Sampling soil wood charcoals at a high spatial resolution: a new

methodology to investigate the origin of grassland plant communities

Dutoit, Thierry1�; Thinon, Michel

2,3; Talon, Brigitte

2,4; Buisson, Elise

1,5& Alard, Didier

6

1Universite d’Avignon, IUT, Institut mediterraneen d’ecologie et de paleoecologie UMR CNRS IRD, Site Agroparc, BP

1207, F-84911, Avignon, Cedex 9, France; 2Aix-Marseille Universites, Institut mediterraneen d’ecologie et de

paleoecologie, UMR-CNRS IRD, case 462, faculte Saint-Jerome, F-13397 Marseille, Cedex 20, France; 3E-mail

michel.thinon@univ-cezanne.fr; 4E-mail brigitte.talon@univ-cezanne.fr; 5E-mail elise.buisson@univ-avignon.fr;6Universite de Bordeaux, Ecologie des Communautes, UMR INRA 1202, Biogeco, F-33405 Talence, France;

E-mail d.alard@ecologie.u-bordeaux1.fr;�Corresponding author; Fax 133 4 90840377; E-mail thierry.dutoit@univ-avignon.fr

Abstract

Questions: (i) Can sampling of soil wood charcoals at highspatial resolution produce new evidence concerning thepresence of chalk grassland before or during the Neolithic,Bronze and Iron Ages? (ii) Are there correlations betweenvegetation history and archeological data during theseperiods at this particular site?

Location: The chalk hillsides of Saint-Adrien in the lowerSeine Valley, Upper Normandy, northwest France.

Methods: The study was carried out at a high spatialresolution in chalk grassland using soil wood charcoalanalysis, in which charcoals found in the soil wereidentified and dated in an area of several hundred squaremeters.

Results: Late-successional woody species (Fagus sylvati-ca, Quercus sp.) were still present in the study site in anarea inconsistent with the existence of large chalk grass-land herbaceous plant communities (several hectares)in the Neolithic (6500–3800 BP) and Bronze Age (3800–2700 BP).

Conclusions: The presence of late-successional woodyspecies on the studied hillside suggests that fires in theNeolithic were linked to forest clearance for pastoralactivities, as already demonstrated for similar ecosystemsin eastern France and Germany. Nevertheless, our meth-odology clearly demonstrates that palaecological studiesneed to take into account the spatial organisation of plantcommunities as a complementary element to validate theirpotential existence in former times.

Keywords: Chalk grasslands; France; Paleoecology; Plantcommunities; Upper Normandy.

Nomenclature: Lambinon et al. (1993).

Introduction

The origin of open or semi-open landscapes innorthwestern Europe has been debated since thebeginning of the 20th century. Open landscapes aregenerally considered to be the result of either landclearance during the Neolithic (4500–1800 BC;Tansley 1939) or the grazing impact of wild herbi-vores (Vera 1999). Chalk grasslands, which aretypical old grasslands of open landscapes inWesternEurope, are believed to have formed under bothhuman and non-human associated processes.Nevertheless, several authors (Bush & Flenley 1987;Bush 1988, 1989) have shown that chalk grasslandsmay have existed since the Late-Glacial (13 000–10 000 BC) and persisted during the forested eras ofthe Pre-Boreal (10 000–9000 BC) and Boreal (9000–8000 BC) due to (i) land clearing for hunting duringthe Mesolithic (9000–4500 BC; Bush 1993), (ii) theimpact of wild herbivores (Buckland & Edwards1984), or (iii) soil conditions that did not allow theestablishment of woody species (Ellenberg 1988).Thus, the long-term history of chalk grassland sitesand the age of their formation are still debated, be-cause the spatial precision of palynological studies isnot sufficient to discriminate vegetation types at thescale of chalk grassland sites (Thomas 1989; Waller& Hamilton 2000; Bradshaw 2002; Svenning 2002),and because grazing periods and the impact of her-bivores on vegetation are difficult to assess atspecific sites (Bradshaw &Mitchell 1999).

A clear understanding of the origin and persis-tence of open landscapes in Western Europe isimportant for managers of natural areas. Indeed,some scientists (Vera 1999), arguing that openlandscapes exist naturally without anthropogenic

Journal of Vegetation Science 20: 349–358, 2009& 2009 International Association for Vegetation Science

disturbances, denounce active ecological restoration(brush cutting, grazing, mowing, control burns,topsoil removal, etc.) of European cultural land-scapes (heathlands, rangelands, wet meadows,alpine meadows, dry grasslands, wooded pasture,etc.) where traditional agricultural practices havebeen abandoned.

We used soil wood charcoal analysis (pedoan-thracology), a technique in which charcoal piecesfound in the soil are identified and dated (Thinon1992), to assess vegetation history for a chalk hill-side in Upper Normandy (northwest France). Incontrast to palynological records, pedoanthracol-ogy allows study of the composition of past plantwoody communities at a fine spatial scale. Althoughcharcoal can easily disperse through surface run-off,large-scale aerial dispersal by wind and smokeis limited, particularly for fragments larger than400 mm (Clark 1988; Clark et al. 1998; Blackford2000; Figueiral & Mosbrugger 2000; Ohlson & Try-terud 2000; Gardner & Whitlock 2001; Lynch et al.2004), which are the fragments that can be identifiedand dated. Even though very small charcoals (sizeo10 mm) can travel by wind over very long distances(Benedict 2002), most larger size charcoals originatefrom woody plant communities that are burnedon site, or from an area limited to a few tens of me-ters in radius, and are buried in the soil through thecombined activity of soil homogenisation by in-vertebrates, colluvial processes and root growth.Because soil wood charcoal analysis providesinformation with great spatial precision, it is parti-cularly relevant to the study and description ofpast forest plant communities growing in dry sites(Thinon 1992; Carcaillet 1998, 2001; Talon et al.1998; Carcaillet & Brun 2000; Carnelli et al. 2004).However, this technique does not provide directevidence of herbaceous species presence.

A primary purpose of our study was to de-termine whether soil charcoal analysis could detectorigin and persistence at spatial resolutions as fine asthe 40–500m2 minimal area for the above commu-nity (de Foucault & Frileux 1988). If woody speciesof mature forest phases are found in several rela-tively closely spaced pits for the same historic orprehistoric period, it can be deduced that chalkgrassland communities were not on that site duringthat particular period. This approach matches pa-leoecological sampling protocols aimed at charac-terising actual plant communities: precise informationis obtained at the scale of the plant communities (vander Maarel 2004). This is not the case in previousresearch, where paleoenvironments are reconstructedfrom paleoecological data, which only provide a list

of species scattered at several sites, without in-formation on the potential co-existence of speciesat the plant community scale (Thomas 1989). Forexample, concerning the origin of dry grasslandplant communities, past research has used soil woodcharcoals but the methodology was based on multi-site investigations at a regional scale and on identi-fication and datation of charcoals originating fromearlier woody species that generally colonise drygrasslands, e.g. Juniperus communis (Schwartz et al.2005), without consideration of the minimal arearequired to confirm the existence of a dry grasslandplant community at a local scale. Some of these au-thors have pointed out the need for more localinformation that addresses the existence of herbac-eous plant communities in a landscape matrixdominated by forest communities (Baumann 2006;Goepp 2007).

We use our results to address two questions forour study area: (i) Could a chalk grassland have ex-isted in the study site at Saint-Adrien (northwestFrance) before or during the Neolithic, Bronze andIron Ages at the minimal scale required for its ex-istence? (ii) If it existed during these periods, arethere correlations between the vegetation history andarcheological data during these periods? Finally, weconsider potential similarities between the history ofour local chalk grasslands in the Seine Valley andother regions with dry grasslands in Europe, andcompare our findings to results already available inthe literature that used other methodologies with aless precise spatial resolution.

Methods

Study area

The study site of Saint-Adrien covers 32 ha(110703000E 4912202200N) in Upper Normandy innorthwest France (Fig. 1). The substrate is chalkfrom the Cretaceous Period (145.5–65.5 kyr BP),shaped by the Seine River and its tributary, theBecquet River, and out-cropping along abrupt cliffsrecently exposed by fluvial erosion. Altitude variesbetween 50 and 110m. Currently, vegetation ofchalk grasslands in the area is dominated by Sesleriacaerulea (L.) Ard. (Poaceae) and Bromus erectusHudson (Poaceae). Some plant ecologists (de Fou-cault & Frileux 1988) believe that these grasslandsrepresent relicts of herbaceous vegetation that devel-oped at the beginning of the Holocene (Post-Glacial)(9000–0 BC) on cliffs and unstable screes and there-fore have never been colonised by woody species

350 Dutoit, T. et al.

because of the shallowness of the soils and, as in therest of northwest Europe, these areas were burnt,grazed and ploughed for many centuries (Wilmans1997; Poschlod &Wallis De Vries 2002; Dutoit et al.2003; Alard et al. 2005).

Sampling and taxonomic identification

Charcoal pieces were sampled from blocks ofsoil extracted from specific layers of soil profiles(Thinon 1992). Five profiles were dug in soils thatvaried in their geomorphological site conditions,such as occurrence in pinnacles and screes, to revealas much spatial heterogeneity as possible in thesampling (Table 1). Four profiles (1–4) were devel-oped for a small area, consistent with minimal areasfor chalk grassland plant communities (around500m2). The last (5) was realised in another smallchalk grassland several hundred meters from thefirst site (Fig. 2). All these profiles were realised at asufficient distance (4100m) from the present edgesbetween the forest and the opening to ensure thatlarger charcoal particles had not just washed out

into the grasslands after burning of nearby forest(Fig. 2). As revealed in previous historical ecologystudies, this forest edge has moved over time fol-lowing former land uses and was more remote fromthe study site during the Middle Ages and Modernperiods because there were more cultivated plotsand heavy grazing pressure (sheep) at those times(Dutoit & Alard 1995; Dutoit et al. 2003).

Soil samples were undertaken according to themethods of Carcaillet & Thinon (1996). Soil profileswere dug to bedrock and 10 to 12L (ca. 15kg) of soilwere sampled for each of the soil horizons identified bycolour, texture and structure following Baize & Jabiol(1995), starting from the deepest horizon to preventcontamination from upper layers (Fig. 3). Sampleswere sieved (2 cm) to exclude stones and gravel. Four-teen samples were taken from the five profiles (Table 1).

Samples were dried and weighed to calculate thequantity of charcoal per kilogram of soil. The drymaterial was then carefully wet-sieved with a de-floculant (Na4P2O7) through four sieves of 5mm,2mm, 800 mm and 400 mm (400 mm corresponds tothe minimum size for handling and anatomicalidentification of charcoal). Charcoal was extractedfrom the mineral fraction (sand) by flotation in acolumn with an ascending water current (furtherdetails in Carcaillet & Thinon 1996), and from theorganic fraction (roots and other plant remains) byhand sorting under a low-power binocular micro-scope. Larger charcoal pieces were cleaned using anultrasonic wave generator, and more fragile char-coal pieces were treated with HF (70%) and HCl(35%) to destroy clays. Charcoals were identified bywood anatomy under an incident light microscope(episcopic microscope equipped with differential in-terference contrast) at magnifications of �200, �500and �1000. We used the charred wood reference col-

Fig. 1. Aerial photograph showing the location in UpperNormandy (France) of the study site and its present vege-tation.

Table 1. Characteristics of the five soil profiles sampled for charcoal on the Saint-Adrien site (Upper Normandy, France).

Profilenumber

Elevation(m)

Location Slope(1)

Orienta-tion (1)

Former landuse (AD 1822-1914)

Soildepth(cm)

Number ofcharcoalpieces dated

Number ofcharcoal piecesidentified

Depth ofeach sampledlayer (cm)

1.I 65 Base ofhillside

28 100 Pasture 45 0 6 0–15

1.I 2 15–452.I 80 Top of

hillside20 120 Cultivation 25 0 11 7–25

3.I 85 Top ofhillside

15 120 Cultivation 80 7 13 20–40

3.II 10 55–804. I 75 Top of

hillside29 230 Pasture 55 7 6 0–15

4.II 8 15–354.III 8 35–555. I 60 Base of

hillside29 185 Pasture 30 0 4 10–30

- Sampling soil wood charcoals at a high spatial resolution - 351

lection from the Mediterranean Institute of Ecologyand Palaeoecology (Marseille, France) and atlases ofwood anatomy (Jacquiot 1955; Greguss 1959; Jac-quiot et al. 1973; Schweingruber 1990).

Data presentation and dating

The charcoals from soils at Saint-Adrien werevery fragmented due to past cultivation of these veryshallow soils (mean depth o50 cm) and more than50% of the pieces were vitrified, had a scoria-likeappearance and could not be identified (Fig. 4).While the quantity (anthracomass) of charcoal pie-ces found for each species in each soil profile doesnot represent relative frequency and/or biomass inpast arborescent plant communities, the frequencyof each species in the various profiles at one site ispresumably correlated with their relative abundancein former arborescent plant communities (Thinon1992). However, this relationship is complicated bythe possibility that, in each profile, several charcoalfragments could have been a part of the same plant. Inorder to compare samples, the charcoal composition

(identified fraction 40.4mm) of each sample was ex-pressed as the specific anthracomass per taxon (SAT),expressed in mg (Thinon 1992; Talon et al. 1998).

Fourteen charcoal fragments of mass between0.8 and 4.0mg were radiocarbon dated at the Uni-versity of Arizona, Tucson (USA), and at the PoznanRadiocarbon Laboratory (Poland) using AcceleratorMass Spectrometry (AMS) to avoid any bias in la-boratory manipulations. Six dates were recognisedfromQuercus sp., four from Fagus sylvatica and fourfrom Taxus baccata. The 14C dates were calibrated asAD/BC using CALIB 5.0 software (Stuiver et al.2006). Dating confirmed that soil layers were dis-turbed and that charcoals of various ages were mixedin the soils (Talon et al. 1998; Carcaillet 2001).

Results

Twenty-one woody taxa were identified amongall the charcoal assemblages sampled (Table 2). Allthese species are presently found in the environs ofthe site (de Foucault & Frileux 1988); no local ex-

Fig. 2. Aerial photograph (3/4) showing the geomorphology of the study sites and location of the five soil profiles realised tocollect soil wood charcoal (D. Alard). Cliffs are around 80m high.

352 Dutoit, T. et al.

tinctions of woody plants are documented for theHolocene. These taxa are common in recent woodyplant communities on chalk substrates in UpperNormandy, including early-successional species(Cornus sanguinea, Crataegus monogyna, Prunusspinosa, Pinus sylvestris, Juniperus communis), mid-successional species (Carpinus betulus, Taxus bacca-ta), and late-successional species (Quercus sp.,Fagus sylvatica). Deciduous oaks were found in allsoil layers, and all soil profiles studied indicated thatthese taxa contributed the greatest proportion of thecharcoal mass (Fig. 5). Fagus sylvatica had the sec-ond highest charcoal mass, but was only found inthree soil profiles. Taxus baccata was found in allprofiles except one, with a significant, but lower,charcoal mass. Pinus sylvestris type was as frequentas Quercus but its mass was always relatively low.Finally, the high frequency, but low charcoal massof Prunus spinosa, a shrub with a high light require-ment, confirms the presence of frequent openingswithin the habitat. Profile 3 was the richest in char-coal quantity and diversity, attributable to a gentlerslope and deeper soil (Fig. 2). Charcoal pieces fromearly-, mid- and late-successional species were mixedin the soil. Their simultaneous presence providesconfirmation that the site supported both pioneerand mature phases of forest dynamics. Presence ofcharcoal of 4400mg indicates that these plant spe-cies were burned locally, suggesting episodes of fireat various successional stages of heterogeneous

Table 2. Species occurrence and mass of identified charcoal types (fraction40.4mm in mg) listed by their overall frequencyin the soil profiles on the Saint-Adrien site (Upper Normandy, France).

Soil profiles 1 2 3 4 5

Sampling layers 1.I 1.II Mass 2.I Mass 3.I 3.II Mass 4.I 4.II 4.III Mass 5.I Mass

Quercus sp. (deciduous) 1 1 0.23 1 0.26 1 1 1.14 1 1 1 0.63 1 1.19Pinus sylvestris L. type 1 1 0.06 1 0.03 1 1 0.06 1 1 1 0.16 1 0.02Taxus baccata L. 1 0.10 1 0.12 1 1 0.57 1 1 1 0.16 1 0.26Prunus spinosa L. 1 0.02 1 0.05 1 1 0.07 1 1 1 0.05Fagus sylvatica L. 1 0.18 1 1 1.86 1 1 1 0.33Prunus mahaleb L. 1 1 1 1

Betula sp. 1 1 1

Corylus avellana L. 1 1 1

Cornus sanguinea L. 1 1 1

Crataegus monogyna Jacq. 1 1

Helianthemum sp. 1 1

Amelanchier ovalis Medik. 1 1

Ruscus aculeatus L. 1 1

Acer sp. 1 1

Carpinus betulus L. 1

Prunus avium L. 1 1

Acer campestre L. 1

Cornus sp. 1

Juniperus communis L. 1

Genista tinctoria L. 1

Rosa sp. 1

Small unidentifiable charcoal 0.53 0.94 4.33 1.67 1.55

Fig. 3. Soil profile number 2 showing shallowness ofthe soil. This profile was realised in a plot cultivated inthe 19th century (M. Thinon). Measuring tape is 25 cmlong.

- Sampling soil wood charcoals at a high spatial resolution - 353

forested communities. We dated charcoal fragmentsof Quercus sp. and Fagus sylvatica, clearly identifiedas species only found in mature forested ecosystems,

and of Taxus baccata, found across the whole suc-cession on the chalk substrate. The 14 datesobtained from two soil profiles spread from the re-cent Atlantic (8000–5000 BP) to the Subatlantic(2500 BP–present; Table 3).

Discussion

The Neolithic is known to have been a transi-tional period, based on the size and composition ofdomestic herds. Herds were principally composed ofcattle bred in semi-forested habitats at the beginningof the period, while herds were later dominated bygoats and sheep bred in open spaces at the end ofthe period (Habasque 1990). Our data are con-sistent with those already obtained from otherpaleoenvironmental and archaeological studies atthe regional scale in Upper Normandy. Palynolo-gical studies in the Seine Valley have shown thatforest openings began to occur in the PreBorealperiod (Elhaı 1963; Huault 1986). Nevertheless,Pastre et al. (2003) and Sebag (2002) have shownthat this forest opening must has been localised to aforested landscape because significant episodes ofsilt accumulation in sediments in the Seine Valley(which occurred simultaneously with episodes ofsoil erosion on slopes) started only after 2700 BC.

Among the charcoal pieces dated from theNeolithic, some species are found in late succes-sional forests, but this does not provide evidencefor the extent of forest openness in our study site.Taxus baccata, for example, is a tolerant species ableto colonise chalk grasslands even when grazed be-cause it is toxic and, in Upper Normandy, it canalso establish in the shade of mature species, suchas Fagus sylvatica and Quercus species. Althoughthe most probable Quercus species have high lightrequirements (Q. pubescens, Q. robur), they do notdirectly colonise chalk grasslands after grazingabandonment. They establish in clearings of early-successional forests composed of pioneer andmid-successional woody shrubs (Bardat 1989).Late-successional forest species were found in allprofiles, including steeper slopes. This pattern in-validates the hypothesis that low-soil fertility wasan obstacle to woody species establishment duringthe Neolithic and Bronze Age in our study site.

The fact that charcoals ofQuercus sp. and Fagussylvatica were found for each period in several pro-files in close proximity since the oldest Neolithic,confirms that co-existence and inter-conversion oflate-successional forest with small grasslands canoccur, as revealed in old documents available for the

Table 3. Radiocarbon dates of the charcoal pieces sam-pled in the soil profiles on the Saint-Adrien site (UpperNormandy, France).

14C age(years BP)

Calibratedage (yearsBC/AD) andcivilisations

Charcoalspecies

Approximateweight (mg)

Profiles anddepth (cm)

Modern105 � 35 1803–1937

ADTaxusbaccata

4 3 I (20–40)

210 � 35 1727–1812AD

Fagussylvatica

1.8 3 I (20–40)

300 � 30 1489–1603AD

Fagussylvatica

1.2 3 I (20–40)

365 � 35 1446–1531AD

Quercussp.

1.2 4 II (15–35)

460 � 60 1392–1524AD

Quercussp.

2.1 3 II (55–80)

795 � 40 1171–1-279AD

Quercussp.

2.2 3 II (55–80)

Middle Ages/Roman Empire1190 � 35 771–901 AD Quercus

sp.1.7 4 III (35–55)

1990 � 40 59 BC–86AD

Fagussylvatica

0.8 4 III (35–55)

Bronze Age3260 � 40 1625–1433

BCTaxusbaccata

1 3 II (55–80)

3680 � 45 2147–1940BC

Quercussp.

1.4 3 II (55–80)

Late Neolithic3905 � 40 2474–2279

BCTaxusbaccata

1.1 4 III (35–55)

3975 � 60 2623–2291BC

Taxusbaccata

0.9 4 II (15–35)

Oldest Neolithic5435 � 40 4355–4232

BCFagussylvatica

1.3 4 I (0–15)

5840 � 40 4796–4584BC

Quercussp.

1.6 4 III (35–55)

Fig. 4. Charcoal fragments (�10), mainly from Fagussylvatica and other plant remains in samples collected insoil profile number 3, layer II (M. Thinon).

354 Dutoit, T. et al.

Middle Ages (Fig. 6). Some botanical features of theSeine Valley suggest that small areas of open grass-lands existed in the Holocene period. These features

include (1) the importance in the recent vegetationof refugial species from the northwestern Europeansteppe of the Late Glacial (13 000–10 000 BC; Stipa

Fig. 5. Pedoanthracological diagram of the five soil profiles realised in the site of Saint-Adrien (Upper Normandy, France).Charcoal identifications were by M. Thinon. The length of the black bars represents the specific anthracomass per taxon(SAT) in mg. Number and depth (cm) of soil profiles are given on the vertical axis. See Table 1 for codes and characteristics.

Fig. 6. Detail of an illumination L’endormissement de Saint-Maclou from the Sainte-Catherine Monastery near our studysite and dating from the middle of the 15th century. This painting shows the co-existence of itinerant sheep grazing onherbaceous plant communities and the openess of a forested landscape (large number of old dead trees and stumps), withpermission of the Archives departementales de Seine-Maritime.

- Sampling soil wood charcoals at a high spatial resolution - 355

pennata L., Polygala amarella Crantz) and (2) thehigh numbers of endemic species (Viola hispidaLam., Galium fleurotii Jordan, Biscutella neustriacaBonnet) occurring in extreme habitats such as un-stable chalk screes and cliffs. This endemismsuggests limited gene flow in geographically isolatedhabitats and localised but continuing openness ofthe plant canopy (Pigott & Walters 1954). A fores-ted environment suggested by the charcoal data isclearly compatible with such features, but is prob-ably not compatible with the existence of large areasof chalk grassland during the Preboreal and Borealperiods (Elhaı 1963; Huault 1986). Long-term pre-sence of late-successional forest trees alsocorroborates the hypothesis that perennial Poaceaedid not become dominant in herbaceous commu-nities of chalk grasslands before the late MiddleAges (Poschlod & Wallis De Vries 2002), when in-creased farming resulted in the destruction ofwoodlands and the development of species-rich her-baceous grasslands, as revealed by previoushistorical ecology studies (Behre 1988; Wilmans1997; Gaillard et al. 2007).

During the Mesolithic, the study site may havesometimes been inhabited by hunters, as shown bycaves decorated with horses 500m above the Saint-Adrien site and dating from the Upper Paleolithic(35 000–9000 BC). However, no campsites or settle-ments have been found nearby for this period(Paulet-Locard 1990). Our results from 14C datingof charcoal fragments showed that fires appeared inthe Neolithic and their frequency increased duringthe Bronze Age. This is consistent with the generaltransformation of the landscape induced by agro-pastoral practices detected during the Bronze Age inthe Parisian Basin (Leroyer 1997).

Our results, for one chalk grassland and at ahigh spatial resolution, confirm those of colleagueswho have already dated forest clearings with similarherbaceous plant communities, such as uplandgrasslands of the Vosges Mountains (easternFrance). The occurence and datation of Juniperuscommunis charcoals (an earlier successional speciesthat colonises dry grasslands) indicates that uplandgrasslands existed at least since the Late Iron Age(Schwartz et al. 2005; Goepp 2007). In the JurassicMountains of the Franconian Alb (Bavaria, south-ern Germany), charcoals extracted and dated fromthe Bronze and Iron Ages in a prehistoric settlementhave revealed the presence of species such as Pinussylvestris, which is also an early-successional speciesthat colonises dry calcareous grasslands (Baumann2006; Poschlod et al. 2008). Nevertheless, in thesestudies the charcoals were sampled in different sites

without any consideration at the local scale of theminimal area necessary for the expression of agrassland community. Lack of spatial precision atthe local scale for palynological studies has longbeen a source of controversy (Bush & Flenley 1987;Bush 1988, 1989; Thomas 1989); our results showthat a similar debate could exist for soil wood char-coal analyses if, in future research, the regionalmulti-site approach is not correlated with samplingat a high spatial resolution on the local scale com-patible with the minimal area need for existence ofherbaceous plant communities.

The existence of fires during the middle Holo-cene in our study site is proven by the presencecharcoals of Quercus sp. These fires may be ex-plained by the creation of pastures for goats andsheep, whose domestication occurred more orless contemporaneously in Upper Normandy. Thisstudy emphasizes the debate on whether chalkgrasslands are the result of grazing practices overcenturies rather than the heritage of open plantcommunities that could have developed throughnatural processes before the Pre-Boreal.

Acknowledgements. Thanks to colleagues, M. Bush (Flor-

ida Institute of Technology, USA), C. Labandeira

(Smithsonian Institution, National Museum of Natural

History, Washington D.C., USA), P. Poschlod (Institute

of Botany, University of Regensburg, Germany), C. Car-

caillet (University of Montpellier, France), F. Magnin

(University Paul Cezanne, France) for reading drafts of

this manuscript and for providing comments. Thanks also

to Dr. Olivier Chabrerie (University of Picardie, France),

Mr. Philippe Touflan (University Paul Cezanne, France)

and Dr. Thierry Otto (University of Toulouse) for techni-

cal assistance. Two anonymous referees, Sara Hotchkiss

(University of Wisconsin, USA) and Kerry Woods (Ben-

nington College, USA) provided useful comments on

early versions of this paper.

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