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Soil erosion in the humid tropics: A systematic
quantitative review
Nicolas Labrière, Bruno Locatelli, Yves Laumonier, Vincent Freycon, Martial
Bernoux
To cite this version:
Nicolas Labrière, Bruno Locatelli, Yves Laumonier, Vincent Freycon, Martial Bernoux. Soil erosion
in the humid tropics: A systematic quantitative review. Agriculture, Ecosystems and Environment,
Elsevier Masson, 2015, 203, pp.127-139. �10.1016/j.agee.2015.01.027�. �cirad-01117271�
Soil
erosion
in
the
humid
tropics:
A
systematic
quantitative
review
Nicolas
Labrière
a,b,*
,
Bruno
Locatelli
a,c,
Yves
Laumonier
a,c,
Vincent
Freycon
a,
Martial
Bernoux
daUPRBSEF,CIRAD(CentredeCoopérationInternationaleenRechercheAgronomiquepourleDéveloppement),AvenueAgropolis,34398MontpellierCedex5,
France
b
AgroParisTech,DoctoralSchoolABIES,19AvenueduMaine,75732ParisCedex15,France
c
CenterforInternationalForestryResearch,JalanCIFOR,SituGede,SindangBarang,Bogor(Barat)16115,Indonesia
d
UMREco&Sols,IRD,2placeViala,34060MontpellierCedex2,France
ARTICLE INFO
Articlehistory:
Received22October2014
Receivedinrevisedform26January2015 Accepted30January2015 Availableonlinexxx Keywords: Ecosystemservices Systematicreview Quantitativeanalysis Landscape Landuse Land-usetype Managementpractices ABSTRACT
Healthysoilsprovideawiderangeofecosystemservices.Butsoilerosion(onecomponentofland degradation)jeopardizesthesustainabledeliveryoftheseservicesworldwide,andparticularlyinthe humid tropics where erosion potential is high due to heavy rainfall. The Millennium Ecosystem Assessment pointed out the role of poor land-use and management choices in increasing land degradation.Wehypothesizedthatlandusehasalimitedinfluenceonsoilerosionprovidedvegetation coverisdevelopedenoughorgoodmanagementpracticesareimplemented.Wesystematicallyreviewed theliteraturetostudyhowsoilandvegetationmanagementinfluencesoilerosioncontrolinthehumid tropics.More than3600measurements ofsoillossfrom55referencescovering21countrieswere compiled.Quantitativeanalysisofthecollecteddatarevealedthatsoilerosioninthehumidtropicsis dramaticallyconcentratedinspace(overlandscapeelementsofbaresoil)andtime(e.g.duringcrop rotation).Nolanduseiserosion-proneperse,butcreationofbaresoilelementsinthelandscapethrough particularlandusesandotherhumanactivities(e.g.skidtrailsandloggingroads)shouldbeavoidedas muchaspossible.Implementationofsoundpracticesofsoilandvegetationmanagement(e.g.contour planting,no-tillfarminganduseofvegetativebufferstrips)canreduceerosionbyupto99%.Withlimited financialandtechnicalmeans,naturalresourcemanagersandpolicymakerscanthereforehelpdecrease soillossatalargescalebypromotingwisemanagementofhighlyerosion-pronelandscapeelementsand enhancingtheuseoflow-erosion-inducingpractices.
ã2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).
1.Introduction
Theecosystemserviceofsoilerosioncontrol,forthedeliveryof which vegetation cover plays an important role, has been degrading worldwide (Millennium Ecosystem Assessment, 2005). As this regulating service is lost, soil formation can no longercompensateforsoillossduetoanincreaseinerosion,which depletessoilresourcesandtheecosystemservicestheysupport
(Lal,2003;Morgan,2005).TheMillenniumEcosystemAssessment
(2005)identifiedunwiseland-usechoicesandharmfulcroporsoil
management practices as the major drivers of increasing soil erosion.Soilerosionhasmultipleon-and off-siteconsequences such as decreasing crop yields, increasing atmospheric CO2
concentration, decreasing water quality (turbidity and particle-born pollutants), sedimentation of reservoirs, and
disturbedhydrologicalregimessuchasincreasedfloodriskdue toriverbedfillingandstreamplugging(ChomitzandKumari, 1998;
Lal, 2003; Millennium Ecosystem Assessment, 2005; Morgan,
2005;Locatellietal.,2011).
Researchonfactorsinfluencingsoillosshasresultedinwidely used models, such as the RUSLE (revised universal soil loss equation). Thismodel was built fromplot dataof experiments carriedoutintheUnitedStatesandpredictssoillossfromclimatic (rainfall erosivity), edaphic (soil erodibility) and topographic (slope length and slope steepness) factors,as well as soil and vegetationmanagementpractices(WischmeierandSmith,1978;
Renardetal.,1997).Managementofsoilandvegetationhaslong
been recognized as the most efficient and effective way to influencetheextentofsoilloss,andthereforesoilerosioncontrol
(Goujon,1968).
The humid tropics are rich in carbon and biodiversity and attract major attention because of the rapid loss of rainforests (Strassburget al., 2010; Saatchi et al., 2011; Tropek et al.,2014).Becauseof thelargeamountandhighintensityof
* Correspondingauthor.Tel.:+33467593726;fax:+33467593909. E-mailaddress:nicolas.labriere@cirad.fr(N.Labrière).
http://dx.doi.org/10.1016/j.agee.2015.01.027
0167-8809/ã2015TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
ContentslistsavailableatScienceDirect
Agriculture,
Ecosystems
and
Environment
rainfallin thehumidtropics, soil erosioncanpotentially reach dramaticlevelsinthis region(El-Swaifyet al.,1982; Lal,1990). Tropical ecosystems with healthy soils can support multiple ecosystem services (e.g. water regulation, climate regulation through carbon storage and biodiversity support) and support locallivelihoods.Abetterunderstandingofsoilerosioncontrolin thehumidtropicsisthereforevital(Locatellietal.,2014).
Theoretically, empirical models of erosionpredictionshould onlybeappliedunderconditionsandforpurposessimilartothose oftheirdevelopment(e.g.predictingerosionfromcroplandsinthe UnitedStates for the RUSLE). Adapting an empirical model to out-of-range conditions would require parameter calibration, which can consume both time and resources (Nearing et al., 1994).Whilesomestudieshaveadaptedtemperatemodelfactors totheirowngeographicalcontexts(e.g.StreckandCogo,2003for surface soil consolidation and Diodato et al., 2013 for rainfall erosivity), others havedirectly appliedmodels developed for a temperatecontext to predictsoil erosionin thehumid tropics (e.g.Angimaetal.,2003;Hoyos,2005).
Yet thereis little consensusaboutthedirect applicabilityof modelssuchasRUSLE(anditspredecessors)toatropicalcontext. Despiteover-andunder-estimationofsoillossdependingonthe croppingphase,AlmasandJamal(2000)foundtheRUSLEmodelto correctlypredictthe overallsoil loss froma banana–pineapple intercroppingsysteminMalaysia.Ontheotherhand,Cohenetal.
(2005)showedthaterosionriskpredictionwaspoorlyachievedby
theUSLE(universalsoillossequation)inawatershedofwestern Kenya,andcalledforgroundsurveystoproperlycalibratetheUSLE andsimilarempiricalmodels.
In the face of this lack of agreement, studies that directly measuresoillossareofgreatinterestastheycanhelpshedlighton theinfluenceofvegetationandsoilmanagementonsoilerosion control.Synthesizingandanalyzingavailabledatafrommultiple sourcesisnecessarygiventhediversityofstudycontextsandthe impossibilityofdrawinggeneralconclusionsfromasinglestudy. Such syntheses are availablefor some regions of theworld. FocussingonEuropeandtheMediterranean,Maetensetal.(2012)
reviewed datafrom227 stations and1056 soilerosion plotsto analyzetheeffectoflanduseonerosionandrunoff.Theyfoundthat (semi-)naturalvegetationproducedlowererosion(<1Mg/ha/yr) than vegetation directly influenced by human activities (e.g. croplands and vineyards; 6–20Mg/ha/yr). Montgomery
(2007)alsocompilederosiondatafromgloballydistributedstudies
(some in the humid tropics) and showed that conventional agriculture,i.e.withtillage,produced10–100timesmoresoilloss thanconservationagriculture,i.e.with no-tillage,butconditions were highly variable. For example, plots under conventional agricultureweremoreerosion-prone(withmaximumslopeof37 andmaximumannualprecipitationof5600mm/yr)thanthoseof plots under conservation agriculture (17 and 2000mm/yr).
Table1
Land-usetypesandsubtypes.
Land-usetype Land-usesubtype Definitions
Bare Landhasbeenopenedandkeptbareforvariousreasons(includespre-sowingandpost-harvestingcropland andskidtrails).
Tilled High-disturbancesoilmanagementtechniques(e.g.ploughingandraking)areused.
Untilled Low-disturbancesoilmanagementtechniques(e.g.slashandburnandweedingwithaknife)areused.
Cropland Cropsaresownandharvestedwithinasingleagriculturalyear,sometimesmorethanonce(excludes perennialcrops).
Crop,non-established,without conservationpractices
Cropwasrecentlyplantedandcropcoverisnotdeveloped;noconservationtechniquesarepracticed.
Crop,established,without conservationpractices
Cropcoverisdeveloped;noconservationtechniquesarepracticed.
Cropwithvegetation-related conservationpractices
Cropcovermayormaynotbefullydeveloped.Vegetation-relatedconservationtechniques(e.g.hedgerows, intercroppingandmulching)arepracticed.
Cropwithvegetation-andsoil-related conservationpractices
Cropcovermayormaynotbefullydeveloped.Bothvegetation-related(e.g.hedgerows,intercroppingand mulching)andsoil-related(e.g.no-tillfarmingandcontourplanting)conservationtechniquesarepracticed.
Grassland Vegetationisdominatedbygrasses(includesopengrasslandsandpastures).
Pasture Landisusedforgrazingandmanagedthroughagriculturalpracticessuchasseeding,irrigationanduseof fertilizer.
Opengrassland Landisunmanagedandhasnotreesorshrubs.
Shrubland Vegetationisdominatedbyshrubsbutcanalsoincludegrasses,herbsandgeophytes.
Openshrubland Atransitionalplantcommunityoccurstemporarilyastheresultofadisturbancesuchasloggingorfire. Tree-dominated
agrosystem
Plantedvegetationisdominatedbytrees,includingperennialtreecropssuchasrubber,fruitandnuttrees.
Treeplantation Agroupofplantedtreesisgrownintheformofanagriculturalcrop,usuallywiththeaimofharvesting wood.
Treecropwithoutcontactcover Apermanentcrophasbeenplanted;ithasnocontactcover(suchasgrassorcovercrops)underneath. Treecropwithcontactcover Apermanentcrophasbeenplantedandhascontactcover(suchasgrassorcovercrops)underneath. Simpleagroforest Onewoodyperennialspeciesisplantedwithoneannualcrop.
Complexagroforest Multiplespeciesofwoodyperennials,oftenwithnaturalvegetationregrowth,areplanted(usually intercropped)withannualcrops.
Forest Groundiscoveredwithnaturalvegetationdominatedbytrees(excludestreeplantations).
Secondaryforest Foresthasregeneratednaturallyafterclear-cutting,burningorotherland-clearingactivitiesandcontains vegetationinearlysuccessionalstages.
Old-growthforest Forestisecologicallymature,containingtreesofvarioussizesandspecies(thelaststageinforest succession).
Logged-overforest Foresthasbeenlogged-over.
Degradedforest Foresthasbeendegradedbyhumanactivitiesotherthanloggingorbyanaturallyoccurringeventsuchasa fireorseverestorm.
Selectingerosionmeasurementsavailableforthetwoagriculture typesunderthesameconditionssubstantiallyreducedthesample. Nosynthesis(toourknowledge)hasbeendonesofarforthe humid tropics. The purpose of this study was therefore to quantitatively analyze available data (collected via systematic reviewoftheliterature)onsoilerosioninthehumidtropicsto studyhowsoilandvegetationmanagementinfluencesoilerosion control in this region. Effects of the measurement protocol (method,duration andarea) andcontext (rainfall,slope length, slopesteepnessandsoilerodibility)werecontrolledfortokeepa consistentdatasetandfocusontheinfluenceofsoilandvegetation managementonsoilerosion.
Theunderlyinghypothesisisthatlandusehasalimitedinfluence onsoilerosionprovidedvegetationcoverisdevelopedenoughor goodmanagementpracticesareimplemented.Thishypothesiswas previouslyconclusivelytestedinafewsinglestudiesonecosystems such as rangelands (e.g. Snelder and Bryan,1995; Chartier and
Rostagno,2006),butneversystematicallynorforthehumidtropics.
Thisstudyaimstocontributetothescientificunderstandingofthe relationshipbetweensoilerosionandvegetation/soilmanagement inthehumidtropics,tohelpclarifytheapplicabilityofwidelyused modelssuchastheRUSLE,andtoprovidetostakeholdersinvolvedin naturalresource managementand protectionasynthesisonsoil erosioncontrolanditssoundmanagement.
2.Materialsandmethods 2.1.Materials
Wesearchedforstudiesoferosioninthehumidtropics,defined for the purpose of this review as the “Af” (tropical rainforest climate)and “Am” (tropical monsoonclimate) Köppen climatic classes(Köppen,1936;Peeletal.,2007).Querieswerebuiltonthe conjunctionofelementsfromthreethematicclusters:“scope”and “outcome”and“measurement”.The“scope”clustercorresponded to:tropic*orregion(listofbroadlydefinedrelevantregions,e.g. Africa)or specificcountry(all countriesunder eitherAf or Am climate were considered, e.g. Brazil). The “outcome” cluster encompassed the following terms:soil erosion, water erosion, soilloss,soildepletion,landdegradation,sedimentation,sediment production and siltation. The “measurement” cluster included keywordsdefiningmethodologicalapproachesandmeasurement methodssuchas“runoff plot” and “sedimenttrap”. Inorder to selectstudieswithhomogeneouslanduse;weexcludedmeasures atthecatchmentscale.Additionally,toavoidbiasintheanalysisof reportedmeasurements,indirectmeasuresandestimates(e.g.the useof137Csasatracer—seeSidleetal.,2006)werenotconsidered. As suggested by the Collaboration for Environmental Evidence
(2013),avarietyofpeer-reviewedandgreyliteraturesourceswere
searched. Details about queries and sources are available in AppendixA.Querieswerecarriedoutduringthesecondhalfof April2013inEnglish,FrenchandSpanish.
Searchesledto5183referencesafterremovingduplicates.After irrelevant references were removed, based on information in article titles and abstracts about topic,geographical scopeand
erosionmeasurementmethod,thedatabaseshrankto114 refer-ences.Finally,afterscreeningthefulltextsofthosereferences,we kept55ofthem(moredetailsareavailableinAppendixB).Foreach reference,weretrieveddataonsoilloss(expressedasquantityof soilmassperunitofarea)inoneormorecases.Acasewasdefined as one erosion measurement, characterized by an associated measurement method (profilemeter, rootexposition,sediment trap,unboundedplotorrunoffplot,allwithnaturalrainfall,and runoffplotwithsimulatedrainfall),areaandduration, topograph-icalfeatures(slopelengthandsteepness),rainfall,andland-use type and subtype (see definitions in Table 1). For each case, building on the classification proposed by Moench (1991), vegetationcoverwas alsodescribedbythepresenceorabsence offourlayers:high(4m),intermediate(atleast1mbut<4m), low(atleast0.1mbut<1m)andground(<0.1m).
The final data set consisted of 3649 measurements from 55referencescovering21countriesinthehumidtropics(Fig.1,
Table2).Mostreferencesoriginatedfrompeer-reviewedjournals
(n=44) and used runoff plots to quantify soil loss (n=48). Publication years ranged from 1973 to 2012, with half of the referencespublishedbefore1997(Fig.2a).Thenumberofcasesper studywashighlyvariable,andthesixreferenceswiththemost casescontributedhalfthetotalnumberofcasesinthefinaldataset
(Fig.2b,Table2).Studylengthrangedfromtwodays(studiesunder
simulated rainfall) to 17 years (Fig. 2c). References generally reported erosion values per rainfall event, per year or for the durationof thestudy(Fig.2d).Mostreferencesassessedoneto threeland-usetypes(Fig.2e),ofwhichbaresoilsandcroplands werethemoststudied(Fig.2f).
Rainfall erosivityand soil erodibilitywereassessed foreach case.AnindicatorofrainfallerosivitysensuRenardetal.(1997)
could not be obtained or computed for most cases because monthlydatawerenotavailableorbecausemeasurementduration wastooshorttoapplyanannualerosivityindex.Wethususedtotal rainfallasanindicatorofrainfallerosivitybasedonthefindingby
Maetensetal.(2012)thatsoillossdoesnotcorrelatebetterwith
erosivityindicesthanwithtotalrainfall.
Forsoilerodibility,wecombineddifferentindicesbecauseof thediversewayssoilsweredescribedinthestudies.Foreachcase, wecalculatedthreesoilerodibilityindicesfromsoiltextureand organic matterdata with an empirical table and two different equations(Stewartetal.,1975;SharpleyandWilliams,1990;Torri etal.,1997).Ifsoildatawerenotavailableinastudy,weextracted themfromtheISRICglobalsoildataset(resolutionof1km)using measurement coordinates (ISRIC-WorldSoilInformation,2013). For each index, soils weresplit into low-, medium- and high-erodibilityclassesofequalsizes.Asoilwasthenclassifiedashighly erodibleifitwasconsideredhighlyerodiblebyatleasttwoofthe threeindices,lowifitwasconsideredlowbyatleasttwoindices andmediumotherwise(moredetailsareavailableinAppendixC). 2.2.Dataanalysis
Alldatatransformationandstatisticalanalysisweredoneusing
R (R CoreTeam, 2013).Due tohighly skewed distributions, all
Fig.1.Locationofstudysites(n=61).Somedotsrepresentseveralreferences,andsomereferencescontributemorethanonedot.Reddotsshowlocationsprovidedbythesix referenceswiththemostcases.Af(tropicalrainforest)climaterangesaredisplayedindarkblueandAm(tropicalmonsoon)climaterangesinlightblue.(Forinterpretationof thereferencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthisarticle.)
Table2
Contributingreferencesbygeographicallocation.ReferencesfromSoutheastAsiaandNortheastAustralia(n=29)madeupmorethanhalfofallreferences(n=55).The 30referenceswiththefewestcasesprovidedabout10%ofallcases(n=3649).The6referenceswiththemostcasesareprintedinbold.
Reference Country Sourcetype Method Rainfalltype Soil dataa
Land-use type(s)b
Cases Casetimeframe(s) Studylength
Africa(n=11)
Ambassa-KikiandNill (1999)
Cameroon Journalarticle Runoffplot Natural ST+OM 3(B,C,T) 3 Study 2years
BoyeandAlbrecht(2004) Kenya Projectreport Runoffplot Simulation ST+OM 1(B) 10 Rainfallevent 2days
Collinet(1983) Côted’Ivoire Projectreport Runoffplot Natural None 2(C,F) 24 Year,study 3years
Collinet(1988) Côted’Ivoire PhDthesis Runoffplot Simulation None 2(B,C) 189 Rainfallevent 2months
DefershaandMelesse (2012)
Kenya Journalarticle Runoffplot Natural ST+OM 3(B,C,G) 87 Rainfallevent,month 1month
Kamara(1986) SierraLeone Journalarticle Runoffplot Natural ST+OM 2(B,C) 14 Month 2 years
Lundgren(1980) Tanzania Journalarticle Runoffplot Natural ST+OM 2(F,T) 33 Year,study 2years
Ngatungaetal.(1984) Tanzania Journalarticle Runoffplot Natural ST+OM 3(B,C,G) 36 Season,year 1year
Odemerhoand Avwunudiogba(1993)
Nigeria Journalarticle Runoffplot Natural ST 2(C,G) 126 Rainfallevent,study 5months
Roose(1973) Côted’Ivoire PhDthesis Runoffplot Natural None 5(B,C,F,G, T)
431 Rainfallevent,day,month, season,year
17years
Våjeetal.(2005) Tanzania Journalarticle Runoffplot Natural ST+OM 2(B,C) 10 Rainfallevent,season 2years
America&NorthPacificOcean(n=10)
AlegreandCassel(1996) Peru Journalarticle Runoffplot Natural OM 3(B,C,F) 4 Study 52months
AlegreandRao(1996) Peru Journalarticle Runoffplot Natural OM 3(B,C,F) 50 Season,year,study 5years
Bellangeretal.(2004) Venezuela Journalarticle Runoffplot Natural ST+OM 3(B,C,T) 41 Rainfallevent,week,season 5months
DanglerandEl-Swaify (1976)
USA(Hawaii) Journalarticle Runoffplot Simulation None 1(B) 16 Rainfallevent 1.75years
Francisco-Nicolasetal. (2006)
Mexico Journalarticle Runoffplot Natural OM 1(C) 18 Year,study 8years
FritschandSarrailh (1986)
France(French Guiana)
Journalarticle Runoffplot Natural None 2(B,F) 38 Month,season,year,study 32months
McGregor(1980) Colombia Journalarticle Runoffplot natural ST 3(C,F,G) 7 Study 8week
Ruppenthaletal.(1997) Colombia Journalarticle Runoffplot Natural None 2(B,C) 32 Season 2years
Sarrailh(1981) France(French Guiana)
Projectreport Runoffplot Natural None 2(F,G) 50 Month,season,year,study 20months
WanandEl-Swaify (1999)
USA(Hawaii) Journalarticle Runoffplot Simulation ST+OM 2(B,C) 6 Rainfallevent 2days
SEAsia&NEAustralia(n=29)
Afandietal.(2002a) Indonesia Journalarticle Runoffplot Natural ST+OM 1(T) 54 Month 3.5years
Afandietal.(2002b) Indonesia Journalarticle Sediment trap
Natural ST+OM 4(C,F,G,T) 77 Month,study 11 months
AlmasandJamal(2000) Malaysia Journalarticle Runoffplot Natural None 3(B,C,T) 52 Season 9months
Baharuddinetal.(1995) Malaysia Journalarticle Runoffplot Natural None 3(B,F,G) 90 Month,year 2years
Bons(1990) Indonesia Conference
proceedings
Runoffplot Natural None 2(S,T) 2 Year,study 26months
Chatterjea(1998) Singapore Journalarticle Runoffplot Natural None 2(B,G) 30 Rainfallevent 1.3years
Comiaetal.(1994) Philippines Journalarticle Runoffplot Natural ST+OM 1(C) 16 Year,study 3 years
DañoandSiapno(1992) Philippines Conference proceedings
Runoffplot Natural None 1(T) 22 Year,study 2years
Hartantoetal.(2003) Indonesia Journalarticle Runoffplot Natural None 2(B,F) 135 Rainfallevent,season 2.5months
Hashimetal.(1995) Malaysia Journalarticle Runoffplot Natural ST+OM 2(B,T) 152 Rainfallevent,season,study 1.5years
Jaafaretal.(2011) Malaysia Journalarticle Runoffplot Natural ST+OM 1(F) 6 Year 1 year
Leigh(1982) Malaysia Journalarticle Sediment trap
Natural ST 1(F) 11 Year 1year
Malmer(1996) Malaysia Journalarticle Unbounded plot
Natural None 2(B,F) 3 Year,study 1year
Moehansyahetal.(2004) Indonesia Journalarticle Runoffplot Natural ST 3(C,G,T) 156 Rainfallevent,season,study 8 months
Moench(1991) India Journalarticle Runoffplot Natural OM 1(T) 21 Study 9months
PandeyandChaudhari (2010)
India Journalarticle Runoffplot Natural ST 3(C,F,T) 44 Year,study 3years
Paningbatanetal.(1995) Philippines Journalarticle Runoffplot Natural ST+OM 1(C) 168 Rainfallevent,season 3years
Poudeletal.(1999) Philippines Journalarticle Runoffplot Natural ST+OM 1(C) 35 Season,study 2.5years
Poudeletal.(2000) Philippines Journalarticle Runoffplot Natural OM 1(C) 12 Year 2.5years
Presbitero(2003) Philippines PhDthesis Runoffplot Natural OM 2(B,C) 433 Rainfallevent 2.5years
Proveetal.(1995) Australia Journalarticle Profilemeter Natural None 1(C) 14 Year 6years
RossandDykes(1996) Brunei Bookchapter Runoffplot Natural ST 1(F) 24 Month 8months
Shimokawa(1988) Indonesia Bookchapter Root exposition
Natural None 1(F) 21 Year 1year
SiebertandBelsky(1990) Indonesia Journalarticle Runoffplot Natural ST+OM 1(C) 3 Season 9months
Sinunetal.(1992) Malaysia Journalarticle Runoffplot Natural None 3(B,F,G) 78 Month,year 1year
Sudarmadji(2001) Indonesia Conference proceedings
Runoffplot Natural ST 1(F) 3 Study 4months
SyedAbdullahand Al-Toum(2000)
Malaysia Journalarticle Sediment trap
Natural ST+OM 1(F) 12 Year 1year
vanderLinden(1980) Indonesia Journalarticle Runoffplot Natural ST+OM 3(B,C,G) 88 Rainfallevent,study 3months
continuousvariables(erosion,duration,area,rainfall,slopelength andslope steepness)werelog10-transformedtonormalizetheir
distribution.Ifnotspecified,furthermentionof valuesof these variableswillrefertotheirlog10-transformedvalues.Becausenull
valuescannotbelog10-transformed,eachnullvalueofmeasured
soil loss (664 values, expressed in g after transforming values reportedinotherunitsinthepapers)wasreplacedbyarandom valuetakenfromauniformdistributionintherangeof0.001–1g, anintervalarbitrarilychoseninwhich1grepresentsa measure-mentdetectionthreshold(Chiappettaetal.,2004).After substi-tutingthenullvalues,measuredsoilloss(g)wasconvertedintosoil loss per unit of area and per year (g/m2/yr). Replicating the substitutionprocess10times,wecheckedthattherandomnessof thedatareplacementdidnotaffectthesubsequentresults.
Inordertoanalyzetheeffectofsoilorvegetationmanagement on soil erosion, we controlled first for the effect of the measurementprotocol(method, durationand area)(Hairetal., 2006). Annual soil loss values obtained from extrapolation of measurestakenoverasingleraineventarelikelytobelargerthan valuesfrommeasuresoveroneyear,andsoillossvaluesperunitof areaareprobablyhigherinsmallplotsthaninlargerareasbecause ofsedimentdeposition(Boix-Fayosetal.,2006).Weusedonlythe twoquantitativedescriptorsofmeasurementprotocol(areaand duration), as they weregood proxies for method (60% correct determination, jackknifed classification following discriminant functionanalysis).Wetransformedthelog10valuesofsoillossand
contextvariables(rainfall,soilerodibility,slopelengthandslope steepness) intothe residuals resulting froma linear regression against duration, area and the interaction between the two variables(all threesignificantatp<0.001;Table D1).Residuals werefurtheradjusted to correspond toa reference protocolof measurementsoveroneyearand100m2(thisvaluecorresponding
totheorderofmagnitudeofthemedianarea).
We then controlled for theeffect of context on soil loss by calculatingtheresidualsofagenerallinearmodelrelatingsoillossto context(valuesofrainfall,slopelengthandslopesteepness,after factoring out theeffects ofprotocol, aswell assoilerodibility classes). Allthecontextvariableshadasignificanteffectonsoilloss(p<0.05; TableD2).Theresidualswereadjustedtoa“referencescenario” withthemedianvaluesforannualrainfall(exclusivelyfromcases whererainfallwasmeasuredforoneyearormore),slopelength, slopesteepness(back-transformedvaluesbeing2444mm,16.4m and16.5%,respectively),andasoilerodibilityofclass“medium”.
Allsubsequentstatisticalanalyses(ANOVAandTukey’sHSD) usedthese log10-transformedsoil lossvalues, corrected for the
effect of the measurement protocol and context and scaled to correspondtoareferencescenario.Wetestedfordifferences(at p<0.001)insoillossdependingon(1)land-usetype,(2)land-use subtypeand(3)thenumberand(4)natureoflayersconstituting the vegetation cover. As six references provided half the total
numberofcases,wetestedwhethertheyhadadominanteffecton theoverallresults.Todoso,wereanalyzedthedataafterremoving these references one byone, but no significant changes in the resultsandnochangesinthefindingswereobserved.
3.Results
Soillosswasmaximumonbaresoilsandstrikinglyexceeded that ofallotherland-usetypes(Fig.3).Minimumsoillosswas foundinforests.Croplandshadthesecondhighestsoillossvalue among land-usetypes.Mean soillossvaluesfor grasslandsand shrublands were about half that of croplands. The ratio (of geometricmeansinthenaturalscale)shrankto1:3formeansoil loss between tree-dominated agrosystems and croplands. The erosionrateinforestswasca.one-tenthandone-150ththanthatof croplandsandbaresoils,respectively.Theratioofsoillossvalues betweentwoconsecutivelanduses(sortedbydecreasingmean soil loss) was much higher between bare soils and croplands (ca.20:1)thanbetweenotherland-usetypes(ratiosbelow3:1).
Soillossdifferedsignificantlybetweensubtypesoflanduses withinthesametype.Soillosswasminimumfortreecropswith contactcover(e.g.grassorcovercrop)andmaximumontilledbare soils,witharatioof1:1,200betweenthetwovalues(Fig.4).Among baresoils,soillosswas40%higherwithtillagethanwithout(the latterstillhadahighabsolutevalueofsoilloss).Amongcroplands, recently planted crops without vegetation-relatedconservation practices(e.g.hedgerows,mulchingorintercropping)haderosion ratessimilartothoseofbaresoils(eithertilledornot),whereas well-establishedcropsonsimilarlandsreducedsoillossby89%on average. Vegetation-related conservation practices reduced soil lossby93%inrecentlyplantedcroplandbutdidnotreducesoilloss significantlyinlandwithestablishedcrops.Simultaneoussoil-and vegetation-relatedconservationpractices(e.g.no-tillfarmingand hedgerows)decreasedsoillossincroplands(upto99%compared tonoconservationpracticesinlandwithrecentlyplantedcrops). Among tree-dominatedagrosystems, tree cropswith contact coverfaced99%lesssoillossonaveragethantreecropswithout contactcover.Simpleagroforestshadgreatersoillossthancomplex ones(3:1ratio);however,thedifferencewasnotsignificant.Among thefiveleasterosion-proneland-usesubtypes,threewereofforest type(old-growth,secondary,andlogged-overforests).
Thenumberoflayersconstitutingthevegetationcoverhada significantimpactonsoilloss.Soillosswasmaximalwithoutany layerandminimalwithfourlayers.Soillosswasone-tenthasmuch withonelayeraswithout,andone-70thasmuchwithtwolayersas without(Fig.5).The90%reductioninsoillossbetweenoneandtwo layerswasalsosignificant.Conversely,nosignificantdifferencein meansoillosswasfoundbetweentwoandfourlayers.
The type of layers constituting the vegetation cover had a significantimpactonsoilloss.Thepresenceofhigh,intermediary,
Table2(Continued)
Reference Country Sourcetype Method Rainfalltype Soil dataa
Land-use type(s)b
Cases Casetimeframe(s) Studylength
Caribbeanislands(n=5)
Khamsouk(2001) France (Martinique)
PhDthesis Runoffplot Natural, simulation
ST+OM 3(B,C,T) 429 Rainfallevent 1.5years
Larsenetal.(1999) USA(Puerto Rico)
Journalarticle Unbounded plot
Natural ST 3(B,G,S) 177 Month,season,year 3.75years
McDonaldetal.(2002) Jamaica Journalarticle Runoffplot Natural ST+OM 3(B,C,F) 24 Year,study 5years
MohammedandGumbs (1982)
Trinidadand Tobago
Journalarticle Runoffplot Natural ST+OM 2(B,C) 6 Rainfallevent,season 3months
RamosSantanaetal. (2003)
USA(Puerto Rico)
Journalarticle Runoffplot Natural None 3(B,G,T) 8 Month 1month
a
ST:soiltexture;OM:organicmatter.
0 1 2 3 4 5 1980 1990 2000 2010 Year of publication Frequenc y 0 5 10 15 0 100 200 300 400
Number of cases per reference
Frequenc y 0 5 10 0 5 10 15
Length of the study (years)
Frequenc y 0 5 10 15 20 25
r.event day week month season study year
Case time frames
Frequenc y 0 5 10 15 1 2 3 4 5 6
Number of land-use types per reference
Frequenc y 0 10 20 30
bare cropland forest grassland shrubland tree-dom. Land-use type Frequenc y (a) (b) (c) (d) (e) (f)
Fig.2. Frequencydistributionof(a)yearofpublicationofthecontributingreferences(n=55),(b)numberofcasesperreference(totalcases=3649),(c)lengthofthestudy,(d) casetimeframes,(e)numberofland-usetypesinvestigatedperreference,(f)land-usetypesinvestigated.Totalfor(d)>55becausesomereferencesprovidedataonmorethan onetimeframe;totalfor(f)>55becausemostreferencesreportedonmorethanonelanduse.R.event:rainfallevent;tree-dom.:tree-dominatedagrosystem.
low and ground layers influenced soil loss significantly and differently (Table 3): soil loss under a unique layer of high vegetation(4m)wastwicethatoccurringonbaresoils,whereas otherlayersdecreasedsoillosscomparedtobaresoilsbyafactorof 5,8and5forintermediary,lowandgroundlayersrespectively,and afactorof200foracombinationofthethreelayers.
4.Discussion
4.1.Soilerosionisconcentratedinspaceandtime
Soilerosioncontrolcanabruptlybelostwhenvegetationcover isnot developedenoughand/or whenpoorsoiland vegetation management practices are implemented (Figs. 3–5). While we foundtheratioofsoillossvaluesbetweenbaresoilsandcroplands
tobeca.20:1inthehumidtropics,theratiorangedfrom2:1to 10:1 in Europe and the Mediterranean (Cerdan et al., 2010;
Maetensetal.,2012).Thissuggeststhatsoilerosioncontrolisstill
provided in the humid tropics to a certain extent for crop-and grass-dominated land uses but is alarmingly depleted in baresoils,withdramaticconsequencesonsoilloss.The 2-order-of-magnitude difference in soil loss between one and zero vegetation layer also suggests that some vegetation cover is necessaryfor soilerosioncontroltobeprovided. Consequently, baresoilsshouldbeavoidedatalltimes.
The abruptloss of soilerosioncontrol depictedinFigs. 3–5
suggeststhat,inmostlanduses,erosionisconcentratedspatially (over bare soil, e.g. logging roads or non-protected crop fields betweenrotations)andtemporally(e.g.beforevegetationisfully established).Soillosswaslowestinplotsundertreecropswith
Fig.3.Impactofland-usetypeonsoillossunderreferencescenario(significantdifferenceatp<0.001).Geometricmeansalongwith95%confidenceintervalsonthenatural scaleareplottedonalog10scaleforthesakeofreadability(bottompanel).Log10-transformedmeansoillossvalueswiththesameletterarenotsignificantlydifferent(Tukey’s
HSD,p<0.01).Geometricmeansarealsoplottedonthenaturalscaletohighlightthelossofsoilerosioncontrolfromcroplandtobareland(toppanel).Tree-dom.: tree-dominatedagrosystem.
contactcover,butsuchcropsmightnotbetotallyerosion-neutral. Similarly, the fact that soil loss in logged-over forests is not differentfromthatinold-growthforestsshouldnotleadtothe delusiveconclusion thatlogging doesnot increasesoil erosion. Baresoilelementsexclusivelyrelatedtologgingandfarming(e.g. roads and trails) contribute to disproportionately increase the overallerosionrateofsuchactivities(e.g.Rijsdijk,2005;
Gómez-Delgado, 2010). Much attention should therefore be given to
managingthese elements(e.g. through water diversion, useof vegetativebufferstripsandtrailconsolidation)soastoreducethe overallimpactofsuchactivities.
Attentionmustalsobegiventotemporaltransitionsbetween landuses, for example when establishing crops or plantations.
Although this findinghasbeenreported before (Sarrailh,1981;
Baharuddinetal., 1995;AndersonandMacdonald, 1998;Bruijnzeel
etal.,1998;Rijsdijk,2005;DefershaandMelesse,2012),ourstudy
brings a strong quantitative endorsement to it because of the numberofstudiesandcasestakenintoconsideration.
Studiesinvestigatingtheconsequencesofland-usechangesfor soilerosionoftenusedasynchronicapproach(comparingdifferent landusesindifferentplotstoinfertheconsequencesofaconversion, inasingleplot,fromonelandusetotheother).Unlikeadiachronic approach measuring soil lossbefore, during and afterland use change(e.g.FritschandSarrailh,1986;Malmer,1996),asynchronic approachdoesnotrecordthetransition(e.g.throughclear-cuttingor tillage)fromonelandusetotheother.Thistransitionappearstobe
Fig.4. Impactofland-usesubtypeonsoillossunderreferencescenario(significantdifferenceatp<0.001).Geometricmeansalongwith95%confidenceintervalsonthe naturalscaleareplottedonalog10scaleforthesakeofreadability(bottompanel).Log10-transformedmeansoillossvalueswiththesameletterarenotsignificantlydifferent
(Tukey’sHSD,p<0.01).Geometricmeansarealsoplottedonthenaturalscaletohighlightthelossofsoilerosioncontrolfromtreecropswithcontactcovertotilledbaresoils (toppanel).B:bare;C:cropland;G:grassland;F:forest;S:shrubland;T:tree-dominatedagrosystem;estab.:established;VCP:vegetation-relatedconservationpractice(s); V&SCP:vegetation-andsoil-relatedconservationpractice(s).
criticalforunderstandingtheconsequencesofland-usechangesfor soillossinthehumidtropics,wherevegetationregrowthisrapidbut mostoftheannualsoillossispotentiallycausedbyalimitednumber ofextremerainfallevents(e.g.Poudeletal.,1999;Defershaand
Melesse,2012).Comparingsynchronicanddiachronicapproaches
forsoilcarbonsequestrationassessment,CostaJunioretal.(2013)
found that results depended on the selected approach, and recommendeduseofthediachronicapproachwheneverpossible. Becauseofintrinsicvariationsinsoilcharacteristics(e.g.texture) betweensitesunderthesamelanduseormanagementpractice,a diachronicapproachshouldalwaysbepreferred.Ontheotherhand, asynchronicapproachusingmultiplereplicatesmakesitpossibleto highlight trends in the consequences of land use change or management.
In this respect, the sequence of land uses—bare untilled, cropland, opengrassland, openshrubland,secondary forestand old-growth forest—can beinterpreted assnapshots of different successionalstages followingshiftingcultivation (afterclearing, cultivation, and subsequent natural regeneration). This review showedthatsoilerosiondecreasedalongthesequence,attestingto therecoveryofsoilerosioncontrol.Martinetal.(2013)highlighted asimilarincreasingtrendforcarbonstorageandplantdiversity duringpost-disturbanceforestrecovery.Thissuggestsasynergy (or a joint increase in multiple ecosystem services following implementation of a practice—forest regeneration in this case) betweensoilerosioncontrol,carbonstorageandplantdiversity. But the evaluation of a wider range of ecosystem services (including e.g. water regulation) is advised so as to avoid
Fig.5.Impactofthenumberofvegetationlayersonsoillossunderreferencescenario(significantdifferenceatp<0.001).Geometricmeansalongwith95%confidence intervalsonthenaturalscaleareplottedonalog10scaleforthesakeofreadability(bottompanel).Log10-transformedmeansoillossvalueswiththesameletterarenot
significantlydifferent(Tukey’sHSD,p<0.01).Geometricmeansarealsoplottedonthenaturalscaletohighlightthelossofsoilerosioncontrolfromonelayerofvegetationto none(toppanel).
promotingmeasures(e.g.afforestation)thatwouldbedetrimental forthedeliveryofotherservices.
4.2.Whatmattersinsoilerosioncontrolbyvegetation?
ThechangeofslopeinFig.4highlightsfourlandusesinwhich soilerosioncontrolisdepleted.Inadditiontotwosituationsofbare soils, recently planted croplands without vegetation-related conservationpractices also provide a low level of soil erosion control.Thishighlights theimportanceofgood managementof croplands: vegetation-related conservation practices (such as hedgerows)canensurethat,evenduringinter-orearly-rotation periodswhen cropcover is not yet developed, erosioncan be preventedorminimized.
Treecropswithoutcontactcoveralsoprovidecriticallylowlevels ofsoilerosion control, which is confirmedbytheanalysisoftheeffect ofvegetationlayers:thepresenceofa solehigh layerincreases erosioncomparedtobaresoil.Thisisconsistentwithotherstudies thatpointedouttheroleoftreecanopyinmodifyingrainfallkinetic energy(e.g.Wiersum,1985;Brandt,1988;Calder,2001).Leavesof thecanopylayerhelpbreakthekineticenergyofraindrops,but secondarydropsfallingfromthecanopy(particularlyfromlarge leaves)areoftenlargerthantheraindropsandreachthegroundwith a higher kinetic energy than in areas without a canopy layer
(Wiersum, 1985;Brandt, 1988).Thisresultsinincreasedsoilerosion,
particularlywhenthecanopyishighandthereisnounderstorey vegetation.Teak(TectoniagrandisL.f.)plantations,forexample,have oftenbeenassociatedwithhigherosionratesbecauseoflackof understoreyandlargetreeleaves(Calder,2001).Butarecentstudy showedthatpoorvegetation and soil managementrather than intrinsic teak leaf morphology was responsible for those high erosionrates(Fernández-Moyaetal.,2014).
Litterand understoreybothhelp breakthekineticenergyof raindropsand thereforedecreasesplash erosion(Brandt,1988). Multiple layers of vegetation are necessary in plantations to minimizesoilerosion,andnon-compliancewithsound manage-mentrules(e.g.therepeateduseoffiretocleargroundcoverand understorey)directlyanddramaticallyincreasessoilloss( Wier-sum,1984).Overall, whatever theland use, we foundlow and groundlayersofvegetationtobeessentialindecreasingsoilloss
(Table 3). This is consistent with plot-derived results from
northernVietnam,whichidentifiedacriticalvalueofunderstorey biomass(130g/m2)abovewhichsoillosswasnegligible(Anhetal.,
2014).Therefore,lowandgroundcoversshouldberestoredand/or maintainedwhateverthelanduse.
4.3.Soilerosionunderhuman-impactedormanagedvs.natural vegetation
Thisstudyalsoshowedthatthedifferencebetween “human-impactedormanaged”and“natural”vegetationdoesnotexplain
soil loss in the humid tropics (although intuitively one would expectlowersoilerosionundernaturalvegetation).Forexample, wefoundthatsoillossinold-growthforestishigherthanintree cropswithcontactcover.Soilerosionisanaturalphenomenonthat alsooccurs inold-growthforest despiteitscomplexvegetation structureandhighgroundcover(mostlyleaflitterorwooddebris). InTanzania,Lundgren(1980)suggestedthatgoodland manage-mentpractices(e.g.mulchingandnoburning)accountedforlower erosionratesinagrosystemsthaninnaturalforest,eventhough thisobservationwasmadeduringnormalrainfallconditionsandit wasimpossibletopredicthowthehuman-managedsystemwould havereactedtoextremerainfallevents.InSouthAndamanisland,
Pandeyand Chaudhari (2010) showed that coconutplantations
withacontactcoverofPuerariaphaseoloideshadsimilarsoillossas nearbynativeevergreenforestand thereforerecommendedthe use of contact cover in plantations for soil erosion control on theisland.
Our quantitative analysisstronglysupports theidea that no landuse(exceptbaresoils)iserosion-proneperseandthatsound management of soil and vegetation can reduce soil erosionin managedareastolevelsevenlowerthaninareasundernatural vegetation.
4.4.Differencesinsoilerosioncontrolbetweentropicalvs.temperate regions
Comparingtheeffectoflanduseonsoilerosioninthehumid tropics(thisreview)andintemperateregions(Renardetal.,1997;
Burke and Sugg, 2006), we foundthat changes in soil erosion
controlalong agradientof landuseshadsimilarshape inboth temperateandtropicalareas(Fig.6).Adifferencebetweenthese climaticzonesisobservedingrasslandsandcroplands,wheresoil erosioncontrolishigherinthehumidtropicsthansuggestedby theRUSLE.Ouranalysisshowsamuchmorepronouncedthreshold effectintherelationbetweenvegetationandsoilerosioncontrol thangivenbytheRUSLE,whichsuggeststhatsoilerosionismore concentrated in space and time in the humid tropics than elsewhere. The differencecan be explained by the more rapid developmentofdensevegetationprotectingsoilincroplandsand grasslandsofthehumidtropics.Becauseofthe“universal”nature ofthemechanismofsoilerosion,theRUSLE,anempirically-based model that integrates all the factors known to influence soil erosion(e.g.soilerodibility,rainfallerosivity),couldpotentiallybe
Fig.6.Ratioofcover-managementfactorsfortheRUSLEfor5differentlanduses (referencebeingerosiononbaresoils),andratioofsoillossperlandusetosoilloss onbaresoilsfromoursystematicreview(SR).
Table3
Coefficientsofthegeneralizedlinearmodelregressionofannualsoilloss(log10
-transformed values) against presence/absence of high (4m), intermediate (1mheight<4m),low(0.1mheight<1m)andground(<0.1m)vegetation layers.
Estimate Standarderror p Intercept(bare) 2.97 0.044 *** High 0.22 0.071 ** Intermediary 0.66 0.054 *** Low 0.91 0.058 *** Ground 0.71 0.068 *** AdjustedR2 :0.204 Numberofobservations:3649 ** p<0.01. *** p<0.001.
used to predict soil erosion for any geographical context. But factors’parameterswerecomputedfromdatacollectedexclusively intemperateregionsandthedirectapplicationoftheRUSLEtoa tropicalcontextwouldleadtosoillossmisestimationespeciallyfor croplandsandgrasslands.Properlycalibrating allRUSLEfactors’ parameters (especially those related to soil and vegetation management)usingdataacquiredinatropicalcontextistherefore criticaltoachieveaccuratepredictionofsoilerosioninthehumid tropics.
4.5.Limitationsofthestudy
Thisanalysisfaced challengesrelated todataavailability. As soilsweresometimespoorlydescribed, wehad touseaglobal databasetoestimatetextureandcarboncontent,whichprobably influencedtheaccuracyofoursoilerodibilityindices.Thestructure ofthevegetationcover(e.g.numberandheightoflayers,planting densityandpresenceorabsenceofgroundcover)wasnotalways well described. For example, Sinun et al. (1992) studied an abandonedloggingtrackwhereasharpdecreaseinsoillosswas recordedovertime;butwhilesoillosswasmeasuredonamonthly basisoveroneyear,vegetationwasnotdescribedovertime.Two noticeable exceptions were Khamsouk (2001) and Presbitero
(2003),inwhichvegetationcoverwasregularlyandsystematically
estimated,but withdifferentapproaches (e.g.crown coverand contactcover).
Theaimofthisstudywastoquantitativelyanalyzesoilerosion controlinthewholehumidtropics,butreferencesonlycovered 21 countries and some sub-regions were critically under-represented,e.g.theBrazilianpartoftheAmazonandtheCongo basin(Fig. 1,Table2).YetKöppenclimaticclasses“Af”and“Am”are homogeneous in term of temperature, rainfall pattern and vegetationtype(Köppen,1936),whichsupportstheapplicability ofthisstudy’sfindingstounder-representedsub-regions.Research should nevertheless be carried out in the Amazon and the Congo basin to document the effect of local human activities (e.g.small-and large-scaleagriculture,fuelwoodcollectionand industriallogging)onsoilerosion.
Becausesixreferences(fromfourcountries)representedhalf thetotalnumberofcases,wetestedfortheirdominanteffecton the overall results, but no such effect was found; this further supportstherelevanceofthisstudytothewholehumidtropics. Meanannualsoillossvaluesinthisstudyappearedtobeintheline of benchmarks provided byother studies. For example,annual erosionratesrangedfrom0.1to90and3to750Mg/hainhumid West Africafor croplands and bare soils, respectively(Morgan, 2005), compared to1 and16Mg/haonaverageinouranalysis. Otherbenchmarksare0.03to6.2,0.1to5.6,and1.2to183Mg/ha for old-growth forests and tree crops with and without contact cover, respectively (Wiersum, 1984), compared to 0.1, 2and5Mg/hainouranalysis.
Sinceweusedlog10-transformeddatatocarryoutstatistical
analyses,back-transformingmeansledtogeometricmeansinthe naturalscalethatareintrinsicallylesssensitivetoextremevalues
(BlandandAltman,1996).Thisexplainsthefactthatourvalueslie
inthelowerpartoftherange. 5.Conclusion
Soilerosioninthehumidtropicsisdramaticallyconcentrated bothspatially(overbaresoil)andtemporally(beforevegetation coverestablishes), andlow andgroundlayersof vegetationare essentialinmitigatingsoilerosion.Becausesoilerosionappears moreconcentratedinspaceandtimeinthehumidtropicsthan elsewhere,modelsdevelopedintemperateregionsshouldnotbe directly applied in the humid tropics, and thorough research
should be conducted to calibrate model parameters. As a preliminarysteptoanswertheUNcallforactiontoreverseland degradation(UN,2012),westresstheneedtoestablishstandard measurementproceduresforsoilerosionandinfluencingfactors, tomirrorwhatwasachievedforterrestrialcarbonmeasurement
(Walker et al., 2012). For improving soil and vegetation
management,uncoveredorunprotectedsoilsshouldbeavoided atalltimes,andlowandgroundlayersofvegetationshouldbe restoredand/ormaintainedwhateverthelanduse.
No land use(except bare soils) is erosion-prone per se and natural resourcemanagers and policymakersneed topromote soundmanagementofsoilandvegetation(e.g.contourplanting, no-tillfarming,intercroppinganduseofcovercrops)toreducesoil loss from erosion-prone landscape elements. Because of the relativeaffordabilityandsimplicityofsuchmanagementpractices, substantialdecreaseinsoillosscanbeattainedatthecatchmentor regionalscalewithlimitedfinancialandtechnicalmeans.Sincesoil erosionappearstodecreaseduringthedifferentphasesofforest regeneration,soilecosystemservices(e.g.nutrientcycling,flood regulation,waterpurification),thedeliveryofwhichisgreaterin healthiersoils,mightbegoodcandidatesforecosystemservices bundlingwithbiodiversityprotectionandcarbonstorage. Acknowledgements
We thank the library staffs of the Center for International Forestry Research and Centrede Coopération Internationale en RechercheAgronomiquepourleDéveloppement(CIRAD)fortheir helpinretrievingsomestudiesusedinthissystematicreview.We also thank ErvanRutishauserand Ghislain Vieilledent for their recommendationsaboutstatisticalanalysis.Wearegratefultothe twoanonymousreviewersfortheirconstructivecomments that helped toimprovethequalityof themanuscript. Thisresearch receivedfinancialsupportfromCIRAD,AusAID(Agreement63650 withtheCenterforInternationalForestryResearch),ABIES(Ecole DoctoraleAgriculture,Alimentation,Biologie,Environnementset Santé) and CRP-FTA (ConsortiumResearch Program onForests, Trees,andAgroforestry).
AppendixA.Supplementarydata
Supplementarydataassociatedwiththisarticlecanbefound,in theonlineversion,athttp://dx.doi.org/10.1016/j.agee.2015.01.027. References
Afandi,Manik,T.K.,Rosadi,B.,Utomo,M.,Senge,M.,Adachi,T.,Oki,Y.,2002a.Soil erosionundercoffeetreeswithdifferentweedmanagementinhumidtropical hillyareaofLampung,SouthSumatra,Indonesia.J.Jpn.Soc.SoilPhys.91,13–14.
Afandi,Rosadi,B.,Maryanto,Nurarifani,Utomo,M.,Senge,M.,Adachi,T.,2002b. Sedimentyieldfromvariouslandusepracticesinahillytropicalareaofthe Lampungregion,SouthSumatra,Indonesia.J.Jpn.Soc.SoilPhys.91,25–38.
Alegre,J.C.,Cassel,D.K.,1996.Dynamicsofsoilphysicalpropertiesunderalternative systemstoslash-and-burn.Agric.Ecosyst.Environ.58,39–48.
Alegre,J.C.,Rao,M.R.,1996.Soilandwaterconservationbycontourhedginginthe humidtropicsofPeru.Agric.Ecosyst.Environ.57,17–25.
Almas,M.,Jamal,T.,2000.UseofRUSLEforsoillosspredictionduringdifferent growthperiods.Pak.J.Biol.Sci.3,118–121.
Ambassa-Kiki,R.,Nill,D.,1999.Effectsofdifferentlandmanagementtechniqueson selectedtopsoilpropertiesofaforestFerralsol.SoilTillageRes.52,259–264.
Anderson,D.M.,Macdonald,L.H., 1998.Modellingroadsurfacesedimentproduction usingavectorgeographicinformationsystem.EarthSurf.ProcessesLandforms 23,95–107.
Angima,S.D.,Stott,D.E.,O’Neill,M.K.,Ong,C.K.,Weesies,G.A.,2003.Soilerosion predictionusingRUSLEforcentralKenyanhighlandconditions.Agric.Ecosyst. Environ.97,295–308.
Anh,P.T.Q.,Gomi,T.,MacDonald,L.H.,Mizugaki,S.,Khoa,P.V.,Furuichi,T.,2014. Linkagesamonglanduse,macronutrientlevels,andsoilerosioninnorthern Vietnam:aplot-scalestudy.Geoderma232,352–362.
Baharuddin,K.,Mokhtaruddin,A.M.,NikMuhamad,M., 1995.Surfacerunoffandsoil lossfromaskidtrailandaloggingroadinatropicalforest.J.Trop.For.Sci.7, 558–569.
Bellanger,B.,Huon,S.,Velasquez,F.,Vallès,V.,Girardin,C.,Mariotti,A.,2004. Monitoringsoilorganiccarbonerosionwithd13Candd15Nonexperimental fieldplotsintheVenezuelanAndes.Catena58,125–150.
Bland,J.M.,Altman,D.G.,1996.Transformations,means,andconfidenceintervals. Br.Med.J.312,1079.
Boix-Fayos,C.,Martínez-Mena,M.,Arnau-Rosalén,E.,Calvo-Cases,A.,Castillo,V., Albaladejo,J.,2006.Measuringsoilerosionbyfieldplots:understandingthe sourcesofvariation.EarthSci.Rev.78,267–285.
Bons,C.A.,1990.Acceleratederosionduetoclearcuttingofplantationforestand subsequentTaungyacultivationinuplandWestJava,Indonesia.In:Ziemer,R.R., O’Loughlin,C.L.,Hamilton,L.S.,InternationalUnionofForestryResearch Organizations(Eds.),ResearchNeedsandApplicationstoReduceErosionand SedimentationInTropicalSteeplands.IAHSPublicationNo.192.International AssociationofHydrologicalSciences,Wallingford,Oxfordshire,UK,pp.279–288.
Boye,A.,Albrecht,A.,2004.Soilerodibilitycontrolandsoilcarbonlossesunder shorttermtreefallowsinwesternKenya.Bull.RéseauEros.23,123–143.
Brandt,J.,1988.Thetransformationofrainfallenergybyatropicalrain-forest canopyinrelationtosoil-erosion.J.Biogeogr.15,41–48.
Bruijnzeel,L.A.,VanEijk,B.,Purwanto,E.,1998.Runoffandsoillossfrombench terracesinuplandWestJava,Indonesiaandimplicationsforprocessmodelling. In:Summer,W.,Klaghofer,E.,Zhang,W.(Eds.),ModellingSoilErosion,Sediment TransportandCloselyRelatedHydrologicalProcesses.IAHSPublicationNo.249. InternationalAssociationofHydrologicalSciences,Wallingford,Oxfordshire, UK,pp.211–220.
Burke,L.,Sugg,Z.,2006.Hydrologicmodelingofwatershedsdischargingadjacentto theMesoamericanReef.WorldResourcesInstitute,Washington,DC.
Calder,I.R.,2001.Canopyprocesses:implicationsfortranspiration,interceptionand splashinducederosion,ultimatelyforforestmanagementandwaterresources. PlantEcol.153,203–214.
Cerdan,O.,Govers,G.,LeBissonnais,Y.,VanOost,K.,Poesen,J.,Saby,N.,Gobin,A., Vacca,A.,Quinton,J.,Auerswald,K.,Klik,A.,Kwaad,F.J.P.M.,Raclot,D.,Ionita,I., Rejman,J.,Rousseva,S.,Muxart,T.,Roxo,M.J.,Dostal,T.,2010.Ratesandspatial variationsofsoilerosioninEurope:astudybasedonerosionplotdata. Geomorphology122,167–177.
Chartier,M.P.,Rostagno,C.M.,2006.Soilerosionthresholdsandalternativestatesin northeasternpatagonianrangelands.RangelandEcol.Manage.59,616–624.
Chatterjea,K.,1998.Theimpactoftropicalrainstormsonsedimentandrunoff generationfrombareandgrass-coveredsurfaces:aplotstudyfromSingapore. LandDegrad.Dev.9,143–157.
Chiappetta,P.,Roubaud,M.C.,Torrésani,B.,2004.Blindsourceseparationandthe analysisofmicroarraydata.J.Comput.Biol.11,1090–1109.
Chomitz,K.M.,Kumari,K.,1998.Thedomesticbenefitsoftropicalforests:acritical review.WorldBankRes.Obser.13,13–35.
Cohen,M.J.,Shepherd,K.D.,Walsh,M.G.,2005.Empiricalreformulationofthe universalsoillossequationforerosionriskassessmentinatropicalwatershed. Geoderma124,235–252.
CollaborationforEnvironmentalEvidence,2013.GuidelinesforSystematicReview andEvidenceSynthesisinEnvironmentalManagement.Version4.2. EnvironmentalEvidence:www.environmentalevidence.org/Authors.htm. Collinet,J.,1983.Hydrodynamiquesuperficielleetérosioncomparéesdessols
représentatifsdessitesforestiersetcultivésdelastationécologiquedeTaï (Sud-Ouestivoirien):premierbilansurparcellesexpérimentalesrecevantdespluies naturelles(campagnes1978-1979-1980)etsimulées(campagnedenovembre 1978etmars1979).CahiersORSTOM.
Collinet,J.,1988.Comportementshydrodynamiquesetérosifsdesolsdel’Afriquede l’Ouest:évolutiondesmatériauxetdesorganisationssoussimulationsde pluies.Strasbourg,France.
Comia,R.A.,Paningbatan,E.P.,Håkansson,I.,1994.Erosionandcropyieldresponse tosoilconditionsunderalleycroppingsystemsinthePhilippines.SoilTillage Res.31,249–261.
CostaJunior,C.,Corbeels,M.,Bernoux,M.,Piccolo,M.C.,Neto,M.S.,Feigl,B.J.,Cerri, C.E.P.,Cerri,C.C.,Scopel,E.,Lal,R.,2013.Assessingsoilcarbonstoragerates underno-tillage:comparingthesynchronicanddiachronicapproaches.Soil TillageRes.134,207–212.
Dangler,E.W.,El-Swaify,S.A.,1976.ErosionofselectedHawaiisoilsbysimulated rainfall.SoilSci.Soc.Am.J.40,769–773.
Daño,A.M.,Siapno,F.E.,1992.Theeffectivenessofsoilconservationstructuresin steepcultivatedmountainregionsofthePhilippines.In:Walling,D.E.,Davies,T. R.H.,Hasholt,B.(Eds.),Erosion,DebrisflowsandEnvironmentinMountain Regions.IAHSPublicationNo.209.InternationalAssociationofHydrological Sciences,Wallingford,Oxfordshire,UK,pp.399–405.
Defersha,M.B.,Melesse,A.M.,2012.Field-scaleinvestigationoftheeffectoflanduse onsedimentyieldandrunoffusingrunoffplotdataandmodelsintheMara Riverbasin,Kenya.Catena89,54–64.
Diodato,N.,Knight,J.,Bellocchi,G.,2013.Reducedcomplexitymodelforassessing patternsofrainfallerosivityinAfrica.GlobalPlanet.Change100,183–193.
El-Swaify,S.A.,Dangler,E.W.,Armstrong,C.L.,1982.Soilerosionbywaterinthe tropics.CollegeofTropicalAgricultureandHumanResources.Universityof Hawaii,Honolulu.
Fernández-Moya,J.,Alvarado,A.,Forsythe,W.,Ramírez,L.,Algeet-Abarquero,N., Marchamalo-Sacristán,M.,2014.Soilerosionunderteak(TectonagrandisL.f.) plantations:generalpatterns,assumptionsandcontroversies.Catena123, 236–242.
Francisco-Nicolas,N.,Turrent-Fernandez,A.,Oropeza-Mota,J.L.,Martinez-Menes, M.R.,Cortes-Flores,J.I.,2006.Soillossanderosion-productivityrelationshipsin foursoilmanagementsystems.TerraLatinoamericana24,253–260.
Fritsch,J.M.,Sarrailh,J.M.,1986.Lestransportssolidesdansl’écosystèmeforestier tropicalhumideguyanais:effetsdudéfrichementetdel’aménagementde pâturages.Cah.ORSTOM,SérPédol.22,209–222.
Gómez-Delgado,F.,2010.Hydrological,EcophysiologicalandSedimentProcessesin aCoffeeAgroforestryBasin:CombiningExperimentalandModellingMethods toAssessHydrologicalEnvironmentalServices.Montpellier,France.
Goujon,P.,1968.ConservationdessolsenAfriqueetàMadagascar:1èrepartie:les facteursdel’érosionetl’équationuniverselledeWischmeier.BoisFor.Trop. 118, 3–17.
Hair,J.F.,Tatham,R.L.,Anderson,R.E.,Black,W.,2006.MultivariateDataAnalysis, 6thEdPearsonPrenticeHall,UpperSaddleRiver,NJ.
Hartanto,H.,Prabhu,R.,Widayat,A.S.E.,Asdak,C.,2003.Factorsaffectingrunoffand soilerosion:plot-levelsoillossmonitoringforassessingsustainabilityofforest management.For.Ecol.Manage.180,361–374.
Hashim,G.M.,Ciesiolka,C.A.A.,Yusoff,W.A.,Nafis,A.W.,Mispan,M.R.,Rose,C.W., Coughlan,K.J.,1995.Soilerosionprocessesinslopinglandintheeastcoastof PeninsularMalaysia.SoilTechnol.8,215–233.
Hoyos,N.,2005.Spatialmodelingofsoilerosionpotentialinatropicalwatershedof theColombianAndes.Catena63,85–108.
ISRIC-WorldSoilInformation,2013.SoilGrids:anautomatedsystemforglobalsoil mapping.Availablefordownloadathttp://soilgrids1km.isric.org.
Jaafar,O.,SyedAbdullah,S.M.,Al-Toum,S.,2011.TheTekalaForestReserve:astudy onsurfacewashandrunoffusingclosesystemerosionplots.Geogr.Malay.J. Soc.Space7,1–13.
Kamara,C.S.,1986.Mulch-tillageeffectsonsoillossandsoilpropertiesonanultisol inthehumidtropics.SoilTillageRes.8,131–144.
Khamsouk,B.,2001.Impactdelaculturebananièresurl’environnement:influence dessystèmesdeculturesbananièressurl’érosion,lebilanhydriqueetlespertes ennutrimentssurunsolvolcaniqueenMartinique(casdusolbrunrouilléà halloysite).Montpellier,France.
Köppen,W.,1936.DasgeographiscaSystemderKlimate.In:Köppen,W.,Geiger,G.(Eds.), Handbuchderklimatologie.GebrüderBorntraeger,Berlin,Germany,pp.1–44.
Lal,R.,1990.Soilerosioninthetropics:principlesandmanagement.McGraw-Hill, NewYork.
Lal,R.,2003.Soilerosionandtheglobalcarbonbudget.Environ.Int.29,437–450.
Larsen,M.C.,Torres-Sánchez,A.J.,Concepción,I.M.,1999.Slopewash,surfacerunoff andfine-littertransportinforestandlandslidescarsinhumid-tropical steeplandsluquilloexperimentalforest,PuertoRico.EarthSurf.Processes Landforms24,481–502.
Leigh,C.,1982.SedimenttransportbysurfacewashandthroughflowatthePasoh ForestReserveNegriSembilan,PeninsularMalaysia.Geogr.Ann.Ser.A.Phys. Geogr.64,171–180.
Locatelli,B.,Imbach,P.,Vignola,R.,Metzger,M.J.,Hidalgo,E.J.L.,2011.Ecosystem servicesandhydroelectricityinCentralAmerica:modellingserviceflowswith fuzzylogicandexpertknowledge.Reg.Environ.Change11,393–404.
Locatelli,B.,Imbach,P.,Wunder,S.,2014.Synergiesandtrade-offsbetween ecosystemservicesinCostaRica.Environ.Conserv.41,27–36.
Lundgren,L.,1980.Comparisonofsurfacerunoffandsoillossfromrunoffplotsin forestandsmall-scaleagricultureintheUsambaraMts.Tanzania.Geogr.Ann. Ser.A.Phys.Geogr.62,113–148.
Maetens,W.,Vanmaercke,M.,Poesen,J.,Jankauskas,B.,Jankauskien,G.,Ionita,I., 2012.EffectsoflanduseonannualrunoffandsoillossinEuropeandthe Mediterranean:ameta-analysisofplotdata.Prog.Phys.Geogr.36,597–651.
Malmer,A.,1996.Hydrologicaleffectsandnutrientlossesofforestplantation establishmentontropicalrainforestlandinSabah,Malaysia.J.Hydrol.174,129–148.
Martin,P.A.,Newton,A.C.,Bullock,J.M.,2013.Carbonpoolsrecovermorequickly thanplantbiodiversityintropicalsecondaryforests.Proc.R.Soc.Lond.,Ser.B: Biol.Sci.280,20132236.
McDonald,M.A.,Healey,J.R.,Stevens,P.A.,2002.Theeffectsofsecondaryforest clearanceandsubsequentland-useonerosionlossesandsoilpropertiesinthe BlueMountainsofJamaica.Agric.Ecosyst.Environ.92,1–19.
McGregor,D.F.M.,1980.AninvestigationofsoilerosionintheColombianrainforest zone.Catena7,265–273.
MillenniumEcosystemAssessment,2005.EcosystemsandHumanWell-Being: Synthesis.IslandPress,Washington,DC.
Moehansyah,H.,Maheshwari,B.L.,Armstrong,J.,2004.FieldEvaluationofSelected SoilErosionModelsforCatchmentManagementinIndonesia.Biosys.Eng.88, 491–506.
Moench,M.,1991.Soilerosionunderasuccessionalagroforestrysequence:acase studyfromIdukkiDistrict,Kerala,India.Agrofor.Syst.15,31–50.
Mohammed,A.,Gumbs,F.A.,1982.Theeffectofplantspacingonwaterrunoff:soil erosionandyieldofmaize(ZeamaysL.)onasteepslopeofanultisolinTrinidad. J.Agric.Eng.Res.27,481–488.
Montgomery,D.R.,2007.Soilerosionandagriculturalsustainability.Proc.Natl. Acad.Sci.USA104,13268–13272.
Morgan,R.P.C.,2005.SoilErosionandConservation.Wiley-Blackwell,Oxford,UK.
Nearing,M.A.,Lane,L.J.,Lopes,V.L.,1994.Modelingsoilerosion.In:Lal,R.(Ed.),Soil Erosion:ResearchMethods.SoilandWaterConservationSocietyandSt.Lucie Press,Ankeny,Iowa,pp.127–156.
Ngatunga,E.L.N.,Lal,R.,Uriyo,A.P.,1984.Effectsofsurfacemanagementonrunoff andsoilerosionfromsomeplotsatMlingano,Tanzania.Geoderma33,1–12.
Odemerho,F.O.,Avwunudiogba,A.,1993.Theeffectsofchangingcassava managementpracticesonsoilloss:aNigerianexample.Geogr.J.159,63–69.
Pandey,C.B.,Chaudhari,S.K.,2010.Soilandnutrientlossesfromdifferentlanduses andvegetativemethodsfortheircontrolonhillyterrainofSouthAndaman. IndianJ.Agric.Sci.80,399–404.
Paningbatan,E.P.,Ciesiolka,C.A.A.,Coughlan,K.J.,Rose,C.W.,1995.Alleycroppingfor managingsoilerosionofhillylandsinthePhilippines.SoilTechnol.8,193–204.
Peel,M.C.,Finlayson,B.L.,McMahon,T.A.,2007.Updatedworldmapofthe Köppen-Geigerclimateclassification.Hydrol.EarthSyst.Sci.11,1633–1644.
Poudel,D.D.,Midmore,D.J.,West,L.T.,1999.Erosionandproductivityofvegetable systemsonslopingvolcanicash-derivedPhilippinesoils.SoilSci.Soc.Am.J.63, 1366–1376.
Poudel,D.D.,Midmore,D.J.,West,L.T.,2000.Farmerparticipatoryresearchto minimizesoilerosiononsteeplandvegetablesystemsinthePhilippines.Agric. Ecosyst.Environ.79,113–127.
Presbitero,A.L.,2003.SoilErosionStudiesonSteepSlopesofHumid-tropic Philippines.Griffith,Australia.
Prove,B.G.,Doogan,V.J.,Truong,P.N.V.,1995.Natureandmagnitudeofsoilerosion insugarcanelandonthewettropicalcoastofnorth-easternQueensland.Aust.J. Exp.Agric.35,641–649.
RCoreTeam,2013.R:Alanguageandenvironmentforstatisticalcomputing.R FoundationforStatisticalComputing,Vienna,Austria.ISBN3-900051-07-0, URLhttp://www.R-project.org/.
RamosSantana,R.,Martínez,G.,Macchiavelli,R.,Rodríguez,J.E.,Guzmán,J.L.,2003. Potentialoftreesgrasses,andturflegumesforrestoringerodedsoils.Commun. SoilSci.PlantAnal.34,2149–2162.
Renard,K.G.,Foster,G.R.,Weesies,G.A.,McCool,D.,Yoder,D.,1997.Predictingsoil erosionbywater:aguidetoconservationplanningwiththereviseduniversal soillossequation(RUSLE).AgricultureHandbookNo.703.U.S.Departmentof Agriculture,WashingtonDC.
Rijsdijk,A.,2005.Evaluatingsedimentsourcesanddeliveryinatropicalvolcanic watershed.In:Horowitz,A.J.,Walling,D.E.(Eds.),SedimentBudgets1.IAHS PublicationNo.291.InternationalAssociationofHydrologicalSciences, Wallingford,Oxfordshire,UK,pp.1–9.
Roose,E.,1973.Dix-septannéesdemesuresexpérimentalesdel’érosionetdu ruissellementsurunsolferrallitiquesableuxdebasseCôted’Ivoire: contributionàl’étudedel’érosionhydriqueenmilieuintertropical.Abidjan, Côted’Ivoire.
Ross,S.M.,Dykes,A.,1996.Soilconditions:erosionandnutrientlossonsteepslopes undermixeddipterocarpforestinBruneiDarussalam.Monogr.Biol.74, 259–270.
Ruppenthal,M.,Leihner,D.E.,Steinmüller,N.,El-Sharkawy,M.A.,1997.Lossesof organicmatterandnutrientsbywatererosionincassava-basedcropping systems.Exp.Agric.33,487–498.
Saatchi,S.S.,Harris,N.L.,Brown,S.,Lefsky,M.,Mitchard,E.T.A.,Salas,W.,Zutta,B.R., Buermann,W.,Lewis,S.L.,Hagen,S.,Petrova,S.,White,L.,Silman,M.,Morel,A., 2011.Benchmarkmapofforestcarbonstocksintropicalregionsacrossthree continents.Proc.Natl.Acad.Sci.USA108,9899–9904.
Sarrailh,J.M.,1981.Parcellesélémentairesd’étudeduruissellementetdel’érosion: analysedesrésultatsobtenusdurantlesdeuxpremièrescampagnesdemesure. Ecosyst.For.Guyan.Bull.LiaisonGroupeTrav.ECEREX4,45–51.
Sharpley,A.N.,Williams,J.R.,1990.EPIC-erosion/productivityimpactcalculator:1. Modeldocumentation.USDATechnicalBulletinNo.1768.U.S.Departmentof Agriculture,Washington,DC.
Shimokawa,E.,1988.Effectofafireoftropicalrainforestonsoilerosion.In:Tagawa, H.,Nirawan,N.(Eds.),AResearchontheProcessofEarlierRecoveryofTropical RainforestafteraLargeScaleFireinKalimantanTimur,Indonesia.Occasional paperN14,KagoshimaUniversity,ResearchCenterfortheSouthPacific,Japan,
pp.2–11.
Sidle,R.C.,Ziegler,A.D.,Negishi,J.N.,Nik,A.R.,Siew,R.,Turkelboom,F.,2006.Erosion processesinsteepterrain–truthsmyths,anduncertaintiesrelatedtoforest managementinSoutheastAsia.For.Ecol.Manage.224,199–225.
Siebert,S.F.,Belsky,J.M.,1990.BenchterracingintheKerinciuplandsofSumatra, Indonesia.J.SoilWaterConserv.45,559–562.
Sinun,W.,Meng,W.W.,Douglas,I.,Spencer,T.,1992.Throughfall,stemflow, overlandflowandthroughflowintheUluSegamaRainForest,Sabah,Malaysia. Philos.Trans.R.Soc.Lond.,Ser.B:Biol.Sci.335,389–395.
Snelder,D.J.,Bryan,R.B.,1995.Theuseofrainfallsimulationteststoassessthe influenceofvegetationdensityonsoillossondegradedrangelandsinthe BaringoDistrict,Kenya.Catena25,105–116.
Stewart,B.A.,Woolhiser,D.A.,Wischmeier,W.H.,Caro,J.H.,Frere,M.H., 1975.Control ofWaterPollutionfromCropland.U.S.EnvironmentalProtectionAgency, Washington,DC.
Strassburg,B.B.N.,Kelly,A.,Balmford,A.,Davies,R.G.,Gibbs,H.K.,Lovett,A.,Miles,L., Orme,C.D.L.,Price,J.,Turner,R.K.,Rodrigues,A.S.L.,2010.Globalcongruenceof carbonstorageandbiodiversityinterrestrialecosystems.Conserv.Lett.3, 98–105.
Streck,E.V.,Cogo,N.P.,2003.Reconsolidationofthesoilsurfaceaftertillage discontinuity,withandwithoutcultivation,relatedtoerosionanditsprediction withRUSLE.Rev.Bras.Cienc.Solo27,141–151.
Sudarmadji,T.,2001.Impactofloggingandforestfiresonsoilerosionintropical humidforestinKalimantan.RehabilitationofDegradedTropicalForest Ecosystems:WorkshopProceedings,2–4November1999,Centerfor InternationalForestryResearch,Bogor,Indonesia,pp.35–44.
SyedAbdullah,S.M.,Al-Toum,S.,2000.Astudyonsurfacewashandrunoffusing opensystemerosionplots.PertanikaJ.Trop.Agric.Sci.23,43–53.
Torri,D.,Poesen,J.,Borselli,L.,1997.Predictabilityanduncertaintyofthesoil erodibilityfactorusingaglobaldataset.Catena31,1–22.
Tropek,R.,Sedlacek,O.,Beck,J.,Keil,P.,Musilova,Z.,Simova,I.,Storch,D.,2014. CommentonHigh-resolutionglobalmapsof21st-centuryforestcoverchange. Science344,981.
UN,2012.Conferenceonsustainabledevelopment,Outcomeoftheconference,A/ CONF.216/L.1.RiodeJaneiro,Brazil.
Våje,P.I.,Singh,B.R.,Lal,R.,2005.Soilerosionandnutrientlossesfroma volcanicashsoilinKilimanjaroRegion,Tanzania.J.SustainableAgric.26, 95–117.
vanderLinden,P.,1980.Theapplicationofaparametricgreyboxtypeapproachto investigatesurfacerunoffanderosionduringrainstorms.Anerosionplotcase studyincentralJava,Indonesia.Indones.J.Geogr.10,23–42.
Verbist,B.,Poesen,J.,vanNoordwijk,M.,WidiantoSuprayogo,D.,Agus,F.,Deckers, J.,2010.Factorsaffectingsoillossatplotscaleandsedimentyieldatcatchment scaleinatropicalvolcanicagroforestrylandscape.Catena80,34–46.
Walker,S.M.,Pearson,T.R.H.,Casarim,F.M.,Harris,N.,Petrova,S.,Grais,A.,Swails,E., Netzer,M.,Goslee,K.M.,Brown,S.,2012.StandardOperatingProceduresfor TerrestrialCarbonMeasurement:Version2012.WinrockInternational, Arlington,Virginia.
Wan,Y.,El-Swaify,S.A., 1999.Runoffandsoilerosionasaffectedbyplasticmulchina Hawaiianpineapplefield.SoilTillageRes.52,29–35.
Wiersum,K.F., 1984.Surfaceerosionundervarioustropicalagroforestrysystems.In: O’Loughlin,C.L.,Pearce,A.J.(Eds.),EffectsofForestLandUseonErosionand SlopeStability.InternationalUnionofForestryResearchOrganizations,Austria, pp.231–239.
Wiersum,K.F.,1985.EffectsofvariousvegetationlayersinanAcaciaauriculiformis forestplantationonsurfaceerosioninJava,Indonesia.In:El-Swaify,S.A., Moldenhauer,W.C.,Lo,A.(Eds.),SoilErosionandConservation.Soil ConservationSocietyofAmerica,Ankeny,Iowa,pp.79–89.
Wischmeier,W.H.,Smith,D.D.,1978.Predictingrainfallerosionlosses:aguideto conservationplanning.AgricultureHandbookNo.537.U.S.Departmentof Agriculture,Washington,DC.
