Late Pleistocene and Holocene landscape history of the central Palatinate forest (Pfälzerwald, south-western Germany)

Quaternary International 222 (2010) 129–142

Contents lists available at ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Late Pleistocene and Holocene landscape history of the central Palatinate forest (Pfa¨lzerwald, south-western Germany) Christian Stolz*, Jo¨rg Grunert Johannes Gutenberg-University, Department of Geography, Johann-Joachim, Becher-Weg 21, D-55099 Mainz, Germany

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 11 September 2009

Field studies on the Late Pleistocene and Holocene landscape history were conducted in the central ¨ lzerwald, Rhineland-Palatinate, Germany) near the village of Johanniskreuz. The Palatinate Forest (Pfa structure and composition of periglacial cover beds, the young floodplain sediments of the Aschbach, Schwarzbach und Moosalbe valleys, and the sediment structure in some dry valleys, of alluvial fans and slope colluvia, were studied. The sandy cover beds are less than 10% aeolian, and in all cases only the main and basal layer are present, with no evidence of the intermediate layer. In general, the cover beds resemble those of other parts of the Central German Uplands (Mittelgebirge). As a rule, their total thickness is 100 cm, and that of the main layer 45–55 cm. Evidence from valley-floor and spring bogs, sediment sections, and historic charcoal-burning sites was used to identify palaeo-climatological, seminatural and anthropogenic landscape changes. Based on alluvial fans and slope colluvia, the following sedimentation phases could be identified for the Holocene: Preboreal, Boreal, and Subboreal (natural impact factors) and the Late Holocene, since the High Middle Ages (anthropogenic impact factors, e.g. deforestation). The influence that historical charcoal production and tillage have had on accelerating surface runoff and the formation of colluvia is discussed. This study represents the first ever chronostratigraphy of the Pleistocene cover beds and Holocene valley floor sediments of the Palatinate Forest Mts. Ó 2009 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction The slopes of the central-European uplands are coated by cover beds developed during the cold stages of the Pleistocene, most recently during the LGM and Late Glacial, after the earlier ones had been almost completely eroded. They generally show the same structure, consisting of a main, middle and basal layer (Haupt-, Mittel- und Basislage cf. Semmel, 1968; Fried, 1984; Felix-Henningsen et al., 1991; Vo¨lkel, 1995; Kleber, 1997; Sauer and FelixHenningsen, 2006; Leopold et al., 2008). The main upper layer, on average 50 cm thick, generally contains loess and volcanic key minerals of the Laacher See eruption (12.88 ka, Schmincke, 2009). The orientation of the particles of the autochthonous debris with their long axes downslope identifies them as the product of cold-phase gelifluction during summer melting. In wind- and erosion-protected positions, a middle layer could develop, rich in loess, but with little debris. The basal layer underneath, overlying the bedrock, exclusively consists of para-autochthonous periglacial

* Corresponding author. Tel.:þ49 6131 39 20975; fax: þ49 6131 39 24735. E-mail address: [email protected] (C. Stolz). 1040-6182/$ – see front matter Ó 2009 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2009.08.022

debris, also well-oriented, that represents the last Glacial, but is older than the LGM (Hu¨lle et al., in preparation). The nature of periglacial cover beds of the Bunter Sandstone ¨ lzerwald, Fig. 1) so far has region of the central Palatinate Forest (Pfa only been noted in the context of official soil mapping, but has not yet been subject to any detailed study. There is also hardly any information on the structure of the floodplains there or the floodplain sediments correlative with slope erosion. It is only from general geographical descriptions of the Pfa¨lzerwald (Pemo¨ller, 1969; Schaub and Braun, 1999; Zintl, 2006), but also from the (in part) voluminous studies on the forest and vegetation history of the Pfa¨lzerwald (Precht, 1953; Hildebrandt et al., 2007; Wolters, 2007) that information may be derived on the balancing of soil erosion and floodplain dynamics in space and time. Therefore the present study starts from the most recent publications by Hildebrandt et al. (2007) and Wolters (2007). From two pollen profiles of the vicinity of the study area (Großes Schwanental and Spesstal valleys near Johanniskreuz; Fig. 2), Hildebrandt et al. (2007) reconstructed the Late Holocene vegetation and land-use history of the Pfa¨lzerwald since the beginning of the Iron Age, from which phases of increased land use and its effect on floodplain dynamics may be derived.

130

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

¨lzerwald). Fig. 1. Location of the detailed map within Germany and the study area in the central Palatinate Forest (Pfa

The aim of this study is to develop a first chronostratigraphy for the Palatinate Forest Mts. which may also be representative for other uplands in Central Europe, especially sandstone uplands. A comprehensive geomorphological study of the Pfa¨lzerwald has been presented by Liedtke (1968), with emphasis on the escarpment and the stream terraces. An analysis of the periglacial cover beds of the slopes is followed by the study of Holocene floodplain and spring bogs as well as the semi-natural processes originating from agricultural land use, such as floodplain sedimentation and the formation of alluvial fans and Holocene colluvia. Finally, there will be a discussion of some historic stepped field margins under forest in the Lauberwald area. 2. Regional setting The Pfa¨lzerwald is the northwestern mountain rim of the Upper Rhine Graben as well as a part of the southwest-German scarplands (Fig. 1). Its highest point, the Kalmit (673 m a.s.l.) is close to Neustadt. The Pfa¨lzerwald is constructed as a whole of Bunter Sandstone. It represents the largest contiguous forest area of Germany. The much dissected escarpment of the central Pfa¨lzerwald has mainly been shaped from the (maximum) 540 m thickness of Bunter Sandstone, in particular the red sandstones and sandstone conglomerates of the Trifels, Rehberg and Karlstal beds of the Middle Bunter, tilted 1–3 WSW. Farther to the west they are overlain by the partly clayey Upper Bunter and the Lower Muschelkalk limestone (Liedtke, 1968). The study area is located near the hamlet of Johanniskreuz (Fig. 1), 470 m a.s.l., on the east-facing rim of the Karlstal scarp (Middle Bunter Sandstone, Fig. 2), the divide between the obsequent Speyerbach, draining to the Upper Rhine Graben, and the consequent Schwarzbach, with the Moosalbe tributary to it, draining westward to the Blies and Saar rivers. The escarpment (not represented in Fig. 2) consists of the Karlstal and Trippstadt beds, 80 to 140 m thick, underlying the plateau of the ‘‘Karlstal-Landterrasse’’, in the terminology of Liedtke (1968). All seven study sites (Fig. 2) are located west of the divide, on the slopes of the V-shaped

and floodplain valleys of Schwarzbach, Moosalbe and their tributaries, as well as on the floodplains themselves. With an average annual temperature of 6–7, the climate is submontane (Wolters, 2007). Above 500 m a.s.l., precipitation is as much as 1,000 mm/a. In spite of its moderate height, the Pfa¨lzerwald is classified as a subhumid upland (Mittelgebirge; Geiger et al., 1987). At the poorer sites, there are mainly stands of beech forest (Luzula-Fagetum; Alter, 1970), interspersed with planted oaks (Quercus sp), spruce (Picea abies), Douglas fir (Pseudotsuga meziesii), and occasional firs (Abies alba). Dry south-facing slopes carry mixed oak and pine forests. Wet sections of the floodplains are used as permanent grassland, and agriculture is presently restricted to the alluvial fans of the small tributaries. Large parts of the valley floors are fallow, or have been reforested decades ago, mainly with spruce.

3. Materials and methods Field work largely followed the standard of the official Bodenkundliche Kartieranleitung, 5th edition (Ad-Hoc-Arbeitsgruppe Boden, 2005) and of the international World Reference Base for Soil Resources 2006 (International Union of Soil Sciences, 2006). At nine locations in the Moosalbe, Schwarzbach and Aschbach valleys, seven of them discussed here, numerous pits were dug along selected catenas in the floodplains, on valley slopes and the adjacent plateaus. Augering to depths as much as 6 m was used to record the sediment structure of the valley floors.. All sampling points were tachymetrically surveyed. The samples taken were analyzed for grain size (Ko¨hn), organic matter (loss on ignition), pH (CaCl2), and carbonate content, and also in some cases for heavy-mineral content of the fine-sand fraction (0.063–0.2 mm), at the Geoecological Lab of the department (methods according to Blume, 2000). Dateable charcoal pieces from alluvium and colluvium were separated by an archaeobotanical elutriation procedure (Jacomet and Kreuz, 1999), determined under

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

131

Fig. 2. Study sites near the hamlet of Johanniskreuz.

the microsope by episcopic illumination. Some were the Physics Department, University of Erlangen.

14

C-dated at

4. Results 4.1. Pleistocene landscape development 4.1.1. Structure and thickness of periglacial cover beds The central parts of the Palatinate Forest are highly dissected. A typical V-shaped valley is presented in Fig. 3. The slopes are covered by beech forest, mixed with pines in south-facing sites. For the following parts of the study, it is important to describe a typical non-eroded cover bed profile (profile 1). The floodplain sediments consist of similar grain size distribution, indicating their origin from cover beds. Profile 1 (Fig. 4, 5) is situated on the slightly inclined plateau surface at the Moosalbsprung (spring) near Johanniskreuz (R 3412973, H 5466726; 465 m a.s.l.). Throughout the 115 cm depth of the pit, the material is almost free of skeletal material. The Ah horizon, only 7 cm thin, grades into the pale-brown BEw horizon, reaching 28 cm depth. The underlying Bs/C horizon is reddishbrown, developed in the lower half of the main layer, to a depth of 46 cm. The clay content of above 10% in both horizons is remarkably

high compared to the bedrock, and may reflect initial soil formation. The total silt content of the main layer is only 9%, indicating a low aeolian influence. The bedrock is nearly silt-free. Autochthonous fine and medium sand, in contrast, compose two-thirds of the grain-size spectrum. In contrast to Holocene colluvium, the main layer has a radiant reddish brown colour, is more compact and free of charcoal. Underneath the main layer there is 20 cm of the pale-red and very sandy basal layer, almost free of silt, indicating a lack of aeolian influence. The basal layer has a similar grain size distribution to the bedrock (see Fig. 3). At 66 cm the highly weathered, saprolitisized Middle Bunter Sandstone is reached, with its typical red and white banding. The saprolite could be easily dug down to 115 cm. Profile 2 (see Fig. 6 and Fig. 7) is situated on the upper slope of the Großes Schwanental (R 3414500, H 5468875; 335 m a.s.l.). It shows a typical cover bed profile of a slope position in the Palatinate Forest. On the valley slopes (Fig. 2) there are places with large boulders of Bunter Sandstone, part of a main layer about 50 cm thick. A downslope increase of skeletal material in the basal layer is typical. The SSW-oriented slope profile (Fig. 6) is more podzolic than profile 1, and may thus be classified as a cambic podzol. The humus of the Ah horizon has clearly been displaced to the Ae horizon,

132

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Fig. 3. Typical succession, central Pfa¨lzerwald.

which is grey with reddish stripes, grading to an ochre–brown horizon at 23 cm depth. The silt content is below 10%, with the clay content being a mere 3%. At 66 cm an almost skeletal-free sandy basal layer begins, to a depth of at least 100 cm. 4.1.2. Primary loess loam and colluvia: Kurz Dell At one of the ten sites studied, in the lower reach of the Kurz Dell (Fig. 2), a completely skeletal-free loess loam was identified (pH 5.5). This is of very local character. The loess loam is distributed quite unevenly across the valley section (Fig. 8). On the east-exposed slopes of the broad dry hollow there is no loess loam at all, but only the main layer with low silt content. On the west-exposed slope there are patches of 20 to 50 cm of primary loess loam overlying the sandy basal layer. It is thus a Late Glacial deposit, probably dating to the Younger Dryas, and correlates with the main layer on the opposite slope. The loess continues across the valley floor as a layer 10–15 cm thick of pure loess loam, buried by Holocene colluvium 100–120 cm

thick (Fig. 8). The silt content is more than 50%, compared to merely 4% in the overlying sandy colluvium, equivalent to that of the main layer up-valley. The layer, as well a part of an underlying sand of basal layer material, show numerous black manganese oxide spots, and may thus be regarded as the fossil Bg horizon of a stagnosol. The organic content of nearly 6% equally suggests former pedogenic development. This sediment had thus already been buried by colluvium in early Holocene. In spite of systematic elutriation of 10 litres of soil, no charcoal particles or any other archaeobotanical macro-remains could be found, suggesting that it had not been affected by human activity. The area overlain by the colluvium is more than 80 m wide. Underneath a thick, black Ah horizon, the sediment is uniformly grey–brown to a depth of 43 cm. This is not interpreted as a cambic horizon, but rather as evidence of the young age of the sedimentation of humic colluvium. At 5.5–7.5% silt and 86–92% sand, the sediment is sandier than the colluvia further upstream, suggesting some sorting down the hollow. There is hardly any skeletal

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

133

Fig. 4. (Profile 1): Cover beds on the plateau surface above the Moosalbsprung.

material, but much charcoal, decreasing down the profile. The loess loam is charcoal-free, as is the underlying basal layer. The interpretation of the profile shows that the elutriation-method generally applied in archeobotany is suitable for determining the age of a sediment as Holocene, with further information to be obtained by the archaeobotanical analysis of tree species (Schweingruber, 1990). The pH-value of the colluvium is close to 4.5. A rise to pH 5.5 coincides with the change to the loess loam. A pH value of more than 5.0 is not common for the Pfa¨lzerwald. Another cut in the upper reach of the Kurz Dell 170 m up-valley revealed a total of 2 m of alluvial fan deposits, without any loess layer at its base. This is regarded as having being deposited simultaneously with the colluvium in the centre of the Kurz Dell, though the latter is underlain by loess.

The fan deposits are almost free of skeletal material (<1%), and their grain-size composition is the same as described above. To a depth of 1.6 m, the sediment body contains numerous charcoal particles. Radiocarbon dating of a piece taken from a bright-ochre, pseudo-gleyic colluvium between 1.1 m and 1.6 m depth gave the age of 1120 – 979 BC (1s 66.8%, Erl-11138), evidence of a Subboreal phase of slope wash that was stronger than in the recent past. An anthropogenic element, although it cannot be fully excluded, is unlikely, as no archaeological evidence of settlement in the mountains during that time has been found.

4.2. Holocene and anthropogenically affected landscape development 4.2.1. Spring- and slope-situated bogs Spring and slope bogs occur in the branched headwaters of the streams as well as the small spring depressions without surface runoff during much of the year, and seepage springs, both dependent on clay beds within the Bunter Sandstone. On the acidic, nutrient-poor Middle Bunter Sandstone, round to oval small bog areas, with diameters from 10 to 20 m are common, with their mosses, mostly Sphagnum spp., underlining their oligo- to mesotrophic raised-bog character. Among the macro-remains, Sphagnum is the dominant species. Thickness of the peats rarely exceeds 130 cm. In a small bog in the headwater area of the Großes Schwanental peat thickness is 120 cm. A sand layer between 42 and 58 cm depth is evidence of a phase of colluvial deposition. Underneath the bog profile a basal layer of medium-grained sand was found, derived from saprolithic sandstone. The absence of the main layer suggests that there has been some erosion between the Late Glacial and Early to Middle Holocene.

Fig. 5. (Profile 1): Cover beds on the plateau surface above the Moosalbsprung.

4.2.2. Semi-natural floodplain sediments and buried valley-floor bogs The bogs of the Aschbach, Schwarzbach, and Moosalbe valleys are rather long, from a few hundred metres to several km, but narrow, following abandoned stream channels subparallel to the

134

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Fig. 6. (Profile 2): Cover beds of the upper slope of the Großes Schwanental valley.

presently active one. Sediments are hardly ever more than 80 cm thick, and they only occur along the middle and lower reaches, where a floodplain has developed. In most cases bog formation came to an end during the High Middle Ages, as they became buried by sandy to silty floodplain sediments originating from soil erosion on the valley slopes.

4.2.2.1. Bog of the Aschbach valley. In the Aschbach valley, upstream of Alte Schmelz south of the city of Kaiserslautern, valleyfloor bogs were studied. Several pits were dug and a cross-valley

Fig. 7. (Profile 2): Cover beds of the upper slope of the Großes Schwanental valley.

and lengthwise catena of 28 auger holes (Pu¨rckhauer) was drilled. The wet-meadow ridges only affect the uppermost 30 cm of the profiles. In former stream beds, and in particular on the south bank, the peat is up to 80 cm thick, in all cases buried beneath 30 – 40 cm of sandy to silty flood loam. In no place was peat found at the surface. Peat formation was interrupted once or twice, as indicated by the intercalation of clastic sediments, but not everywhere. The flood loam extends to both rims of the floodplain and thus covers a much larger area than the bogs which only occur close to the present streambed. It is underlain everywhere by a sandy sediment with well-rounded sandstone pebbles, the Wurmian Lower Terrace (Liedtke, 1968). Profile 3 (see Fig. 9 and Fig. 10) is situated on the floodplain of the Aschbach (southern bank) at the rim of a filled-in former stream channel (49 23’30’’ N, 744’42’’E, 287 m a.s.l.). The uppermost 32 cm of the typical profile represents artificially deposited material, grey–brown, sandy to loamy and with occasional brickand numerous charcoal fragments. To 57 cm depth is a yellow-grey, bedded flood loam with a high charcoal content decreasing with depth. The substrate is sandy to loamy, with total sand content of 69%, total silt 20%, and clay 11%. With its high silt component, it is quite similar to the main layer of the slopes and is therefore interpreted as washed down main-layer sediment. Underneath, to a depth of 90 cm, there is black valley-floor peat. At this location, no sand layers were intercalated. In the sandy transition to the overlying flood loam the organic fraction is about 35%, suggesting that the bog became gradually ‘‘choked’’ in the course of several exceptional flood events. The peat is underlain by the Lower Terrace of sandstone pebbles in a grey reduced middle sand layer. Peat samples for radiocarbon dating taken at the base (90 cm depth) and top (60 cm) reveal that bog formation started 3700 years ago, in the early Subboreal (cal. 1757 BC, 1s 67%, Erl-11138) and ended about 800 years ago (cal. 1150 AD–1216 AD, sigma 1, 42.2%, Erl-11137), during the High Middle Ages.secd. 4.2.2.2. Schwarzbach valley bog. In the Schwarzbach valley, northeast of the village of Clausen, the situation is similar. In the floodplain 100–120 m wide, along the road from Leimen to

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

135

Fig. 8. Cross section of the lower part of the Kurz Dell hollow.

Waldfischbach, there are large but thin bog areas, most likely of the same age as in the Aschbach valley, transformed into permanent grassland. In this case, however, the flood loam had not completely blanketed the peat. Instead, the upper horizon of the former bog, in a mixture of peat and sand, shows a repeated alternation of clastic sedimentation and resumed bog growth. The top of the mixed horizon, preserved under the rim of an alluvial fan, yielded the radiocarbon Iron Age date of cal. 807 BC–751 BC (1s, 43.1%, Erl11134). Underneath the mixed peat-and-sand layer are several layers of pure sand, between 37 and 90 cm thick, and below them several thin layers of peat, placed in the Late Glacial from a pine charcoal fragment dated at cal. 8657 BC – 8539 BC (1s 39.9%, Erl. 11133). The sandy layers indicate flood events which interrupted peat formation. Profile 4 (see Fig. 12 and the right part of Fig. 11) is situated on the floodplain of the Schwarzbach, NE of Clausen (4916’19’’N, 741’56’’E, 273 m a.s.l.). This profile is typical for the Schwarzbach valley floor. The surficial mixed peat-and-sand horizon extends to a depth of 37 cm, a young sandy to silty floodplain sediment typical for the

Pfa¨lzerwald. Underneath a sand layer to 47 cm depth is a dark black layer of peat, 6 cm thick, from which the dated piece of pine charcoal was taken. The peat is underlain by is sand to 61 cm, and to a depth of 90 cm by a humus sandy loam (14% organic matter, 23% silt, 19% clay). This is most likely a Late Glacial sediment with a considerable part of loess admixed, supported by the fact that in 5 litres of sediment not a single piece of charcoal was detected, suggesting that deposition took place in a still unwooded landscape. At 90 cm depth, the white sand and some pebbles of the Lower Terrace are reached. From the lower reach of the Schwarzbach, near where it joins the Blies River, Liedtke (1968) reported 120 cm of a light brown flood loam overlying 70 cm of humus sand and loam, with the upper 70 cm rich in clay, interpreted as a slackwater deposit from the Blies. He also identified at least three different Pleistocene river terraces along the Schwarzbach, from which he reconstructed a drainage pattern different from the present one. 4.2.3. Holocene alluvial fans. Due to the nature of the sandstones, the Pfa¨lzerwald is rich in small dry valleys with only intermittent

Fig. 9. (Profile 3): Alluvium-covered valley-floor bog in the Aschbach valley.

136

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Fig. 10. (Profile 3): Alluvium-covered valley-floor bog in the Aschbach valley.

runoff. Wherever they join a major valley, their alluvial fans have spread on its floodplain. Their stratigraphy and intercalation with the floodplain indicate the local landscape history. Two such fans, a smaller one in the Aschbach and a larger one in the Schwarzbach valley, were studied in detail with the whole range of methods mentioned above. 4.2.3.1. Alluvial fan of the Reif-Dellchen valley (Aschbach valley). On the north slope of the Aschbach valley, south of Kaiserslautern, upstream of the ‘‘Alte Schmelz’’, is the Reif-Dellchen, a V-shaped valley about 550 m long and 40 m deep. The alluvial fan at its mouth (Fig. 11), of oval shape, is 60 m wide (centre at 49 23’30’’N; 744’42’’E). The uppermost layer, to a depth of 30 cm, is dark brown, and underneath the colour changes to a bright ochre. The continuous decrease of its clay content from 10 to 4% suggests that the brown colour is due to in situ initial pedogenic browning. To a depth of 40 cm, there are archaeologically non-datable brick fragments and, to a depth of 77 cm, some charcoal fragments. The entire fan is very sandy throughout (total sand content 70–80%), and there is almost no skeletal material. It is barely elevated by 1 m above the foot of the slope and floodplain of the Aschbach valley. Its total thickness is 145 cm, evidence that the basal part of the fan has been buried by the floodplain sedimentation of the Aschbach, which thus has to be younger than the initiation of fan formation. None of the valleyfloor peat described above was found underneath the fan deposits.

Fig. 12. Profile 4: Floodplain of the Schwarzbach, northeast of Clausen.

Consequently the base of the fan is older than 1700 BC, the age of the bog (see above). The inferred age could be corroborated by radiocarbon dating of a piece of charcoal taken from the very base of the fan. It yielded the Boreal age of ca. 5665 B.C–5605 B.C (1s, 42.5%, Erl.-11135). Underneath the fan a thin, dark-grey floodplain gleysol in a sandy to silty sediment (silt 35%) has been buried. Below the centre of the fan some boggy material was found, most likely tracing the former thalweg of the Reif-Dellchen (Fig. 11). Outside the thalweg is a charcoal- and skeleton-free sediment of greybrown colour, which changes downward to a clear bright grey sediment. This represents the Lower Terrace sediment of the Aschbach, LGM in age. It consists mostly of medium-sized sand and contains a few sandstone pebbles. The origin of the alluvial fan thus dates to the Early Holocene, although the information gathered does not tell when exactly the increase of erosion upstream of the Reif-Dellchen occurred that led to the growth of the alluvial fan. From the small, undatable brick fragments it can be inferred that the upper 48 cm, representing about 40% of the volume of the fan, was deposited during the time of medieval agricultural expansion into the forested mountains. Thus at least for the formation of the younger part of the fan a strong anthropogenic component has to be assumed. 4.2.3.2. Alluvial fan of the Dinkelsbach valley (middle reach of the Schwarzbach valley). NNE of Clausen, the perennial Dinkelsbach has spread an alluvial fan almost 200 m wide on the Schwarzbach

Fig. 11. Cross section of the Aschbach valley upstream of Alte Schmelz, south of Kaiserslautern.

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

137

Fig. 13. Cross section of the alluvial fan of the Reif-Dellchen (Aschbach valley).

floodplain (centre at 4916’19’’N; 741’56’’E). Part of the fan is under cultivation, so that only its north-eastern rim could be studied. The fan sediment (Figs. 13 and 14) is quite rich in skeletal material (3–13%), some layers of coarser sediment indicating excessive runoff events. Charcoal content is moderate. 70–80% of the brown–ochre coloured fines, changing downwards to grey reduced iron, are medium and fine sand, the silt content rarely exceeding 10%. The clay content decreases downward. The highest value of 7% was found in the black–brown topsoil. The situation is comparable to that of the Aschbach valley. Part of the surrounding boggy floodplain of the Schwarzbach, with a humus boggy soil on top, extends underneath the rim of the fan, indicative of its younger age. This is confirmed by a charcoal sample from the humus layer at its base, which yielded a radiocarbon age of ca. 807 BC–751 BC (1s, 43.1%, Erl-11134). This was a humid phase of the Late Subboreal during which denudation processes were facilitated. As no information could be obtained from the centre of the fan, it can only be speculated that it dates to the Early Holocene or, because of its considerable size, even to the Late Pleistocene. 4.2.4. Holocene Colluvia of the historical era 4.2.4.1. Holocene Colluvia triggered by charcoal production (Kurz Dell). The Kurz Dell (dialect form for short valley; Fig. 16), 2 kmW of Johanniskreuz, is a broad dry valley, but only 500 m long, with two headwater reaches. Hildebrandt et al. (2007) have described 17 historical charcoal kiln sites of the 18th and 19th century from the

area. The charcoal was produced there for the smelters in the Karlstal valley (Forest Office Johanniskreuz, undated). The area was part of the Trippstadt private forests (Zintl, 2006; Hildebrandt et al., 2007). By means of microscopic analysis of wood species, the authors have reconstructed the aspect of the forest and its use during the time of charcoal production. In particular, during the heyday of charcoal burning during the 18th and 19th century, with the rising demand of the iron smelters, large-scale deforestation and devastation have to be assumed for the Pfa¨lzerwald and many other parts of the German Uplands. The ores, originating from Cretaceous to Tertiary chemical weathering (Felix-Henningsen, 1990), locally dug from the Bunter Sandstone, had a high content of iron (Liedtke, 1968). The reduced retention capacity led to surface wash and soil erosion in the hollows and dry valleys of mostly Pleistocene age (Liedtke, 1968). The demand for charcoal in this area rose since 1724, when the local barons (Freiherren) of the von Hacke family set up an iron smelter and several hammer mills in the Karlstal (Moosalbetal) valley, later owned and operated, up to the 1860s, by the von Gienanth family. Special attention was given to six kiln sites at the lower end of the north-eastern incised valley in the upper reach of the Kurz Dell. One of the kiln sites there is located at the bottom of a steeply inclined trench that was obviously used as a chute (Riese, Fig. 16) for sliding wood. When the wall stabilizing the circular kiln site on the down¨ bbewall) was taken down in 2004 (Hildebrandt et. al., valley side (Stu 2007), four beds of charcoal tar were exposed, each representing a period of kiln operation, separated by three beds of slopewash

Fig. 14. Cross-section of the rim of the Dinkelsbach alluvial fan in the Schwarzbach valley.

138

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Fig. 15. Lengthwise section through the layered kiln site in the Kurz Dell hollow.

sediment originating from the main and basal layer (Figs. 15 and 17). Although the authors did not exclude the possible Holocene colluvial origin of the sandy layers, they preferred the interpretation that the sand was spread there by the charcoal burner each time that charcoal production was resumed, referring to a description of that technique in a contemporary study (von Berg, 1860). During a renewed study of the kiln site, unequivocal evidence was found that the sediment layers are indeed of colluvial origin, reflecting several large runoff events in the hollow (see below). Sliding wood down the chute is likely to have accelerated the erosion. Under the present, rather dense stands of beech and old spruce, no surface wash is taking place. Some deforestation thus has to be assumed for the time of the wash processes. Hildebrandt et al. (2007) found evidence that the area had temporarily been cleared and used for agriculture in the 18th and 19th century. If there had been any major runoff events following the end of charcoal burning in the second half of the 19th century, it would not be the charcoal, but young colluvium that would make up the uppermost layer of the kiln sites.

The main argument for the quasi-natural origin of the intermediate sand layers is their irregular distribution over the kiln site. A cut through the site to the upslope rim revealed the three sediment layers referred to are directly behind the retaining wall, but six are on the opposite side. It can hardly be assumed that this reflects different numbers of repair and planation work on the opposite sites of the platform. It is more likely, instead, that during only three out of six sediment deposition events the distal side of the kiln site was reached. Another argument is that the ‘‘sand’’ is not of uniform grain size. With its content of 10% silt and 6% clay it fully corresponds to the colluvium found up- and downslope of the kiln site in the Riese-trench, as well as in the footslope colluvium to the northwest. The deviation in grain size between the several kiln layers and the surrounding colluvia is barely more than 1% in each

Fig. 16. The Riese trench in the Kurz Dell as seen from the kiln site.

¨ bbewall retaining wall. Fig. 17. Section through the Stu

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

139

Fig. 18. The lengthened profile in the balk (a) and the truncated one on the terrace surface (b).

fraction, which excludes the possibility that the sand was brought in from another place for preparing the kiln site. From the charcoal samples, the layering developed from the first half of the 18th to the second half of the 19th century. In that time interval there was a shift from an open stand of oaks with only some birch to a more open oak-beech forest with 14% birch. During the terminal phase of mass charcoal production, around 1850, the proportion of beech trees had risen to 85%. The opening of the forest by large-scale charcoal production was the cause of soil erosion in the hollow, in spite of the high permeability of the sandy substrate. 4.2.4.2. Colluvia triggered by agriculture (Lauberwald). A characteristic element of the central European cultural landscapes are landforms that are either fully man-made or developed in a quasior semi-natural way as the unintended results of human activity. It is thus not only in the Pfa¨lzerwald that such landform elements occur as terraced field margins of former agriculture that are now under forest or pasture. They are either evidence of deserted settlements or the relics of a former alternation of field and forest on the same plots (Feld-Wald-Wechselwirtschaft, cf. Born, 1989). During the medieval expansion of agricultural lands, time and again fields were cleared in parts of the forest on unsuitable soils. Years or decades later they would be abandoned, only used for grazing, or would revert to forest again. One of those deserted field areas is located in the Lauberwald forest district southwest of Johanniskreuz. There, at the margin of a plateau at 410 m a.s.l., two former field terraces, close to 150 m long and separated by a balk and step 1.2 m high, can still be clearly recognized in an open stand of beech trees (Fig. 19). In the surrounding area, numerous clearance cairns (Lesesteinhaufen) as well as a number of less well preserved terraces (cf. Zintl, 2006), are further evidence of former agriculture in the area. Hildebrandt et al. (2007) place the origin of high steps between field terraces, thought to reflect a prolonged period of ploughing in open agricultural land, in the High Middle Ages. For the time around A.D. 1600, they quote a report by forester Philipp Velmann, according to which the Lauberwald had been considerably overused and much of it had been degraded to heathland, but that there still were stands of old oaks around that were suitable for timber. There is also mention of a forest-field rotation system, which did not leave unequivocal traces in the forest. Taking all the evidence, there is thus a very likely relationship between the field terraces and High

Medieval agriculture of the monastic grange of Lauberhof, belonging to the Cistercian monastery of Eußerthal, founded in A.D. 1148. For a pedological analysis of the relict fields, several pits were dug and catenas sampled. It appeared that in the balk a natural cambisolprofile had been buried by colluvium and thus been lengthened, whereas the soil profile on both terraces had been truncated. In profile 5 (see Fig. 18, left), pit within the balk (lengthened profile), dark-brown colluvium from the field surface upslope is up to 47 cm deep. Its colour and rather high organic content of 4–6.5% suggest that it is quite young, possibly related to the forest-field rotation system. Occasional buried clearance cairns are present. Underneath the colluvium is a fossil truncated Bw horizon developed in the periglacial main layer, with a silt content of 8%. The soil surface had been eroded before being buried by the colluvium. The reddishbright basal layer, of almost pure sand, extends from 69 to 98 cm, to the highly weathered saprolithic bright-red Bunter Sandstone. In profile 6 (see Fig. 18, right), pit on the terrace below the step (truncated profile), the soil profile proper is overlain by 25 cm of dark-brown colluvium, with up to 15% skeletal material, fanning out from the higher balk above the step. The ochre–brown in-situ Bv horizon underneath is developed in the main layer which is truncated to about 15 cm. It extends to a depth of 61 cm, above the almost skeletal-free basal layer of pure sand. The typical thickness of the main layer in the Central German Uplands is about 50 cm (c.f. Fried, 1984; Vo¨lkel, 1995). The bright-red, highly weathered Bunter Sandstone, with the bedding structure still preserved, is reached at 93 cm. Both profiles confirm the quasi- or semi-natural origin of the balk and step pattern by plough-induced soil erosion below and trapping of colluvium by the grassy or shrubby vegetation above the step. The morphologically visible height difference between the depositional balk level and the top of the colluvium on the terrace below is 120 cm. Despite the archival and field evidence, the age of the field terraces can as yet only be speculated upon. 5. Discussion 5.1. Structure and thickness of periglacial cover beds In the central Pfa¨lzerwald, the Late Pleistocene periglacial cover beds are exclusively double-layered. Their total thickness within the largest contiguous forest area of Germany is around 100 cm.

140

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Fig. 19. Longitudinal slope profile in the Lauberwald.

Reflecting the ubiquitous presence of saprolitic sandstone, the substrate is invariably sandy, and the main layer has a noncarbonate, probably aeolian component (silt), of generally less than 10%. It overlies the basal layer, made up of pure reddish sand, into which, on the lower slopes, may be incorporated angular blocks of sandstone as much as 40 cm in diameter. The soils developed in them are practically carbonate-free, mostly podzolic cambisols. Only rankers have developed on the rocky parts of the escarpment rim. Pseudogleys occur in places on the plateau surface related to poor drainage above clayey Tertiary saprolite. The average thickness of the main layer, as measured in the seven pits around Johanniskreuz, is comparable with that described from other parts of the Central German Uplands, such as the Taunus (cf. Semmel, 1968; Sabel 1989; Stolz, 2008), Hunsru¨ck (Felix-Henningsen et al., 1991), or Bavarian Forest (Bayerischer Wald, Vo¨lkel, 1995). The latter described an average thickness of between 40 and 60 cm in almost all relief positions. The figures for the Pfa¨lzerwald vary between 45 and 55 cm, the thickness being quite constant throughout a valley cross section. However, it has been much less thinned by sheet erosion than, for instance, in the Hintertaunus Mountains (Stolz, 2008). This may be due to a history of less intensive agricultural land use in the Pfa¨lzerwald, as well as the high infiltration capacity of the sandy substrate, and thus reduced overland flow (cf. Liedtke, 1968). The thickness of the basal layer, as well as its composition, varies in different relief positions. In all places, though, the basal layer

consists of nothing but fully disintegrated rocks of Bunter Sandstone, without any allochthonous material. In places, as on the Lauberwald Plateau (R 3412045, H 5466740), cryoturbation forms are evident. Sandstone blocks more than 40 cm in diameter are frequent in the sandy matrix on the lower slopes. On the upper slopes, as well as on the plateau, the basal layer is almost skeletalfree, the remains of the Mesozoic-Tertiary weathering rind, within which hardly any solid rock particles have been preserved. Underneath the basal layer, the saprolitic sandstone frequently shows its preserved bedding structure, whereby it can be easily distinguished from the periglacial profile. As the plateau remnants are almost perfectly level, the thickness of the basal layer there hardly exceeds 25 cm. On the steep upper slopes the thickness is similarly low, because of the higher erosion rate there during formation of the basal layer. Consequently, due to the additional input from above, on the lower slopes the basal layer may be more than 1 m thick. Compared to other upland regions, such as the Taunus Mountains, where thicknesses of several metres have been found (Stolz, 2008), this is quite low. Primary loess loam (decalcified in-situ loess) is hardly found in the Pfa¨lzerwald, except for wind-sheltered sites in hollows and, in a single case, in a lee position to easterly winds, the likely source area being the Upper Rhine Graben. In all profiles studied, the loess has been decarbonatized. Aside from those places, loess only occurs as a component of the main layer. The same results were obtained by Sauer and Felix-Henningsen (2006) and Semmel (1968) in the

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

Rhenish Slate Mts., by Fried (1984) in the Odenwald Mts., and by Vo¨lkel (1995) in the Bavarian Forest. 5.2. Spring- and slope-situated bogs The rather humid climate of the Pfa¨lzerwald favoured the formation of spring and valley-floor bogs since the Subboreal, in particular from 1500 to 500 BC. During this time, increased humidity and cooling of the climate are known to have reigned, following the mid-Holocene Climate Optimum (Lamb, 1977; Ku¨ster, 1999). Wolters (2007) and Hildebrandt et al. (2007) have published palynological studies from the Speßtal and Schwanental bog, northwest and north of Johanniskreuz. The base of the Speßtal bog was radiocarbon-dated from a charcoal fragment, to between 400 and 200 BC. However, the base of the Schwanental bog is older than 1600 BC. The pollen spectra have been subdivided into eight zones representing developmental phases reflecting the course of vegetation and climate since the Subboreal, as well as human impact. Well-documented is the enormous spread of beech trees (Fagus silvatica) from around 750 BC to 0 BC. Since then, there has been a decrease of Fagus in favour of Quercus and Pinus (Wolter,s 2007). The simultaneous rise of the Cerealia curve suggests that there was an increasing human pressure on the forest environment since Imperial Roman times. A major human impact on the forest environment is not felt before 1100 A.D., the High Middle Ages, by the rise of the Secale (rye) pollen curve, a number of other settlement

141

indicators, and Betula spec. which, because of its demand for light, is indicative of forest clearing. There is thus evidence for the High Medieval expansion of settlement into the Pfa¨lzerwald. From the studies presented here at the Schwanental bog, it appears that soil erosion set in as early as the Roman period. This is indicated by the 16 cm layer of sand, with the peats above and below dated by Wolters (2007) to this period. 5.3. Semi-natural floodplain sediments and buried valley-floor bogs In the Aschbach valley, peat samples for radiocarbon dating taken at the base and top reveal that bog formation started 3,700 years ago, in the early Subboreal (cal. 1757 BC, 1s 67%, Erl-11138). The beginning was clearly climate-induced, as there is no evidence of human settlement for that period, unlike at the end, when it became buried in the High Middle Ages, about 800 years ago (cal. 1150 AD – 1216 AD, 1s, 42.2%, Erl-11137). This is conclusive evidence of the High Medieval expansion of agriculture in the Aschbach drainage (see Fig. 20). Forest clearing led to accelerated erosion on the slopes, so that the Aschbach, which only flows intermittently today, became temporarily overloaded with the finegrained sediment that buried the bog areas. In the Schwarzbach valley the stratigraphic situation is similar, although the valley-floor bog has a lesser organic content of 11%, compared to 36% in the Aschbach valley. It has not been covered everywhere by the younger sediments, but from the covered parts the onset of bog formation can equally be placed in the Subboreal.

Fig. 20. Synthesis of the landscape history of the central Palatinate Forest Mts.

142

C. Stolz, J. Grunert / Quaternary International 222 (2010) 129–142

In the sediment underneath the bog, remains of an older, initial bog formation have been found, with 14% of organic substance, dated from a piece of charcoal to ca. 8657 BC–8539 BC (1s, 39.9%, Erl. 11133), and thus to the Early Preboreal. The growth of the younger bog was locally interrupted by the deposition of an alluvial fan ca. cal. 807 BC–751 BC (1s, 43.1%, Erl-11134). 5.4. Alluvial fans The two alluvial fans studied were mostly shed from their tributaries during the Late Holocene, but their beginnings date at least back to the Boreal. Three phases of activity can thus be distinguished: (1) incipient formation during the Boreal, (2) reactivation during the Subboreal, and (3) considerable growth since the High Middle Ages. Field work in the Taunus Mts. yielded similar results (Stolz, 2008). The incipient formation during the Boreal is based on a radiocarbon date from the base of the Aschbachtal fan (ca. 5665 BC–5605 BC). The reactivation during the Subboreal is confirmed by the interruption of valley-bog formation in the Schwarzbach valley due to the deposition of the Dinkelsbach fan. From the brick fragments in the upper parts of the fan in the Aschbach valley,it can be calculated that at least 40% of it was deposited in historical times, in reaction to deforestation of the small tributary catchments and the soil erosion resulting (cf.. Hildebrandt et al., 2007; see Fig. 20). 5.5. Historical soil erosion Historical soil erosion in the Palatinate Forest predominantly since the High Middle Ages, going hand in hand with deforestation, was facilitated by the sandy nature of the cover beds. The reasons for reducing the tree cover were the expansion of agriculture to marginal soils, as could be documented for the gently sloping Lauberwald plateau, and the expansion of charcoal production to serve the needs of the iron smelters of the region. For the kiln site in the headwaters of Kurz Dell (Fig. 16), forest clearing accelerated runoff and led to repeated colluviation. The charcoal kiln site studied has been out of use for at least 150 years (Hildebrandt et al., 2007), but is still well-preserved, despite its location on the bottom of a V-shaped valley. As the site has not been destroyed by surface wash, it can be concluded that this process lost its significance with the regrowth of the forest after charcoal production had come to an end. In the Lauberwald, colluviation was the immediate outcome of agriculture-induced soil erosion. The occurrence of field terraces dating back as far as to the Middle Ages is well known and has frequently been described in the literature (e.g. Born, 1989). 6. Conclusions The study presented is the first of is kind for the Palatinate Forest. The results obtained are in good agreement with those on the Late Pleistocene and Holocene landform development in those other parts of the Central German Uplands that were not significantly settled before the Middle Ages. Due to the Tertiary saprolitic weathering of the Bunter Sandstone, both the cover beds of the slopes and the colluvia on the valley floors are sandy throughout. At certain periods, surface wash and colluviation also took place due to climate-induced fluctuations of forest density, as in Boreal and Subboreal times. Since the High Middle Ages, at the earliest perhaps since Roman occupation times, human economic activity caused soil erosion and colluviation. The field evidence is in good agreement with the results of pollen analysis for the region. With the introduction of modern forestry to the region in the middle of the

19th century and resulting forest recovery, soil erosion came to a complete standstill. The same happened with the retreat of agriculture from marginal soils. References Alter, W., 1970. Pfalzatlas. Speyer. Boden, Ad-hoc-Arbeitsgruppe, 2005. Bodenkundliche Kartieranleitung, 5. Auflage, Stuttgart. von Berg, C.E., 1860. Anleitung zum Verkohlen des Holzes. Ein Handbuch fu¨r Forstma¨nner. Hu¨ttenbeamte. Technologen und Cameralisten, Darmstadt. Blume, H.P. (Ed.), 2000. Handbuch der Bodenuntersuchung. Terminologie, Verfahrensvorschriften und Datenbla¨tter; physikalische, chemische, biologische Untersuchungsverfahren; gesetzliche Regelwerke. Weinheim, New York. Born, M., 1989. Die Entwicklung der deutschen Agrarlandschaft, 29. Ertra¨ge der Forschung, Darmstadt. Felix-Henningsen, P., Spies, E.-D., Zakosek, H., 1991. Genese und Stratigraphie periglazialer Deckschichten auf der Hochfla¨che des Hunsru¨cks (Rheinisches Schiefergebirge). Eiszeitalter und Gegenwart 41, 56–69. Felix-Henningsen, P., 1990. Die mesozoisch-tertia¨re Verwitterungsdecke im Rhei¨ berpra¨gung. Relief, nischen Schiefergebirge. Aufbau, Genese und quarta¨re U Boden. Pala¨oklima, 6. Forstamt Johanniskreuz, undated. Spurensuche.Kultur- und Forstgeschichte im Johanniskreuzer Wald. Teil 1 (Faltblatt), Trippstadt. Fried, G., 1984. Gestein, Boden und Relief im Buntsandstein-Odenwald. Frankfurter Geowissenschaft Arbeir D4, 201. Geiger, M., Preuß, G., Rothenberger, K.-H., 1987. Der Pfa¨lzerwald. Portra¨t einer Landschaft, Landau. Hildebrandt, H., B. Heuser-Hildebrandt and S. Wolters, 2007. Kulturlandschaftsgenetische und Bestandsgeschichtliche Untersuchungen von Kohlholzspektren aus historischen Meilerpla¨tzen, Pollendiagrammen und archivalischen Quellen im Naturpark Pfa¨lzerwald, Forstamt Johanniskreuz. Mainzer Geogr. Studien, Sonderband 3, Mainz. Hu¨lle, D., Hilgers, A. and Radtke, U., (in preparation). The potential of Optically Stimulated Luminescence for dating periglacial slope deposits – A case study from Germany. Geomorphology (Applications of luminescence dating in geomorphology). International Union of Soil Sciences, 2006. World Soil Resources reports. World reference base for soil resources. A framework for international classification, correlation and communication, 103. FAO, Rome, p. 145. Jacomet, Kreuz, 1999. Archa¨obotanik. Aufgaben, Methoden, und Ergebnisse vegetations- und agrargeschichtlicher Forschung Stuttgart. Kleber, A., 1997. Cover-beds as soil-parent materials in midlatitude regions. Catena 30, 197–213. Ku¨ster, H., 1999. Geschichte der Landschaft in Mitteleuropa. Von der Eiszeit bis zur Gegenwart, Mu¨nchen, p. 424. Lamb, H.H., 1977. Climatic history and the future. Climate – present, past and future, 2. Routledge, London, p. 835. Leopold, M., Dethier, D., Vo¨lkel, J., 2008. Shape, thickness and distribution of periglacial slope deposits at Niwot Ridge, Rocky Mountains Front Range, Colorado, USA. Zeitschrift fu¨r Geomorphologie N.F. 52 (Suppl. 2), 77–94. Liedtke, H., 1968.Die geomorphologische Entwicklung der Oberfla¨chenformen des Pfa¨lzerwaldes und seiner Randgebiete. Arbetien, Geographische Institutt Saarlandes, Saarbru¨cken. Pemo¨ller, A., 1969. Die naturra¨umlichen Einheiten auf Blatt 160 Landau i.d. Pfalz. Naturra¨umliche Gliederung Deutschlands zur Geographische Landesaufnahme 1, 200000. Bad Godesberg. Precht, V., 1953. Pollenanalytische Untersuchungen zur Kiefernfrage im Pfa¨lzerwald. Mitt. der Polichia III. Reihe 3, 150–153. Bad Du¨rkheim. Sabel, K.-J., 1989. deZur Renaissance der Gliederung periglazialer Deckschichten in der deutschen Bodenkunde. In: Frankfurter Geowissenscheften Arbeits, Serie D, Band 10, pp. 9–16. Sauer, D., Felix-Henningsen, P., 2006. Saprolite, soils and sediments in the Rhenish Massif as records of climate and landscape history. Quaternary International 156/157, 4–12. Schaub, H.-P. and G. Braun, 1999. deDer Pfa¨lzerwald. Pflanzen, Tiere, Felsen. Karlsruhe. Schmincke, H.-U., 2009. Vulkane der Eifel. Aufbau, Entstehung und heutige Bedeutung, Heidelberg. p.160. Schweingruber, F.H., 1990. Microscopic Wood Anatomy. Birmensdorf. Semmel, A., 1968. Studien u¨ber den Verlauf jungpleistoza¨ner Formung in Hessen. Frankfurter Geographische Hefte, 45. Stolz, C., 2008. Historisches Grabenreißen im Wassereinzugsgebiet der Aar zwischen Wiesbaden und Limburg. Geologische Abh, Hessen, 117, Wiesbaden. Vo¨lkel, J.,1995. Periglaziale Deckschichten und Bo¨den im Bayerischen Wald und seinen Randgebieten als geogene Grundlagen landschaftso¨kologischer Forschung im Bereich naturnaher Waldstandorte. Zietschrift fur Geomorpholgie N.F (Suppl. 96). Wolters, S., 2007. Zur spa¨tholoza¨nen Vegetationsgeschichte des Pfa¨lzerwaldes. Neue pollenanalytische Untersuchungen im Pfa¨lzer Berg- und Hu¨gelland. Eiszeitalter und Gegenwart 56, 131–161. Zintl, H., 2006. Johanniskreuz – Im Herzen des Pfa¨lzerwaldes. Eine Forst- und Waldgeschichte, Mainz.