Combining functional weed ecology and crop stable isotope ratios to identify cultivation intensity

17 Pages·2015·4.1 MB·English

by  Amy Bogaard

VegetHistArchaeobot(2016)25:57–73
DOI10.1007/s00334-015-0524-0
ORIGINAL ARTICLE
Combining functional weed ecology and crop stable isotope ratios
to identify cultivation intensity: a comparison of cereal production
regimes in Haute Provence, France and Asturias, Spain
Amy Bogaard1 • John Hodgson1 • Erika Nitsch1 • Glynis Jones2 • Amy Styring1 •
Charlotte Diffey1 • John Pouncett1 • Christoph Herbig3 • Michael Charles1 •
Fu¨sun Ertug˘4 • Osman Tugay5 • Dragana Filipovic6 • Rebecca Fraser1
Received:2December2014/Accepted:10March2015/Publishedonline:19March2015
(cid:2)TheAuthor(s)2015.ThisarticleispublishedwithopenaccessatSpringerlink.com
Abstract This investigation combines two independent in a previous study of intensively managed spelt wheat in
methods of identifying crop growing conditions and hus- Asturias, north-western Spain: as expected, weed eco-
bandrypractices—functionalweedecologyandcropstable logical data reflect higher soil fertility and disturbance in
carbon and nitrogen isotope analysis—in order to assess Asturias. Similarly, crop stable nitrogen isotope values
their potential for inferring the intensity of past cereal distinguish between intensive manuring in Asturias and
production systems using archaeobotanical assemblages. long-term cultivation with minimal manuring in Haute
Present-day organic cereal farming in Haute Provence, Provence. The new model of cereal cultivation intensity
Francefeaturescropvarietiesadapted tolow-nutrient soils based on weed ecology and crop isotope values in Haute
managed through crop rotation, with little to no manuring. Provence and Asturias was tested through application to
Weed quadrat survey of 60 crop field transects in this re- two other present-day regimes, successfully identifying a
gion revealed that floristic variation primarily reflects high-intensity regime in the Sighisoara region, Romania,
geographical differences. Functional ecological weed data and low-intensity production in Kastamonu, Turkey. Ap-
clearlydistinguishtheProvencefieldsfromthosesurveyed plication of this new model to Neolithic archaeobotanical
assemblages in central Europe suggests that early farming
tended to be intensive, and likely incorporated manuring,
but also exhibited considerable variation, providing a finer
CommunicatedbyC.C.Bakels.
grained understanding of cultivation intensity than previ-
Electronicsupplementarymaterial Theonlineversionofthis ously available.
article(doi:10.1007/s00334-015-0524-0)containssupplementary
material,whichisavailabletoauthorizedusers.
Keywords Archaeobotany (cid:2) Weed ecology (cid:2)
& AmyBogaard Stable isotopes (cid:2) Agricultural intensity (cid:2) Neolithic
[email protected]
1 SchoolofArchaeology,UniversityofOxford,36Beaumont
Introduction
Street,OxfordOX12PG,UK
2 DepartmentofArchaeology,UniversityofSheffield,
Agricultural intensity—defined here in terms of labour
NorthgateHouse,WestStreet,SheffieldS14ET,UK
inputs per unit area of arable land—represents a crucial
3 Abt.Vor-undFru¨hgeschichte,Institutfu¨rArcha¨ologische
axisforassessingthescaleandproductivityofpastfarming
Wissenschaften,J.W.Goethe-Universita¨t,Gru¨neburgplatz1,
60323Frankfurt/Main,Germany regimes,andtheirsocialandwiderecologicalimplications
4 Orhangazicaddesi,Kumbas¸ıyoluno109,Iznik,Bursa, (Gilman 1981; Sherratt 1997; Trigger 2003). An earlier
Turkey studyofthefloristiccompositionandfunctionalecological
5 BiyolojiBo¨lu¨mu¨,FenFaku¨ltesi,Selc¸ukU¨niversitesi, profileofweedflorainEvvia,Greeceidentifiedaparticular
Selc¸uklu,42075Konya,Turkey setofweedfunctionalattributesrelatingtosoilfertilityand
6 InstituteforBalkanStudies,SerbianAcademyofSciences disturbance that distinguished intensive ‘garden’ and ex-
andArts,KnezMihailova35/IV,Belgrade,Serbia tensive ‘field’ cultivation of broad beans and other pulses
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58 VegetHistArchaeobot(2016)25:57–73
(Jones et al. 1999, 2000). This contrast between high- and intensive management of relatively small-scale production
low-intensity regimes, framed using discriminant analysis, in Asturias, Spain (Charles et al. 2002), and larger scale,
was applied to another crop type (spelt wheat) and region low-intensity production in Haute Provence, France. The
(Asturias, Spain) as a modern ‘test’ and found to identify presentinvestigationextendspreviousstudiesintwoways.
intensive cereal cultivation successfully (Charles et al. First, while floristic/ecological weed data and crop stable
2002). Application of this same approach to Neolithic ar- isotope values are available for intensively managed ce-
chaeobotanical weed data from central Europe charac- reals in Asturias (Charles et al. 2002; Fraser et al. 2011),
terised early farming as intensive ‘garden’ cultivation data on organically grown cereals managed with low in-
(Bogaard 2004). tensityhavebeenlacking.Moreover,sincethed15Nvalues
Subsequent work on the stable carbon and nitrogen of pulses are affected by fixation of atmospheric nitrogen,
isotope composition of crops grown under a range of ex- previous isotopic survey of high- and low-intensity pulse
perimentaland‘traditional’regimesidentifiedthed15Nand cultivation in Evvia (Fraser et al. 2011) cannot be ‘trans-
d13C values of cereals and pulses as useful parameters for lated’ for cereals. A study of large-scale, low-intensity
assessing the contribution of manuring and watering, re- organiccerealproductioninHauteProvencewastherefore
spectively,tosoilproductivity(Fraseretal.2011;Wallace conducted inorder tofill these gaps. Secondly,the present
et al. 2013). Intensive fertilisation of crops with animal studyseekstocharacterizetheecologicalcontrastbetween
dung results in 15N enrichment due to the volatilisation of high-andlow-intensitycerealproductionsystemsthatlack
lighter 14N in ammonia, and hence elevated crop d15N irrigation, in contrast to more arid systems where supple-
values, while long-term cultivation without manuring re- mentary watering is a likely potential component of in-
sults in low crop d15N values (Choi et al. 2003; Bol et al. tensive cultivation. A further objective is therefore to
2005; Bogaard et al. 2007). Crop d13C values, by contrast, assesstherangeandcausesofvariationincropd13Cvalues
reflectwaterstatusduetoincreasingdiscriminationagainst where no artificial watering was practised. Moreover, to
13C when stomata are closed in dry conditions (Farquhar test the general applicability of the new ‘weed ? isotope’
andRichards1984;Condonetal.1987;Arausetal.1999). model of cereal cultivation intensity, we apply it to two
There are clear advantages to combining weed ecology other present-day cereal regimes: small-scale/intensive
and crop isotope determinations in order to assess agri- cultivation of einkorn and other cereals in the Sighisoara
cultural practice (cf. Ferrio et al. 2007; Bogaard et al. region, Romania, and large-scale/low-intensity cultivation
2013).Weedecologyisneededtoassessthepermanenceof of einkorn and emmer in Kastamonu, Turkey (Fig. 1). Fi-
arable land (Bogaard 2002, 2004), and also provides evi- nally, to investigate its archaeobotanical utility, this study
dence of soil disturbance levels (due to tillage and weed- includespreliminaryreassessmentoftheintensityofcereal
ing). While weeds also give a general index of soil production systems in Neolithic central Europe, building
productivity, crop d15N indicates the composition of on previous work by Bogaard (2004), through application
available soil N (including possible manuring effects, of the new multi-stranded model.
naturally abundant organic matter—in both cases with
preferential loss of 14N through ammonia volatisation— The study region in Haute Provence
and the action of denitrifying bacteria under anaerobic
conditions—Billy et al. 2010), while crop d13C values re- The geographical focus of this study is a region within
flectwaterstatus(resultingfromwatermanagementaswell Haute Provence, south-eastern France, framed by the
as natural sources such as precipitation). Stable isotope limestone massifs of Mont Ventoux (the region’s highest
determinationsofcropsthereforeprovideadirectmeansof peak,1912 m)andtheMontagnedeLureinthenorth,and
assessingthepossiblecontributionsofmanuringandwater the Lube´ron massif in the south (Fig. 2). The study area
management tocrop growth,within the overall framework includes two calcareous plateaux (Sault and Albion) at c.
of arable fertility, disturbance and permanence established 800–1,000 m altitude to the south-east of Mont Ventoux,
throughweedecology.Functionalecologicalattributesand and more varied ‘molasse’ geology (including calcareous
plant stable isotope values are subject to different sources sandstones and clays) and fractured topography in the
of error and ambiguity; interpretations that incorporate northern Lube´ron (c. 500–700 m).
evidence from both approaches are more robust and in- Climatically, this area occupies a transitional position
formative than inferences based on only one form of evi- between the semi-humid Mediterranean coast and ocean-
dence (Bogaard 2015). ic/continentalconditions—MontVentouxisconsideredthe
Thecentralaimofthepresentstudyistocombineweed absolute limit of broadly Mediterranean bioclimate in the
ecological analysis and crop stable isotope determinations region—and experiences persistent cooling by the mistral
inordertocharacterize acontrastinintensitybetweentwo and transmontane winds (Blondel et al. 2010, 103). The
cereal production regimes in south-western Europe: Lube´ron range to the south of the study area forms an
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VegetHistArchaeobot(2016)25:57–73 59
Fig.1 Mapshowingmodern
agriculturalstudylocations
approximate boundary between the classic mediterranean cereals, forage legumes and sometimes pulses; in three
conditions to the south and oceanic/continental climate cases Triticum monococcum, einkorn, was grown as an
further north: in Ko¨ppen–Geiger climate classification initial annual crop following aromatics (Table 1). At the
terms the Sault area is temperate-oceanic (Cfb), while the remainingfarmsrotationregimesfocussedonannualcrops
northern Lube´ron area around Apt is temperate-mediter- of cereals and forage legumes; in some regimes forage
ranean (Csb). Average annual precipitation ranges from c. legumesorSinapisarvensis, mustard, were ploughedinas
900 mm around Sault to c. 700 mm around Apt; rainfall a green manure to enhance fertility.
around Sault remains high year-round, with peaks in Oc- Producers emphasised the importance of growing ce-
tober and May, while rainfall in the southern part of the real varieties adapted to stony soils of moderate to low
study area around Apt follows a more mediterranean pat- nutrient status. These included a local variety of einkorn
tern, being distinctly higher in winter (peaking in October wheat, protected under an IGP (Indication Ge´ographique
and February) than summer. Prote´ge´e) designation. This variety was almost always
A total of 57 crop fields was studied near Sault (c. autumn-sown (normally in October) and had the longest
800 maltitude),Saint-Christol(c.800–1,000 m)andMurs growing season, ripening in August or even September
(c. 500 m) in the Vaucluse, and near Vache`res (c. 700 m) (as in 2013—a particularly wet summer—on the plateau
and Montfuron (c. 500 m) in Alpes-de-Haute Provence d’Albion) after the other cereals and lavender had been
(Fig. 2). The fields belonged to seven organic farms; con- harvested. Another local variety was the ble´ meunier
tacts to producers were established through the chambre d’Apt, a low-gluten bread wheat (Triticum aestivum) re-
d’agricultureinSaultandtheparcnaturelduLube´ron.The vived in the 1980s in the northern Lube´ron and also
farms ranged from relatively large-scale holdings protected as an IGP landrace. Other (commercial) vari-
(240–300 ha) on the plateau d’Albion, comprised of fields eties included several other naked wheats (mostly hex-
averaging 8–9 ha each, to smaller farms of\100 ha with aploid), T. spelta, spelt (on one plateau d’Albion farm),
fields averaging c. 1–2 ha (Table 1). Crop rotation was six-rowed hulled barley (Hordeum vulgare), rye (Secale
practised on all farms and considered crucial for main- cereale) and oats (Avena spp.) Cereals were mostly au-
taining soil fertility in the (virtual) absence of manuring tumn-sown; spring-sown cereals followed autumn-sown
(seebelow).Atfourofthefarms,rotationregimesfeatured ones in some rotation regimes. Pulses (Lens culinaris,
8–10? years of [perennial] aromatic crops (especially lentil, and Cicer arietinum, chickpea) were sown over the
Lavandulaangustifolia,lavender,andL.hybrida,lavandin) winter or spring on some farms, in one case (Farm 2)
followed by a shorter period of annual crops including only on stone-free alluvial soils.
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60 VegetHistArchaeobot(2016)25:57–73
Fig.2 Mapshowingthestudy
areainHauteProvence,France
andthelocationsoftheseven
farms;thefieldssurveyedare
indicatedinblackshading
Priortosowing,fieldsweretilledbytractor,oftenusing All of the farms surveyed were organic, being managed
a disc plough. Though no hand-weeding of cereals is without chemical fertilisers or herbicides, and most had
practisednowadays,cerealswereharrowedinAprilaround been so for decades (Table 1). Four of the seven farms
Sault and Saint-Christol in order to remove early spring practised no manuring with animal dung, relying entirely
weeds, with 2–3 passes in the case of einkorn, which was on crop rotation and in some cases a ‘green manure’ crop
considered to recover better than other cereals due to its (forage legume or mustard) to maintain a modest level of
strong tillering capacity. Further south, on the more clay- fertility. Several farmers observed that cereals clearly
rich soils of the northern Lube´ron, harrowing was not benefitedfromtheadditionalnitrogenfixedbyapreceding
practisedsinceittoreupthecropduetotheformationofa leguminous crop, especially when ploughed in as a green
hardclay‘crust’onthesoilsurface.InonefarmnearSault manure. One farmer (Farm 6) also noted that ploughing in
(Farm2,Table 1),pulsefieldswereintensivelyworkedby the bottom c. 20 cm of einkorn straw helped to maintain
vibroculteur (a sort of harrow with vibrating teeth) to re- fertility,whileanother(Farm2)hadbeguntospreadrotted
move spring weed growth. lavender straw (composted for 2 years) on fields to be
A broad contrast can be drawn between the clay-rich, planted with bread wheat or barley. On one Sault farm
calcareous soils of the northern Lube´ron and the more (Farm 3), the producer’s aunt raised sheep that provided
friable soils around Sault that permitted spring harrowing dung for aromatic crops; sheep manure was applied at a
but also tended to be acidic due to the formation of rate of c. 30 t/ha in the fifth or sixth year of lavender
sesquioxides,andhadinsomeareasbeentreatedwithlime growth, meaning that a hectare of land would receive c.
in the past to raise the soil pH. One farmer (Farm 5) re- 30 tons every 15 years or so. On the two farms (Farms
ported pH levels of c. 4.0 on his plateau d’Albion fields. 6–7)onalkalinesoilsinthenorthernLube´ron,fowl(andin
Farmers also observed more local variation in soil type, one case also sheep) dung was applied to cereals at low
ranging in the Sault area from loamy alluvial soils along rates (B3 t/ha); one farmer indicated that fowl dung was
the river Nesque, where soils were less stony and more applied in order to lower soil pH and hence to prevent the
humid, to fields on the plateau d’Albion covered by a formation of calcium crystals on cereal roots that impede
continuous scatter of flint. water uptake. Several farmers commented that sheep dung
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VegetHistArchaeobot(2016)25:57–73 61
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123
62 VegetHistArchaeobot(2016)25:57–73
Table2 ComparisonofHauteProvenceandAsturiasstudyareas
HauteProvence Asturias
Ko¨ppen–Geiger Temperate-oceanic(Cfb)totemperate- Temperate-oceanic(Cfb)
climatezone mediterranean(Csb)
Annualprecipitation 700–900 1,000–1,100
(mm)
Farmingscale 1–2ha(\100hafarms)to8–9hafields Plotsof15–800m2,fewfieldsperproducer
([100hafarms)
Manuring Minimal(niltofewt/ha/year) 15–40t/ha/year
Weeding Nohand-weeding;springharrowingaround Ploughingcombinedwithhoeingtopreparesoil;hand-weeding
Sault duringgrowingseason
used to be applied to cereal fields since many farms GPSdataforindividualfieldsandisotopesampleswere
formerly raised sheep alongside arable crops. A farmer in recordedusingahandheldGPSunitduringthefieldsurvey.
the northern Lube´ron (Farm 1) observed that in the mid- GPS data recorded included the boundary of every field
20th century sheep were allowed to graze vegetative ce- surveyed and the specific location of every quadrat within
realsonclay-richsoils,bothinordertotrampledownroots each field. The data were analysed using ArcGIS 10.1 in
raisedbyfrostsandtopreventlodging(cf.Halstead2006). order to detect any associations between topographical
Cerealsandpulseswereharvestedearlierinthenorthern variables and weed floristic composition or crop isotope
Lube´ronthanintheSaultarea; thetimingvaried fromlate values.
June to August (September) depending on the crop and Ecological attributes of the most commonly occurring
localsetting,einkornbeingharvestedlater(Augustoreven weed species identified in this survey were measured dur-
September) than other cereals (Table 1). The 2013 harvest ing the same study season. Species were selected for the
was about 15 days later than usual due to an abnormally measurement of functional attributes if they occurred in
wet and cool spring and summer. 5 % or more of the fields (i.e. three or more fields). These
Comparison of the cereal production regime in Haute speciesarelistedinSupplementaryTable 1.Theattributes
Provence with a more intensive system in Asturias, Spain measured were those found most useful for the identifica-
(Fig. 1) (Charles et al. 2002) using a combination of weed tion of cultivation intensity in the original Evvia study
ecologicalandcropisotopicanalysisiscentraltothisstudy. (Jones et al. 2000), and are summarised in Table 3 (see
Table 2 summarises climatic and agronomic contrasts be- Charles etal.1997;Bogaardetal.1999;Jonesetal.2000;
tweenthesetwoareas.Thoughbothareasfalllargelywithin Bogaard et al. 2001; Charles et al. 2003 for fuller expla-
theCfbzone,Asturiasexperiencessomewhathigherannual nations).Amphistomaty(relativedistributionofstomataon
rainfall. Obvious agronomic contrasts between the Haute upper and lower leaf surface), an indicator of shade toler-
Provence and Asturias production regimes concern their ance, was excluded here since stomatal attributes were not
scaleandtheirintensityofmanagement(Table 2). measured in the Provence study.
Only well-grown specimens were selected for mea-
surement of functional attributes so that species potential
Materials and methods was assessed rather than individual plant performance un-
der variable conditions. Detailed protocols for the mea-
Field methods surementofeachoftheseattributesaregiveninJonesetal.
(2000) and Bogaard et al. (2001). Canopy height and di-
InJune–July,2013,afloristicsurveywascarriedoutofthe ameter were converted to a log scale. Attributes such as
weeds in 57 cereal or pulse fields in this region, using duration and onset of flowering were extracted from
methods comparable to those employed in similar surveys Rothmaler (1995).
of the weeds associated with different husbandry regimes A total of 23 pairs of isotopic measurements (d13C and
in Spain (Jones et al. 1995; Charles et al. 2002), Jordan d15N)wasobtainedfrom24fieldsinHauteProvence(two,
(Palmer1998;CharlesandHoppe´ 2003)andGreece(Jones ABI01 and ABI02, were merged); those fields to which
et al. 1999). The weed species present in each of ten 1 m2 fowldunghadbeenapplied(Table 1)wereexcludeddueto
quadrats were recorded along a linear transect from one the distinctive effect of this form of manure on plant d15N
end of the field to the other. Three fields had distinct to- values (cf. Szpak 2014). In some cases crops were col-
pographical subdivisions and were recorded using two lected ripe during the weed surveys. In that case, one ear
separate transects, for a total of 60 field transects. was taken from each of the ten quadrats. For fields where
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VegetHistArchaeobot(2016)25:57–73 63
Table3 Theweedfunctionalattributesmeasuredandtheirpossibleecologicalsignificancewithinanarablecontext
Functionalattribute Ecologicalattributeforwhich Relationshiptohabitatconditions References
measured measurementisasurrogate
Attributesrelatingtothedurationandqualityofthegrowthperiod
Maximumcanopy Maximumplantsize,theproduct Positivelycorrelatedwithpotential Grime(1979),Molesetal.(2009)
heightanddiameter ofgrowthrateandperiodof productivity,negativelywith
growth disturbanceofhabitat
Leafareapernode/leaf Plantgrowthrate Positivelycorrelatedwithpotential Jackson(1967),Dale(1982),
thickness productivityofhabitat Givnish(1987),Jonesetal.(2000)
Meanspecificleafarea Plantgrowthrate Positivelycorrelatedwithpotential Reichetal.(1992),Reich(1993),
(leafarea/dryleaf productivityofhabitat Wrightetal.(2004),Poorteretal.
weight) (2009)
Attributerelatingtoseasonalityand/orthecapacitytoregenerateunderconditionsofhighdisturbance
Lengthofflowering Durationoflifecycleand Positivelyassociatedwithdisturbance Grimeetal.(1988),Sansand
period potentialtoregeneratefrom Masalles(1995),Bogaardetal.
seed (2001)
ripecropswereobtainedaftertheharvest,tenrandomears the number of quadrats in which each taxon was found);
werechosenacrosseachfield.Grainsfromtheseearswere andsemi-quantitatively(usingpresence/absenceofspecies
threshedbyhand,andarandomsubsetof50waspowdered in each cultivated field). The latter is more directly com-
using a Spex 2760 FreezerMill. Since inter- and intra- ear parable betweenmodern andarchaeobotanicaldatasetsbut
isotopicvariabilitycanbesignificant(Bogaardetal.2007; involves some loss of information.
Heatonetal.2009)homogenizingalarge(n[15)number Discriminantanalysiswasusedtodistinguishcropfields
of seeds ensures that measurements are adequately repre- cultivated under the two different intensity regimes, in
sentative of the average signature for each field (Kanstrup Haute ProvenceandAsturias.Forthispurpose, anaverage
et al. 2012; Nitsch et al. submitted). scoreforeachattributewasdeterminedforeachcultivated
field as follows:
Laboratory analysis
X .X
nak nk
i i i i i
The homogenized powders were weighed into tin capsules
for IRMS analysis on a SerCon EA-GSL mass spec- Forthequantitativemeasure:k istheno.ofquadratsin
i
trometer, with d13C and d15N measured separately. An which the ith species was recorded, a is the value of at-
i
internalalaninestandardwasusedtocalculaterawisotopic tribute for the ith species, and n is the no. of species
ratios.Ford13Ctwo-pointnormalizationtotheVPDBscale recorded in each field.
was obtained using four replicates each of IAEA-C6 and Forthesemi-quantitativemeasure,kisalwaysequalto1
IAEA-C7, while for d15Nthe standards were USGS40 and and so the numerator is simply the sum of the attribute
IAEA-N2. Reported measurement uncertainties are the values for the species in the cultivated field and the de-
calculated combined uncertainty of the raw measurement nominator is the number of species in each field.
andreferencestandards,afterKragten(1994).Theaverage The success of the discriminations was measured in
measurement uncertainty for d13C was ±0.07 and terms of the percentage of fields correctly reclassified as
±0.35 % for d15N. These calculations were performed ‘low intensity’ (in Haute Provence) or ‘high intensity’ (in
using the statistical programming language R. (3.0.2). Asturias),usingthediscriminantfunctionextractedineach
analysis. The same discriminant functions were used to
Data analysis classify the cereal fields from Sighisoara and Kastamonu
and archaeobotanical samples from Neolithic central Eur-
In the modern weed studies discussed here, the number of ope,allofwhich wereenteredintotheclassificationphase
quadrats out of ten in which each taxon occurred was oftheanalysisassamplesof‘unknown’cultivationregime.
recorded. By contrast, archaeobotanical data, to which the SPSS version 20.0 was used to perform discriminant ana-
model developed here is ultimately applied, are quantified lyses, using the ‘leave-one-out’ option.
on the basis of numbers of seeds. The quantitative data Canoco for Windows 4.5 and CanoDraw for Windows
from the modern weed survey studies are therefore not (ter Braak and Smilauer 2002) were used to carry out
directly comparable with archaeobotanical data. Analysis correspondence analyses of the weed survey data from
wasthereforeconductedintwoways:quantitatively(using Haute Provence in order to explore variation in floristic
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64 VegetHistArchaeobot(2016)25:57–73
vibroculteur once the early spring weeds had germinated.
The weed species associated with the intensively worked
pulse fields belonged in phytosociological terms to the
Chenopodietea, garden or row-crop weeds (Fig. 3b).
Although some Chenopodietea species are associated with
low intensity cereal (and pulse) cultivation, the vast ma-
jority of species associated with low intensity cultivation
belongtotheclassSecalinetea.Thesmallnumberoffields
did not permit full ecological characterisation of the more
intensive form of pulse cultivation in Haute Provence, but
theevidentcontrastwithlessintensivelymanaged fieldsis
relevant to comparison with intensive cultivation in As-
turias (see below).
In a second correspondence analysis, excluding the in-
tensively worked pulse fields, the geographical distinction
betweentheSaultarea(right)andtheLube´ron(left)remains
dominant on axis 1 (Fig. 4a). Axis 2 distinguishes the
Fig.3 Correspondence analysis of Haute Provence fields and weed Cavalon and Chaffe`re drainages in the Lube´ron (Fig. 4b).
taxa:aplotof60fieldtransects,codedbyregimeandregion;bplotof Figure 4a,codedbyfarm,revealssubregionalclusteringof
weed species, coded by phytosociological class (Chenopodi-
farmsintheSaultregionandCavalondrainage;theChaffe`re
etea=root/row-crop ‘garden’ weeds; Secalietea=cereal field
weeds).Axis1horizontal,axis2vertical drainage (upper left) is represented by a single farm. The
dominance ofgeographyas acorrelate with floristic varia-
composition among fields. In the figures, correspondence tioninHauteProvenceindicatesacontrastwiththestudyof
axis 1 is plotted horizontally and axis 2 vertically. Statis- ‘garden’and‘field’cultivationinEvvia,Greece,whereany
tical calculations related to the isotopic data were per- geographicalvariationintheweedflorawassubordinateto
formed using the statistical programming language R. thegradientinagriculturalintensity(Jonesetal.1999).
(3.0.2). Comparisons between the four different study re- While the contrastbetween the Cfbclimate ofthe Sault
gions were calculated using a one-way ANOVA, with region and themoremediterraneanclimateofthe Lube´ron
pairwise differences reported as 95 % confidence intervals likely contributes to the geographical trend on axis 1, the
with Tukey-HSD-adjusted p values. contrast also involves different soil types. This is reflected
FortheHauteProvencestudy,topographicanalysiswas in a contrast in weed species between those preferring
based on the BDALT25 digital elevation model (URL: acidicsoilsaroundSaultandthosepreferringalkalinesoils
http://professionnels.ign.fr/bdalti#tab-1). A wide range of in the Lube´ron (Fig. 5a). These different soil types also
topographic variables was analysed, using the Hydrology, encouragedifferentagriculturalpractices:springharrowing
Solar Radiation and Surface toolsets in ArcGIS 10.1. of cereals is associated with the soil types of the Sault/
Albion plateau but is not practiced on the more clay-rich
soils in the Lube´ron (Fig. 4c). This explains the tendency
Results for long-flowering annuals, able to recover from distur-
bance,tobelocatedtowardsthepositive(right)endofaxis
Causes of floristic variation in the Haute Provence 1 (Fig. 5b). It is clear, however, that it is the location of
weed flora fields (which determines soil type), rather than harrowing,
thatgovernsthedistributionoffieldsinthecorrespondence
Correspondence analysis of all 60 crop field transects in analysis, because the few unharrowed fields in the Sault
Haute Provence (Fig. 3a) on the basis of 78 weed species area cluster with the other (harrowed) Sault fields rather
occurring in at least 5 % of fields presents a clear contrast thantheunharrowedfieldsoftheLube´ron(Fig. 4),andthe
on axis 1 (horizontal) between the Sault region (right) and associationofweedspeciespreferringacidicsoilswiththe
the Lube´ron (left). Axis 2 (vertical) distinguishes between Saultareaisstrongerthantheassociationoflong-flowering
the majority of fields (including both cereals and pulses) species with harrowing (Fig. 5).
concentrated at the negative (bottom) end from four in- Asnotedabove,manuringofcerealsintheLube´ronwith
tensively worked pulse fields towards the positive end. chickendungisameansofreducingthesoilpH;manuring
These were fields of spring-sown lentils and chickpeas on rates are very low, however, and no differences in weed
loamy stone-free soils along the river Nesque near Sault functionalattributesrelatingtosoilproductivityareapparent
(Farm 2, Table 1) ‘weeded’ mechanically using a (plotsnotshown).Finally,neithercropsowingtimenorcrop
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VegetHistArchaeobot(2016)25:57–73 65
Fig.4 Correspondence analysis of the weed species in 56 Haute Fig.2); c harrowing. Axis 1 horizontal, axis 2 vertical; circles Sault
Provencefieldtransects(excludingintensivelycultivatedpulses),plot area,squaresLube´ronarea
of transects coded by a farm (see Table1); b river drainage (see
Fig.5 Correspondenceanalysis
oftheweedspeciesin56Haute
Provencefieldtransects
(excludingintensively
cultivatedpulses),withplotof
speciescodedbyaEllenberg
reaction(pH)scale(a1–9scale
where1indicatorofextreme
acidity,7weaklyacidicto
weaklybasicand9basic
reactionandlimeindicator,
alwaysfoundoncalcareous
soils—Ellenbergetal.1992);
bfloweringduration.Axis1
horizontal,axis2vertical
taxonshowanyclearpatterning(plotsnotshown).Forex- Provence and small-scale/intensive cereal farming in As-
ample,theanalysisdidnotdetectanydifferencesintheweed turias, on the basis of the five functional attributes previ-
floraofeinkornfieldsduetotheirlaterharvestingtime. ouslyshowntodistinguishbetweenhigh-andlow-intensity
Overall, the weed flora of the Provence fields primarily pulse cultivation regimes in Evvia, Greece as discriminat-
vary according to their geographical location (in response ing variables (Table 3). Though geographical differences
to soil type and perhaps climate), and only secondarily in betweenthetwoareasmayaffectthediscrimination(Jones
response to agricultural practice (notably harrowing). et al. 2010), our hypothesis was that the strong agronomic
contrasts (Table 2) would enable the regimes to be distin-
Ecological comparison of Haute Provence guished along predictable lines using these attributes. All
andAsturiasregimesonthebasisofweedfunctional oftheAsturiasfieldssurveyed(Charlesetal.2002),and56
attribute values of the Haute Provence field transects, were included in the
discrimination; the four intensively worked pulse fields in
Discriminant analysis was used to distinguish between the Haute Provence (Fig. 3a) were entered into the classifica-
weedfloraoflarge-scale/low-intensityproductioninHaute tion phase of the discriminant analysis.
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66 VegetHistArchaeobot(2016)25:57–73
Fig.6 The relationship of Haute Provence fields (open circles,
n=56)andAsturiasfields(filledcircles,n=65)tothediscriminant
function extracted to distinguish these two groups on the basis of
a fully quantitative; b semi-quantitative (presence/absence) weed
attribute scores. Larger symbols indicate group centroids; grey
squares intensively worked pulse fields in Haute Provence entered
intotheclassificationphaseoftheanalysisonly
Figure 6 shows that the Haute Provence and Asturias
fields are clearly distinguished on the basis of fully quan-
titative(98 % correctly reclassified, 119of121)and semi-
quantitative (presence/absence) data (100 % correctly re-
classified; Fig. 6). Functional attributes characterise the
two regimes in accordance with ecological predictions
(Fig. 7). In both analyses, weed species with tall, broad
canopies, high specific leaf area (SLA) and a high leaf
area:thickness ratio are associated with intensive cereal
farming in Asturias, and vice versa for the less fertile
Provence fields; a long flowering period is also associated
with greater disturbance inAsturias (cf.Jones et al.2000).
Fig.7 Correlations between the functional attribute scores used as
It is worth noting that three of the four more intensively
discriminating variables and the discriminant function based on
worked pulse fields in Haute Provence—those that
afullyquantitativedata;bsemi-quantitative(presence/absence)data
emerged as distinct in the correspondence analysis
(Fig. 3a)—wereclassifiedasintensivelycultivatedbyboth application in long-term agricultural experiments (Fraser
discriminant functions (Fig. 6). etal.2011).AgronomicobservationsinAsturiasshowthat
ThefunctionalattributesdiscriminatebetweentheHaute manure is applied at rates equivalent to c. 15–40 tons per
Provence and Asturias regimes as predicted based on year for 1 ha (Table 2; Bogaard 2012), spanning ex-
contrasts in agronomic practice, despite geographical dif- perimentalmedium(c.10–15 t/ha)tohigh(30? t/ha)rates
ferences between the two areas (Table 2; cf. Jones et al. (Fraser et al. 2011). With two exceptions, the Haute
2010). Moreover, pronounced geographic variation within Provence fields exhibit d15N values lower than 3 %, as
Haute Provence (above) does not obscure the predicted predicted by long-term agricultural experiments where
ecological contrast with Asturias. there is continuous cultivation with little to no manuring
(Fraser et al. 2011). The exceptions are two einkorn fields
Comparison of Haute Provence and Asturias (Farm 3, Table 1) located near Sault along the river Nes-
regimes on the basis of cereal stable isotope values que.Manuringcanbeexcludedasacauseofthehighd15N
values for these two fields, which were managed in the
Table 4 and Fig. 8 show that the production regimes in samewayastheotherfieldsonFarm3),sonaturalorganic
HauteProvenceandAsturiasexhibitlargelydistinctranges matter or anaerobic denitrification are more likely expla-
of d15N values (a difference of 2.36 %, 95 % CI 0.71, nations (see also below).
4.01 %, p = 0.002). TheAsturias fields exhibit arange of Higher d15N values coincide with higher mean dis-
valuesequivalentto‘medium’and‘high’levelsofmanure criminant scores in the weed functional attribute analysis
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