HAL Id: hal-00959127
https://hal.archives-ouvertes.fr/hal-00959127
Submitted on 14 Mar 2014
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps
rivers
Paul Cavaillé, Fanny Dommanget, Nathan Daumergue, Gregory Loucougaray, Thomas Spiegelberger, Eric Tabacchi, André Evette
To cite this version:
Paul Cavaillé, Fanny Dommanget, Nathan Daumergue, Gregory Loucougaray, Thomas Spiegel- berger, et al.. Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps rivers. Ecological Engineering, Elsevier, 2013, vol. 53, pp. 23-30.
�10.1016/j.ecoleng.2012.12.105�. �hal-00959127�
Open Archive TOULOUSE Archive Ouverte (OATAO)
OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.
This is an author-deposited version published in : http://oatao.univ-toulouse.fr/
Eprints ID : 11172
To link to this article : doi:10.1016/j.ecoleng.2012.12.105 URL : http://dx.doi.org/10.1016/j.ecoleng.2012.12.105
To cite this version : Cavaillé, Paul and Dommanget, Fanny and Daumergue, Nathan and Loucougaray, Gregory and Spiegelberger, Thomas and Tabacchi, Eric and Evette, André Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps rivers. (2013) Ecological Engineering, vol. 53 . pp. 23- 30. ISSN 0925-8574
Any correspondance concerning this service should be sent to the repository
administrator: [email protected]
Biodiversity assessment following a naturality gradient of riverbank protection structures in French prealps rivers
Paul Cavaillé
a,∗, Fanny Dommanget
a, Nathan Daumergue
a, Gregory Loucougaray
a, Thomas Spiegelberger
a, Eric Tabacchi
b, André Evette
aaIrstea,UREMGR,2ruedelapapeterieBP76,38402Saint-Martin-d’Hères,France
bCNRS,UniversityofToulouse,InstitutNationalPolytechnique,EcoLab,Bât.4R1,118routedeNarbonne,31062Toulousecedex9,France
Keywords:
Beetlediversity Bioengineering Plantdiversity Riverbank Ripariancorridors
a b s t ra c t
Erosioncontrolofriverbankisfrequentlynecessarytoprotecthumaninvestmentssituatedalongrivers.
Thetechniquechosenforsucherosioncontrolconstructionmayhavemajorimpactsonbiodiversityand onthefunctioningofrivercorridors.Evenifthereisagreement,thatbiodiversityshouldbeonecriterion forchoosingembankmentstechniqueslittleisknownaboutwhethersuchtechniquescanaccommodate biodiversity.
Weaimedtodeterminecoleopteranandplanttaxonomicdiversitiesalonganaturalitygradientof riverbankprotectionsystems,rankingfromentirelycivilengineeringstructures,throughcombinedcon- structions(mixingcivilengineeringandbioengineering),topurelybioengineeringstructures.
Fifteensites(fivesitesofeachtechnique)weresampledintheRhône-Alpesregion(S.E.France).On eachsite,vegetationwassampledalongthreetransectsfromthebottomtothetopoftheriverbankand flyingbeetlesbytrapping.
Intotal,werecorded148plantspeciesand78beetlegenera.Wefoundsignificantlyloweranimaland plantdiversitieswithincivilengineeringconstructionsthanintheothertwotechniques.Diversitiesof bothtechniquestendedtobehigher,althoughnotsignificantly,incombinedtechniquesthaninpurely bioengineeringones.Furthermore,civilengineeringstructuresweremoresubjecttoinvasionbyexotic plantspeciesthanthetwoothertechniques.Theseresultsquantifyandhighlighttheinterestofbioengi- neeringtechniquescomparedtocivilengineeringinenhancingbiodiversityandlimitinginvasivespecies techniques.
1. Introduction
In addition to its high level of biodiversity, riparian corri- dorssupplymultipleecosystemservicessuchasnutrientcontrol, floodcontrol,shadingeffectandsocialaspects.Ripariancorridors havethereforebeenwidelyrecognizedaskeycomponentinland- scapes(Décamps,2011).Thereisastrongcausallinkagebetween biodiversityandecosystemfunctioning(Maestreetal.,2012).Bio- diversity loss may induce a modification of natural ecosystem functioningandecosystemservices(McNeely,2010).
However,WesternEuropeanripariancorridorsandtheirveg- etation have been widely affected by centuries of human use.
Rivercorrectionsandassociatedfloodcontrolhavebeenprimar- ilyperceivedhasagreat humanachievementin environmental
∗Correspondingauthor.
E-mailaddress:[email protected](P.Cavaillé).
control.However,shortlyafterinitialsuccesssuchartificialland- scapes spotlight a major conflict between riparian ecosystem conservationandhumanpatrimonyprotection(Pahl-Wostl,2006), assuchriverstraighteninghasleadtoadrasticlossofbiodiversity in riparian systems. In urbanized areas as well as in agricul- tural landscapes,spaceavailableforriparianvegetationisoften reducedtotheriverbankonly.Thus,organismscanhardlycircu- latealongthereremnantsofthepastripariancorridorsespecially whencivilengineeringerosioncontrolstructuresareused(Nilsson etal.,2005).Suchinterruptionsinthecorridormosaicmaylower biologicalcontinuitybyreducingcirculation,refugeandfeeding opportunities,andbyincreasingthermalcontrastsduringsummer.
Alteredlandscapesanddisruptedcorridorresultinaglobalripar- ianecosystemloss(Poffetal.,1997;TocknerandStanford,2002).
Consequently,biodiversityconservationshouldbeastrategyfor practitionerstoenhanceecosystemfunctioning(Isbelletal.,2011).
In addition, direct exposure to flood and high flood fre- quencyleadtohighpropagulefluxesonbaresoilsandpromote
http://dx.doi.org/10.1016/j.ecoleng.2012.12.105
colonizationbyexoticspeciesandsubsequentlyinvasion(Décamps et al., 1995). Therefore, exotic species richness is significantly greaterinriparianzonescomparedtouplandsites(Stohlgrenetal., 1998).
Habitat restoration hasbeen clearly identified as a key ele- menttoreversenegativeanthropic impactsonbiodiversityand ecosystemsfunctioning(Helfieldetal.,2012).Publicpolicysuch astheEuropeanWaterFrameworkDirective(WFD;2000/60/EC) encouragesaglobal“goodecologicalstatus”ofaquaticenviron- mentincludingmorphologicalconditionssuchasstructureofthe riparianzone.Astudyorderedin2005bytheFrenchMinistryof EcologyandSustainableDevelopmenthighlightsthat51%ofthe surfacewatermasswouldnotreachtheobjectiveof“goodecologi- calstatus”by2015(IFEN,2006).Improvingbiodiversityonartificial riverbanksmayactinfavourofthisobjectiveandinparticularif alternativestocivilengineeringareusedsuchasbioengineering techniques(LiandEddleman,2002).
Bioengineeringtechniquesforerosioncontrolconsistsinthe uses of living plantsin order tomimic natural vegetationable to resist intense scouring (Gray and Sotir, 1996; Norris et al., 2008;EvetteandFrossard,2009).Bioengineeringappliedtoriver- banksaimsatcombiningbothartificialandnaturalcomponents toprovideprotectionattheentirebanklevel(Evetteetal.,2012).
Inadditiontotheirerosioncontrolcapacity,bioengineeringstruc- turesaresupposedpromotingtherecoveryofindigenousspecies andtoensurebetterplantcoveragethanartificiallyreconstructed embankmentsusingcivilengineeringtechniques(Pezeshkietal., 2007).One oftheargumentsgiven forchoosingbioengineering structuresinsteadofcivilengineeringonesisthatthefirstpro- mote the re-establishment of a functional and self-sustainable ecosystem;however,toourknowledge,noquantitativescientific evidenceshave been produced to supportthis idea. Untilnow socio-economicalissuesarethemainreasonstowhetherprotect ornot.Riverandlandmanagers’finaldecisiononwhichriverbank protectiontechniquewillbeusedismainlybasedonseveralcru- cialpointssuchashydro-engineeringaspects,bedmaterialand watercoursebankstability(SchiechtlandStem,1996).However,no quantitativeecologicalaspectisforthemomenttakenintoaccount inthedecisionline.
Todate,many scientificstudiesonbioengineeringstructures alongriversfocusonmethodologicalaspectssuchasstructures, construction methods, mechanical resistanceand thechoice of species(Bretonetal.,underreview),comparedtothefewworks whicharededicatedtobiodiversitysubsequentlyrelatedtoero- sioncontrolstructuresonwatercoursebanks.Since2002andthe earlyworkontheenvironmentalandecologicaladvantagesofbio- engineeringstructures(LiandEddleman,2002),fewstudieshave usedquantitative methodstoinvestigaterelation betweenbio- diversityanderosioncontrolstructures.Someworksaredealing withplantspeciesand habitatdiversity assessmentbut remain studycasesonveryfewsites(Lietal.,2006;SudduthandMeyer, 2006).Ontheotherhand,studieshavebeendoneonriverbank restorationbyremovingbankfixationorprotectionandcompar- ativebiological surveyonrestoredandnon-restored siteswere made(Helfieldetal.,2007;Januschkeetal.,2011).Thoughthereis abigknowledgegapconcerningquantitativebiologicalcompari- sonofriverbanktechniquesforerosioncontrolandtheirimpact onecosystemproperties(Pahl-Wostl,2006).Toourknowledge, nostudyhasyetdemonstratedtherelationshipbetweenmaterials andtechniquesusedforerosioncontrolandassociatedchangesin biodiversityontheconstructions.
Theaimsofthisstudywere(i)toevaluateandcompareanimal andvegetalbiodiversityonthreeriverbanktechniquesforerosion controland(ii)toassessthecapacityofdifferentriverbankpro- tectiontechniquestolimitinvasionofexoticspecies.Theapplied
aimofthisstudywastointegrateecologicalaspectsintothedeci- sionlinebyproviding ecologicaldata.Weprovideguidelinesto practitionersonwhatecologicalconditionstheycanexpectonthe riverbanktechniquechoseninordertodevelopstrategieslinkedto riverbankmanagementandallowrestorationofecosystemgoods andservices.Wehypothesizethatcivilengineeringtechniquesdo notpromotebiodiversityasgoodasbioengineeringtechniques.
2. Materialsandmethods 2.1. Sites
Weassessedbiologicaldiversityonfivereplicatesofthreeriver- banktechniques(Fig.1):
-Civilengineeringembankments:riprapprotection(rocksusedto stabilizeshorelines,againstscouranderosion)notedas“Min- eral”.
-Mixed embankments combining civil engineering techniques (riprapatthelowerpartofthebank)andbioengineeringtech- niques(cuttingsandwoodyplantationattheupperpart)noted as“Mixed”.
-Completely bioengineeringembankments: (willow fascines at thelowerpartofthebankwithcuttingsandwoodyplantation attheupperpart)notedas“Vegetal”.
Thesethreetechniqueswereconsideredasthreelevelofanat- uralitygradient.Naturalitycanbedefinedbytheamountofliving vegetationusedintheconstructionasclassificationkeycriterion (Brunel,2009;Werdin-Pfistereretal.,2009).Mineralstructures wereconsideredasman-madeenvironmentswithlittleplantcov- erage,differentfromtheenvironmentfoundonnaturalmountain riverbank.Mixed methods showintermediate plant cover with revegetationon halfof thebank.Bioengineering structuresare completelyvegetalandthereforeareexpectedtoshowthehigh- estvegetationcoverandthusthehighestlevelofnaturality.These threeengineeringtechniquestherefore constitutethreedistinct levelsonanaturalitygradient.
WeselectedfifteenriverbanksalongsixdistinctFrenchprealps riversbelongingtotheRhonecatchmentarea.Alargeandintense prospectionatterritorialunitsforrivermanagementorganizations wasperformedtolistenoughcomparablebanks.Table1listssites characteristics.Asaltitudeprofoundlyaffectsecologicalcommu- nitycomposition,studysiteswereselectedatanarrowrangeof 270m(between200and470masl).Onlysitesbetween20and 30mlongandwithanestablishedvegetationwerechosenforanal- ysis.AllthestudysiteswerelocatedinthefoothillsoftheFrench Alpscharacterizedbyhighlyfragmentedhabitats.
2.2. Vegetation
VegetationwasassessedusingthecontactpointmethodinJune andJuly2009.Thismethodencompassestheverticalorganiza- tionofthevegetation(tree,shrubandherbaceouslayers).Plant speciesdiversityandfrequencieswereestimatedusinga2-m-long stickwitha diameterof1cm. Measurementsweretakenevery metrealongthree20mtransectsplacedparalleltotheshoreone locatedatthewaterline(Transect1),oneinthemiddle(Transect 2)andoneatthetop(Transect3)oftheriverbankembankment (sixtymeasurementsper site).Vegetationwasidentified tothe specieslevelusingvariousidentificationkeysandflora(Rameau, 1994;LauberandWagner,1998;Aeschimannetal.,2004).Exotic speciesweredefinedonthebasisofestablishedlistsrelevantto thearea(Mulleretal.,2006),alistofexoticinvadersinSwitzerland
Fig.1.Schematicrepresentationofriverbanktechniquesstudied.(a)Civilengineeringembankments:riprapprotection,notedas“Mineral”.(b)Mixedembankments combiningcivilengineering(riprapatthelowerpartofthebank)andbioengineeringtechniques,notedas“Mixed”.(c)Completelybioengineeringembankments:willow fascinesatthelowerpartofthebankwithcuttings,notedas“Vegetal”.
(LandoltandBäumler,2010)andalistestablishedfortheadmin- istrativedistrictofIsère(Gentiana,2006).
2.3. Fauna
Coleopteranswereidentifiedtogenus(Insecta,Coleoptera).This order, and more specifically theCarabids, is used as proxy for habitatdiversity,hydromorphologicalprocessesandhabitathealth status(Boscainietal.,2000;Kleinwaïchteretal.,2003).Moreover, morphologicalattributesofColeopteranscanprovideinformation ontheirfunctionalandtrophicstatus(VanLooyetal.,2005).Flying coleopteransweretrappedusingtwoFlora®“YellowWell”traps, locatedatthetwoextremitiesin themiddle ofthebank(tran- sect2)andplacedatthecanopylevel.TrapsweresetinJuneand
July2009andremainedinthefieldforsevendays.Insectswere identified using a binocular microscope and appropriate refer- enceworks(Picard,1929;Paulian,1941;Hoffmann,1945;Guignot, 1947;Balachowsky,1949).
2.4. Statisticalanalysis
Differencesinplantspeciesandcoleopterangenerarichness, andinfrequencyandnumberofexoticspeciesamongthethree typesofdevelopmentwasassessedusingKruskal–Wallistests.In caseofasignificantmaineffect,pairedMann–Whitneytestswere carriedouttodetectdifferencesbetweeneach technique.Over- allstatisticalriskwasassessedusingtheHolm’scorrection(Holm, 1979).Aninter-classprincipalcomponentanalysis(PCA)(Doledec
Table1
Characteristicsandlocalizationsofembankments.
Sitecode Constructiontype Locality River Latitude Longitude Constructionworkyear Altitude(masl)
6V Vegetal LesEchelles Guiersvif 45◦26’19.15”N 5◦45’36.75”E 2005 393
35V Vegetal VillardBonnot Vorz 45◦15’01.29”N 5◦54’01.62”E 2006 242
7V Vegetal StGeoireenValdaine Ainan 45◦28’02.24”N 5◦39’40.90”E 2004 381
38V Vegetal LeGrandSerre Galaure 45◦15’45.62”N 5◦06’29.65”E 2007 370
39V Vegetal Cluse Arve 46◦04’13.98”N 6◦33’18.72”E 2005 470
6Mix Mixed LesEchelles Guiersvif 45◦26’19.15”N 5◦45’36.75”E 2005 393
30Mix Mixed Grenoble Isère 45◦11’55.65”N 5◦44’02.36”E 2002 210
32Mix Mixed Gière Isère 45◦11’20.94”N 5◦47’20.62”E 2005 210
39Mix Mixed Cluse Arve 46◦04’13.98”N 6◦33’18.72”E 2005 470
40Mix Mixed Bonneville Arve 46◦04’33.18”N 6◦24’26.63”E 2004 444
7Min Mineral StGeoireenValdaine Ainan 45◦28’02.24”N 5◦39’40.90”E 2004 381
35Min Mineral VillardBonnot Vorz 45◦15’01.29”N 5◦54’01.62”E 2006 242
37Min Mineral ChateauneufdeGalaure Galaure 45◦14’09.59”N 4◦58’30.83”E 2004 257
38Min Mineral LeGrandSerre Galaure 45◦15’45.62”N 5◦06’29.65”E 2007 370
39Min Mineral Cluse Arve 46◦04’13.98”N 6◦33’18.72”E 2004 470
Fig.2.Meanplantspeciesnumbersforeachriverbankprotectiontechniqueaccord- ingtotheirpositionsonthebank.Differentlettersindicateastatisticaldifference betweensamples.Errorbarsindicatestandarderrors.The“Alltransect”barrepre- sentthemeanofthetotalnumberofplantspeciesfoundforeachtechnique.
and Chessel,1987)wascarriedouttoanalyzetheoverallplant pattern. AMonte-Carlo test wasprocessedtodetectsignificant differencesinfloristic compositiononstructuresusingdifferent engineeringtechniques(MetropolisandUlam,1949).Alltestswere performedusingRstatisticallanguage(R,2005)withade4package (Thioulouseetal.,1997)formultivariateanalysis.
3. Results 3.1. Vegetation
Weidentified126plantspeciesfromthe15sampledsites.
Plant species richness differedalong thenaturality gradient (Kruskal–Wallistest:p-value=0.006,Table2).“Vegetal”or“Mixed”
techniques having higher species plant diversity compared to
“Mineral”technique(Mann–WhitneyUtestwithHolmcorrection:
p-value=0.024and0.036,Table2).Therewasnosignificantdif- ferencebetweenmeanspeciesrichnesson“Vegetal”and“Mixed”
techniquesalthoughdiversitytendedtobehigheronthelatter, especiallyinthemiddleandatthebottomofthebank(Fig.2).
Floristiccompositiondifferedsignificantlyalongthenaturality gradient(Monte-Carlotest:p-value=0.003).Thedistributionand spacingofthethreesphericalclusters(mn:Mineral;mx:Mixed;
v:Vegetal)onthePCAfactorialmapprovidesinformationonthe variabilityoffloristiccompositions(Fig.3).However,somespecies contributemorethanotherstothesegregationofthethreesets,e.g.
multipleSalicaceaespecies(SalixviminalisL.,SalixpurpureaL.,Salix triandraL.,SalixfragilisL.,SalixmyrsinifoliaSalisb.andSalixpen- tandraL.)characterized“Vegetal”technique.“Mineral”technique wascharacterizedbyspecieslikeBuddlejadavidiiFranch.,Humulus lupulusL.,RobiniapseudoacaciaL.,UrticadioicaL.andParthenocis- susquinquefoliaL.“Mixed”techniquewasmainlycharacterizedby thepresenceofCornussanguineaL.,CalamagrostisepigeiosL.,Salix incanaL.,ViburnumopulusL.andLoniceraxylosteumL.(Fig.4).The inertiaoftheinter-classanalysisrepresents18.19% ofthetotal varianceamongthesites.Inaddition,66.16%oftheinformation explainedbythisinter-classPCAwasexplainedbyaxis1.Salicaceae speciesaswellasshrubslikeC.sanguineaandV. opulusmainly explainedaxis1componentonthepositivesideoftheaxis,andto alesserextentbyspecieslikeB.davidiiandR.pseudoacaciaonthe negativeside.Axis2expressed33.84%oftheinformation.Inthe upperpartofthisaxis,thediscriminatoryspeciesweremainly:S.
viminalis,S.purpureaandS.triandra.Inthelowerpart,C.sanguinea,
Fig.3. Inter-classanalysisofvegetationonthreeriverbanksprotectiontechnique.
mn:Mineral;mx:Mixed;v:Vegetal.Thedistributionandspacingbetweenthethree sphericalclustersprovidesinformationonthevariabilityoffloristiccompositions betweenthedifferenttechniques.Thesizeoftheellipseprovidesinformationabout intra-techniqueplantspeciesvariability.
C.epigeios,S.incanaandV.opuluswerethediscriminatoryspecies (Fig.4).
The area of the ellipse provided information about intra- techniquesplantspeciesvariability(Fig.3).“Mixed”and“Vegetal”
techniquesshowcomparablevariabilityofplantspeciescomposi- tion,higherthanthatof“Mineral”technique.
Fig.4. Spatialdistributionofallspeciesencounteredonthethreeriverbankspro- tectiontechnique.Speciescodesrefertothefirstthreelettersofthegeniusand thespeciesnames.Percentagesofvarianceobservedaregivenoneachaxis.A correspondencetableisgivenintothesupplementaryfiles.
Table2
ProbabilityvaluesoftheKruskal-WallistestandMann-Whitneytestforvegetationsurvey,flyingcoleopteraandinvasivespecies.
Statisticaltests Pairwisecomparison Vegetationsurvey Aeriancoleoptera Invasivespecies
Probabilityvalues Probabilityvalues Number Frequency
Kruskal–Wallis 0.006** 0.006** 0.308 0.027*
Vegetal/Mixed 0.247 0.083 0.817 1
Mann–Whitney Mixed/Mineral 0.024* 0.03* 0.363 0.063
Vegetal/Mineral 0.036* 0.038* 0.812 0.045*
*Indicatestatisticalsignificantdifferences(p-value<0.05).
**Indicatehighlysignificantdifferences(p-value<0.01).
3.2. Fauna
Weidentified42distinctgeneraofflyingColeopterafromthe 14sampledsites(everytrapshavebeenlostforonesitefromthe
“Vegetal”technique).Fig.5indicatesthemeannumbersofflying ColeopterageneracollectedinFlora®yellowtrapsforeachthree techniques.“Vegetal”supportedameanof12.2differentgenera ofcoleopterans,“Mixed”onessupported7.2and“Mineral”tech- niquessupported3.0genera.Ageniusnameslistwasincludedin supplementaryfiles.
Riverbank techniques significantly influenced the number of coleopterangenera (Kruskal–Wallisp-value=0.006,Table 2).
“Mixed”and“Vegetal”techniquesweresignificantlyricherthan
“Mineral”technique(Mann–WhitneyUtestwithHolmcorrection:
p-value=0.03and0.038;Table2).
WeobservedmanygeneraassociatedwithSalicaceaeincluding varioussaproxylicCetoniaspecieswithlarvaegrowingindecom- posingwood(Cetoniaaurata,Potosiacupreabourginii).Therewere alsoCerambycidaespecieslikeLamia textor,ofwhich thelarvae developinwillowstumpsandroots,Necydalismajorinthehigh cavitiesoftrees,andAromiamoschata,ofwhichthelarvaedevelop in rottingstumps and branches.Many herbivorouscoleopteran specieswereidentified,especiallyVariimordassp.(oftenseenon Apiaceae),Hopliafarinosa(whichfeedsonpollen),Oedemerassp.
(the adultof which isherbivorous and thelarva xylophagous).
SomewereassociatedwithSalicaceaelikeC.aurata,Chaetocnema aridulaandAlticaaenescens.Predatoryspecieswerealsoidentified, includingthecarnivorousAdrastuslimbatusandOrchesiamicans.
3.3. Exoticplantspecies
Althoughexoticplantspeciesweresometimesfoundonsites thathavebeenconstructedusingbioengineering,theywerenot amongthetendominantspeciesobservedinthestudy.Incon- trast, two exotic species, B.davidii and R. pseudoacacia, belong
Fig.5.Coleopterameangenusnumbersinyellowtrapsonthethreeriverbankspro- tectiontechnique.Differentlettersindicateastatisticaldifferencebetweensamples.
Errorbarsindicatestandarderrors.
Fig.6.Exoticmeanspeciesnumbersonthethreeriverbanksprotectiontechnique.
Differentlettersindicateastatisticaldifferencebetweensamples.Errorbarsindicate standarderrors.
tothetenmostabundantspecieson“Mineral”structure (100%
of observed exotic species). Fallopia sp. was the main genius representedon“Mixed”structure(83%ofobservedexoticspecies) andon“Vegetal”structure(100%ofobservedexoticspecies).Over- all exoticspeciesrichness variedfrom 1.75to 2.2betweenthe techniques (Fig.6)anddidnot differsignificantly betweenthe three techniques(Kruskal–Wallis test p-value=0.308; Table 2).
Invasivespeciesfrequencywassignificantlydifferentaccordingto thetechnique(Kruskal–Wallistestp-value=0.027;Fig.7),reaching amaximumonmineraldevelopments(42.5)comparedtovegetal (10)and mixed(13).Frequencyofinvasivespecies wassignifi- cantly differentbetween“Mixed” and“Mineral” techniquesbut not between“Vegetal”and “Mixed”techniquesbecauseofhigh variability on“Vegetal”developments(fromf=0.34 tof=22.71;
Mann–WhitneyUtestwithHolmcorrection:p-value=0.063and 0.045;Table2).Exoticinvasivespeciesweredifferentaccordingto thetechnique.
Fig.7.Exoticmeanspeciesfrequenciesonthethreeriverbanksprotectiontech- nique.Differentlettersindicateastatisticaldifferencebetweensamples.Errorbars indicatestandarderrors.
4. Discussion
4.1. Vegetationdiversity
Thissurvey providesa firstassessment ofplant speciesand Coleoptera genera richness associated with three categories of riverbankprotectiontechniques.Basedonfieldobservations,we highlightsignificantdifferencesinplantdiversitybetweencon- ventionalcivilengineeringandbioengineering.Inaccordancewith ourhypothesis,significantlyfewerplantspecieswerefoundcon- structionusingon“Mineral”structuresthanoneitherofthetwo othersprobablyduetothesubstratein“Mineral”structuresthat physicallylimitscolonizationbyplants. Incontrast,weobserve nosignificantdifferencesinplantspeciesrichnessbetween“Vege- tal”and“Mixed”techniques.Thehighernumberofplantspecies werefoundon“Mixed”structurescomparedto“Vegetal”onesmay beexplainedbyalargeproportionofwillowsfromthefascines installedatthewaterlinewhichshowanimportantgrowthrate;
willowsarepartoffast-growing speciesusuallyusedriverbank bioengineering (Adamet al.,2008).Thiswillowcanopy rapidly developsadensecoveragethatcanpartiallyinhibitcolonizationof theunderstorybyherbaceousplants.Forthe“Mixed”technique, thepresenceofvegetationfreeriprapatthebottomofthebank restricts colonizationand coverageby Salicaceae species tothe upperpart.Riprapattheinterfacebetweentheaquaticenviron- mentandthefirstwillowcuttingsprovideopenspaceavailablefor colonizationbyhalophyticspecies(Chenetal.,2010).Thislower partconstitutesadifferenthabitat,distinctfromthatofferedby the“Vegetal”techniquewherewoodyspecies,mostlywillows,pre- dominate.Speciestypicallyfoundonthis“Mixed”structuresare(i) typicalwetlandspecieslikeTetragonolobusmaritimus,Juncusacu- tiflorus,CarexpseudocyperusandPhragmitesaustralis,(ii)meadow specieslikeHolcusmollis,(iii)edgespeciesandspeciesofwoodland fringeslikeLigustrumvulgare,L.xylosteumandCrataegusmonog- ynaand(iv)treesfromalluvialzoneslikePopulusnigraandPopulus alba.Mostofthosespecieswerenotfoundon“vegetal”structures becauseofthepredominanceofwillowsduetoalackoflightand space.Finally,periodicsedimentationfillsinthegapsbetweenthe blocksandcreatesaloam-richsubstratefavourableforcoloniza- tionbyhelophyticspecies.Ourresultsarethereforeconsistentwith otherstudieswherethepresenceofsomelitterandloamincreases both thedensity and diversity of pioneerplants (Langladeand Décamps,1996).
4.2. Faunadiversity
FlyingColeopteraweremorediverseon“Vegetal”(12.2genera onaverage)and“Mixed”(7.2generaonaverage)structureswhich havemorecomplexvegetationandgreaterfloristicdiversitythan on“Mineral”(3.0generaonaverage)structures.Ourresultsare consistentwithotherstudieswhichshowthattheabundanceof Coleopteranspeciescanberelatedtothepresenceofdifferentveg- etationstrata,fromgrassesthroughbushestotrees(Burel,1989).
Ingeneral,insectpopulations––especiallyCarabidae––dependon vegetation structure and heterogeneous habitats (Verdonschot etal.,2007).Alongrivercorridors,hotspotsofbiodiversityareprin- cipallysituatedinregionswherehabitatdiversityishigh(Tews etal.,2004).Suchhabitatheterogeneityprimarilyreflectsgradients ofdisturbance,sedimentgrainsize,moistureandfertilitythatare tightlylinkedtoriverdynamicsthatrecurrentlyrenewsthehabi- tatmosaicanddrivessuccession.Inparticularsmallandmedium floodscreatemorespatialvariabilityandthereforemorehetero- geneity(Pollocketal.,1998;Helfieldetal.,2007).
Although “Mixed”structures harbour greaterbiodiversity in terms of plant species richness (30 species on average), more
generaof flying Coleopterawere foundon “Vegetal”structures (12.2generaonaverage).Thissuggeststhattheplantspeciesiden- tityhasamajorimpactoninsectdiversity.Salixspeciesprobably attractsmany nectar-feedinginsectsbyproviding animportant nectarsourceavailableearlyintheyear(inJanuaryandFebruary) when other nectar sources are scarce(Newsholme, 1992).The highnumberofcoleopteraassociatedwithSalicaceaefoundinthis studyconvergeswithNewsholme’s observations.Vegetal cover and biomass werehigher on “Vegetal”structures compared to thetwootherswhatcouldexplainthehighercoleopterandiver- sityon“Vegetal”structures.Moreoverthat shorezonescontain largenumberofpredatorsandscavengersincludingcarabidbee- tlesthatfeedonwrackorcarrionthathasbeendeposedonthe shore(Kleinwächteretal.,2003).Wecanassumethat“Vegetal”and
“Mixed”structuressupportmorevegetationcomparedto“Min- eral” structuresand canthus producemore wrack and induce higheranimaldrowningmortality.Ingeneral,shorezonesarean importantfeedingzoneformanyspeciesincludingcarabidspecies (StrayerandFindlay,2010).
4.3. Invasivespecies
Thisstudydidnotrevealanysignificantdifferenceinthenum- berof exotic plants between “Mineral”, “Mixed”and “Vegetal”
techniques (respectively 1.75; 2.2 and 1.8). The occurrence of exotic plantspecies hasbeen often related tothe intensity of humanactivity(Pyˇseketal.,2010).Alltechniquesstudiedinvolve heavyhumaninterventionlikeearthmovingordiggingactivities.
Itcan beassumedthat thesoilswereallsubject toanequiva- lentdegreeofperturbationand comparablepropagulepressure explainingwhythedifferenttechniquesharbourasimilarnumber ofexoticplantspecies.Incontrast,thisstudyshowsthatthefre- quencyofexoticspecieswashigheron“Mineral”structuresthan ontheothertechniques.Exotic plantsspecies identifiedin this studyarecharacterizedbyhighgrowthrateswhichgavethema competitiveadvantageinpioneerhabitats(CallandNilsen,2003;
Tallent-HalsellandWatt,2009).Moreovertherelativeabundance ofinvasiveplantscouldbeexplainedbybioticinteractions,notably relatedtocompetition(Levineetal.,2004).Thepresenceofcom- petitorson“Mixed” and “Vegetal”structures couldrestrict the vigourandinhibitthepropagationofexoticspecieswhatisinpar- ticularseenonbioengineeringstructures;whereitisverylikely thatthehighdensityofwillowrestrictedtheperformanceofexotic species. Interestingly,B. davidii wasthe only species on “Min- eral”techniqueandFallopiasp.wastheonlyinvasivespecieson
“Vegetal”technique.Asmineralstructurescouldexperiencehigher temperaturesduringsunnyweatherthanvegetalizedbanks,high temperatureonmineraltechniquescouldbeherehypothesized asanenvironmentalfilterforspeciessensitiveforheatstress.B.
davidiiisaMediterraneanandtropicalspecies,canbesupposed tostandhightemperatures(Tallent-HalsellandWatt,2009;Watt etal.,2010).Colonisablesubstrataavailablecanalsobeanexpla- nation;Fallopiasp.rhizomesneedmorespacetodevelopandend upinaviableorganism.
4.4. Perspectivesandapplications
Theapplicativepurposeofthisstudyistoprovideusefulinfor- mationtodecision-makersforplanningsustainablemanagement strategiesofmountainriverbanks.Alongsmallrivers,riverbank protectionsshouldbeplantinsteadofself-recoveryofnaturalveg- etationin order topromote a rapid vegetal cover and to limit exoticspeciesinvasion.Thebioengineeringtechniquesusingwill- ows controls erosion, limit colonization by exotic heliophilous speciesandprovidesfoodresourcesandhabitattoentomofauna.
Salicaceae are particularly adapted to riverbank restoration techniques. The morphological (deep roots, dense coverage), mechanical(flexiblewood)andphysiological(rapidgrowth,pro- duction of large amounts of nectar and pollen) properties of thisgenus limiterosionandensurea goodreturn tonaturality (SchiechtlandStem,1996;FrossardandEvette,2009).However, suchrestorationtechniquesshouldalwaysincludealargediversity ofspeciesandgrowthforms.Thus,creatingdifferentplantstrata (grasses,bushes,andtrees)ensureshabitatdiversity.Riverrestora- tionprogrammecouldalsoaimatincreasinghabitatdiversity.For instance,itispossibletopromotetherecruitmentofhelophytic species by creatinginterface areasbetween thewater and the bank,freeofbushesandtreesandwheresedimentcanbedeposed tofacilitatetheaccumulationofacolonisablesubstrate.“Mixed”
techniquewithriprapatthebaseofthebankandbioengineering techniquesontheupperpartrepresentatrade-offbetweenvegetal coveringandhabitatdiversity.
Finally yet importantly, bioengineering structures represent agood alternativeintheFrenchEnvironmentalLaw, asadmin- istrative procedures are simpler (Decree n◦93-743 of the law 92-3article10).Forcivil-engineeringstructures,anenvironmen- talimpactassessmentisrequiredwhatbringstheadministrative delayto6–9monthstoobtainaconstructionpermit.
5. Conclusion
Theintensificationofhumandisturbancealongmountainriver lead to a dramatic decrease in riparianbiodiversity. Maintain- ingbiologicalcontinuitybetweensmallremnantrefugezonesis apriorityfortheconservationofbiodiversitythreatenedspecies (Miller,2006).Thepresentstudyshowsthecapacitiesofrestora- tionecology and,more specifically,bioengineering, topromote the recovery of coleopteran and plants of riparian forests. In addition,“Mixed”and“Vegetal”embankmenttechniquesenhance connectivitybetweendifferenthabitatsandthuscontributetothe restorationofecologicalcorridors.Increasedconnectivitybetween fragmentedlandscapepatchesislikelytoincreasegeneticdiversity withinmodifiedlandscapes(Neavesetal.,2009).
Inafurtherstep,thisstudyshouldbeextendedtotheaquatic compartment.Benthic invertebratesseemstobeagood indica- torofnaturalitywiththeirdiversitycorrelatedtotheamountof organicsubstrate(woodand roots)onthebanks(Sudduth and Meyer,2006).Thequestioningcouldalsoberaisedtoafunctional analysisoftherestoredecosystems(LavorelandGarnier,2002;
Hooperetal.,2005).
Acknowledgements
Thisworkwouldnothavebeenpossiblewithoutthehelpof theEco-ErosionUnitof theMountainEcosystemResearch Unit ofIrstea,GrenobleandtheUniversityofToulouse,CNRSEcoLab, Toulouse.TheFrench-SwissInterregIVProjectGeni’Alpandthe Agencedel’EauRhone-Alpesarethankedforprovidingfunding.
AppendixA. Supplementarydata
Supplementary data associated with this article can be found,intheonlineversion,athttp://dx.doi.org/10.1016/j.ecoleng.
2012.12.105.
References
Adam,P.,Debiais,N.,Gerber,F.,Lachat,B.,2008.Legénievégétal,Unmanueltech- niqueauservicedel’aménagementetdelarestaurationdesmilieuxaquatiques.
Ministèredel’écologie,dudéveloppementetdel’aménagementdurables,Paris, 290pp.
Aeschimann,D.,Lauber,K.,Moser,D.-M.,Theurillat,J.-P.,2004.FloraAlpina.Belin, Bern,2672pp.
Balachowsky,A.,1949.FaunedeFrance(tome50):ColéoptèresScolytides.Lecheva- lier,Paris,320pp.
Boscaini,A.,Franceschini,A.,Maiolini,B.,2000.Riverecotones:carabidbeetlesasa toolforqualityassessment.Hydrobiologia422,173–181.
Breton,V.,Forestier,O.,Guindon,O.,Evette,A.Ecologicalrestorationunderpressure frominvasiveanimalspecies:useofSalicaceaecuttingsinariverbank.River ResearchandApplications,underreview.
Brunel,J.P.,2009.Sourcesofwaterusedbynaturalmesquitevegetationinasemi- aridregionofnorthernMexico.Hydrol.Sci.J.54(2),375–381.
Burel,F.,1989.Landscapestructureeffectsoncarabidbeetlesspatialpatternsin westernFrance.Landsc.Ecol.2(4),215–226.
Call, L.J.,Nilsen, E.T.,2003.Analysisofspatial patternsandspatialassociation betweentheinvasivetree-of-heaven(Ailanthusaltissima)andthenativeblack locust(Robiniapseudoacacia).Am.Midl.Nat.150(1),1–14.
Chen,S.Y.,Zhang,J.L.,Jia,P.,Xu,J.,Wang,G.,Xiao,S.,2010.Effectsofsizevariation andspatialstructureonplasticresponseofplantheighttolightcompetition.
Chin.Sci.Bull.55(12),1135–1141.
Décamps,H.,2011.Rivernetworksasbiodiversityhotlines.C.R.Biol.334(5–6), 420–434.
Décamps,H.,Planty-Tabacchi,A.M.,Tabacchi,E.,1995.Changesinthehydrological regimeandinvasionsbyplantspeciesalongripariansystemsoftheAdourRiver, France.Regul.Rivers:Res.Manage.11(1),23–33.
Doledec,S.,Chessel,D.,1987.Seasonalsuccessionsandspatialvariablesinfreshwa- terenvironments.I.Descriptionofacompletetwo-waylayoutbyprojection of variables (Rythmessaisonniers et composantes stationnellesen milieu aquatique.I.Descriptiond’unpland’observationcompletparprojectionde variables).ActaOecol.8(3),403–426.
Evette,A.,Balique,C.,Lavaine,C.,Rey,F.,Prunier,P.,2012.Usingecologicaland biogeographicalfeaturestoproduceatypologyoftheplantspeciesusedin bioengineeringforriverbankprotectionineurope.RiverRes.Appl.28(10), 1830–1842.
Evette,A.,Frossard,P.A.,2009.Lesvégétauxontdugénie.EspacesNaturels26, 35–37.
Frossard,P.A.,Evette,A.,2009.Legénievégétalpourlaluttecontrel’érosionen rivière:unetraditionmillénaireenconstanteévolution.I.E.A.T.,99–109.
Gentiana,2006.Lesespècesenvahissantesdel’Isère.Conseilgénéraldel’Isère, Grenoble,32pp.
Gray,D.,Sotir,R.,1996.BiotechnicalandSoilBioengineeringSlopeStabilization– APracticalGuideforErosionControl.JohnWileyandSons,Inc.,NewYork,400 pp.
Guignot,F.,1947.FaunedeFrance(tome48):ColéoptèresHydrocanthares.Lecheva- lier,Paris,294pp.
Helfield,J.M.,Capon,S.J.,Nilsson,C.,Jansson,R.,Palm,D.,2007.Restorationofrivers usedfortimberfloating:effectsonriparianplantdiversity.Ecol.Appl.17(3), 840–851.
Helfield,J.M.,Engström,J.,Michel,J.T.,Nilsson,C.,Jansson,R.,2012.Effectsofriver restorationonriparianbiodiversityinsecondarychannelsofthePiteRiver, Sweden.Environ.Manage.49(1),130–141.
Hoffmann, A., 1945. Faune de France (tome 44): Coléoptères Bruchides et Anthribides.Lechevalier,Paris,184pp.
Holm,S.,1979.Asimplesequentiallyrejectivemultipletestprocedure.Scand.J.Stat.
6(2),65–70.
Hooper, D.U.,Chapin, F.S.,Ewel,J.J.,Hector, A.,Inchausti, P.,Lavorel,S.,Law- ton,J.H.,Lodge,D.M.,Loreau,M.,Naeem,S.,Schmid,B.,Setala,H.,Symstad, A.J.,Vandermeer, J.,Wardle,D.A.,2005. Effects ofbiodiversityonecosys- temfunctioning: aconsensusofcurrentknowledge.Ecol. Monogr.75(1), 3–35.
IFEN,2006.L’environnementenFrance–Edition.IFEN,500pp.
Isbell,F.,Calcagno,V.,Hector, A.,Connolly,J.,Harpole,W.,Reich, P.,Scherer- Lorenzen,M.,Schmid,B.,Tilman,D.,vanRuijven,J.,Weigelt,A.,Wilsey,B., Zavaleta,E.,Loreau,M.,2011.Highplantdiversityisneededtomaintainecosys- temservices.Nature477(7363),199–202.
Januschke,K.,Brunzel,S.,Haase,P.,Hering,D.,2011.Effectsofstreamrestorations onriparianmesohabitats,vegetationandcarabidbeetles.Biodivers.Conserv.20 (13),3147–3164.
Kleinwächter,M.,Eggers,T.O.,Henning,M.,Anlauf,A.,Hentschel,B.,Larink,O.,2003.
Distributionpatternsofterrestrialandaquaticinvertebratesinfluencedbydif- ferentgroyneformsalongtheRiverElbe(Germany).LargeRivers15(1–4), 319–338.
Kleinwaïchter,M.,Larink,O.,Eggers,T.,Anlauf,A.,2003.Impactofmodifiedgroynes onCarabidbeetles.In:Proceedingsofthe“LowlandRiverRehabilitation2003”
Conference,Wageningen,TheNetherlands.
Landolt, E., Bäumler, B., 2010. Flora indicativa:ökologische Zeigerwerte und biologischeKennzeichen zurFlorader Schweizundder Alpen=ecological indicator values andbiological attributesofthe Floraof Switzerlandand theAlps.ConservatoireetJardinbotaniquesdelavilledeGenève,Genève, 376pp.
Langlade,L.-R.,Décamps,O.,1996.Effetdel’accumulationdelimonsurlacolonisa- tionvégétaled’unbancdegaletsenrivière.C.R.Acad.Sci.,Paris318,1076–1082.
Lauber,K.,Wagner,G.,1998.FloraHelvetica,secondedition.P.HauptEditions, Berne/Stuttgart/Vienne,1614pp.
