Veget Hist Archaeobot (1997) 6:69-77 Vegetation History and

Archaeobotany © Springer-Verlag 1997

Logn , a peat bog of European ecological interest in the Massif Armorican, western France: bog development, vegetation and land-use history

Delphine Barbler and Lionel Vlsset

Laboratoire d'Ecologie et des Paltoenvironnement Atlantiques, Facult6 des Sciences de Nantes and UMR 6566 CNRS, BP 92208, F-44322 Nantes Cedex 3, France

Received Ocotober 10, 1996 / Accepted February 6, 1997

Abstract: Logn(, one of three raised bogs (Hochmoor) in the Massif Armorican, was officially designated as a nature reserve in 1987 and is of considerable ecological interest from botanical, ornithological and herpetolo- gical aspects. Palynological investigations reveal the history of local and regional vegetation during the last ca. 4000 years. From the end of the Neolithic Age to the present day, changes in the bog appear to have been con- siderably influenced by variations in local watertable level that may be of natural origin or caused by human activity. Alder carr with Osmunda regalis, which was the dominant vegetation around the periphery of the bog at ca. 4200 B.P., underwent many changes. Its final demise occurred in Gallo-Roman times when the local land- scape took on a distinctly open appearance. The first clear evidence for cereal cultivation relates to the Bronze Age. After a decline in farming at the beginning of the Iron Age, there was a strong renewal of farming in the La Ttne period, which included a distinct arable component and also records for Juglans and Castanea pollen. The timing of the introduction of walnut and chestnut to the Massif Armorican is discussed.

Key words: Palaeoenvironment - Human impact - Raised bog - Massif Arruorican

Location and nature of the site

Logn6 bog, with an area of 120 ha, lies in a depression within Brioverian schists (Visset 1968, 1969) in the lower valley of the Erdre, a tributary of the Loire (Fig. 1). It is irrigated by the Hupitres stream and immedi- ately surrounded by a lagg or transitional zone with tall sedges including Carex elata, C. pseudocyperus, C. paniculata as well as Peucedanum palustre I. This marshy area gives way to carr vegetation that includes Salix atrocinerea, Alnus glutinosa, Frangula alnus,

l Plant nomenclature follows Jalas and Suominen (1973-1983)

Correspondence to: Lionel Visset

Betula pubescens, Myrica gale and Osmunda regalis. The raised bog in the centre occupies 30 ha, in addition to which there is some 70 ha of fen vegetation.

This peat bog, within a bocage landscape in a fairly flat region, is of considerable scientific interest in the European context. The site, which was first designated as a nature reserve in 1987, contains three plant species that are protected at a national level (Drosera intermedia, D. rotundifolia and Hammarbya paludosa), and nine species protected at a regional level, i.e. Potentilla palustris, Eriophorum vaginatum, E. angusti- folium, Myrica gale, Narthecium ossifragum, Vaccinium oxycoccos, Rhynchospora alba, Utricularia minor and Pinguicula lusitanica (cf. Des Abbayes and Corillion 1953; Des Abbayes and Hamant, 1946). Herpetological interest relates to the presence of Coronella austriaca Lactp. and Lacerta viridis Laurenti. The tan-tailed war- bler (Cisticola juncidis Rafinesque) and probably the teal (Anas crecca L.) also nest here which gives consid- erable ornithological to the site.

Logn6 is the southern-most raised bog in the south- western European lowlands (Corillion 1950). Only two other bogs of this type are known from the Armorican Massif, namely Landemarais at Parign6 in Ille et Vilaine (Visset 1989) and Venec at Brennilis in Finisttre (Visset and Marguerie 1995).

The developmental history of the mire is briefly as follows. Sphagnum invaded the former lake from the pe- riphery toward the centre and initially formed a floating mass which later sank. Eventually, a peat body, 4.25 m thick at the centre, formed which has the general appear- ance of a convex lens and with highest point at c. 1 m above the peripheral lagg (Fig. 2). The bog is acidic (pH 3.5 to 4.5) and ombrotrophic, and from the point of view of species composition is of Atlantic type but with a high Nordic component (30% and 38% of the species assign- able to these categories, respectively) (Cotillon 1971). On account of its exceptional flora, the bog has attracted botanists for over a century (Gadeceau 1895).

During World War II, the peat was exploited in a tra- ditional manner. In 1945 and 1946, drainage canals were dug to enable mechanical extraction to take place, but this was abandoned for reasons of safety and aecessibil-

70

Major Imman impact I,akes or ponds Wet meadows and reed communities Swamp species and A/lyriecl gale Raised bog (I lochmoor) Raised bod and peaty coppice Peaty coppice with ()smzmda regalia

Wet cart

"~" Position of the pollen profile

2 5 0 m ( ¢ I

Fig. 1. Map showing the location of coring, and the main vegetation types at Logn6 bog and its immediate surrounds. Inset map shows the location of Logn6 within France. After L. Visset and V. Hugonnot

ity. In 1947, a Dutch firm attempted to partially drain the mire to facilitate cultivation of tulips but this project proved impracticable. In 1974, extraction of the peat was undertaken without any investigations as to the conse- quences, and in 1986 an order of the Prefect permitted continued extraction o f peat but under the supervision of scientists. In 1987, an order protected the site as a nature reserve but allowed extraction to continue. Finally, the bog has benefited from European funding (LIFE Nature programmes) and is now designated by the Habitats di- rective as part o f the Natura 2000 network of sites with natural habitats and species of European interest with a view to preservation of biological diversity.

Methods

Cores were taken within the area of the raised bog where maximum peat depth (4.25 m) was recorded (1°30 ' 4" W, 47 ° 19' 42" N; +4 m NGF2; Fig. 1). The equipment used was that developed by Visset and Hauray (1980, 1988) which consists of a corer based on the Soviet GIK type. Sediments down to 441 cm, i.e. the bottom of the basin, were sampled.

The lithology at the boring point consisted of alternating black, brown and light-coloured peat overlying 15 cm of mud. Microscopic examination of the peat indicated that it con-

2 Nivellement G6n6ral Fran~ais (present mean sea level at marseille, France)

sisted only of Sphagnum. Subsampling for pollen analysis was carried out at intervals of 5 cm in the top 180 cm and at larger intervals between 180 and 425 era. The basal mud was sam- pled at 2-cm intervals. Standard methods of preparation were used and, in the case of the clay-rich samples at the base re- moval of the mineral fraction was achieved by density separa- tion using Thoulet's fluid. Five radiocarbon dates were ob- tained. These have been calibrated according to Stuiver and Pearson (1993).

Table 1. Radiocarbon dates fbr core from Logn6 bog

l~C Lab. Depth Peat type Age Age no. (cm) (B.P.) (calibrated,

2or range)

A8106 60 - 65 Light peat 610 4- 50 A.D. 1290-1428 A8697 85 - 90 Black peat 670 4- 55 A.D. 1268-1406 A7593 150 -155 Light peat 2265 ± 65 406- 168 B.C. A7594 340 -345 Brown peat 2995 4- 65 1404-1006 B.C. A7592 427 -432 Peaty mud 4190 +100/-95 3023-2471 B.C.

Pol len analyt ical results

The pollen percentage data are based on the sum of all taxa except fern spores and Selaginella (Fig. 3). Four- teen local pollen assemblage zones have been distin- guished as follows:

Zone a (441-425 cm) This corresponds to the muddy layer and reflects the be- ginning of colonisation by pioneer aquatic and semi- aquatic species (Sphagnum, Potamogeton, Nymphaea, etc.). There is high arboreal pollen (AP) representation (80 to 90%), with Alnus (50 to 60%) and Quercus domi- nant. Other arboreal taxa are sporadical ly represented and the decline o f Tilia has begun.

Zone b (425-405 cm) Peat formation has now begun (cf. change in lithology) and this continues to the top of the diagram. Alnus is dominant in the carr and Carex species, Osmunda regalis

71

and helophytes are present in the lagg. On the surround- ing hillsides, Quercus is dominant whereas Tilia and Corylus have practically disappeared.

Zone c (405-3 70 cm) This zone is marked by a considerable decline in Alnus which now accounts for no more than 20% but AP re- mains at c. 80% due to increase in Salix, Rhamnus and Corylus. Aquatic taxa are poorly represented.

Zone d (370-350 cm) In this zone Alnus increases to achieve 40%, whereas the curves for Salix and Quercus decline sharply. Corylus, Myrica and Rhamnus show an appreciable increase, and there is a small increase in Poaceae. The first K oxy- coccos pollen is recorded 350 cm.

Zone e (350-315 cm) This zone is characterised by a sharp decline in Alnus which tends to stabilise at ca. 10%. At the same time, the curves for Salix, Myrica and Rhamnus decline and Poaceae representation rises sharply to achieve 40% and there is also increased representation of Cichorioideae, nitrophilous taxa and Cyperaceae. This results in a sub- stantial shift o f the AP/NAP ratio with AP declining to ca. 40%. Fagus and Polypodiaceae are also represented and there is a single record of Juglans at 350 era.

Zone f(315-295 cm) In this zone Alnus continues to decline and falls to less than 10%. Poaceae representation falls sharply to less than 10% and Cichorioideae, nitrophilous taxa and Cyperaceae also decline. There are peaks in the curves for Fagus, Corylus, Quercus and Polypodiaeeae.

Zone g (295-265 em) This zone is characterised by a rapid rise in Alnus, the values for which then remain steady at ca. 60%. Poaceae and Cyperaceae decline to less than 5% and AP once again is close to 80%.

Zone h (265-205 cm) Near the base of there is a decline in Alnus which then almost recovers to its initial value. The curves for Salix, Corylus and Rhamnus rise, Poaceae, Cyperaceae and

+In

-l~r

can cart ,,.~,~.~ lagg • ' I

raised bog I I

~ ~ : , < , ; ) , ~ -.e' : : , , ; 2 : ~,:,~., , : e ; . , L £ r r " ; ~ : .....

heather and Myrica gale J ~ ~ - ~ ..... ' " :~-~-._'=-._-" "__~-'2:=.

Sphagnum peat - freshwater

• grey m~ld -

Fig. 2. Sectional view showing the stratigraphy at Logn6 bog

72

Polypodiaceae have very low representation and Osmunda achieves its maximum.

cal phases are characterised mainly by substantial varia- tion in the curve of Alnus.

Zone I (205-160 cm) This zone is characterised by the substantial decline in Alnus to ca. 5% and also a decline in Rhamnus and Salix so that there is a considerable decrease in AP. At the same time, Poaceae rises to 30% and also the curves of the nitrophilous taxa, especially Plantago and Brassica- ceae, and Rosaceae rise. Cyperaceae and Polypodiaceae also rise and the first rise in Ericaceae (Erica and Calluna) is recorded.

Zonej (160-110 cm) In this zone Cerealia, which are recorded sporadically in earlier levels, now form a substantial curve. Other taxa indicative of arable farming, as well as Poaceae, nitrophilous species and Asteroideae increase, there is a short Juglans curve, and the first pollen of Castanea ap- pears. Cyperaceae and Polypodiaceae achieve maximum values, the Osmunda curve is interrupted and Sphagnum peaks for the first time. Quercus, which increased con- siderably in the preceding zone, reaches its maximum (35%) and then declines sharply (to 10%).

Zone k (110-95 cm) Much charcoal was noted in samples from this zone, which suggests firing both within and in the vicinity of the bog. This probably accounts for the lack of records in one or more samples for several pollen taxa, including Rumex, Cerealia, Calluna, Plantago, Asteroideae, Cichorioideae, Corylus, Fagus and Sphagnum. Quercus, however, increases to more than 30% but the other AP curves remain stable.

Zone I (95-50 cm) This zone is characterised by the expansion of Calluna (to ca. 70%) andErica. Quercus declines from 30% at 95 cm to only 5% at 80 cm and Alnus is poorly represented. Myrica, on the other hand, rises. Castanea and Juglans are fairly consistently recorded and there is also a marked increase in Cerealia and taxa associated with ar- able farming. Sphagnum achieves two high peaks in this zone and the Cyperaceae curve declines to low values and shows no recovery after this.

Zone m (50-15 cm) Myrica achieves substantial values in this zone and Poaceae also increase. Cerealia achieve maximum repre- sentation and arable indicators, as well as the trees, Cas- tanea and Juglans, attain maximum representation. Fagopyrum and Cannabis are also well represented and Quercus declines. Sphagnum achieves has high values.

Zone n (15-5 cm) In this, the uppermost zone, present conditions are repre- sented. Note the substantial representation of Calluna, Erica, Corylus, Betula and Myrica. Taxa indicative of arable farming decline and AP also decreases.

In addition to the local pollen zones, six ecological phases are also distinguished [phases I-VI, Fig. 3; cf. Voeltzel (1987) for definition of a phase]. The ecologi-

Interpretation and discussion

Chronology

Radiocarbon dating, the curve for Fagus, and the very low values for Tilia and Ulmus all point to the fact that the record relates mainly to the Subatlantic period (from 400 cm, i .e.c. 3600 B.P., to the top of the profile) as recognized in the Armorican chronology (Morzadec- Kerfourn 1974; Visset 1979;Voetzel 1987; Marambat 1992). Only the first centimetres of sediment (411 to 400 era) belong to the Subboreal period. Thus, this diagram covers prehistoric times (from the end of the Neolithic Age to around 3800 BP) and protohistoric times (Bronze Age, i.e. 3800-2800 B.P., and Iron Age, 2800-2200 B.P.) as well as historic times from the Gallo-Roman period (200 to 1200 B.P.) to the Middle Ages into the present day.

The pollen data

The pollen diagram reveals the changes in vegetation that occurred in three different habitats, namely, in the mire, at the mire periphery and on the surrounding min- eral soils (Fig. 4; Table 2). The development of the veg- etation will be considered in terms of six phases.

Phase L A mud-lined basin existed before the develop- ment of Sphagnum-rich bog at the end of the Neolithic (ca. 4190 B.P.). This basin supported aquatic and semi- aquatic plants and was surrounded by alder woodland with Osmunda (a character species of carr communities) and some BetuIa, Salix and Fraxinus. The adjacent hill- sides were covered with oaks and small populations of Tilia and Corylus. Quercus ilex, which is native to the region, may also have been present.

Sphagnum peat began to form from the margins to- ward the centre of the basin. This change is reflected in the change in stratigraphy at 4.25 m. During this phase, and until the end of zone j in phase VI, Sphagnum repro- duced essentially by vegetative means, with very little sporulation.

Phase 11. At the beginning of this phase, the alder wood- land declined steadily and this trend continued during the greater part of the Bronze Age. This probably facili- tated the development, at the edge of the small lake, of a willow-dominated carr with Myrica and Rhamnus. Thus, there was a transition from a closed formation (alder carr with Osmunda) to more open formations with helophytes (Thalictrum, Scrophulariaceae, Lysimachia, Sparga-

) Fig. 3. Percentage pollen diagram from Logn6. Archaeologi- cal periods are as follows: N, Neolithic period; B, Bronze Age; /, Iron Age; G.R., Gallo-Roman period; M.A., Middle Ages; A, Modem and recent time. 14C dates are in years B.P., non-cali- brated

73

5 L~7~odem~m~- / -~ ..... :_~=.~._~=~,:~ . ~ _ ~ . . . _ ~ ====================== presentperiod ~ - ~ i i : : i : : ! i ! i ! i i ! ~

25 . . . . . . . ~ , ~ ! : ~ : ~ . ~ ~ , . . . • . .

~ ? . : : : : : ! : : : : : i : : i ' :

- - ~ = ~ - ' ~ : i : : i : : : : : : ~:: i : - ~

85. Middle Ages ..~_~_ :

105

125 . . . . . . . : :~

": Gallo-Roman period ~:: : .~:~J~; !i!i 145 :~ . . . . . . . . . . . . . . . . . . J'"~:

165

190 Iron Age

225

255

5 10 15 20 25 i i J i

• 2265 4. 65 B.P.

30 35 40 %

II 610 • 50 B.P.

11670.4. 55 BJP.

•ubatlantic

285 - -

310

340 Bronze Age

370

405 -

429 Neolithic

438 441

(=n)

~] Ruderals

B2995 4- 65 B.P.

14190 4" 100 B.P.

3600 B.P.

Subboreal

f~ Composi tae

[~] Cereal ia-type

[ ] Other cult ivated plants

Fig. 4. Summary percentage pollen diagram with composite curves for the anthropogenic indicator indicators

nium, Butomus and Iris). These developments may have been the result of a rise in watertable levels which may have caused the asphyxia of aider.

Phase III. During the Bronze Age, the landscape became increasingly open and the margins of the bog were domi- nated by Poaceae and tall sedges. At the end of the Bronze Age (ca. 2800 B.P.), when the alder woodland had practically ceased to exist, a peak of monolete spores (almost certainly the fern Thelypteris palustris) suggests open wetland communities with T. palustris. Corylus and Fagus-dominated woodlands developed on the hillsides (marking the Subboreal/Subatlantic transi- tion), and the first records of cultivated plants appeared (Cerealia and Juglans pollen beginning at 350 era).

These developments are probably connected with the rise in water level which reached its maximum during this period. It is debatable whether this brief flooding should be ascribed to natural changes or human activity. The initiation of arable farming in this area appears to parallel developments in the Massif Armorican where arable farming assumed importance in the middle of the Bronze Age. To sustain this increased level of activity, it may have been necessary to build a dam for irrigation purposes even though the climate then, as now, had a distinct Atlantic character.

Phase IV. At the very beginning of the Iron Age, alder carr with O. regalis developed again at the bog margins, resulting in a transition from an open to a closed envi-

74

ronment. This development may have been facilitated by a drop in the water level, allowing alder growth around the basin. Oak continued to be important on the mineral soils and lime, though remaining a minor component, increased in importance.

Phases V and VI. From the Iron Age onwards, alder re- mained unimportant. The increase in Poaceae and helophyte taxa also suggest an open environment. These developments appear to be related to another rise in the water level.

At the 160-cm level (ca. 2400 B.P., i.e. the Gallo- Roman period), the landscape changed radically. Alder practically disappeared along the borders of the bog, whereas tall sedges and birches became more abundant and so the area took on more or less its present-day open appearance. On the hillsides, woodland, with Quercus and also some Corylus and Fagus, increased in impor- tance. There is now a substantial Cerealia curve as well as good representation of Rumex, Centaurea, Plantago and Ranunculaceae, which attests to considerable arable and also pastoral farming activity.

At the beginning of the Middle Ages, Calluna-domi- nated heath communities appear to have developed on the surrounding hillsides which may be a consequence of increased anthropogenic activity influence (cf. increased Cerealia representation and also Cannabis). Calluna was probably also important during this time on the bog it- self. Oak woodland increased in importance also. This may reflect the effects of human intervention that fa- voured oak.

In the late Middle Ages, the effects of the war of suc- cession in Brittany (1341-1364) may be reflected in zone k. On the hillsides, arable farming was totally abandoned for lack of manpower due to loss of life in warfare, e.g. the siege of Nantes, plague and famine (Leguay and Martin 1982). The severe reduction of ling was certainly due to fires (natural phenomena or perhaps as a result of warfare) which affected the bog as can be seen in the particularly charcoal-rich peat. A similar event has been described for the Landemarais peat bog at Parign6 in the Massif Armorican (Visset 1989).

The beginning of the modern era is marked by the development of bog communities in which Calluna, Myrica and Erica tetralix played an important role. Cas- tanea and Juglans were planted, and, at the same time, the oak forest regressed considerably as a consequence of intensive farming.

Kramm (1978), in a study of bogs between the rivers Ems and Hase in Germany, found that Calluna-domi- nated communities expanded rapidly between A.D. 1750 and 1800, apparently in conjunction with woodland clearance in that region and bog drainage. Similar devel- opments have also been recorded in the Srrent peat bog in the Massif Armorican (Visset 1994).

In the most recent part of the record, current trends, which include development of woody vegetation on the bog surface, can be seen. Thus, there was a marked in- crease in Betula and Myrica in the bog itself. In the sur- rounding countryside, arable farming has greatly dimin- ished. Oak woodlands continue to regress, hazel scrub is of increased importance, and Pinus, Abies, Picea and Cedrus pollen arrive from distant sources.

The substantial Sphagnum peaks in zones 1 and m clearly reflect strong local sporulation. There is evi- dence that Sphagnum was present locally from early stages in the development of the bog but high values first register at only 95-cm depth. This is probably the result of changing conditions which probably favoured the es- tablishment of other Sphagnum species and also the ex- pansion of Calluna, Myrica and Betula.

K oxycoccos pollen, which was observed sporadi- cally from 350 cm upwards, occurs more frequently at and above zone 1. The pollen diagram clearly shows that the later conditions on the bog, which probably favoured development of communities such as those classified in the association Erico tetralicis-Sphagnetum acutifolii Touffet 1969 (Clement 1978; C16ment and Touffet 1980). V. oxycoccos seed were probably transported by migrating birds. In view of this evidence for late expan- sion of this circumboreal species, it is unnecessary to in- voke relict survival from the last interglacial (Wiirm) as an explanation for its present-day distribution pattern.

Human influence on vegetation

Composite pollen curves of anthropogenic indicator taxa show the changing patterns of human activity with time (Fig. 4). The composite curves are as follows: Cerealia, Compositae (Cichorioideae and Asteraceae), Ruderals (arable weeds including Centaurea, Linaria, Rumex, Mercurialis annua and nitrophilous plants such as Con- volvulus arvensis, Solanaceae, Polygonum aviculare, Plantago, Brassicaceae, Chenopodiaceae, Caryophylla- ceae, Arctium, Boraginaceae, and Artemisia), and culti- vated plants (Fagopyrum, Juglans, Cannabis, Castanea and Buxus).

The main developments in the course of human im- pact since the end of the Subboreal period, which are clearly reflected in Fig. 4, are as follows.

In the Neolithic period, anthropogenic impact was quite limited. No Cerealia pollen were observed, but low values for ruderals and Compositae may result from spo- radic human activity.

The first Cerealia pollen are recorded in the Bronze Age, and cereal cultivation was important in this period. Ruderals and Compositae have also substantially in- creased representation. A noteworthy feature at the be- ginning of the Bronze Age is the appearance of Juglans, which revives the debate over just when walnut (and also the chestnut tree) was introduced into the Massif Armorican. In view of the type of deposits involved and the care taken with coring and preparing the pollen sam- ples, we are satisfied that the pollen records are valid. Moreover, the hypothesis that walnut and chestnut trees where present in Armorica earlier than the Gallo-Roman phase, which is normally regarded as the period when these trees were introduced (Andrieu 1991; Ruffaldi 1993), seems to be confirmed by studies at other sites. Marguerie (1992) suggested that the chestnut tree may have been present already in the later Iron Age (450 to 50 B.C.), and two recent studies in the region of Carnac (Morbihan) - in the Kerdual marsh (Visset et al. 1995) and at Locmariaquer (Visset et al. 1996) - have shown that walnut and chestnut in these areas date from the mid-Bronze and mid-Neolithic Ages, respectively.

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5-6-i$c$g3$EE2$i6i4$$3$4$46 - & 4 4 ~ ii $4 ,, ii &i$i & , 4,: 2 4 6, k , gity p ~ x ' r : N 9 1 ' M

P I / K C IIAI.<IL<I<,IC/I 1 - I ' t l < iO l>S

x 0

P O L Y P O O I A C E A E LYCDPodium U t r i c u l a r i a

Hydrochar ls Myr iopnyl lum s p ~ c a t u m Myr iophyl lum v e r t i c i l l a e u m NYr iounyl lum a l t e r n i f l o r u m PotamQgeton Nymunaea sag1 t t a r 1 e A L I S M A C E A E HvdrocRar3s

~e~~~ L i t t o r e l l s Hyperlcum n ~ l o d e s Ho f ton ia Gentians pneumanantne Drosers r o t u n d l f o l i e Menyantnes wacc,"*um

0 H Y P E R I C A C E A E

m

0 C Y P E R A C E A E But omus I r i s Pseu~acorus spargsnium Typns l a t z f o l x a

LO ryuna a n g u s t l f D l l a

LO LySimaCRia 0 .p . Lyszmachie v u l g a r l s Lythrum F i l i p e n d u l a rna,rcrrum POI ygonum ConYOl YYlUS Rumex hybrolapatnurn S C R O P H U L A R I A C E A E R U B I A C E A E Hydrocoty le A P I A C E A E convo1 vu1us seoium V A L E R I A N A C E A E S A X I F R A G A C E A E P R I M U L A C E A E P o t e n f i l l s c i r caea

LO sp i raea

LO ROSACEAE F A B A C E A E MerCUria l lS perennzs EuURorOia LatnyrUs L A N I A C E A E G E R A N I A C E A E RANUNCULACEAE cen raurea

Cerea l la - t ype Melarnpyrum CAMPANULACEAE C R A S S U L A C E A E G E N T I A N A C E A E C I S T A C E A E E r i c a

Cal luna veroens Epl lobium O I P S A C A C E A E scsaioss convolvulus arve S O L A N A C E A E Polygonurn ev lcu l Planfago B R A S S I C A C E A E C H E N O P O O I A C E A E C A R Y O P H Y L L A C E A E Arct ium B O R A G I N A C E A E &-fernisla A S T E R O I O E A E C I C H O R T O I O E I E

P O A C E A E

A . P . / N . A . P

Ainus

.ns i s

a re

Table 2. Summary of vegetation development on the bog and surrounding landscape and the main factors involved

75

Zones

n

m

1

k

J

I

h

Phases

VI

V

IV

III

II

Main vegetation types

B: Calluna and Erica moor invaded by Myrica and birch E: Colonisation by birch and hazel H: Clearance of oak

Intensive arable farmin$ but declining in the most recent period H: Oak + abandoned cultivation B: Filling-in of the bog E: Residual alder woodland H: Oak + cultivation

B: Increase in Sphagnum E: Crrasses, helophytes

Reduction in Osmunda-alder cart, willows and buckthorn H: Oak + lime

B: Increase in Sphagnum E: Domination of helophytes and Carex

Sudden renewed development of Osmunda-alder carr H: Oak + lime

B: Increase in Sphagnum E: Grasses, helophytes, Carex

Near-disappearance of Osmunda-alder cart H: Oak + beech + cultivation

B: Development of Sphagnum E: Colonisation by Cyperaceae, helophytes and grasses

Decline of Osmunda-alder carr Development of willow cart with buckthom and Myrica

H: Oak woodland

B: Free water at the time of colonisation by Sphagnum mosses and other pioneer species

E: Osmunda-alder carr H: Mixed oak + lime and hazel

Hydrological events and other factors

Rise in water level and anthropogeulc influences

Open conditions at edge of bog

Rise in water level Closed conditions at edge of bog

Rise in water level Closed conditions at edge of bog

Maximal rise in water level and possible anthropogenie intervention Open conditions at edge of bog

Rise in water level

Closed conditions at edge of bog

Constant water level

Closed conditions at edge of bog

B, On the bog; E, on the bog margins; H, in the surrounding mineral soils

Walnut and chestnut are considered to be native to Anatolia and to have spread to Greece around 3500 B.P. (Bottema 1980), reaching Italy during the first century B.C. (Behre 1988). Recently, Rfsch (1992) has shown that, in the Lake Constance area, Juglans pollen is re- corded toward the end of La Trne at most sites studied, but in the Feuenried profile in has been noted at ca. 400 BC. It is concluded that walnut was introduced relatively early to these areas.

In the investigations by Kramm (1978), which relate to north-west Germany, Juglans was recorded in the Speller Dose Moor at 31604-50 B.C., i.e. in the early Neolithic and in Hahnenmoor (Niedersachsen) before 13304-50 B.C., i.e. at the end of the Neolithic or begin- ning of the Bronze Age. The author interprets this as in- dicating that Juglans regia var. germanica was present during the Atlantic period in the local mixed-oak forests. However, these records have not been confirmed by more recent pollen diagrams from that region.

Oldfield and Huckerby (1979) noted the presence of the Juglans during the Atlantic period in the Le Moura peat bog in the northern Basque country. Firmin (1984)

emphasized the sporadic appearance of Juglans at Cuiry- les-Chaudardes, in the Aisne valley, during the Neolithic and at Carsac in Languedoc during the Bronze Age. However, these last two results should be considered with due caution since the samples analysed are from mineral-rich soils taken from archeological contexts in which the pollen content may be subject to corrosion, selective preservation and even intrusion by non-con- temporaneous pollen. Castanea, however, has been re- corded at Camprafaud in the Hrrault as charcoal at ca. 3000-4000 B.P. (Vernet 1975). Castanea and Juglans pollen have been assigned to the early Wiirm period in the Basque region o f the Iberic peninsula in deposits from the Lezetxiki cave (Sanchez Goni 1988). It has been suggested that these two taxa occupied refuge zones during certain cold periods throughout the Quater- nary, particularly in the western Mediterranean basin (Huntley and Birks 1983). However, this is not yet gen- erally accepted and, in particular, the pre-Roman occur- rence of Castanea is still contentious. It is, however, ob- vious that there was considerable human impact throughout most o f the Bronze Age.

76

At the beginning of the Iron Age there was a distinct reduction in agricultural activity. Cereals appear not to have been cultivated and there is a considerable decrease in ruderals and Compositae. It is not until the La Trne period that arable farming is again important (Cerealia and associated weed taxa markedly increase) and chest- nut tree is planted.

As noted by Marguerie (1992), agriculture in Armorica intensified and diversified during the Gallo- Roman period (early Roman Empire), which is indicated in our diagram by a sudden increase in cereals and ruderals. This was followed by a reduction in agriculture during the late Roman Empire period. Cerealia values decrease considerably, though representation of ruderal species is maintained. This phenomenon, observed throughout Armorica (Van Zeist 1964) and in other re- gions o f the Roman Empire, is interpreted by Giot (1977) as the expression of an economic and demo- graphic decline during the Late Empire and, in particu- lar, developments at the end of the 3rd century A.D. which included social and political disorders, pirate at- tacks on the coasts and epidemics (LangouSt 1988). However, as suggested by Ferdirre (1988), the reduction in arable farming may be a consequence of shift in em- phasis towards cattle, which would also account for the continued strong representation of ruderals.

In the 9th and 10th centuries, farming prospered in the Armorican countryside (Marguerie 1992). Crops, in- cluding cereals and hemp and walnut and chestnut, were widely planted. However, this prosperous period ended with the war of succession in Brittany (1341-1364). In addition to military operations, the winters were very cold (extremely so in 1342-1343), with destruction o f crops and, as a result, famine (Leguay and Martin 1982). These events are expressed on the diagram by the abrupt disappearance of Cerealia and other cultivated plants so that only some ruderals persist. Subsequently, farming activity again increased and this continued until recent times. High Cerealia values and also the Cannabis and Fagopyrum curves show that arable farming was of con- siderable importance. The curves for Compositae and ruderals also expand which probably reflects consider- able emphasis on cattle rearing, as well. There was also widespread planting of chestnut and walnut, and the oak woodlands were largely cleared to make way for farm- ing. In the most recent times, the reversal of these trends and the decline in arable and pastoral farming is clearly reflected in the uppermost pollen spectra.

Acknowledgements. We are grateful to J. Gray, University of Nantes, for translating this paper into English. Technical sup- port was provided by G. Hauray and L. Charrieau, University of Nantes.

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