes >5e10 cm, >3e5 cm and >10 cm show that a mixture of timber with small and bigger diameters was used (Fig. 2). The mean diameter of Quercus charcoal is 7 cm. Therefore the charcoal originates primarily from branches and young stems, or is a mixture of small branches and bigger stems. If only huge stems were used for the construction, significantly higher mean diameters would have been expected. The highest number of Ilex charcoal pieces is in the diameter class >10 cm, and Ilex has a mean diameter of 7 cm e nearly the same as Quercus. Thus, besides Quercus, Ilex could have been used for the construction of this enclosure with comparable mean diameters. The Ilex findings may originate from one single trunk (square 2552, rampart) due to the small scale of this excavation and the little amount of Ilex found. The mean annual ring width has a high variability within a range of under 0.07 up to 8.5 mm. Comparing the mean annual ring widths of Quercus, Ilex and Corylus the majority of pieces have a range from 0.6 to 2 mm (Fig. 5). There are no big differences in the mean annual growth ring width between the different diameter classes of Quercus. The fragments of the lower diameter classes seem to contain no coppiced wood, because this would have resulted in a wider growth ring width, which was not observed. Branches usually show a lower growth ring width, thus the material in the lower diameter classes comes at least in considerable part
from branches of oak. To sum up, the wood used in this enclosure comes partly from stem material as well as from crown material of bigger and older oaks. For these trees, based on our dendroanthracological approach, a mean annual ring width of 1.69 mm was calculated, thus being larger than 1.25 mm, the value calculated by Marguerie and Hunot (2007) for the Quercus construction wood of one building in the Neolithic settlement near La Hersonchatel, Ille-et-Vilaine). Jansen (2013) also measured the nais (Ple mean growth ring width and contrasted them with the number of growth rings. Grouping of charcoal findings concerning growth € rfler and Wiethold (2000) rings and radius has also been done by Do in order to make assumptions about the forest structure. In the present absence of other investigations in the region, the mean ring width serves as a base for further studies. In the future, mean ring width values and their ranges should be established from modern stems and branches and wood from trees of the region as references to be compared to the anthracological data. Furthermore, data from different areas with differing site conditions should be taken into account for comparison. Some charcoal pieces with a minimum diameter up to 10 cm show a high number of tree rings. Therefore, branches of older trees and/or slow growing trees have also been used for the construction of the enclosure. The possible origins of pieces with a bigger diameter (more than 10 cm) with a higher cambial age are manifold: age trend of older trees and/or stress (like growing on wet soil). They could originate from a thick trunk with limited growth in girth (like old trees exhibiting an age trend) or from thin trunks,
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Fig. 5. Annual growth ring width for the most represented taxa at this site (Quercus, Ilex and Corylus) varies from 0.07 mm (Corylus) to 7.5 mm (Quercus). Boxplots on the left and right side show the average growth ring width in mm from the whole analysed Quercus (standard deviation ¼ 1.01), Ilex (standard deviation ¼ 0.78) and Corylus (standard deviation ¼ 0.87) material, and in the middle part in detail the ring width of Quercus for the different diameter classes.
of bigger construction wood remains were sampled. Therefore a small section with its high and spatially differentiated number of samples seems to be sufficient to contribute to the reconstruction of the enclosure. The rich species spectrum in the cultural layer mirrors the diverse wood usage of the settlement activity. Interestingly Populus and Pyrus/Malus/Crataegus were only found at the palisade and the rampart, pointing to its use for construction rather than fire wood, which is in contrast to high amounts of Maloideae charcoals especially in Neolithic samples in central Europe (Kreuz, 1992; Damblon et al., 2001e2002; Jansen et al., 2013; Jansen and Nelle, 2014). According to the excavation the trench and rampart were with maximum 0.9 m height difference relatively flat but a function as fortification cannot be excluded. Therefore the enclosure could have been a symbolic delineation as well as a function as a fortification. Most probable the rampart collapsed and fell into the €rfler (2013) consider trench, after it lost its stability. Arnold and Do that the rampart was agriculturally used in former times, as it probably was done in the Celtic Fields in the sites’ neighborhood. The typical structure of the Celtic Fields is missing here (Arnold and €rfler, 2013): There are no plough marks on the rampart or in the Do soil profile. These structures however can only be observed under ideal circumstances. Another possible function is the use as a sanctuary. Ilex as an evergreen plant with red berries to protect this special place could be some evidence (Lauder, 2004). Nevertheless Ilex is a common plant in these (sub-)atlantic woods and it is more likely that it was a natural constituent of the Iron Age woodland, like it is today. The plant with thorny leaves was possibly indirectly promoted by woodland pasture. 5.2. The surrounding vegetation: combining pollen and charcoal
which are just a little bit thicker than 10 cm in diameter, grown on a bad site, or from a thick branch. Wet soil condition is a plausible cause for wood growth inhibition. The high number of springs in the area nowadays supports this hypothesis. Oaks grown in the shadow of beeches is unlikely since, according to pollen and charcoal evidence, Fagus did not build dense stands during the Iron Age at the site. In the cultural layer there are many different taxa like Quercus, Ilex, Corylus, Acer, Fraxinus, Tilia, Ulmus, Betula, Alnus, Populus, Sambucus, Sorbus, Salix and Pinus (Fig. 4). This indicates a varied use of wood. Many Sambucus seeds were found in the nearby excavated well. Sambucus is promoted by nutrient surplus and plain light conditions in a settlement context. The overall rich taxa diversity shows that not only the remains
In order to reconstruct the ancient vegetation in the area surrounding the enclosure we complemented the charcoal data with pollen evidence from a profile directly next to the archaeological site, as well as discuss our results in the light of a diagram from a € rfler, 2013). Additionally, around mire 800 m away (Arnold and Do 3000 charcoal pieces from 14 small-scale excavations within the area of the Riesewohld, from Neolithic to the Iron Age, and from two kiln sites dating around 1800 C.E. are available (Arnold, 2006; € rfler, 2013). This data-set shows that beside the Arnold and Do important presence of Quercus since the Neolithic, Tilia played (and still plays) a considerable role in the woodland, at least from Neolithic times onwards. As an under-represented pollen type in palynological data, its importance is revealed by anthracology. However, its presence in the woodland declines during the Iron
Fig. 6. Pollen diagram RWI from a spring mire 25 m next to the archaeological site. Black curves: pollen percentages based on terrestrial pollen sum. Grey curves: not included in the terrestrial pollen sum and calculated with the total pollen sum; Exaggeration (line with depth bars) with factor 10.
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Age, as shown in many pollen diagrams in northern central Europe. The absence of Fagus and Carpinus fits well with the timeslot of the material. Both gain in the charcoal assemblages as well as in pollen data significant proportions only after the Iron Age. They immigrate into this western part of Schleswig-Holstein even later than it can be shown by pollen and charcoal evidence for areas further east and south (Robin et al., 2011). However, even in the kiln sites from the modern period, Fagus is absent, though it is a very suitable wood to produce charcoal. Being present in the pollen assemblages but not in the charcoals, the very shadow-tolerant beech trees might have gained only limited importance in some parts of the forest but were not present in other parts. However the name “Büchen”, which is an old German word for Fagus, appears in documents from the 18th century describing the Norderwohld forest (NW of the village of Welmbüttel). This forest is similar to the Riesewohld in structure and lies 5 km north. At the enclosure, Quercus was clearly the preferred construction timber, but the samples from the cultural layer should contain at least some Fagus if it was used as wood fuel. The well which was dated in 2015 had at least three Fagus pieces in its construction timber e and even one piece dates with a wane edge to 27 B.C.E. Probably during the time of the enclosure Fagus grew in the Riesewohld already but was only used as construction timber (at least for buildings inside the settlement). However the absence of this taxon in the charcoal assemblage may be only due to the small sample size of the excavation. The charcoal analysis from the path slope excavation 2004 (272 identifications) supports this hypothesis with 13 pieces of Fagus. The sample from 2004 shows the dominance of Quercus, the other most common taxa are Fraxinus and Acer (Arnold and Denker, 2007). Next to Corylus, which has a broad share at the excavation 2011 and the path slope 2004, some Carpinus was found in the latter case only. Tilia, Sorbus, Salix, Prunus and even Pinus, which is very unusual for that time, were found at both excavation sites. The pollen diagram RWI (Fig. 6) shows the vegetation development between ca. 1000 B.C.E. and the modern period, according to biostratigraphy. High amounts of grass pollen and Pinus, in combination with a rise of Betula, show open woodland at the depth of 36e28 cm. We assume that this is the time of the enclosure, when Tilia has shown its typical Iron Age decline, Quercus is the dominant tree and Fagus as well as Carpinus do not have much importance in the local woodland composition yet. Rosaceae pollen type might represent considerable amounts of Crataegus bushes in semi-open or open woodland situations. Ilex is not present in the pollen samples, but was found in the charcoals, pointing to some minor presence in the vegetation around the site. Cereal pollen have relatively high values and match the pollen diagram from another spring fen, about 750 m distant e around the birth of Christ, as the latter profile is dated by 14C-AMS. This profile, which goes further back in time, shows that there were already settlements in this area during the € rfler, 2013). Because of the good settleBronze Age (Arnold and Do ment situation with sandy soil and the nearby spring, it is not surprising that this place had e as Neolithic, Mesolithic, Bronze Age and Iron Age findings and the pollen diagrams show e a longer settlement history. The light-demanding taxa Corylus is considerably present too e an indication that the woodland was open. Ilex-pollen grains were found in considerable amounts, indicating its presence in the woodland, probably promoted by grazing, and matching the charcoal evidence. Summarizing pollen and charcoal data, the woodland around the enclosure during the Iron Age was dominated by Quercus, with Alnus and Fraxinus trees on wet sites. The woodland was considerably opened up, by wood and timber sourcing, as well as managing arable fields. We assume a mosaic of denser and more open woodland, with a mixture of woodland grazing, cereal cultivation, timber sourcing and fuel wood collection. However, there is no
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evidence for a broader deforestation, since the amount of arboreal pollen remains high throughout both diagrams. Thus the need for wood and timber did not completely destroy the forest, and at this point we cannot counter the hypothesis of an ancient woodland continuity in some areas of the Riesewohld forest. 6. Conclusions It was possible to reconstruct the woodland situation around an Iron Age enclosure from the transition Pre-Roman/Roman Iron Age (around the beginning of the common era) in an old-moraine forest, and the wood and timber use for different purposes by the builders of the enclosure, by using charcoal and pollen evidence. While providing a better understanding of the past, the information from a 2000 plus year old history of moderate disturbance of the woodland helps today's wood management to preserve and restore ecological diversity (Arnold and Denker, 2007; Robin et al., 2012). We postulate that low-intensity disturbances by people increased the structural diversity of the woodland resulting in today's highly valued species composition and “naturalness”. Since the Neolithic era this wood was used by humans. A mixed oak forest grew there before and during the Iron Age, which provided Quercus timber for the palisade. While some areas of the forest were opened up by timber and wood fuel sourcing, others continued to exist as woodland. The occurrence of Ilex (open forest indicator) could indicate wood-pasture as one form of exploitation. The enclosure is outstanding because it is the only known one from this time in Schleswig-Holstein. A woodland composition reconstruction solely based on the remains of timber for construction would fail because of the selective use of Quercus. In combination with samples from the cultural layer, we get a more complete taxa spectrum, even when it is not possible to provide a proportionally correct composition of species. The use of Quercus trees was only on a local scale and did not destroy the entire population, as the pollen diagrams show. Charcoal and pollen data suggest the woodland was rich in Ilex. The builders of the enclosure opened the wood and therefore the light-demanding taxa Corylus grew in this place. We postulate open woodland during the time of the enclosure. The role of Fagus, which was only found in one sample in 2004 and as building material for the well but not at the excavation in 2011, remains ambiguous: being far less suitable for construction compared to oak, its wood is usually used for fuel. Its rarity both in the pollen as well as in the cultural layer charcoal record can only be explained by its rarity in the woodland during the Iron Age, while today it is the dominant taxa. It appears like near-natural beech woodland on not too dry and not too wet mineral sites but actually it is a result of a planting from around 1880-1900. Our study shows that even limited excavations, when sampled for charcoal in a detailed way, are able to provide significant information on prehistoric wood usage and woodland composition. To cross-check their significance, local and regional pollen data, if available, should be consulted to get a more complete picture of past vegetation dynamics. However, taking samples of charcoals as a ubiquitous proxy of woodland usage is still not established as a routine in archaeological excavations, even more what concerns detailed studies with a high spatial resolution. Acknowledgements We thank the voluntary excavation team of 2011 (Walter €hl, Andreas Leistritz, Karl Kollek Denker, Heino Hünken, Karin So et al.) and Jan Hansen and Louise Bradley for proof-reading. Reviewers' comments are much appreciated, helping to improve the manuscript considerably.
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Appendix/Pictures
Table 1 Number of analysed charcoal pieces concerning square field and degradation.
Table 2 Absolute taxa number from excavation 2011
mD ¼
Taxon
Number
Quercus Ilex Corylus Acer Fraxinus Tilia Ulmus Prunus Pyrus/Malus/Crataegus Betula Alnus Populus Sambucus Sorbus Salix Pinus indet
875 50 45 35 25 16 7 4 3 3 2 2 2 2 1 1 1
nI 1cm þ nII 2:5cm þ nIII 4cm þ nIV 7:5cm þ nV 15cm PV i¼I ni
Formula 1 Calculation of the mean diameter (mD). i 2 {I, II, III, IV, V} describes the number of samples for each diameter class. References Arnold, V., 2006. Der Riesewohld e zur kultur- und vegetationsgeschichtlichen Bedeutung eines historischen Waldgebietes auf der Dithmarscher Geest. In: €rtner, S., Matthes, L., Nissen, M. (Eds.), Arkæologi i Slesvig/Archa €ologie in Kleinga Schleswig. Wachholtz, Neumünster, pp. 9e18. Arnold, V., Denker, W., 2007. Der Riesewohld e Dithmarschens KultUrWald. Von €ische Vereinigung zur Fo €rderung der der Urzeit bis in die Zukunft. In: Europa €ologie: Experimentelle Archa €ologie in Europa. Bilanz experimentellen Archa 2007. Isensee, Oldenburg, pp. 240e246. http://museum.steinzeitparkalbersdorf.de/arnolddenker07.pdf. date of access 04.03.2013. € rfler, W., 2013. Pollen, Holzkohle- und Gela €ndeanalysen aus dem Arnold, V., Do schleswig-holsteinischen Riesewohld, 69/79, pp. 53e70. Kreis Dithmarschen. Offa. Asouti, E., Austin, P., 2005. Reconstructing woodland vegetation and its exploitation by past societies, based on the analysis and interpretation of archaeological wood charcoal macro-remains. Environ. Archaeol. 10, 1e18. Badal, E., Bernabeu, J., Vernet, J.L., 1994. Vegetation changes and human action from
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I.A. Lorenz et al. / Quaternary International xxx (2017) 1e9 flintbek (SchleswigeHolstein, northern Germany). Veg. Hist. Archaeobot. 22, 335e349. http://dx.doi.org/10.1007/s00334-012-0386-7. €ns, J., 2010. The Elbe-Weser region in northern Germany. In: Ludowici, B., Jo €ns, H., Jo €rtner, S., Scheschkewitz, J., Hardt, M. (Eds.), Trade and Communication Kleinga Networks of the First Millennium AD in the northern part of Central Europe. Central Places, Beach Markets, Landing Places and Trading Centres. Neue Studien zur Sachsenforschung, vol. 1, pp. 69e89. Suttgart. Kreuz, A., 1992. Charcoal from ten early Neolithic settlements in Central Europe and its interpretation in terms of woodland management and wildwood resources. te Bot. Fr. 139, 383e394. Bull. Socie €ts, sixth Lauder, D., 2004. Mythos Baum. Geschichte e Brauchtum e 40 Baumportra ed., pp. 180e183 München. Ludemann, T., 1996. Die W€ alder im Sulzbachtal (Südwest-Schwarzwald) und ihre €hlerei. In: Mitteilungen des Vereins für ForNutzung durch Bergbau und Ko stliche Standortskunde und Forstpflanzenzüchtung, vol. 38, pp. 87e118. Ludemann, T., Nelle, O., 2002. Die W€ alder am Schauinsland und ihre Nutzung durch €hlerei. Freiburger Forstl. Forsch. 15, 140. Freiburg. Bergbau und Ko Marguerie, D., Hunot, J.-Y., 2007. Charcoal analysis and dendrology: data from archaeological sites in north-western France. J. Archaeol. Sci. 1e17. http:// dx.doi.org/10.1016/j.jas.2006.10.032. Moore, P.D., Webb, J.A., Collinson, M.E., 1991. Pollen Analysis, second ed., p. 216 Oxford. Nelle, O., 2002. Charcoal burning remains and forest stand structure - examples from the Black Forest (south-west Germany) and the Bavarian Forest (southbault, S. (Ed.), Charcoal Analysis. Methodological Apeast Germany). In: Thie proaches, Palaeoecological Results and Wood Uses, Proceedings 2nd Int. Meeting of Anthracology, Paris, Sept. 2000, vol. 1063. Archaeopress, Oxford, pp. 201e207. British Archaeological Reports 1063. € rfler, W., 2008. A summary of the late- and post-glacial vegetation Nelle, O., Do history of Schleswig-Holstein. In: Dengler, J., Dolnik, C., Trepel, M. (Eds.), Flora, Vegetation and Nature Conservation from Schleswig-Holstein to South America e Festschrift for Klaus Dierßen on Occasion of his 60th Birthday. Abteilung der Geobotanik in Schleswig-Holstein und Hamburg, vol. 65, pp. 45e68. Kiel.
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Nelle, O., Dreibrodt, S., Dannath, Y., 2010. Combining pollen and charcoal: evaluating Holocene vegetation composition and dynamics. J. Archaeol. Sci. 37, 2126e2135. Nelle, O., Jansen, D., Overbeck, M., 2013. Charcoals from iron smelting furnaces e fuel supply and environment of a medieval iron smelting site near Peppange/ Luxembourg. In: Damblon, F. (Ed.), Proceedings of the Fourth International Meeting of Anthracology. Brussels, 8e13 September 2008. Royal Belgian Institute of Natural Sciences. BAR International Series 2486. Archaeopress, Oxford, pp. 165e172. Robin, V., Rickert, B.-H., Nadeau, M.-J., Nelle, O., 2011. Assessing Holocene vegetation and fire history by a multiproxy approach: the case of Stodthagen Forest (Northern Germany). Holocene 22 (3), 337e346. http://dx.doi.org/10.1177/ 0959683611423687. Robin, V., Talon, B., Nelle, O., 2012. Pedoanthracological contribution to forest naturalness assessment. Quat. Int. 1e11. http://dx.doi.org/10.1016/ j.quaint.2012.02.023. €n, M.D., 2000. Die Heidenschanze bei Sievern e eine fast 2000 Jahre alte Scho Befestigung. In: Arch€ aologie in Niedersachsen, vol. 3. Isensee, Oldenburg, pp. 57e59. Schweingruber, F.H., 1990. Mikroskopische Holzanatomie. Formenspektren Mitte€ischer Stamm- und Zweigho €lzer zur Bestimmung von rezentem und leuropa € ssische Anstalt für das forstliche Versubfossilem Material, third ed. Eidgeno suchswesen, Birmensdorf, p. 226. Thiessen, H., 2011. Wildnis in schleswig-holstein. In: Schriftenreihe Landesamt für €ndliche Ra €ume des Landes Schleswig-Holstein e Landwirtschaft, Umwelt und la Natur, vol. 17, p. 113. Howaldtsche Buchdruckerei, Kiel. Vernet, J., 2002. Preface to: charcoal analysis. Methodological approaches, palaeobault, S. (Ed.), Proceedings 2nd Internalogical results and wood uses. In: Thie tional Meeting of Anthracology. Paris. Sept. 2000, v-vi. Wiethold, J., 1998. Studien zur jüngeren postglazialen Vegetations- und Sied€stlichen Schleswig-Holstein (mit einem Beitrag von H. lungsgeschichte im o €tsforschungen zur pra €historischen Archa €ologie, Habelt, Erlenkeuser). Universita Bonn, p. 365.
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Iron Age wood usage at an enclosure in northern Germany Insa Alice Lorenz a, *, Volker Arnold b, Doris Jansen c, Mareike Grootes d, Oliver Nelle a €sidium Stuttgart, Fischersteig 9, 78343 GaienhofenDendrochronologisches Labor, Landesamt für Denkmalpflege Baden-Württemberg im Regierungspra Hemmenhofen, Germany b Berliner Str. 61, 25746 Heide, Germany c Institute for Ecosystem Research, Christian-Albrechts-University Kiel, Olshausenstr. 75, 24098 Kiel, Germany d Cornelis Dopperlaan 9, 2343 ME Oegstgeest, The Netherlands a
a r t i c l e i n f o
a b s t r a c t
Article history: Received 14 June 2016 Accepted 15 February 2017 Available online xxx
The first known Iron Age enclosure in the northern German state of Schleswig-Holstein was discovered in 2010. Archaeological excavation revealed a trench, a palisade and an occupation layer. The function of the wall and trench system remains unknown but there are several possibilities: It could have been used for protection, as a type of symbolic separation or to demarcate a cult site. The enclosure was constructed around the year zero. Charcoal samples were taken in a spatially detailed manner during excavation, as well as a new pollen core from a small spring mire directly next to the site. Anthracological analysis showed that Quercus (oak) was the main type of wood used in the construction of this enclosure. Thirteen additional wood taxa were identified, of which the next best represented is Corylus (hazel) and surprisingly a significant amount of Ilex (holly) was found. The samples did not contain Fagus (beech) or Carpinus (hornbeam), which are both common in the area today. According to pollen data, Fagus had begun to establish in the local woodland during the time of the enclosure, but did not gain importance before the migration period. By diameter analysis of the charcoals the size of the used wood (branch or trunk) was reconstructed. In addition, mean annual tree ring widths of the used wood e especially Quercus e show that the wood comes from young stems and/or branches of older trees and probably not from coppiced wood. The study shows that even small-scale archaeological excavations can yield important new data on wood utilization with a high spatial precision, which contributes to the reconstruction of local woodland composition. © 2017 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Iron Age Environmental archaeology Anthracology Landscape history Paleoecology Pollen analysis
1. Introduction The analysis of charcoal from archaeological sites provides information on ancient wood use, the composition of forests, and human influence on the landscape (e.g. Asouti and Austin, 2005; Jansen and Nelle, 2014). In the cooperation between anthracology, being a paleoecological discipline, and archaeology (also named “archaeoanthracology”, e.g. Vernet, 2002) research strategies have to be developed adjusted to the individual excavation. Depending on resources and archaeological management samples of different quantities are taken for charcoal analysis and subsequently analysed. While a wealth of archaeoanthracological studies exists in the Mediterranean part of Europe, there are still only few examples for detailed charcoal studies in the more northern parts
* Corresponding author. E-mail address: [email protected] (I.A. Lorenz).
of the continent. Given several layers over a longer time period, archaeoanthracology can show the wood usage and even the vegetation changes over a certain time, in a way comparable to pollen diagrams (e.g. from Neolithic until Bronze Age: Badal et al., 1994; for Mesolithic and Neolithic: Heinz, 1991; Heinz and Barbaza, 1998). Badal et al. (1994) differentiate between diachronous and synchronous paleoecological interpretations, the latter being relevant for the study presented here, where charcoal from an Iron Age site was obtained during a small-scale excavation. Due to limited resources or monument protection reasons, excavation areas may be small and are exploratory or exemplary. In archaeological care and preservation of monuments, invasive and destructive action at sites which are not endangered is usually kept to the minimum necessary. That said if small excavation areas are sampled in detail for natural sciences investigations, and each archaeological layer is considered, the knowledge acquired can be important even in relation to the small size of intervention. In this paper, we explore the potential as well as the limitation of
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a detailed analysis of charcoal from an Iron Age enclosure, which we complement with pollen evidence from a spring fen directly next to the site. Enclosures are circular ramparts which were built from the Neolithic till the Middle Ages. They were used either as €hn fortifications, as religious separation or as a meeting place (Da € ller-Wiering, 1999). Another famous Iron Age enclosure is and Mo Biskupin in Poland dated to 747-722 B.C.E. (Grenz and Rajewski, 1978). The Riesewohld site was discovered in 2010 by the use of Lidardata and is located in the Riesewohld forest in northern Germany as the first known of its type for the Iron Age period. An enclosure similar in size and time of construction is the structure formed by the inner wall of the ‘Heidenschanze von Sievern‘ (Niedersachsen, € rfler, 2013; see also Scho € n, 2000; Jo €ns, Germany; Arnold and Do 2010). The forest shows features of a natural, broad-leaved Central European forest with potentially ancient continuous woodland. We complement the archaeoanthracological data set with pollen data from neighbouring small spring mires to discuss the evidence for local woodland composition and change (Nelle et al., 2010). Though small in area, the charcoal sampling was very detailed, with the aim of relating samples to the enclosure structures. Our intention was (i) to identify the kind of wood (taxa and diameter) which was used by the Iron Age people, (ii) to characterize the construction of the fort by charcoal data, and (iii) to give a possible woodland scenario for the time of construction by means of combining charcoal and pollen data. The study also contributes to increase the general knowledge of prehistoric wood usage in a region where archaeoanthracological studies are still rare. Exceptions are e.g. the analysis of charcoal from an iron smelting site of the €rfler, 2000; Do €rfler and Wiethold, 2000) or a Roman Iron Age (Do diachronic study of wood utilization in burial contexts from the Neolithic until the Iron Age (Jansen et al., 2013).
2. Regional setting and study site 2.1. The archaeological site The enclosure is the first one discovered dating to the Iron Age in Schleswig-Holstein (Northern Germany) and was found by the use of Lidar-data on the area of the Riesewohld Forest, at 55e64 m a.s.l. €st’ and the Infostation It lies between the ‘Landweg Osterwohld-Ro Riesewohld (Fig. 1). A shallow trench and low wall (height
difference of maximum 0.9 m) surround the inner part, which is shaped as an irregular ellipse, 240 m long and 100 m wide, covering € rfler, 2013). In 2004, a small a total area of 1.8 ha (Arnold and Do archaeological excavation took place inside the enclosure. Ceramics findings placed the construction in the Pre-Roman Iron Age. New sections excavated in 2011e2015 revealed more ceramics, pointing to a settlement character of the structure. Dendrochronological analyses by Karl-Uwe Heußner (DAI Berlin, opinion of 30.10.2015, lab number C 81742-81768) date four Quercus, four Fraxinus and one Fagus wood samples from a well e all with a wane edge e between 11 and 31 B.C.E. This well is located in a sink at the inner rim of the east wall and near to the 2011 excavation. The AMSdating of one isolated post hole to 976-816 cal. B.C.E. shows that some activities preceded the main building phase which is placed € rfler, 2013) and the dendroaccording to ceramics (Arnold and Do evidence to around the beginning of the Common Area. Back then the wall with a surrounding rudimentary trench and a palisade between wall and trench was built. This palisade was replaced in patches over time. Later a major fire destroyed the wooden construction and produced the majority of the charcoal. The palisade seems to have been replaced after the fire on top of the remains of the levelled wall. Similar to the Riesewohld structure the early construction phase of the ‘Heidenschanze von Sievern‘ had a palisade with a sand rampart on the inside and a trench on the € n, 2000). outside (Scho
2.2. Riesewohld forest The forest covers an area of about 7 km2 (Fig. 1, Coordinates: 54 000 N, 9 120 4000 O). A moraine ridge stretches from the north to the south which originated from a later Saalian Stage. The climate is temperate, with an average annual temperature of 8.6 C and an annual precipitation of about 1000 mm (DWD, 2013). For watersaturated clouds moving eastwards and inland from the North Sea, the moraine ridge and therefore the area of the Riesewohld is the first obstacle, with its height rising from 7 m up to 64 m above sea level. In this way orographic rainfall causes higher humidity. Consequently, many springs, small spring mires and small forest streams characterize the woodland and make the area less attractive for agriculture. The humid parts of the wood especially seem to have a long woodland continuity despite their use by local people, for wood gathering or woodland grazing. The woodland is close to 90
€st’, i ¼ Infostation Riesewohld (Edupics.com Fig. 1. The Riesewohld forest is located in Schleswig-Holstein (Germany), in the district of Dithmarschen. P ¼ ‘Landweg Osterwohld-Ro and Landesamt für Vermessung and Geoinformation Schleswig-Holstein).
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the condition of a natural Central European primeval forest (Thiessen, 2011). Nowadays, besides some conifer plantations, most of the woodland is dominated by (oak-)beech woodland with numerous spots of birch-common oak or alder-ash woods in areas near groundwater and waterlogging (Dierßen, 2004; Arnold and €rfler, 2008). During the last centuries Denker, 2007; Nelle and Do this forest was a communal forest subdivided into small extensively used parcels.
3
diameter for each taxon is shown by histograms (Fig. 2). The mean tree ring width per fragment is calculated by dividing the fragments’ radial width by the ring number (Marguerie and Hunot, 2007). Marguerie and Hunot (2007) propose using only wood pieces from the outer parts of a large tree. In this study, however, we applied the approach also to fragments of smaller diameter, to take into account the possibility of coppicing. Coppiced trees show a fast growth in the first years, thus charcoals would give higher width values than those of branches.
3. Material and methods 3.3. Pollen analysis 3.1. Charcoal sampling Charcoal samples were obtained during an archaeological excavation directed by Volker Arnold in 2011. The excavation included the trench, the rampart and the inner part of the enclosure. The section is divided in a raster (partly in 1 1 m and partly in 1 0.5 m). These square and half square meters are summarized as categories “trench”, “palisade”, “rampart” and “cultural layer” for subsequent interpretation of charcoal collections. Artificial layers comprising 10e15 cm were sampled in each square and half square meter and were numbered from top (3) to bottom (12; Table 1). Samples were dry-sieved with a mesh size of 5.5 mm. In a few cases e if the soil contained too much clay e the mesh size had to be 12 mm.
A 50 cm deep peat profile “RWI” was cut out from a ca. 100 m2 large spring mire ca. 25 m south of the enclosure. Ten 2 cm3; samples (sample vertical depth 1 cm) were treated with standard procedures, including KOH digestion, HF treatment and acetylation (Faegri and Iversen, 1989; Moore et al., 1991). Pollen grains were counted with microscope magnifications of x 400 to x 1000. Pollen percentages are based on the terrestrial pollen sum, which does not include Alnus and Betula, both being treated here as local wetland pollen. The pollen diagram was made using Tilia 1.7.16 (Eric Grimm, Illinois State Museum). 4. Results 4.1. Charcoal analysis
3.2. Charcoal analysis From samples containing sufficient charcoal usually 20 fragments were analysed for every grid square and layer in this section (Table 1). For every piece the number of annual rings, the radial width of the piece, presence/absence of wane edge and the diameter class were recorded (Jansen, 2013). A total number of 1074 charcoal pieces was analysed in this way. Taxonomic identification is based on the wood anatomical atlas by Schweingruber (1990) and the charcoal reference collection of the Paleoecology Research group of the Institute for Ecosystem Research at the University of Kiel. The freshly broken pieces were analysed in their transversal, tangential and radial orientation using a stereoscope with a magnification from x 7.5e112.5 (Nikon SMZ 1500) and an incident-light microscope with a magnification from x 50-500 (Nikon ME 600 Eclipse). The small size of fragments made identification of the taxa difficult at times. Very small pieces down to 1 mm showing uniseriate rays and bigger vessels, but not multiseriate rays, could be both Quercus and Castanea (chestnut), but Castanea did not exist in this area during the time period of the enclosure. The separation of Sorbus and Pyrus/Malus/Crataegus within the subfamily Maloideae is challenging as well because the main anatomical difference e the distinct spiral thickenings of Sorbus e is hard to see on very small fragments. Pyrus pyraster, Malus sylvestris, Crataegus laevigata and Crataegus monogyna cannot be differentiated and are listed together as Pyrus/Malus/ Crataegus. The minimum diameter of the wood was analysed by using a diameter stencil (Ludemann, 1996; Nelle, 2002). The visible curvature of annual rings and the angles of wood rays were used to classify the pieces in one of the five diameter classes (up to 2 cm, >2e3 cm, >3e5 cm, >5e10 cm and >10 cm) as proposed by Ludemann and Nelle (2002). The mean diameter (mD; Formula 1) was calculated for the sum of all pieces from one taxon. It is used as an indicator for the wood diameter. Other studies employing this approach can be compared easily to each other (Jansen et al., 2013). As a reference, experiments resulted in a mean diameter for firewood of 3e4 cm, stump-shoots ca. 8 cm and construction timber 10e13 cm (Nelle et al., 2013). The percentage distribution in
An overall number of 1074 charcoals from 70 samples of the excavation 2011 were taxonomically identified. One single piece remains unidentified. Deciduous Quercus (oak) is by far the most common wood type, constituting 81% of the pieces, followed by 5% Ilex (holly), 4% Corylus (hazel), 3% Acer (maple), 2% Fraxinus (ash), 1% Tilia (lime), and with less than 1% Ulmus (elm), Prunus (stone fruit), Pyrus (pear)/Malus (apple)/Crataegus (whitethorn), Betula (birch), Alnus (alder), Populus (poplar), Sambucus (elder), Sorbus, Salix (willow) and Pinus (pine; Table 2). The charcoal from the 2011 excavation is analysed per grid square and a complete profile analysis is established in Fig. 3 and Table 1. The palisade and the rampart grid squares contained the highest charcoal concentrations. The lower layers of the palisade showed signs of four main poles. Thus more grid squares were analysed in that area. In this section a large proportion of all rampart parts is composed of Quercus (Fig. 4). The lowest number of pieces was found in the trench (52 pieces, all Quercus). Outside the palisade there were one piece each of Corylus, Fraxinus and Prunus and some Ilex pieces. In the middle of the palisade and in the rampart section there was one piece of Populus, respectively. On the inside of the palisade, which is next to the rampart, were two pieces of Ilex, Pyrus/Malus/Crataegus and Corylus. The last two taxa were also present in the middle of the rampart. There were nearly as many Ilex pieces (31) as Quercus pieces (48) at the boundary of the ‘cultural layer’. The cultural layer showed the highest taxa diversity: Apart from Quercus a lot of Corylus, Acer, Fraxinus, some Ilex, Tilia, Ulmus and few Prunus, Betula, Sambucus, Sorbus, Alnus, Salix and Pinus. The charcoal density decreases in the cultural layer with the distance from the enclosure as does the ceramic density. The diameter class distribution and the mean annual ring width provide information whether the used wood comes from older or younger trunks or branches. It was possible to attribute 987 pieces to one of the five diameter classes (1074 pieces total). The overall mean diameter is 7 cm. Most of the charcoal pieces are within the >5e10 cm diameter class, followed by class >3e5 cm and >10 cm. Quercus, Corylus, Ilex, Acer and Tilia are present in all diameter classes. Quercus is most present in the diameter classes 3e5 cm and 5e10 cm (Fig. 2). Ilex shows a very similar distribution as Quercus.
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Fig. 2. Percentage values and distribution of the diameter classes, with the mean diameter (md) value below the taxa and the total number of analysed charcoal (n). Proportion of diameter classes from Quercus, Ilex, Corylus and Acer.
Fig. 3. Classification of the section in a grid square e with designation numbers: grey Fields: analysed, black fields: no charcoal pieces available, white fields: no analysis performed.
The distribution of Corylus however is exceptional because its share is similar in each diameter class, even >10 cm. Acer has a distribution shifted to the higher classes. The total mean diameter ranges from 5.2 cm (Corylus) to 9.7 cm (Acer). Nearly half of the fragments (498 of 1074) had less than five year rings. The number of annual year rings ranges from 0 (not measurable) to 60 (Ilex). Quercus nearly covers all annual ring numbers. Ilex also has a wide spectrum of growth rings. Corylus and Acer have up to 17 rings and all other taxa e except Prunus (one piece with 27 rings) e have less than ten annual rings. The range of the mean width of annual rings varies from 0.07 mm (Corylus) to 8.5 mm (Betula) (Fig. 5).
decline is typical for the Iron Age and can be dated for around 500 € rfler et al., 2012; Arnold and Do €rfler, B.C.E. (Wiethold, 1998; Do 2013) and thus places the diagram in a period before and contemporary to the enclosure. Alnus gains higher values again in zone 3, with a slight decrease of Betula and considerable values of Rosaceae in sample 22 cm. Fagus and Carpinus do not reach values more than 2%, respectively. Quercus shows percentages between 20 and 25%.
4.2. Pollen analysis
Charcoal data are used here to interpret the structure of the circular enclosure. Sampling of charcoal was based on the grid squares. The grid borders do not match the borders of the enclosure parts (trench on the outside, followed by the palisade, the rampart and the ‘cultural layer’) in position and orientation as they have been designed prior to the identification of the (different) structures. Thus single samples might contain charcoals from different structures. Due to this problem, for example the grid squares 2451/ 52 could be included in both the palisade and the rampart (Fig. 3). A vertical evaluation is not considered, because the enclosure is
The pollen diagram includes 10 samples from 16 to 46 cm below surface (Fig. 6). Alnus and Betula were excluded from the terrestrial pollen sum, since they both grow today on the spring mire. The diagram was divided into three local pollen zones (RWI 1e3). Zone RWI 1 is characterised by high Tilia values, as well as considerable amounts of Cyperaceae grains and fern spores. In zone 2, Alnus shows a minimum, paralleled by an increase of Betula, a decrease of Tilia and Cyperaceae and the onset of the Rosaceae curve. The Tilia
5. Discussion 5.1. Enclosure: wood resource usage, construction and function
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Fig. 4. Number of analysed charcoal pieces for each square field part per taxon. The * highlights small values.
supposed to have one construction phase, and charcoal spectra are dominated by Quercus in all vertical samples. The high percentage of Quercus in the charcoal assemblage points to its use as construction timber. The high proportions in the diameter classes >5e10 cm, >3e5 cm and >10 cm show that a mixture of timber with small and bigger diameters was used (Fig. 2). The mean diameter of Quercus charcoal is 7 cm. Therefore the charcoal originates primarily from branches and young stems, or is a mixture of small branches and bigger stems. If only huge stems were used for the construction, significantly higher mean diameters would have been expected. The highest number of Ilex charcoal pieces is in the diameter class >10 cm, and Ilex has a mean diameter of 7 cm e nearly the same as Quercus. Thus, besides Quercus, Ilex could have been used for the construction of this enclosure with comparable mean diameters. The Ilex findings may originate from one single trunk (square 2552, rampart) due to the small scale of this excavation and the little amount of Ilex found. The mean annual ring width has a high variability within a range of under 0.07 up to 8.5 mm. Comparing the mean annual ring widths of Quercus, Ilex and Corylus the majority of pieces have a range from 0.6 to 2 mm (Fig. 5). There are no big differences in the mean annual growth ring width between the different diameter classes of Quercus. The fragments of the lower diameter classes seem to contain no coppiced wood, because this would have resulted in a wider growth ring width, which was not observed. Branches usually show a lower growth ring width, thus the material in the lower diameter classes comes at least in considerable part
from branches of oak. To sum up, the wood used in this enclosure comes partly from stem material as well as from crown material of bigger and older oaks. For these trees, based on our dendroanthracological approach, a mean annual ring width of 1.69 mm was calculated, thus being larger than 1.25 mm, the value calculated by Marguerie and Hunot (2007) for the Quercus construction wood of one building in the Neolithic settlement near La Hersonchatel, Ille-et-Vilaine). Jansen (2013) also measured the nais (Ple mean growth ring width and contrasted them with the number of growth rings. Grouping of charcoal findings concerning growth € rfler and Wiethold (2000) rings and radius has also been done by Do in order to make assumptions about the forest structure. In the present absence of other investigations in the region, the mean ring width serves as a base for further studies. In the future, mean ring width values and their ranges should be established from modern stems and branches and wood from trees of the region as references to be compared to the anthracological data. Furthermore, data from different areas with differing site conditions should be taken into account for comparison. Some charcoal pieces with a minimum diameter up to 10 cm show a high number of tree rings. Therefore, branches of older trees and/or slow growing trees have also been used for the construction of the enclosure. The possible origins of pieces with a bigger diameter (more than 10 cm) with a higher cambial age are manifold: age trend of older trees and/or stress (like growing on wet soil). They could originate from a thick trunk with limited growth in girth (like old trees exhibiting an age trend) or from thin trunks,
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Fig. 5. Annual growth ring width for the most represented taxa at this site (Quercus, Ilex and Corylus) varies from 0.07 mm (Corylus) to 7.5 mm (Quercus). Boxplots on the left and right side show the average growth ring width in mm from the whole analysed Quercus (standard deviation ¼ 1.01), Ilex (standard deviation ¼ 0.78) and Corylus (standard deviation ¼ 0.87) material, and in the middle part in detail the ring width of Quercus for the different diameter classes.
of bigger construction wood remains were sampled. Therefore a small section with its high and spatially differentiated number of samples seems to be sufficient to contribute to the reconstruction of the enclosure. The rich species spectrum in the cultural layer mirrors the diverse wood usage of the settlement activity. Interestingly Populus and Pyrus/Malus/Crataegus were only found at the palisade and the rampart, pointing to its use for construction rather than fire wood, which is in contrast to high amounts of Maloideae charcoals especially in Neolithic samples in central Europe (Kreuz, 1992; Damblon et al., 2001e2002; Jansen et al., 2013; Jansen and Nelle, 2014). According to the excavation the trench and rampart were with maximum 0.9 m height difference relatively flat but a function as fortification cannot be excluded. Therefore the enclosure could have been a symbolic delineation as well as a function as a fortification. Most probable the rampart collapsed and fell into the €rfler (2013) consider trench, after it lost its stability. Arnold and Do that the rampart was agriculturally used in former times, as it probably was done in the Celtic Fields in the sites’ neighborhood. The typical structure of the Celtic Fields is missing here (Arnold and €rfler, 2013): There are no plough marks on the rampart or in the Do soil profile. These structures however can only be observed under ideal circumstances. Another possible function is the use as a sanctuary. Ilex as an evergreen plant with red berries to protect this special place could be some evidence (Lauder, 2004). Nevertheless Ilex is a common plant in these (sub-)atlantic woods and it is more likely that it was a natural constituent of the Iron Age woodland, like it is today. The plant with thorny leaves was possibly indirectly promoted by woodland pasture. 5.2. The surrounding vegetation: combining pollen and charcoal
which are just a little bit thicker than 10 cm in diameter, grown on a bad site, or from a thick branch. Wet soil condition is a plausible cause for wood growth inhibition. The high number of springs in the area nowadays supports this hypothesis. Oaks grown in the shadow of beeches is unlikely since, according to pollen and charcoal evidence, Fagus did not build dense stands during the Iron Age at the site. In the cultural layer there are many different taxa like Quercus, Ilex, Corylus, Acer, Fraxinus, Tilia, Ulmus, Betula, Alnus, Populus, Sambucus, Sorbus, Salix and Pinus (Fig. 4). This indicates a varied use of wood. Many Sambucus seeds were found in the nearby excavated well. Sambucus is promoted by nutrient surplus and plain light conditions in a settlement context. The overall rich taxa diversity shows that not only the remains
In order to reconstruct the ancient vegetation in the area surrounding the enclosure we complemented the charcoal data with pollen evidence from a profile directly next to the archaeological site, as well as discuss our results in the light of a diagram from a € rfler, 2013). Additionally, around mire 800 m away (Arnold and Do 3000 charcoal pieces from 14 small-scale excavations within the area of the Riesewohld, from Neolithic to the Iron Age, and from two kiln sites dating around 1800 C.E. are available (Arnold, 2006; € rfler, 2013). This data-set shows that beside the Arnold and Do important presence of Quercus since the Neolithic, Tilia played (and still plays) a considerable role in the woodland, at least from Neolithic times onwards. As an under-represented pollen type in palynological data, its importance is revealed by anthracology. However, its presence in the woodland declines during the Iron
Fig. 6. Pollen diagram RWI from a spring mire 25 m next to the archaeological site. Black curves: pollen percentages based on terrestrial pollen sum. Grey curves: not included in the terrestrial pollen sum and calculated with the total pollen sum; Exaggeration (line with depth bars) with factor 10.
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Age, as shown in many pollen diagrams in northern central Europe. The absence of Fagus and Carpinus fits well with the timeslot of the material. Both gain in the charcoal assemblages as well as in pollen data significant proportions only after the Iron Age. They immigrate into this western part of Schleswig-Holstein even later than it can be shown by pollen and charcoal evidence for areas further east and south (Robin et al., 2011). However, even in the kiln sites from the modern period, Fagus is absent, though it is a very suitable wood to produce charcoal. Being present in the pollen assemblages but not in the charcoals, the very shadow-tolerant beech trees might have gained only limited importance in some parts of the forest but were not present in other parts. However the name “Büchen”, which is an old German word for Fagus, appears in documents from the 18th century describing the Norderwohld forest (NW of the village of Welmbüttel). This forest is similar to the Riesewohld in structure and lies 5 km north. At the enclosure, Quercus was clearly the preferred construction timber, but the samples from the cultural layer should contain at least some Fagus if it was used as wood fuel. The well which was dated in 2015 had at least three Fagus pieces in its construction timber e and even one piece dates with a wane edge to 27 B.C.E. Probably during the time of the enclosure Fagus grew in the Riesewohld already but was only used as construction timber (at least for buildings inside the settlement). However the absence of this taxon in the charcoal assemblage may be only due to the small sample size of the excavation. The charcoal analysis from the path slope excavation 2004 (272 identifications) supports this hypothesis with 13 pieces of Fagus. The sample from 2004 shows the dominance of Quercus, the other most common taxa are Fraxinus and Acer (Arnold and Denker, 2007). Next to Corylus, which has a broad share at the excavation 2011 and the path slope 2004, some Carpinus was found in the latter case only. Tilia, Sorbus, Salix, Prunus and even Pinus, which is very unusual for that time, were found at both excavation sites. The pollen diagram RWI (Fig. 6) shows the vegetation development between ca. 1000 B.C.E. and the modern period, according to biostratigraphy. High amounts of grass pollen and Pinus, in combination with a rise of Betula, show open woodland at the depth of 36e28 cm. We assume that this is the time of the enclosure, when Tilia has shown its typical Iron Age decline, Quercus is the dominant tree and Fagus as well as Carpinus do not have much importance in the local woodland composition yet. Rosaceae pollen type might represent considerable amounts of Crataegus bushes in semi-open or open woodland situations. Ilex is not present in the pollen samples, but was found in the charcoals, pointing to some minor presence in the vegetation around the site. Cereal pollen have relatively high values and match the pollen diagram from another spring fen, about 750 m distant e around the birth of Christ, as the latter profile is dated by 14C-AMS. This profile, which goes further back in time, shows that there were already settlements in this area during the € rfler, 2013). Because of the good settleBronze Age (Arnold and Do ment situation with sandy soil and the nearby spring, it is not surprising that this place had e as Neolithic, Mesolithic, Bronze Age and Iron Age findings and the pollen diagrams show e a longer settlement history. The light-demanding taxa Corylus is considerably present too e an indication that the woodland was open. Ilex-pollen grains were found in considerable amounts, indicating its presence in the woodland, probably promoted by grazing, and matching the charcoal evidence. Summarizing pollen and charcoal data, the woodland around the enclosure during the Iron Age was dominated by Quercus, with Alnus and Fraxinus trees on wet sites. The woodland was considerably opened up, by wood and timber sourcing, as well as managing arable fields. We assume a mosaic of denser and more open woodland, with a mixture of woodland grazing, cereal cultivation, timber sourcing and fuel wood collection. However, there is no
7
evidence for a broader deforestation, since the amount of arboreal pollen remains high throughout both diagrams. Thus the need for wood and timber did not completely destroy the forest, and at this point we cannot counter the hypothesis of an ancient woodland continuity in some areas of the Riesewohld forest. 6. Conclusions It was possible to reconstruct the woodland situation around an Iron Age enclosure from the transition Pre-Roman/Roman Iron Age (around the beginning of the common era) in an old-moraine forest, and the wood and timber use for different purposes by the builders of the enclosure, by using charcoal and pollen evidence. While providing a better understanding of the past, the information from a 2000 plus year old history of moderate disturbance of the woodland helps today's wood management to preserve and restore ecological diversity (Arnold and Denker, 2007; Robin et al., 2012). We postulate that low-intensity disturbances by people increased the structural diversity of the woodland resulting in today's highly valued species composition and “naturalness”. Since the Neolithic era this wood was used by humans. A mixed oak forest grew there before and during the Iron Age, which provided Quercus timber for the palisade. While some areas of the forest were opened up by timber and wood fuel sourcing, others continued to exist as woodland. The occurrence of Ilex (open forest indicator) could indicate wood-pasture as one form of exploitation. The enclosure is outstanding because it is the only known one from this time in Schleswig-Holstein. A woodland composition reconstruction solely based on the remains of timber for construction would fail because of the selective use of Quercus. In combination with samples from the cultural layer, we get a more complete taxa spectrum, even when it is not possible to provide a proportionally correct composition of species. The use of Quercus trees was only on a local scale and did not destroy the entire population, as the pollen diagrams show. Charcoal and pollen data suggest the woodland was rich in Ilex. The builders of the enclosure opened the wood and therefore the light-demanding taxa Corylus grew in this place. We postulate open woodland during the time of the enclosure. The role of Fagus, which was only found in one sample in 2004 and as building material for the well but not at the excavation in 2011, remains ambiguous: being far less suitable for construction compared to oak, its wood is usually used for fuel. Its rarity both in the pollen as well as in the cultural layer charcoal record can only be explained by its rarity in the woodland during the Iron Age, while today it is the dominant taxa. It appears like near-natural beech woodland on not too dry and not too wet mineral sites but actually it is a result of a planting from around 1880-1900. Our study shows that even limited excavations, when sampled for charcoal in a detailed way, are able to provide significant information on prehistoric wood usage and woodland composition. To cross-check their significance, local and regional pollen data, if available, should be consulted to get a more complete picture of past vegetation dynamics. However, taking samples of charcoals as a ubiquitous proxy of woodland usage is still not established as a routine in archaeological excavations, even more what concerns detailed studies with a high spatial resolution. Acknowledgements We thank the voluntary excavation team of 2011 (Walter €hl, Andreas Leistritz, Karl Kollek Denker, Heino Hünken, Karin So et al.) and Jan Hansen and Louise Bradley for proof-reading. Reviewers' comments are much appreciated, helping to improve the manuscript considerably.
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Appendix/Pictures
Table 1 Number of analysed charcoal pieces concerning square field and degradation.
Table 2 Absolute taxa number from excavation 2011
mD ¼
Taxon
Number
Quercus Ilex Corylus Acer Fraxinus Tilia Ulmus Prunus Pyrus/Malus/Crataegus Betula Alnus Populus Sambucus Sorbus Salix Pinus indet
875 50 45 35 25 16 7 4 3 3 2 2 2 2 1 1 1
nI 1cm þ nII 2:5cm þ nIII 4cm þ nIV 7:5cm þ nV 15cm PV i¼I ni
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Please cite this article in press as: Lorenz, I.A., et al., Iron Age wood usage at an enclosure in northern Germany, Quaternary International (2017), http://dx.doi.org/10.1016/j.quaint.2017.02.014