A
conceptual
framework
for
analysing
and
measuring
land-use
intensity
Karl-Heinz
Erb
1,
Helmut
Haberl
1,
Martin
Rudbeck
Jepsen
2,
Tobias
Kuemmerle
3,4,
Marcus
Lindner
5,
Daniel
Mu¨ller
3,6,
Peter
H
Verburg
7and
Anette
Reenberg
2Largeknowledgegapscurrentlyexistthatlimitourabilityto
understandandcharacterisedynamicsandpatternsofland-use
intensity:inparticular,acomprehensiveconceptualframework
andasystemofmeasurementarelacking.Thissituation
hampersthedevelopmentofasoundunderstandingofthe
mechanisms,determinants,andconstraintsunderlyingchanges
inland-useintensity.Onthebasisofareviewofapproachesfor
studyingland-useintensity,weproposeaconceptualframework
toquantifyandanalyseland-useintensity.Thisframework
integratesthreedimensions:(a)inputintensity,(b)output
intensity,and(c)theassociatedsystem-levelimpactsof
land-basedproduction(e.g.changesincarbonstorageor
biodiversity).Thesystematicdevelopmentofindicatorsacross
thesedimensionswouldprovideopportunitiesforthesystematic
analysesofthetrade-offs,synergiesandopportunitycostsof
land-useintensificationstrategies.
Addresses
1InstituteofSocialEcologyVienna(SEC),Alpen-AdriaUniversity Klagenfurt,Wien,Graz,Schottenfeldgasse29,1070Vienna,Austria 2Department of Geography and Geology, University of Copenhagen, Oster Voldgade 10, 1350 Copenhagen, Denmark
3
DepartmentofGeography,Humboldt-Universita¨tzuBerlin,Unterden Linden6,10099Berlin,Germany
4PotsdamInstituteforClimateImpactResearch(PIK),EarthSystem Analysis, Telegraphenberg A 31, 14473 Potsdam, Germany 5European Forest Institute, Torikatu 34, 80100 Joensuu, Finland 6
LeibnizInstituteforAgriculturalDevelopmentinCentralandEastern Europe(IAMO),Theodor-Lieser-Str.2,06120Halle(Saale),Germany 7InstituteforEnvironmentalSciences,VUUniversityAmsterdam,De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands
Correspondingauthor:Erb,Karl-Heinz([email protected])
CurrentOpinioninEnvironmentalSustainability2013,5:464–470 ThisreviewcomesfromathemedissueonHumansettlementsand industrialsystems
EditedbyPeterHVerburg,OleMertz,Karl-HeinzErbandGiovana Espindola
ForacompleteoverviewseetheIssueandtheEditorial
Availableonline21stAugust2013
1877-3435#2013TheAuthors.Publishedby ElsevierB.V.
http://dx.doi.org/10.1016/j.cosust.2013.07.010
Introduction
Future growthin thehuman population and GDP will
increasethedemandforfood,fibreandfueloverthenext
decades [1,2,3]. Most of the related growth in
land-basedproductionwillhavetorelyonincreasesofoutput
perunitareainagricultureandforestryratherthanonthe
expansionoflanduse:weinhabitaworldinwhichmostof
thefertile landisalreadyusedandonlyonefifth ofthe
global ice-free surface remains largely untouched by
humans[4,5].Thereis an urgingmandateto safeguard
theseremainingundisturbedecosystems,whichareoften
richincarbonandbiodiversity[6].Suchincreasedoutput
on currently used land is commonly described by the
broadly accepted, but ambiguously defined, notion of
‘land-useintensification’.
In the last centuries, increases in agricultural output
without the proportional expansion of agricultural land
were possible because additional inputs in terms of
labour, energy, fertiliser and water were available [7].
However, many of the current techniques of yield
enhancementareassociatedwithfar-reaching,detrimental
ecologicalandsocialeffects[8–10].Thissituationrenders
an explicit valuation of the benefits and trade-offs of
land-useintensificationimportantandcallsforinnovative
ways of measuringand assessingintensification[3,11].
Thedevelopmentofanoperational,consistentmonitoring
systemisparticularlyimportantfor designingpoliciesto
foster sustainable increases in land-based production
[12,13].
Thescientificunderstandingofland-usechange,however,
is still insufficient to characterise the conditions under
which such a ‘sustainable intensification’ [3,14] can
andwilloccur.Manyknowledgegapsrelatetothe
under-lyingprocessesanddeterminantsofthelevels,patternsand
dynamicsofland-useintensity.First,welackacommonly
shared definition and terminology [15,16]. Second,the
casual use of the term ‘intensification’ in the scientific
literature, often used synonymously with the complex
changesrelatedtoagriculturalindustrialisationprocesses
(suchasthoseduringthe‘greenrevolution’)orwithany
detrimental socio-ecological effects of landuse, further
addstotheambiguity.Third,traditionalapproachesoften
onlyexamineone ora fewaspects ofland-use intensity
whiledisregardingthemultidimensionalityofthe
intensi-ficationprocess in the complexlandsystem [6,17].For
example,simplified,monodimensionalhypotheseson
la-nd-useintensification, for example, onthe
interrelation-shipbetweenagriculturalintensificationandareademand,
though initiallyhighlyintuitive,cannotbesubstantiated
whenevaluatedagainstempiricaldata[18,19].
Accord-ingly,simplecausalrelationshipsbetweentheindividual
processes,driversandimpactsofland-useintensification
couldnotbeestablished[20].
Wearguethatimprovementsinthescientific
understand-ingoflanduserequiretwo,interrelatedsteps:(1)
develop-ing an integrative framework for the analysis of
land-use intensity, and(2) generating datasetsthat allowthe
systematicstudyofdriversaswellasimpactsofchangesin
land-useintensity.Here,we brieflyreviewthemost
import-ant scientific approaches concerned with the processes,
drivers andconsequences of land-use intensitychanges.
Building on thisbody of knowledge, we summarise the
differentdimensionsofland-useintensityandsystematise
theimplicitlyorexplicitlyproposedindicatorsfor
measur-ing land-use intensity. Lastly, we proposean integrated
conceptualframeworkforanalysisaimedatfacilitatingthe
developmentofdatasetsforland-useintensityresearch.
Themes
and
topics
in
land-use
intensity
research
Researchhasbeenfocussingondifferentaspectsof
land-use intensity which can be grouped into four general
themes (see supporting online information). (a) The
(agricultural)economistperspective,rootedinthe
semi-nal works by the‘classic’ economistsT.R. Malthus, D.
Ricardo and J.H. von Thu¨nen, focusses on the
inter-relation between input factors (land, labour or capital)
and outputs (produce) from land, mostly in monetary
terms, often entailing arationalchoice (utility
optimis-ation)perspective.(b)Anotherprominentthemefocusses
ondriversofagriculturalchange,inparticulartechnology
andpopulationgrowth.Thisthemegainedimpetusafter
the1960swiththeinfluentialrebuttalofE.Boserup[21]
totheMalthusianviewontheinterrelationofpopulation
changeandtechnology,andisstillvividinhuman
geogra-phy,ecologicalanthropologyandpoliticalecology,witha
strong focus on pre-industrial agriculture. (c) A further
prominent research strandfocussesonpotentially
detri-mental ecological consequences of land-use
intensifica-tion, including livestock systems [22], in particular on
climate and biodiversity, or on essential but
non-mar-ketedecosystemservices([23],SIformorereferences).
Inthelightofemergingnewdemandsforlandproducts
(e.g. bioenergy),the (d)systemic interrelation between
intensification and land expansion (the so-called
land-sparing vs.land-sharing debate) (seee.g. Grau etal.,in
this issue, SI for more references) is another leading
themeof land-useintensityresearch.
Despite their differences in focus, scope and attention
(see SI), a few commonalities among these different
strandsof land-useintensityresearch canbeidentified.
First, afocusonagriculture,particularlycropland,
pre-vails,whereasothercomponentsofthelandsystem(e.g.
urban,forestry)aremostlyneglected.Second,
unconven-tionalmanagementpractices(e.g.fertilisationof
inten-sively managed forests; [24]) and land-system
interrelations (e.g. urban-hinterland linkages; Seto
et al., in this issue; Meyfroidt et al., in this issue) are
largely ignored. Third, monodimensional indicators,
mostly agricultural yieldsorfertiliserapplication rates,
oradata-drivendevelopment ofindicesfrom the
com-binationofinputandoutputdatadominate.Lastly,the
stringencyofeconomicapproaches,whichsystematically
analyse input-output relationships, is onlyrarely
repli-cated in non-economic strands of land-use intensity
research [25]. Additionally, systemic interrelationships
betweenproduction and consumption,such as
supply-demandlinkages,orreboundeffects,arerarelytakeninto
accountinnaturalscience-basedapproaches.Incontrast,
economic approaches rarely consider biophysical
con-straints or the effects of intensification on non-valued
ecosystem services or on biodiversity. Overcoming
theseshortcomingsbydevelopinganintegrated
frame-workofanalysisappearstimely.Inthefollowingsection,
wewillreviewandsystematisetheproposedmeasuresof
land-useintensitytoidentifythecornerstonesofsucha
framework.
Dimensions
of
land-use
intensity
Given thecomplexityofland-useintensity, providinga
single, unambiguous and encompassing definition or
indicatorof land-useintensitydoesnotappear to bean
adequatetarget.Acomprehensiveanalyticalframeworkis
required that considers the multidimensional nature of
land-useintensity.Asynthesisofthedimensionsof
land-use intensity and proposed methods to measure them
(Table1,seealsoTableS1intheSupplementaryOnline
Information)allowsidentificationofthecoreelementsof
suchacomprehensiveframeworkandneedstomeasure
the(a)inputstotheproductionsystem,(b)outputsfrom
the production system, and (c) changes in ecosystem
properties.
Measuring
input
intensification
Traditionalapproachestomeasureinputintensitycanbe
groupedintofourcategories.(a)Apivotalinputindicator
that inspired many authors is provided by Boserup
[21,54].She definesthe intensificationof agriculture as
the increasing frequency of cropping cycles in shifting
cultivation systems, that is,increasing inputsof land to
theproductionsystem.Thisnotionofcroppingfrequency
for measuring land-use intensityis based onthe
obser-vation that,under pre-industrial conditions, the annual
crop yieldofaparcel ofland canscarcely beenhanced,
thus only anincreased croppingfrequencycanincrease
production. Similarly, rotation length is an important
wasfurtherdevelopedbymanyauthors,forexample,by
proposing indicators that consider the differences in
fallow and cropping period (e.g. [26,28]). (b) Cropping
frequency is often complemented by information on
appliedtechnologytoprovideindicatorsofawider
appli-cability [15,27,32]. In such approaches, technologies
under use are ranked according to their intensity and
combined with indices for cropping frequency, an
approach criticised due to the pronenessto tautologies
[55]. (c) The definition by Brookfield [35] places the
substitution of capital,labour,and skills againstland at
thecentre of attention of land-useintensity research,a
definitionfollowedbymanyscholarssince(see,e.g.[25]),
whichisstimulatingforthedevelopmentofindicesbased
on combinations of input data. (d) In contrast to this
approach,manyauthors usesingle productionfactorsas
surrogate indicators for input intensification, including
the amount of N fertiliser or pesticide applied (e.g.
[40,41]).Althoughstudiesofthistypeareabletocapture
some central aspects of intensification, they cannot
accountforsubstitutioneffects(e.g.changesfrommineral
fertilisers to manure) or transitions to resource-sparing,
intensivehigh-techapplications(e.g.precisionfarming).
Arelatedapproach isthegenerationof indicesby
com-bininginputdatasets, sometimes alsowith output data,
suchas theyieldofthedominatingcultivarsorstocking
densityof livestock(e.g. [48]).
Measuring
output
intensification
TurnerandDoolittle[32]andHunt[56]arguethatoutput
indicators would ultimately provide better indicators of
land-useintensitybecausetheyrepresentthepurposeof
agriculture. Netting [25] and Shriar [15] also favour
measuring output intensity, as no presumptions about
the efficiency of inputs on productivity are made. In
biophysical terms, output intensification relates to the
increases in production output per unit area and time
(e.g.tons of cereals harvested, milkproduced or timber
removedfromforestsperunitareaandtimeperiod).
Many intricacies relate to the measurement of output
intensity,referringto(a)theunitofmeasurement(e.g.in
mass,energy,calorificvalue,monetaryvalueperarea)and
(b)themethodologyusedtomeasureoutputconsistently
[56].Because many land systemsare rotational, thatis,
fields are periodically left fallow to maintain the soil
fertility, itis important to relatetheoutputs to thefull
production cycle to generate comparable values. Such
data, however, are usually not readily available or are
highlyuncertain([16,30],Kuemmerleetal.,inthisissue).
Thelargevariationinyieldresultingfromdifferencesin
theclimate, soilconditionsor management history and
thespecificsofindividualcultivarsrendertheuseofyield
data as surrogates for output intensity problematic. To
manage these complexities better, methods have been
developedthatassessthe‘yieldgap’betweenagricultural
yields at theplot, farm orregional level to a reference
yield that is attained under similar conditions of
pro-duction (e.g. [57,58,59]) or standardised management
[45].Forforestry,anintricacyresultsfromtheoccurrence
ofunplannedfellings,forexample,followingnaturalfires,
pests or storms, which eventually results in naturally
inducedincreasesofoutputperareaandyearandrenders
it important to integrate the natural disturbances and
harvests[60].
Table1
Summary of dimensions and indicators of land-use intensity
Proposeddimension/indicator Authors
Inputs
Croppingfrequency,proportionoffallowland,harvestintervalsandrotationlengthinforestry [21,26,27,28,29,30,31] Cropping frequency combined with indices for technology [32,33,15,34] Indices combining inputs of labour and capital (and skills) per land area [35,36,37,38,27,39]
Singleinputsperlandarea [40,41]
Typeofforestregeneration(planting,seedingornaturalregeneration) [42] Outputs
Agriculturalyield(productionperareaandtime) [25,18,43,44,45]
Stockingdensityoflivestocka [46]
Fellingrates(fellingsaspercentofnetannualincrement) [47] Inputsandoutputs
Combinedindicesofinputsandoutputsa [14
,48,49,50] Changesinsystemproperties
Biodiversity [51]
Complexityofecosystems [23]
Net primary production [52]
Carbon stocks [53]
Waterandnutrientcycle [22,51]
a
Measuring
changes
in
system
properties
The systematic observation of the effects of land-use
intensity ontheecologicalpatterns and processes, such
as nutrientcycling,biodiversity,netprimaryproduction
(NPP),carbonstorage,waterqualityandwaterretention
capacity,isanimportantcomponentforacomprehensive
analytical framework for land-use research. Keys and
McConnell[20]and Tscharntke[23]haveplacedsuch
alterations of system properties at the centre of their
general definitions of land-use intensification. Whereas
analyses of the input-output ratio are an established
research theme (see SI), the link to altered ecosystem
propertiesisrarelyexplicit.Thisissurprisingbecausethe
alteration of system properties can be decisive for the
overalldynamicsofthelandsystem([16],Seppelt,inthis
issue).
Considering the effects of changes in the ecosystem
parametersandconsequentialalterationsoftheprovision
of ecosystem services appears important to further our
understanding of land-use intensity and for developing
indicatorsofsystem-leveloutcomes.Themeasurements
of such consequences, for example, the provision of
ecosystem services, have provento bedifficult [61,62].
Biophysicalapproachesexistthatquantifythesechanges
at the system level, for example, by quantifying the
differences between the actual and potential states of
the ecosystemand usingthe distance betweenthe two
states as a proxy for intensity. This notion is closely
related to the ecological definition of disturbance [63].
Examples o such approaches include the disturbance
assessment byHannahet al. [64],thechangesin
biodi-versity proposedbyMatsonetal. [51],theland useand
disturbance intensity index proposed for forestry, as
based on the ecological law of self-thinning [53], or
the human appropriation of net primary production
(HANPP;inthedefinitionof[52,65]).Forfurtherdetails,
seeKuemmerleetal.(in thisissue).
A
conceptual
framework
for
measuring
land-use
intensity
Onthebasisofourreview,wesuggestthattheresearch
aimed at studying land-use intensityor change therein
over time will have to integrate the three dimensions
outlinedabovesystematicallyinaconceptualframework
(Figure1).Theland-basedproductionsystemembedded
withinaterritoryshouldbeatthecentreoftheresearch
onland-useintensity.Theindicatorsforland-use
inten-sityshouldthensystematicallyintegratetheinputstothe
productionsystems(e.g.land,labourandcapital)withthe
outputs (i.e. products). This view, consistent with
economicprinciples,allowsthestudyoftheinput-output
relationships,suchastheeffectsofdiminishingreturnsor
substitutioneffectsoflabour,skillsandcapital[35].The
frameworkisalsocompatiblewiththepivotalBoserupian
notionofcropping frequencyas ameasure for land-use
intensityandallowsanalysingthedynamicrelationships
of intensificationandlandexpansion.
Figure 1 System properties Production System Outcomes Labour Products Territory Substituion Opportunity costs Trade-offs Synergies Feedback loops Land Capital Inputs (c) (a) (b) Outputs Services
Current Opinion in Environmental Sustainability
Aconceptualframeworkofland-useintensity(green:dimensionsofland-useintensity).Weproposeanewperspectiveonland-useintensity thatsystematicallylinksthreedimensions(greenfields):inputs,outputs,andtheassociatedsystemleveloutcomesofland-basedproductionresulting from alterations of the system properties (e.g. biodiversity change, carbon loss, or loss of cultural heritage). This allows one to (a) integrate trade-offs and synergies between land-based production and its associated unintended outcomes; (b) systematically link inputs and outputs; and (c) relate thesubstitutioneffectsattheinputsidetochangesinthesystempropertiesandtheirsocio-ecologicaleffects(dashedorangearrows).These relationshipsarekeyinunderstandingthefeedbackloopsbetweenproductionandconsumptionandtoidentifytheconditionsunderwhich sustainableintensificationcanoccur.
On the basis of biophysical indicators, much can be
gainedfromsuchanintegration:beyondtheagricultural
yield,whichalreadyrepresentstheratiobetweenoutput
(productionperyear)and input(land area),other ratios
couldbecalculatedinanalogytotheproductionfunction
ineconomics. Afew suchbiophysicalindicatorsalready
exist and reinforcethe power of such approaches. The
indicator‘energyreturnoninvestment’(EROI;[66]),for
example, balances energetic inputs and outputs to and
fromlandandcanillustratethenet-effectsof
intensifica-tionstrategies. Timeseriesanalyses reveal that, during
industrialisation, the tremendous gains in labour
effi-ciency come at the expense of a deteriorating energy
balance,which,incertaincases,evenfallsbelowone[67].
Itisimportant,however,tomovebeyondsimply
asses-singinputsandoutputsandtoalsoconsidertheoutcomes
ofland-based production, which are the result of
(fre-quently)unintendedalterationsofthesystemproperties
butare decisiveforthedynamicsofthecoupled
socio-ecological system. Quantifying the trajectories of the
ratiosbetweeninputs,outputsandchangesinecosystem
propertiescanprovidedeepinsightsintosociety-nature
interactionsandwouldallowtheopportunitytobalance
the costs and benefits of land-based production while
explicitly acknowledging and internalising the
unin-tended outcomesof land-use intensificationstrategies.
Only a few empirical examples of such integrative
perspectivesexist: atthelevelofagriculturalproducts,
approachesbasedonlifecycleassessments(LCA)have
beendevelopedtosystematicallyassessthe
environmen-talimpactsofproductionchains(forareviewsee[68]).
Atthelandsystemlevel,theHANPPframeworkallows
thecalculationof HANPPefficienciesoffinal biomass
products(e.g.theamountofHANPPperfinalproductin
tC/yr; [69]) and can, thus, evaluate the environmental
pressure associated with biomass products. A similar
approachisthecarbonfootprintconcept[70],whichaims
to quantify the carbon emission related to the final
consumptionofproducts(e.g.food).Similarly,thelocal
orglobal biodiversity loss ‘embodied’in everyunit of
input or output could be a compelling indicator for
evaluatingland-useoptions andtoidentifysustainable
landsystems[71].Suchaccountingschemeswouldalso
allow to address a growing challenge of land systems
science, that is, the growing teleconnections of land
systems (see Meyfroidt, in this issue; Gu¨neralp, in
thisissue)andtheirrelationtoland-useintensification
pathways.
Ultimately, the further development of indicators that
explicitlyaddressallthreedimensionswouldallow
con-sistentandsystematicintegrationoftheintended
socio-ecological outcomes or land-based production with the
associated direct, indirect and opportunity costs. This
wouldenhance ouranalytical capacityto explore
trade-offs, synergies and feedback loops systematically, and,
thereby,informdecisionmakingforasustainablefuture
landuse.
Conclusions
Satisfying the growing human demand for land-based
production without compromising the natural resource
base requires sustainable land-use intensification. The
formulationofstrategiestofostersustainable
intensifica-tion,however,requiresabetterconceptualisationofthe
land-useintensityitself,inadditiontoimproved
monitor-ingsystemsthatprovideasolidbasisfordecisionmaking.
Unfortunately, to date, neither conceptualisations nor
datasetsare available of sufficient quality and quantity
(Kuemmerleet al., in this issue)to allow for consistent
analysesof land-useintensity.
Inthisarticle,wesuggestthattheanalysisandmonitoring
of land-use intensity should follow an integrative
con-ceptualframework that focuses onthree dimensions of
land-useintensity: inputsto the land,outputs fromthe
land,andthehuman-induced,butunintendedoutcomes
ofland-useintensificationthatarebestmeasured atthe
systemlevel.
Thedevelopmentofsuchamonitoringsystemisagreat
challengethatrequires the concerted effortof multiple
disciplines. However, such an effort would contribute
substantially to advance our analytical capacity for
un-derstandingland-usechangesand,thus, ultimately
pro-videabasisfor forgingsustainableland-usestrategies.
Acknowledgements
The authors acknowledge funding from the Global Land Project (www.globallandproject.org),theEuropeanCommission(ERCGrant ERC-2010-Stg-263522‘LUISE’,EU-FP7Project265104‘VOLANTE’,EU-FP7 Project 265286 ‘I-REDD+’, and ERC Grant ERC-Stg-2012-311819 ‘GLOLAND’),theAustrianScienceFund(FWF)projectP20812-G11,and theEinsteinFoundationBerlin.
Appendix
A.
Supplementary
data
Supplementary material related to this article can be
found,in theonlineversion,athttp://dx.doi.org/10.1016/
j.cosust.2013.07.010.
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