Fire and forest history of central European low mountain forest sites based on soil charcoal analysis: The case of the eastern Harz

Abstract

Long-term environmental changes in some areas of Central Europe are still poorly documented due to the lack of archives suitable for well-established paleoecological approaches. However, paleorecords of such areas would provide important insights into the Holocene vegetation history of Central Europe. To contribute to fill this gap, we conducted soil charcoal analyses to investigate fire and forest history for the eastern Harz Mountains (Germany). Soil from 15 sequences at three investigation sites was analyzed, and charcoal assemblages were extracted. The taxonomic analysis shows Holocene woodland composition changes, from post-glacial pioneer woodland, dominated by pine, to broad-leaf closed forests, dominated by oak, and succeeded by beech. The temporal distribution of accelerator mass spectrometry (AMS)-¹⁴C datings of single charcoal pieces indicates that fire events occurred regionally synchronous, mainly in the late-Pleistocene/early-Holocene and late-Holocene periods. The radiocarbon dating is supported by the description of the sampled soil sequences, which permits the identification of late-Pleistocene/early-Holocene in situ formed soil horizons, as well as evidences late-Holocene erosion-sedimentation processes. Climate seems to have triggered late-Pleistocene/early-Holocene fire events. In contrast, the increase of fires, at both local and regional scales, during the late Holocene in low flammable broad-leaf forests is interpreted as related to human activities. Finally, it is highlighted that the species spectrum of the extracted charcoal assemblages and the radiocarbon ages obtained fits regional and over-regional data, also concerning the soil charcoal concentrations that appear to be included in regional and global ranges of soil charcoal pools.

Keywords

charcoal fire geoanthracology Germany Holocene soil

Introduction

The long-term vegetation history of Central Europe has been investigated for several decades (Berglund et al., 1996; Firbas, 1949, 1952; Kalis et al., 2003). Nevertheless, some areas remain poorly documented, even at the regional level. This is the case of central European low mountain ranges. A better understanding of the vegetation history of these low mountain ranges would provide valuable insight to better understand human influence on vegetation dynamics and species distribution related to biogeography variations along a micro-/meso-climatic gradient. On a regional scale, a more complete picture of the past low mountain range environment might provide important insights into continental post-glacial species migration. Regarding large-scale processes of vegetation reestablishment from refugia, low mountain ranges may have played a key role due to their localization as a crossroad area in Central Europe (Hewitt, 1999; Tinner and Lotter, 2006). While these mountain ranges present suitable paleoarchives like mires and lakes, permitting the application of classical paleoecological approaches such as palynology, they also present considerable areas without chronologically stratified long-term archives for pollen or other paleoproxies due to specific environmental conditions of climatic, soil, and/or topographical features.

We tested a soil charcoal analysis approach in the eastern part of the Harz Mountains (Figure 1) where long-term archiving of paleoindicators in lakes and mires is absent, leaving past landscape changes unclear relative to the western and upper part of this mountain range (Beug et al., 1999; Knapp et al., 2013; Robin et al., 2013a). Thus, soil charcoal assemblages (Carcaillet and Thinon, 1996; Nelle et al., 2013) and soil sediment features (Bork and Lang, 2003) are used to investigate Holocene changes in forest composition (Robin et al., 2012) and fire history (Fesenmyer and Christensen, 2010).

Figure 1.

Maps of localization (GNU free documentation license); (a) the study area in Western Europe; (b) the southeastern part of the Harz Mountains with the sites of investigation ROS (Rosentalskopf), SIE (Siebengemeindewald), DGH (Das Grosse Holz); topographical maps (with isolines of 20 m resolution) of the investigated sites and location of the soil trenches (P) and profiles (1 to X) for (c) ROS, (d) SIE, and (e) DGH.

The aim of the research was to (1) determine the chronological patterns of fire occurrence and compare them with global-scale historical fire records (Carcaillet et al., 2002; Power et al., 2008), (2) examine forest development, and (3) evaluate the role of climate and humans in regulating fire disturbance at both local and regional scales. In addition, the research (4) compares the extracted soil charcoal quantities with other global estimates of soil charcoal (Carcaillet and Talon, 2001; Ohlson et al., 2009).

Investigation area and sites

The Harz Mountains have a northwest/southeast orientation and rise rapidly in elevation in the northwest from c. 300 m a.s.l., reaching a maximum elevation at the Brocken Top (1142 m a.s.l.). The mountain range progressively declines in elevation over a distance of approximately 80 km to the southeast to reach the Elbe alluvial lowland at c. 200 m a.s.l. This diminishing elevation correlates with climate changes from suboceanic in the northwest part at the highest elevation to continental conditions in the southeast at lower elevations. Following this gradient, current vegetation is dominated in the western area by Fagus sylvatica forests at low altitude, F. sylvatica/Picea abies at mid-elevation, and pure P. abies forests at highest elevation. Toward the east, from high montane elevation downward, vegetation changes from P. abies forests, F. sylvatica/P. abies at mid-elevation and pure F. sylvatica forests at the lowest elevation in the inner eastern Harz. F. sylvatica/Quercus petraea are the dominant forests at foothills (Bohn et al., 2004).

Following an altitudinal transect from the inner mountain range to the eastern foothills, three investigation sites were selected (Figure 1). The ‘Rosentalskopf’ (ROS; N51.42.31/E10.52.2) site is in the mountain range hinterland dominated by F. sylvatica at 500 m a.s.l. It presents a flat topography, an annual mean temperature of 6.4°C, and annual rainfall of 789 mm (respectively from Stiege and Hasselfelde climate stations; Deutscher Wetterdienst, 2011). The ‘Siebengemeindewald’ site (SIE; N51.33.1/E10.59.9) is situated approximately 30 km to the southeast at 420 m a.s.l. Forest composition is dominated by F. sylvatica mixed with Carpinus betulus and Quercus sp. It is situated on a western/northwestern facing hill slope of c. 10° inclination. The annual mean temperature is 6.8°C, and the annual rainfall is 669 mm (respectively, from Harzgerode and Hayn/Harz climate stations; Deutscher Wetterdienst, 2011). Finally, ‘Das Grosse Holz’ (DGH; N51.28.4/E11.11.1) is on the southeastern margin of the mountain range in a Quercus spp. dominated forest at 300 m a.s.l. on a south-facing slope. This site has a heterogeneous topography with a small stream valley as side slopes. Average inclination is c. 12°. The annual mean temperature is 8.2°C, and annual mean rainfall does not exceed 612 mm (respectively, from Vatterode-Graefenstuhl and Questenberg-Agnesdorf climate stations; Deutscher Wetterdienst, 2011).

Methods

Field work

On each site, a minimum of four vertical sequences were sampled, with c. 100 m distance between each other and localized at various topographical locations inside the catchment area (i.e. down-slope, mid-slope, and top-slope positions). These vertical sequences were sampled either on soil profiles or on soil trenches. Soil profiles (identified by numbers) were opened to a length of 1 m and extended downward to the bedrock. Soil trenching was conducted when soil stratigraphy was complex and if the heterogeneity of the on-site topography implies to increase the number of samples for a better representativeness. The soil trenches (identified by the letter P) were c. 10 m long and extended downward to the bedrock.

In ROS, only four soil profiles were dug (ROS1 to ROS4) due to the simple topographical and soil features at that site. In SIE, which exhibits more heterogeneous topography and soil types, two soil trenches and two additional 1 m soil profiles (SIE1 and SIE4) were opened. In DGH, which exhibits the greatest soil and topographical heterogeneity, two soil trenches were dug, from which two soil profiles were sampled (DGHP1/6 and DGHP2/5), and five soil profiles were dug (DGH1 to DGH4, and DGH7).

Each soil exposure was carefully cleaned and referenced metrically for both measurement and drawing of soil layers following Bork (2006). Observable horizon structures, border shapes, colors, and skeleton patterns have been used to identify and describe soil horizons, colluvial layers, and stratigraphy (Munsell, 2000; Schoeneberger et al., 2002; Sponagel et al., 2005).

For soil analysis in the laboratory and soil charcoal extraction, soil samples (c. 10 l) were taken from each layer – from the bedrock to the soil surface – following soil horizons, with a maximum height of 10 cm per sample layer to maintain a fine vertical resolution of the extracted charcoal assemblages. Layers were labeled in alphabetical order from surface to bedrock, with ‘A’ denoting the surface layer.

Soil analysis

Soil laboratory analyses complemented field observations to differentiate soil formation and erosion/deposition processes (colluviation; Leopold and Völkel, 2007). Horizons were described using 500 g of soil from each observable layer. Proportions of soil particles >5 mm and 5–2 mm were quantified by wet sieving. Fine particles (<2 mm) were quantified by particle laser scanning (mastersizer2000) to obtain proportions of sand, silt, and clay forming soil texture (Schoeneberger et al., 2002; Van Reeuwijk, 2002). Organic matter content was quantified in proportion to the sub-sample weight by loss-on-ignition, and pH was measured with an electronic diode in a H₂O solution. Soil horizons were described following ‘German soil nomenclature’ (Sponagel et al., 2005) and the ‘World Reference Base for Soil Resources’ (Food and Agriculture Organization (FAO, 2006).

Charcoal analysis

Soil charcoal analysis consists of quantifying and taxonomically identifying assemblies of charcoal pieces greater than 1 mm extracted from soil samples (Carcaillet and Thinon, 1996). Smaller charcoal pieces that were not taxonomically identifiable were excluded since they hardly provide any information on past forest composition. Moreover, charcoal fragments >1 mm are derived from local assemblages, providing signals in high spatial resolution (Dutoit et al., 2009; Touflan et al., 2010), depending on catchment feature and soil history (Robin et al., 2013b). To extract charcoal assemblages, samples were dried and wet-sieved to separate organic matter from mineral material. Extracted organic matter was dried and sieved through three various mesh sizes resulting in three size fractions (1–2 mm, 2–5 mm, and >5 mm). Charcoal pieces were manually selected from each of those size fractions under a stereo lens (Nikon SMZ1500, 7.5× to 112×). The quantity of charcoal is expressed as charcoal concentration (mg) per unit of weight (kg), providing the specific anthracomass (SA) in milligrams per kilogram (Talon, 2010). The SA was calculated per profile (SAP) and per sampled layer (SAL).

Taxonomical analysis was performed to determine what forest type burnt. Wood anatomy is fixed by carbonization, which is influenced by few deformations and/or transformations (Braadbaart and Poole, 2008; Théry-Parisot, 2001). In all, 30 charcoal pieces per size fraction of every sample were randomly selected for microscopic observations. Samples presenting less than 90 charcoal pieces were completely analyzed. If one of the three size fractions per sample presented less than 30 charcoal pieces, additional pieces were identified from other fractions in balanced proportion. The taxonomical identification was performed with a stereo lens (Nikon SMZ1500, 7.5×–112×) and episcopic microscope (Nikon Eclipse ME600, 100×, 200×, 500×). Identification keys and wood anatomy atlases were used (IAWA Committee, 1989; Jacquiot et al., 1973; Schweingruber, 1990a, 1990b). Charcoal pieces were compared with the paleoecology working group’s reference collection (Institute for Ecosystem Research, Kiel). Anatomical observations were performed on transverse/cross, tangential, and radial sections on freshly broken surfaces. Diagnostic criteria were wood type and structure (homogenous/softwood versus heterogeneous/hard wood), distribution ring pores (vessels), junction type between two vessels (perforation), junction type between vessels, parenchyma cells (pit), and so on (Figure 2). Identification at both the genus and species level is generally possible. However, in some cases, taxonomical identification was impossible due to dirty charcoal pieces (cover of clay sediments) and/or over-transformation (vitrified charcoal; McParland et al., 2010). Anatomical features, viewed on very small fragments, only allow taxonomical identification of an anatomical type group, for example, Tilia/Prunus. The amount of charcoal identified per sample was quantified in specific anthracomass per taxa (SAT; in milligrams per kilogram; Talon, 2010).

Figure 2.

Pictures of some wood anatomical structure of charcoal pieces from the reference collection of the Department Palaeoecology of the Institute for Ecosystem Research Institute, Christian-Albrechts University of Kiel. (a) cross-section view, with various type of pores distribution in ring (1: ring porous and multiseriate ray (deciduous Quercus 100×), 2: semi-diffuse (Fagus sylvatica 100×), 3: diffuse (Acer platanoides 200×), 4: radial pore files and aggregate rays (Carpinus betulus 100×), 5: radially oriented pore groups (Tilia platyphyllos 100×), 6: homogeneous wood structure (Pinus sylvestris 200×)); (b) ‘toothed’ pits of tracheid wall in ray (Pinus sylvestris 500×); (c) vessel with spiral thickening (Acer platanoides 200×); (d) scalariform perforation plates with more than 10 bars (Betula pendula 200×); (e) scalariform perforation plates with less than 10 bars (Corylus avellana 500×); (f) simple perforation plates (Fagus sylvatica 200×); and (g) heterogeneous rays (Salix alba 200×).

Dating strategy

Absolute dating of single taxonomically identified charcoal pieces from extracted soil charcoal assemblages yields basic chronological information. However, soils are not chronologically stratified paleoarchives. Thus, extrapolation from a limited number of dates requires important caution. Both physical (e.g. uprooting; Gavin, 2003; Šamonil et al., 2010) and biological processes (e.g. bioturbation due to earth worm activity; Darwin, 1881; Jégou et al., 1998) are sources of soil matrix mixing. Therefore, soil archives do not have strict age-to-depth correlation, so assemblages in soil can appear chronologically ‘disturbed’ (Carcaillet, 2001). To circumvent these limitations, it is necessary to select charcoal pieces for dating that correspond to key identified taxa. These are taxa that either dominate the spectrum of a considered assemblage or have potential key roles in local forest history. They should come from various depths (i.e. horizon or layers) to assess the level of assemblage mixing. Moreover, obtained chronological information should be related to erosion and sediment observations (Bork and Lang, 2003; Emadodin et al., 2011), which may provide a stratigraphic framework. This chronological data, however, should only be interpreted as ‘minimal insights’ providing instance evidence for a minimal fire frequency for a given temporal window.

Dating was done by accelerator mass spectrometry (AMS)-¹⁴C measurement of single charcoal pieces at the Kiel Leibniz-Laboratory (Grootes et al., 2004). Radiocarbon measurements were calibrated with a 2σ confidence interval on the OxCal program (Bronk-Ramsey, 2001) using the IntCal09 dataset (Reimer et al., 2009). Dated charcoal pieces were selected by best compromise between taxonomical significance (identified taxa), size (sufficient carbon for AMS dating), conservation state (dirtiness), localization of sampling profile on the site, and soil profile origin (depth). In all, 24 soil charcoal pieces were dated: 6 from the ROS site (4 from ROS1 and 2 from ROS4), 8 from the SIE site (3 from SIE1, 1 from SIEP2/2, 4 from SIE4), and 10 from the DGH site (2 from DGH2, 4 from DGH3, and DGHP2/5). Each charcoal piece was formally identified and checked.

Results

Soil description

In situ formed organo-mineral soil horizons were identified at each of the three sites. These horizons were of different types (accumulation, Bt or weathered, Bv) and with varying thickness and at various depth levels (less deep profile: SIE4 with 35 cm at max, and deepest profile: DGHP1/6 with 170 cm at max; Figure 3). Generally, the upper 5–30 cm of sampled profiles presented a high organic content forming humic horizons (Ah). Thus, soil sequences at the three sites correspond to intermediary between Cambisol and Luvisol (FAO, 2006), presenting comparable silt texture, whereas DGH samples present slightly more clay. The pH values for all profiles were comparable, oscillating between 3 and 5, depending on the depth and profiles. Organo-mineral soil horizons presented as blocky structure, and the soil sequences in ROS presented relictual plowing marks over the upper c. 20–15 cm (rp). On the upper 30–70 cm of SIE and DGH profile sites (except on DGH7), above the in situ formed organo-mineral soil horizons, brownish soil layers with granular structures corresponding to colluvial layers (M) were identified. For some profiles, it was possible to distinguish various colluvial accumulations forming distinct M layers (e.g. DGHP2/5). Distinction of several colluvial layer identification was not feasible for every sampled sequences, and in these instances, large, undivided M layers were recorded (e.g. SIE1). Only the ROS site presented no colluvial accumulation on excavated soil sequences, indicating that the sequence exclusively consisted of an in situ formed soil horizon.

Figure 3.

Stratigraphic representation of the soil profiles and trenches sequence. Big letters in dark gray circle: name of the layers of sampling, dash line: connection of the identified similar horizons/layers, and letter on the right of the stratigraphic column: type of soil horizon/layer.

Charcoal data

From the three investigated sites, c. 480 kg of dry soil was sampled (98 kg from ROS, 124 kg from SIE, and 258 kg from DGH). From these samples, c. 20 g of charcoal was extracted (7.5 g from ROS, 2.4 g from SIE, and 10 g from DGH), and c. 12.5 g (5.4 g from ROS, 2.1 g from SIE, and 5 g from DGH) was taxonomically analyzed (3764 charcoal pieces, including 1174 from ROS, 982 from SIE, and 1608 from DGH). Indeterminable charcoal pieces (31% of the charcoal pieces from ROS, 66% from SIE, and 24% from DGH) were excluded from taxonomical results, but included in the SAP and SAL, since this carbonized material provides information about fire events.

The investigated ROS soil profiles are rich in charcoal, especially ROS3 (Figure 4). However, there is no clear common pattern of SAL distribution, except the deepest layers of sampling (D, E, and F) presenting generally smaller concentrations of charcoal (Figure 5). The ROS taxonomical assemblages present 12 various identified taxa and two anatomical types (Figure 5). There was no clearly dominant taxon, even if Fagus and Pinus charcoal records were identified in greater amounts. A succession in vertical distribution of SAT was observed with Pinus-rich layers at the deeper parts of profiles than Fagus-rich layers. Other taxa were mainly identified in the upper layers of sampling (Acer, Betula). Quercus charcoal pieces were present but rare and with low SAT. One of the Quercus pieces was dated from the late-Holocene period at 31–255 cal. yr BP, as well as three Fagus charcoal pieces from 1009–1175, 931–1057, and 697–899 cal. yr BP. Two Pinus charcoal pieces dated from the early Holocene, at 10,225–10,415 and 10,771–11,165 cal. yr BP, were also obtained (Table 1). The Holocene is here subdivided in three periods: the early Holocene (11,700–8200 yr BP), the mid Holocene (8200–4200 yr BP), and the late Holocene (4200 yr BP–onward), according to Walker et al. (2012).

Figure 4.

Total soil charcoal concentration per profile (SAP) of the sampling sites ROS (profiles 1, 2, 3, and 4), SIE (profiles 1 and 4, and trenches P2/2 and P1/3) and DGH (profiles 1, 2, 3, 4, and 7, and trenches P2/5 and P1/6).

Figure 5.

ROS soil charcoal concentration (in milligrams per kilogram; x-axis below) per identified taxa (x-axis above) in soil charcoal assemblages of the soil profiles ROS1, ROS2, ROS3, and ROS4. Soil nomenclature, horizons signature, layers and depth (cm) of sampling on y-axis. (p.analy = weight (mg) proportion of taxonomically analyzed charcoal from the total charcoal concentration per profile; n = total number of taxonomically analyzed charcoal pieces (identified + indeterminable charcoal pieces >1 mm); p.indet = number proportion in % of indeterminate charcoal pieces). •: charcoal concentration <1 mg/kg; ▶: radiocarbon dates in calibrated BP (2σ interval); right column, gray stripes: total soil charcoal concentration per layer of sampling (SAL).

Table 1.

AMS-¹⁴C dates of the single charcoal pieces from the investigated sites ROS, SIE, and DGH. Calibration in BP with 2σ confidence interval, based on the IntCal09 dataset (Reimer et al., 2009).

Site	Lab ref	Layer of sampling	Depth (cm)	Taxa	Conv BP	Cal. BP
ROS	KIA38769	4E	45	Quercus	50 ± 25	31–255
	KIA42896	1B	15	Fagus	860 ± 25	697–899
	KIA43763	1D	35	Fagus	1075 ± 35	931–1057
	KIA43764	4B	35	Fagus	1180 ± 25	1009–1175
	KIA38768	1E	45	Pinus	9140 ± 40	10,225–10,415
	KIA42897	1C	25	Pinus	9610 ± 45	10,771–11,165
SIE	KIA44624	2A	5	Fagus	1120 ± 35	938–1168
	KIA43759	4A	5	Fagus	1260 ± 20	1146–1275
	KIA38766	4C	25	Fagus	1765 ± 25	1573–1806
	KIA42904	4B	15	Fagus	1850 ± 25	1715–1865
	KIA38765	1E	45	Pinus	9070 ± 40	10,180–10,280
	KIA42902	1B	15	Pinus	9600 ± 50	10,756–11,161
	KIA42903	4B	15	Pinus	9810 ± 55	11,137–11,331
	KIA43758	1C	25	Pinus	10,300 ± 35	11,848–12,378
DGH	Beta31734	3C	25	Quercus	370 ± 30	317–504
	KIA44619	2B	15	Quercus	1995 ± 25	1887–1995
	KIA43774	5B	41	Quercus	2130 ± 30	2001–2299
	KIA43773	5A	11	Quercus	2140 ± 25	2009–2300
	KIA44621	3A	5	Quercus	2230 ± 25	2154–2334
	KIA44623	5E	80	Quercus	3610 ± 35	3834–4070
	KIA44620	2F	55	Quercus	4030 ± 30	4422–4572
	KIA43775	5E	80	Quercus	6610 ± 35	7438–7566
	KIA43772	3D	35	Pinus	11215 ± 60	12,910–13,277
	KIA43770	3B	15	Pinus	11235 ± 40	12,956–13,285

AMS: accelerator mass spectrometry.

Relatively little SAP was extracted from SIE compared with ROS and DGH (Figure 4). Similar to ROS, no common patterns for SAL were observed (Figure 6). Taxonomical analysis resulted in a large proportion of indeterminable charcoal pieces. Most indeterminable pieces were not wood charcoal, but probably charred bark pieces. Nevertheless, six different taxa and one anatomical type have been identified. Fagus charcoal largely dominates the assemblages, specifically in soil profiles SIEP1/3 and SIE4. These Fagus records decrease with depth in all profiles, showing a less rich SAT below depth of c. 20 cm. The second most represented taxon is Pinus, identified in nearly all layers of sampling with variable SAT at occasional high values (SIE1C and SIE4D). Moreover, Pinus charcoal appeared in higher concentration in samples where Fagus is scarce or absent, especially in the deepest sampled layers. Other less represented taxa have been identified in various concentrations and at various depths. Similar to ROS charcoal assemblages, only a few Quercus charcoal pieces were identified (Figure 6). The chronological indications of soil charcoal assemblages from SIE consist of four Pinus charcoal pieces dated from the late-Pleistocene/early-Holocene period at 11,848–12,378; 11,137–11,331; 10,755–11,161; and 10,180–10,280 cal. yr BP, and also in four Fagus charcoal pieces dated from the late Holocene, at 938–1168, 1146–1275, 1573–1806, and 1715–1865 cal. yr BP (Table 1).

Figure 6.

SIE soil charcoal concentration (in milligrams per kilogram; x-axis below) per identified taxa (x-axis above) in soil charcoal assemblages of the soil profiles SIE1, 4 and soil profile on trenches SIEP1/3 and SIEP2/2. Soil nomenclature, horizons signature, layers, and depth (cm) of sampling on y-axis. (p.analy = weight (mg) proportion of taxonomically analyzed charcoal from the total charcoal concentration per profile; n = total number of taxonomically analyzed charcoal pieces (identified + indeterminable charcoal pieces >1 mm); p.indet = number proportion in % of indeterminate charcoal pieces). •: charcoal concentration <1 mg/kg; ▶: radiocarbon dates in calibrated BP (2σ interval); right column, gray stripes: total soil charcoal concentration per layer of sampling (SAL).

The DGH site presents highly variable SAP values comparable to those of ROS and SIE (Figure 4). The SAL indicates that the upper c. 45–40 cm of each soil profile contains high charcoal concentrations (Figure 7). Deeper layers presented weaker SAL, except for the DGHP2/5 profile. The highest values of SAL were recorded at an intermediate (c. 30–20 cm) depth level. The taxonomical analysis of the charcoal assemblages from DGH samples revealed seven taxa and two anatomical groups (Figure 7). Quercus charcoal largely dominates, best seen in DGH2, DGH4, and DGHP2/5. Fagus and Pinus charcoal records are weak with rare occurrences mainly on DGH3. This latter profile presents a vertical succession with Fagus at 40–60 cm, Pinus at 10–40 cm, and a large quantity of Quercus at 0–40 cm deep. Such taxa distribution is, however, not relevant chronologically since very different ages are present at similar depth. Other taxa are recorded sporadically, with a few cases with significant SAT (e.g. Acer). The chronological dataset from the DGH soil profiles is based on dating of 10 pieces of charcoal. Two Pinus charcoal pieces were dated from the late Pleistocene, at 12,956–13,285 and 12,910–13,277 cal. yr BP. Eight Quercus charcoal pieces were dated and include two from the mid Holocene at 7438–7566 and 4422–4572 cal. yr BP, and six from the late Holocene at 3834–4070, 2154–2334, 2009–2300, 2001–2299, 1887–1995, and 317–503 cal. yr BP (Table 1).

Figure 7.

DGH soil charcoal concentration (in milligrams per kilogram; x-axis below) per identified taxa (x-axis above) in soil charcoal assemblages of the soil profiles DGH 1, 2, 3, 4, and 7 and soil profile on trenches DGHP1/5 and DGHP2/6. Soil nomenclature, horizons signature, layers, and depth (cm) of sampling on y-axis. (p.analy = weight (mg) proportion of taxonomically analyzed charcoal from the total charcoal concentration per profile; n = total number of taxonomically analyzed charcoal pieces (identified + indeterminable charcoal pieces >1 mm); p.indet = number proportion in % of indeterminate charcoal pieces]. •: charcoal concentration <1 mg/kg; ▶: radiocarbon dates in calibrated BP (2σ interval); right column, gray stripes: total soil charcoal concentration per layer of sampling (SAL).

Discussion

Charcoal content in soil

Charcoal was found in all investigated soil sequences, with, however, a large variation of SAs (Figure 4). Actually, varying soil charcoal content can be observed within the high spatial resolution of a few meters (Asselin and Payette, 2005; Ohlson and Tryterud, 2000). Thus, although the constancy of charcoals in soil indicates past local fire events, direct quantitative interpretations are hardly feasible. When comparing extracted charcoal amounts with soil charcoal quantities reported in the literature, the charcoal content in the Central European highland is within the range of anthracomasses variation for other European mountainous areas such as the Alps, Pyrenes, Vosges, and Massif Central, in addition to other biomes like the Mediterranean and boreal areas, and dry grassland ecosystems (Table 2). Overall, these soil charcoal content variations are large, supporting the assumption that charcoal concentrations in soil are greatly heterogeneous at both local and global scales. Thus, it is unsurprising that carbon sequestration in soil (i.e. black carbon; Carcaillet and Talon, 2001; Ohlson et al., 2009) varies greatly, needing consideration at the local scale to permit relevant assessment of carbon storage in soils at broader levels. The large quantitative variability of soil charcoal records is probably due to the very complex process of charcoal formation, recording, and preservation (Forbes et al., 2006; Fréjaville et al., 2013; Ohlson and Tryterud, 2000; Scott et al., 2000). Moreover, the question still remains whether charcoal records are stable through time (De Lafontaine and Asselin, 2012; Eckmeier et al., 2010; Ohlson et al., 2009), related to key taphonomical processes of charcoal burying and fragmentation.

Table 2.

Comparison of the quantification of soil charcoal content in various ecosystems types and biomes at global scale (#: number; -: not given data).

Area	Location, country	Site code	Elevation (m a.s.l.)	mg/kg	vol^C/vol^S	mg	g/m²	Minimal size (µm)	References
Western Central Europe	Harz Mountains, Germany	ROS	500	51–193		578–3006		1000	This study
		SIE	420	15–47		285–948
		DGH	300	4–144		164–4449
	Southern Alps, France	Quey	1950–2919	0.1–9233				400	Talon (2010)
		Uba		0.3–3986
		Rest		0.02–102
		Cair		0.08–0.4
		Ses		0.23–5.85
		PRAI		125–3136				800	Touflan et al. (2010)
		PRAII		340–3774				800	Touflan et al. (2010)
		LOU	1900–2000	52–150		1700–5200		800	Robin et al. (2012)
	Inner Alps, Italy	Cad	1520–2220	100–300				2000	Favilli et al. (2010)
		Rabbi3		100–3300
		For		89,000
		Pejo6		700–2200
		Pejo10B		300–9700
		Pre		100–200
		Rabbi1		100–400
		Pia		100
	Inner Alps, France	MAUR	1960–2360	1–124		3–757		800	Carcaillet and Thinon (1996)
	Inner Alps, Switzerland	AR	2300–2800	0.11–20				400	Carnelli et al. (2004)
		BA-HO		1.7–3
		BA-LE		0.3–0.6
		HT		0–1374
		FK		0–1.6
	Franconian Jura, Germany	Hut			26–889			630	Poschlod and Baumann (2010)
		Stro			79–1224
		Pla			12–84
		Wol			33
	Vosges, France	ROSS	900–1190	0.2–465				400	Schwartz et al. (2005)
	Normandy, France	#	60–85			94–803		400	Dutoit et al. (2009)
	Pyrenees, France	Cerd	1900–2350	1–3444				400	Bal et al. (2010)
	Southern Massif Central, France	Causse Méjean	900–1200			3–156,062		2000	Vernet (2006)
	Western Schleswing-Holstein, Germany	#	30			6–563		630	Jansen et al. (2013)
	Eastern Schleswing-Holstein, Germany	STO	20–40	20–706		1030–15,300		1000	Robin et al. (2012)
	Eastern Schleswing-Holstein, Germany	WES	60	38–222		1760–7900			Robin et al. (2013c)
Mediterranean area	South-eastern France	MAY	>700	0–1500				400	Bergaglio et al. (2006)
Mediterranean area	North-western Corsica, France	FANGO	630–900	811–9979				400	Carcaillet et al. (1997)
Northern Europe	Boreal forest, Norway	#					0.1–450	125	Ohlson et al. (2009)
Northern America	Boreal forest, northern Quebec, Canada	#				0–2000		2000	Asselin and Payette (2005)
Northern America	Cumberland Plateau, Tennessee, USA	#	270–450			100–2500		2000	Hart et al. (2008)
Southern America	Northern Andes, Ecuador	GUA	3500–3900	0.1–300				400	Di pasquale et al. (2008)
Southern America	Northeastern Brazil	#	125–1000	0–1200				Ø handpicked	Pessenda et al. (2010)

Stratigraphy and chronological evidences

Radiocarbon dating of single charcoal pieces provides a temporal frame of fire occurrences. Several past fire events were detected at the local scale of each site investigated. However, because soil charcoal assemblages are not strictly chronologically stratified (Carcaillet, 2001), it remains irrelevant to extrapolate dates obtained to overall corresponding charcoal assemblages. Nevertheless, the temporal distribution of the 24 absolute radiocarbon dating of single charcoal piece, from the investigated sites permits the identification of a ‘minimal trend’ of fire frequency for the central European highland. This regional trend fits the global trend in the history of fire in Central Europe obtained through sedimentary charcoal studies (Clark et al., 1989; Robin et al., 2012, 2013a) and broadscale charcoal syntheses (Carcaillet et al., 2002; Power et al., 2008) that ultimately showed increases of fire occurrences during the late Holocene. In addition, our data concerning the late Holocene show significant fire activity during the late Pleistocene/early Holocene probably related to the presence at such period of easy flammable forest composition and structure, as developed below.

Early-Holocene fire and forest history

Temporal distribution of radiocarbon dating indicates that eight dates are from the late Pleistocene, and all from Pinus charcoal (Figure 8). This Pinus record, together with Betula and Salix, shows the late Pleistocene/early Holocene as a pine-dominated open woodland, which is in accordance with pollen data at the regional (Knapp et al., 2013; Litt, 1992; Voigt et al., 2008) and Central European scale (Lang, 1994; Litt et al., 2001). In the charcoal assemblages of the ROS site, such pioneer forest tree species are identified mainly in samples from the bottom of the sampled soil profiles (Bv horizon; Figure 5). Also in the charcoal assemblages from the SIE and DGH, the evidence of pioneer forest vegetation dominates the taxonomical spectrum only in the bottom layer (Bv or Bt horizons; Figures 6 and 7). Previous observations seem to indicate that late-Pleistocene/early-Holocene fire occurrences induced formation of charcoal assemblages that were recorded on-site and preserved in the formed soil horizon. Fires in such woodlands formed by pioneer vegetation may relate to climatic control of the fire regime, with a natural ignition of the fire events. Indeed, pine-dominated woodland is an easily flammable forest system (Bos, 2010). Thus, potential fires under climatic control may explain the results pointed at late-Pleistocene/early- Holocene dates in colluvial layers, which could have resulted from natural soil erosion related to forest cover opening from ‘wildfire’ occurrences (Pierce et al., 2004). Such early-Holocene erosion processes have already been identified and linked to climate (Dreibrodt et al., 2010). Such climate control on past fire regimes during the late Pleistocene/early Holocene is supported by radiocarbon dating synchronous, closely related to Bond events 6, 7, and 8 (Bond et al., 1997, 2001). These events represent abrupt climate changes yielding conditions more suitable to fire ignition by an increase of dryness and also decrease of temperature causing changes toward more fire-sensitive vegetation composition and structure (e.g. Tinner and Lotter, 2001). However, in its current state, our dataset for the later periods appears too weak to justify any robust hypothesis about the synchronicity of dated fire events and the post-glacial, abrupt climate change. This issue will be investigated further.

Figure 8.

Temporal distribution of the AMS-¹⁴C measurement of 23 single charcoal pieces from ROS (upper box), SIE (middle box), and DGH (lower box). Dating range in cal. yr BP (2σ interval; IntCal09 dataset); plotted on OxCal 4.1 program (Bronk-Ramsey, 2001).

Mid- to late-Holocene fire and forest history

Human impact on the Harz Mountains is scarcely documented from archaeological evidence. Nevertheless, both in the western and eastern parts of the low mountain range, human impact on forest systems is reported, at the earliest, from c. ad 700–800 and linked to mining activities (Alper, 2008; Beug et al., 1999; Matschullat et al., 1997; Von Kortzfleisch, 2008). However, here we hypothesize that humans have had substantial influence on forest systems earlier than the reported timeline. In particular, the DGH site, situated at a lower altitude with the most ‘continental location’, seems to have a long history of human influence. Only this site shows mid-Holocene fire evidences, in charcoal assemblages dominated by Quercus. Such a record appears reliable to investigations from a Neolithic settlement site at approximately 10 km SE in the floodplain of the Helme River. This site also contained an abundance of oak, used for both construction and fuel purposes (Lubos et al., 2011, 2013). In contrast, Fagus dominates charcoal assemblages of the two sites at higher altitude in inner Harz, which shows only late-Holocene–dated fire events (Figure 8). Thus, our results indicate that the outer parts of the mountain range were impacted earlier than the inner parts. Indeed, during the mid Holocene, the only evidence for a broad-leaved forest fire comes from the DGH site. At the more inner SIE and ROS sites exists a dearth of evidence for forest fires during the mid-Holocene period. These forests were probably composed of broad-leaved trees since c. 8000–7000 years and did not burn, or not significantly enough, to find today a clear signal of it, before the late Holocene, in the absence of local human activities.

In contrast, fire occurrences during late-Holocene stages were identified at all three sites (Table 1, Figure 8). These fire events occurred in ‘mature woodland’ (late succession stages) as shows the large dominance of broad-leaved taxa in the corresponding charcoal assemblages. ROS and SIE site records were dominated by Fagus with taxa often associated with the late-Holocene Fagus forest, such as Carpinus and Acer, and depending on the water availability, Alnus and Fraxinus (Figures 5 and 6). At the DGH site, Quercus dominated, with evidence of associated forest species such as Tilia, Acer, and Corylus (Figure 7). Overall, taxonomical spectra are comparable to regional and macro-scale paleoecological reconstruction of the mid- to late-Holocene forest types (Knapp et al., 2013; Lang, 1994; Litt, 1992; Litt et al., 2001; Robin et al., 2013a; Voigt et al., 2008).

The broad-leaved charcoal records from ROS, identified mainly in the upper part of the soil profiles (Ah horizon; Figure 5), result from on-site fire occurrences. Indeed, the soil charcoal assemblages of this site are extremely locally significant, since it was not identified any indications of sediment accumulation, which is fitting with the on-site flat, hilltop, topography (Figure 1). However, charcoal assemblages from the colluvial layers of SIE and DGH sites are also dominated by broad-leaf taxa (Figures 6 and 7). The presence of such colluvial accumulations are related to the steep and contrasting topography of these two sites (Figure 1). The on-site deposits of colluvial sediment probably follow removal of land cover, which could be attributed to severe and/or with high return interval, human controlled fires. This postulation is supported by the overall significant charcoal concentration in colluvial layers (SAL). Thus, the soil and fire history fits with land erosion events during the late Holocene related to removal of vegetation cover by fire in Central Europe (Cerdan et al., 2010; Dotterweich and Dreibrodt, 2010; Dreibrodt et al., 2010). This also affected the broad-leaved forest as identified here. The igniting and controlling factor of these detected fire events cannot be directly and accurately documented based on our dataset. However, because the temperate broad-leaved forests of the late Holocene in Central Europe were not an easily flammable forest structure and fuel (Krivtsov et al., 2009; Pyne et al., 1996), the identified fire events and subsequent soil erosion appear to be linked to human activity. Humans used fire to open landscapes, more or less intensively, and to keep them open (Greisman and Gaillard, 2009; Innes and Blackford, 2003).

Conclusion

Despite the stratigraphical, chronological, and taxonomical limits of soil charcoal analysis, our results report undocumented fire events and identified the related burnt forest types. Human impact on forest systems began later on the higher altitude sites of the inner area of the eastern Harz Mountain range than on southeastern foothills. Regional synchronicities of locally dated, past fire events highlight two main temporal phases of fire occurrences: one during the late Pleistocene/early Holocene and one during the late Holocene. This is consistent with the macro-scale fire history of Central Europe. These fire phases provided a significant amount of charcoal related to soil formation and erosion history permits the identification of a pioneer woodland type for the early-Holocene phase and a mature, broad-leaved forest type for the late Holocene. Such reconstructed forest types and their flammability postulate a combination of climatic control and easily flammable coniferous biomass for most ancient fire events, and human influence for the most recent ones. This insight was gathered on the local scale and extrapolated to the regional level by data comparison, in an area where stratified archives like lakes and bogs are missing, and therefore are particularly valuable. Thus, soil charcoal analysis of the Harz Mountains contributes to our knowledge of the paleoenvironmental context of Central European highlands. Moreover, on-site detected heterogeneity of soil charcoal records point out the local scale variability of fire and forest history impacting the total carbon soil budget. Thus, it appears important to further develop such quantitative aspects of soil charcoal content from local to broadscale.

Footnotes

Acknowledgements

We thank the forest managers and owners, Frank Kostenblatt, Bernd Schwarzbach, Wolf Oldershausen, and Sabine Mané, for authorizing work on the land which they are responsible for; to Olaf Kürbis for advice and discussions; and to Mathias Bahns, Hannes Knapp, Christina Pielke, and Kathleen Ryan for their great support during field work. We are grateful to the anonymous reviewer for the comments that greatly improved the paper.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

References

Alper

(2008) The Eastern Harz Mountains during the Middle Ages – The impact of mining and metal production. In: Bartels

Küpper-Eichas

(eds) Cultural Heritage and Landscapes in Europe. Bochum: Selbstverlag des Deutschen Bergbau-Museums pp. 467–488.

Asselin

Payette

(2005) Late Holocene deforestation of a tree line site: Estimation of pre-fire vegetation composition and black spruce cover using soil charcoal. Ecography 28: 801–805.

Bal

Rendu

Ruas

. (2010) Paleosol charcoal: Reconstructing vegetation history in relation to agro-pastoral activities since the Neolithic. A case study in the Eastern French Pyrenees. Journal of Archaeological Science 37: 1785–1797.

Bergaglio

Talon

Médail

(2006) Histoire et dynamique des forêts de l’ubac du massif des Maures au cours des derniers 8000 ans. Forêt méditerranéenne 27: 3–16.

Berglund

Birks

HJB

Ralska-Jasiewiczowa

. (1996) Palaeoecological Events during the Last 15 000 Years: Regional Syntheses of Palaeoecological Studies of Lakes and Mires in Europe. Chichester: John Wiley & Sons Ltd.

Beug

Henrion

Schmüser

(1999) Landschaftsgeschichte im Hochharz. Goslar: Gesellschaft zur Förderung des Nationalparks Harz e.V.

Bohn

Gollub

Hettwer

(2004) Karte der natürlichen Vegetation Europas. Bonn: Bundesamt für Naturschutz.

Bond

Kromer

Beer

. (2001) Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130–2136.

Bond

Showers

Cheseby

. (1997) A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates. Science 278: 1257–1266.

10.

Bork

(2006) Landschaften der Erde unter dem Einfluss des Menschen. Darmstadt: WBG.

11.

Bork

Lang

(2003) Quantification of past erosion and land use/land cover changes in Germany. In: Lang

Hennrich

Dikan

(eds) Long Term Hillslope and Fluvial System Modelling. Lecture Notes in Earth Sciences 101. Berlin; Heidelberg: Springer-Verlag, pp. 231–239.

12.

Bos

JAA

(2010) Lateglacial and Early Holocene vegetation history of the northern Wetterau and the Amöneburger Basin (Hessen), central-west Germany. Review of Palaeobotany and Palynology 115: 177–212.

13.

Braadbaart

Poole

(2008) Morphological, chemical and physical changes during charcoalification of wood and its relevance to archaeological contexts. Journal of Archaeological Science 35: 2434–2445.

14.

Bronk-Ramsey

(2001) Development of the radiocarbon calibration program. Radiocarbon 43: 355–363.

15.

Carcaillet

(2001) Are Holocene wood-charcoal fragments stratified in alpine and subalpine soils? Evidence from the Alps based on AMS 14C dates. The Holocene 11: 231–242.

16.

Carcaillet

Talon

(2001) Soil carbon sequestration by Holocene fires inferred from soil charcoal in the dry French Alps. Arctic, Antarctic, and Alpine Research 33: 282–288.

17.

Carcaillet

Thinon

(1996) Pedoanthracological contribution to the study of the evolution of the upper treeline in the Maurienne valley (North French Alps): Methodology and preliminary data. Review of Palaeobotany and Palynology 91: 399–416.

18.

Carcaillet

Almquist

Asnong

. (2002) Holocene biomass burning and global dynamics of the carbon cycle. Chemosphere 49: 845–863.

19.

Carcaillet

Barakat

Panaïotis

. (1997) Fire and late-Holocene expansion of Quercus ilex and Pinus pinaster on Corsica. Journal of Vegetation Science 8: 85–94.

20.

Carnelli

Theurillat

J-P

Thinon

. (2004) Past uppermost tree limit in the Central European Alps (Switzerland) based on soil and soil charcoal. The Holocene 14: 393–405.

21.

Cerdan

Govers

Bissonnais

. (2010) Rates and spatial variations of soil erosion in Europe: A study based on erosion plot data. Geomorphology 122: 167–177.

22.

Clark

Merkt

Muller

(1989) Post-glacial fire, vegetation, and human history on the northern alpine forelands, south-western Germany. Journal of Ecology 77: 897–925.

23.

Darwin

(1881) The Formation of Vegetable Mould, through the Action of Worms, with Observations on their Habits. London: John Murray.

24.

De Lafontaine

Asselin

(2012) Soil charcoal stability over the Holocene – Response to comments by Mikael Ohlson. Quaternary Research 78: 155–156.

25.

Deutscher Wetterdienst (2011) Climate + Environment. Federal Ministry of Transport, Building and Urban Development. Available at: http://www.dwd.de/bvbw/appmanager/bvbw/dwdwwwDesktop?_nfpb=true&;_windowLabel=dwdwww_main_book&switchLang=en&_pageLabel=dwdwww_start (accessed January 2011).

26.

Di Pasquale

Marziano

Impagliazzo

. (2008) The Holocene treeline in the northern Andes (Ecuador): First evidence from soil charcoal. Palaeogeography, Palaeoclimatology, Palaeoecology 259: 17–34.

27.

Dotterweich

Dreibrodt

(2010) Past land use and soil erosion processes in central Europe. PAGES News 19: 49–51.

28.

Dreibrodt

Lomax

Nelle

. (2010) Are mid-latitude slopes sensitive to climatic oscillations? Implications from an Early Holocene sequence of slope deposits and buried soils from eastern Germany. Geomorphology 122: 351–369.

29.

Dutoit

Thinon

Talon

. (2009) Sampling soil wood charcoals at a high spatial resolution: A new methodology to investigate the origin of grassland plant communities. Journal of Vegetation Science 20: 349–358.

30.

Eckmeier

Egli

Schmidt

MWI

. (2010) Preservation of fire-derived carbon compounds and sorptive stabilisation promote the accumulation of organic matter in black soils of the Southern Alps. Geoderma 159: 147–155.

31.

Emadodin

Reiss

Bork

(2011) Colluviation and soil formation as geoindicators to study long-term environmental changes. Journal of Environmental Earth Sciences 62: 1695–1706.

32.

FAO (2006) World reference base for soil resources 2006. World Soil Resources Reports, Food and Agriculture Organization of the United Nations, Rome.

33.

Favilli

Cherubini

Collenberg

. (2010) Charcoal fragments of Alpine soils as an indicator of landscape evolution during the Holocene in Val di Sole (Trentino, Italy). The Holocene 20: 67–79.

34.

Fesenmyer

Christensen

(2010) Reconstructing Holocene fire history in a southern Appalachian forest using soil charcoal. Ecology 91: 662–670.

35.

Firbas

(1949) Spät- und nacheiszeitliche Waldgeschichte Mitteleuropas nördlich der Alpen. 1: Allgemeine Waldgeschichte. Jena: G. Fischer Verlag.

36.

Firbas

(1952) Spät- und nacheiszeitliche Waldgeschichte Mitteleuropas nördlich der Alpen. 2: Waldgeschichte der einzelnen Landschaften. Jena: G. Fischer Verlag.

37.

Forbes

Raison

Skjemstad

(2006) Formation, transformation and transport of black carbon (charcoal) in terrestrial and aquatic ecosystems. Science of the Total Environment 370: 190–206.

38.

Fréjaville

Carcaillet

Curt

(2013) Calibration of charcoal production from trees biomass for soil charcoal analyses in subalpine ecosystems. Quaternary International 289: 16–23.

39.

Gavin

(2003) Forest soil disturbance intervals inferred from soil charcoal radiocarbon dates. Canadian Journal of Forest Research 33: 2514–2518.

40.

Greisman

Gaillard

(2009) The role of climate variability and fire in early and mid-Holocene forest dynamics of southern Sweden. Journal of Quaternary Science 24: 593–611.

41.

Grootes

Nadeau

Rieck

(2004) 14C-AMS at the Leibniz-Labor: Radiometric dating and isotope research. Nuclear Instruments & Methods in Physics Research 223–224: 55–61.

42.

Hart

Horn

Grissino-Mayer

(2008) Fire history from soil charcoal in a mixed hardwood forest on the Cumberland Plateau, Tennessee. Journal of the Torrey Botanical Society 135: 401–410.

43.

Hewitt

(1999) Post-glacial re-colonization of European biota. Biological Journal of the Linnean Society 68: 87–112.

44.

IAWA Committee (1989) IAWA list of microscopic feature for hardwood identification. IAWA Bulletin 10: 221–332.

45.

Innes

Blackford

(2003) The ecology of Late-Mesolithic woodland disturbances: Model testing with fungal spore assemblage data. Journal of Archaeological Science 30: 185–194.

46.

Jacquiot

Trenard

Dirol

(1973) Atlas d’anatomie des bois d’Angiospermes. Paris: Centre Technique du Bois et Fond Forestier National.

47.

Jansen

Lungershausen

Robin

. (2013) Wood charcoal from an inland dune complex at Joldelund (Northern Germany). Information on Holocene vegetation and landscape changes. Quaternary International 289: 24–35.

48.

Jégou

Cluzeau

Balesdent

. (1998) Effects of four ecological categories of earthworms on carbon transfer in soil. Applied Soil Ecology 9: 249–255.

49.

Kalis

Merkt

Wunderlich

(2003) Environmental changes during the Holocene climatic optimum in central Europe – Human impact and natural causes. Quaternary Science Reviews 22: 33–79.

50.

Knapp

Robin

Kirleis

. (2013) Woodland history in the upper Harz Mountains revealed by kiln site, soil sediment and peat charcoal analyses. Quaternary International 289: 88–100.

51.

Krivtsov

Vigy

Legg

. (2009) Fuel modelling in terrestrial ecosystems: An overview in the context of the development of an object-orientated database for wild fire analysis. Ecological Modelling 220: 2915–2926.

52.

Lang

(1994) Quartäre Vegetationsgeschichte Europas: Methoden und Ergebnisse. Jena; Stuttgart; New York: G. Fischer Verlag.

53.

Leopold

Völkel

(2007) Colluvium: Definition, differentiation, and possible suitability for reconstructing Holocene climate data. Quaternary International 162–163: 133–140.

54.

Litt

(1992) Fresh investigations into the natural and anthropogenically influenced vegetation of the earlier Holocene in the Elbe-Saale Region, Central Germany. Vegetation History and Archaeobotany 1: 69–74.

55.

Litt

Brauer

Goslar

. (2001) Correlation and synchronisation of Lateglacial continental sequences in northern central Europe based on annually laminated lacustrine sediments. Quaternary Science Reviews 20: 1233–1249.

56.

Lubos

CCM

Dreibrodt

Nelle

. (2011) A multi-layered prehistoric settlement structure (tell?) at Niederröblingen, Germany and its implications. Journal of Archaeological Science 38: 1101–1110.

57.

Lubos

CCM

Dreibrodt

Robin

. (2013) Settlement and environmental history of a multilayered settlement mound in Niederröblingen (central Germany) – A multi-proxy approach. Journal of Archaeological Science 40: 79–98.

58.

McParland

Collinson

Scott

. (2010) Is vitrification incharcoal a result of high temperature burning of wood? Journal of Archaeological Science 37: 2679–2687.

59.

Matschullat

Ellminger

Agdemir

. (1997) Overbank sediment profiles evidence of early mining and smelting activities in the Harz Mountains, Germany. Applied Geochemistry 12: 105–114.

60.

Munsell (2000) Munsell Soil Color Charts. New Windsor, NY: GretagMacbeth.

61.

Nelle

Robin

Talon

(2013) Pedoanthracology: Analysing soil charcoal to study Holocene palaeoenvironments. Quaternary International 289: 1–4.

62.

Ohlson

Tryterud

(2000) Interpretation of the charcoal record in forest soils: Forest fires and their production and deposition of macroscopic charcoal. The Holocene 10: 519–525.

63.

Ohlson

Dahlberg

Økland

. (2009) The charcoal carbon pool in boreal forest soils. Nature Geoscience 2: 692–695.

64.

Pessenda

LCR

Marques Gouveia

Souza Ribeiro

. (2010) Late Pleistocene and Holocene vegetation changes in northeastern Brazil determined from carbon isotopes and charcoal records in soils. Palaeogeography, Palaeoclimatology, Palaeoecology 297: 597–608.

65.

Pierce

Meyer

Jull

AJT

(2004) Fire-induced erosion and millennial-scale climate change in northern ponderosa pine forests. Nature 432: 87–90.

66.

Poschlod

Baumann

(2010) The historical dynamics of calcareous grasslands in the central and southern Franconian Jurassic mountains: A comparative pedoanthracological and pollen analytical study. The Holocene 20: 13–23.

67.

Power

Marlon

Ortiz

. (2008) Changes in fire regimes since the Last Glacial Maximum: An assessment based on a global synthesis and analysis of charcoal data. Climate Dynamics 30: 887–907.

68.

Pyne

Andrews

Laven

(1996) Introduction to Wildland. New York: Wiley.

69.

Reimer

Baillie

MGL

Bard

. (2009) Intcal09 and Marine09 radiocarbon age calibration curves, 0–50,000 years cal BP. Radiocarbon 51: 1111–1150.

70.

Robin

Knapp

Bork

. (2013a) Complementary use of pedoanthracology and peat macro-charcoal analysis for fire history assessment: Illustration from Central Germany. Quaternary International 289: 78–87.

71.

Robin

Knapp

Rickert

B-H

. (2013b) Comparaison de signaux anthracologiques Holocènes issus de différents types d’archives en Allemagne vers une reconstitution plus précise de l’histoire des incendies? Quaternaire 24: 167–177.

72.

Robin

Talon

Nelle

(2013c) Pedoanthracological contribution to forest naturalness assessment. Quaternary International 289: 5–15.

73.

Robin

Rickert

B-H

Nadeau

. (2012) Assessing Holocene vegetation and fire history by a multiproxy approach: The case of Stodthagen Forest (Northern Germany). The Holocene 22: 337–346.

74.

Šamonil

Král

Hort

(2010) The role of tree uprooting in soil formation: A critical literature review. Geoderma 157: 65–79.

75.

Schoeneberger

Wysocki

Benham

. (2002) Field Book for Describing and Sampling Soils, Version 2.0. Lincoln, NE: National Soil Survey Center, Natural Resources Conservation Service.

76.

Schwartz

Thinon

Goepp

. (2005) Premières datations directes de défrichements protohistoriques sur les chaumes secondaires des Vosges (Rossberg, Haut-Rhin). Approche pédoanthracologique. Comptes Rendus Geoscience 337: 1250–1256.

77.

Schweingruber

(1990a) Anatomy of European Woods. Bern; Stuttgart: Verlag Paul Haupt.

78.

Schweingruber

(1990b) Microscopic Wood Anatomy. Birmensdorf: Swiss Federal Institute for Forest, Snow and Landscape Research.

79.

Scott

Cripps

Collinson

. (2000) The taphonomy of charcoal following a recent heathland fire and some implications for the interpretation of fossil charcoal deposits. Palaeogeography, Palaeoclimatology, Palaeoecology 164: 1–31.

80.

Sponagel

Grottenthaler

Hartmann

. (2005) Bodenkundliche Kartieranleitung (5th verbesserte und erweiterte Auflage). Hannover: Bundesanstalt für Geowissenschaften und Rohstoffe.

81.

Talon

(2010) Reconstruction of Holocene high-altitude vegetation cover in the French southern Alps: Evidence from soil charcoal. The Holocene 20: 35–44.

82.

Théry-Parisot

(2001) Economie des combustibles au Paléolithique. Paris: CNRS.

83.

Tinner

Lotter

(2001) Central European vegetation response to abrupt climate change at 8.2 ka. Geology 29: 551–554.

84.

Tinner

Lotter

(2006) Holocene expansions of Fagus sylvatica and Abies alba in Central Europe: Where are we after eight decades of debate? Quaternary Science Reviews 25: 526–549.

85.

Touflan

Talon

Walsh

(2010) Soil charcoal analysis: A reliable tool for spatially precise studies of past forest dynamics: A case study in the French southern Alps. The Holocene 20: 45–52.

86.

Van Reeuwijk

(2002) Procedures for soil analysis. Technical Paper 101, Wageningen: International Soil Reference and Information Centre.

87.

Vernet

J-L

(2006) History of the Pinus sylvestris and Pinus nigra ssp. salzmanni forest in the Sub-Mediterranean mountains (Grands Causses, Saint-Guilhem-le-Désert, southern Massif Central, France) based on charcoal from limestone and dolomitic deposits. Vegetation History and Archaeobotany 16: 23–42.

88.

Voigt

Grüger

Baier

(2008) Seasonal variability of Holocene climate: A palaeolimnological study on varved sediments in Lake Jues (Harz Mountains, Germany). Journal of Paleolimnology 40: 1021–1052.

89.

Von Kortzfleisch

(2008) Die Kunst der schwarzen Gesellen. Köhlerei im Harz. Goslar: Verlag GmbH Clausthal-Zellerfeld.

90.

Walker

MJC

Berkelhammer

Björck

. (2012) Formal subdivision of the Holocene Series/Epoch: A discussion paper by a working group of INTIMATE (Integration of ice-core, marine and terrestrial records) and the Subcommission on Quaternary Stratigraphy (International Commission on Stratigraphy). Journal of Quaternary Science 27: 649–659.