Ecological Economics 77 (2012) 129–138

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Ecological Economics

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Analysis

Long-term trajectories of the human appropriation of net primary production:Lessons from six national case studies

Fridolin Krausmann a,⁎, Simone Gingrich a, Helmut Haberl a, Karl-Heinz Erb a, Annabella Musel a,1,Thomas Kastner a, Norbert Kohlheb b, Maria Niedertscheider a,2, Elmar Schwarzlmüller a,3

a Institute of Social Ecology Vienna (SEC), Alpen-Adria Universitaet, Schottenfeldgasse 29, 1070 Vienna, Austriab Institute of Environmental and Landscape Management, Szent István University (IEL-MSIU), H-2103 Gödöllő, Páter K. u. 1, Hungary

⁎ Corresponding author. Tel.: +43 1 5224000 412; faE-mail address: fridolin.krausmann@aau.at (F. Kraus

1 Current address: Holubstraße 1/7/5, 1020 Vienna, A2 Current address: Wurlitzergasse 93/23, 1170 Vienn3 Current address: Untere Augartenstr. 26/12, 1020 W

0921-8009© 2012 Elsevier B.V.doi:10.1016/j.ecolecon.2012.02.019

Open access under CC BY-NC-

a b s t r a c t

a r t i c l e i n f o

Article history:Received 22 July 2011Received in revised form 2 December 2011Accepted 18 February 2012Available online 14 March 2012

Keywords:Human appropriation of net primaryproduction (HANPP)BiomassLand-use intensityLong-term socio-ecological research (LTSER)Forest transition

The ‘human appropriation of net primary production’ (HANPP) is an integrated socio-ecological indicator mea-suring effects of land use on ecological biomass flows. Based on published data for Austria, Hungary, thePhilippines, South Africa, Spain and the UK, this paper investigates long-term trends in aboveground HANPPand discusses the relations between population, economic growth, changes in biomass use and land-use inten-sity and their influences on national HANPP trajectories. During early stages of industrialization, populationgrowth and increasing demand for biomass drive land-cover change, often resulting in deforestation, whichraises HANPP. During later stages, industrialization of agriculture boosts agricultural yields often faster than bio-mass demand grows, resulting in stable or even declining HANPP. Technological change improves agriculturalarea-efficiency (biomass provision per unit area), thereby decoupling population and economic growth fromHANPP. However, these efficiency gains require large inputs of fossil fuels and agrochemicals resulting in pres-sures on ecosystems and emissions. Our findings corroborate the argument that HANPP alone cannot – as some-times suggested – be used as a simple measure of carrying capacity. Nevertheless, analyses of long-term HANPPtrajectories in combination with accounts of material and energy flows can provide important insights into thesustainability of land use, thereby helping to understand limits to growth.

© 2012 Elsevier B.V.Open access under CC BY-NC-ND license.

4 HANPP is related to global sustainability issues such as endemic malnourishmentof a large proportion of world population (Erb et al., 2009a; FAO, 2005), the ongoing

1. Introduction

There is a long discussion about the carrying capacity of the earth forhumans; that is, on the question how many people the earth can sup-port (e.g., Cohen, 1995; Martinez-Alier, 1987; Pfaundler, 1902). The‘human appropriation of net primary production’ or HANPP measuresthe combined effect of land use and biomass harvest on the availabilityof trophic energy in ecosystems, thereby providing a measure of thescale of human activities as compared to ecological processes in terres-trial ecosystems (Daly, 1992). Following the influential study ofVitousek et al. (1986), who found that humans globally appropriate al-most 40% of terrestrial NPP, HANPP has often been cited by ecologicaleconomists as a particularly striking example for the limits imposedby environmental constraints on further population or economicgrowth (Costanza et al., 1998; Daly, 1992; Meadows et al., 1992).

The basic ideawas simple: Humans competewith all other heterotro-phic organisms for NPP as their source of trophic energy (Vitousek et al.,1986). So if humans use 40% of the NPP today, the consequences would

x: +43 1 5224000 477.mann).ustria.a, Austria.ien, Austria

ND license.

be dire if that number were to grow to 80 or even 100%, which wouldsoon be the case, given the short doubling times resulting from currentrates of population and GDP growth (Costanza et al., 1998; Meadows etal., 1992). This notion has lost credit, however, largely due to the recogni-tion that the links between population and economic growth are a lot lessstraightforward (see Sagoff, 1995 andDavidson, 2000 for a critical discus-sion). Nevertheless, interest in HANPP has remained vivid. In particular,HANPP has recently gained attention as an indicator capable of linkingnatural to socioeconomic processes and of generating an integrated pic-ture of socio-ecological conditions (Haberl, 1997; Haberl et al., 2007;Imhoff et al., 2004; Krausmann et al., 2009; Wright, 1990) — a majorgoal of sustainability science (Kates et al., 2001; Parris and Kates, 2003).4

During the last decades, the concept of HANPPhas been advanced andproposals for a standardization of definitions and methods have beenmade (Erb et al., 2009b; Haberl et al., 2007; Imhoff et al., 2004). A

conversion of valuable ecosystems (e.g., forests) to infrastructure, cropland or grazingland (FAO, 2004; Foley et al., 2005; Lambin and Geist, 2006; Millennium Ecosystem As-sessment, 2005) with its detrimental consequences for biodiversity (Heywood andWatson, 1995; Loreau, 2002) and global, human-induced alterations of biogeochemicalcycles (Crutzen and Steffen, 2003; Steffen et al., 2004). HANPP can be used to mapland-use intensity (Haberl et al., 2007) and to construct scenarios of possible futurefood and bioenergy supply (Erb et al., 2009a; Haberl et al., 2010).

130 F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

considerable number of empirical case studies on global and regional pat-terns of HANPP have been published (e.g., Erb et al., 2009b; Haberl et al.,2007; O'Neill et al., 2007; Vackár andOrlitová, in press), aswell as severallong-term (decadal to centennial) national time series of HANPP(Kastner, 2009; Kohlheb and Krausmann, 2009; Krausmann, 2001;Musel, 2009; Niedertscheider et al., in press; Schwarzlmüller, 2009).

This paper uses existing case studies for a comparative discussion oflong-term changes in the aboveground HANPP in six countries: Austria,Hungary, the Philippines, SouthAfrica, Spain and theUK.Weaim to betterunderstand the processes that drive long-term changes in HANPP at thenational level and to contribute to a better understanding of how popula-tion and economic growth, changes in biomass use and land-use intensityare related, how they shape themagnitude and spatial pattern of HANPP,and what can be learned about these interactions and about ecologicallimits.We address a number of highly policy-relevant issues, in particularrelated to the suitability ofHANPP to serve as an indicator of sustainabilityand to the question of providing sufficient food, feed,fiber and fuel for thegrowing number of humans on earth in a sustainable manner (Evans,1998; Godfray et al., 2010).

In the next section, we briefly define HANPP and give an overviewof the six national case studies that provided the database for ourcomparative analysis. The following section presents the develop-ment of a number of aggregate indicators derived from HANPP datain the case studies in a comparative manner. This is followed by aDiscussion section that analyzes drivers of the observed trends,focusing on the significance of land-cover change, land-use intensity,biomass use, biomass trade and the ecological costs of improving land-use efficiency. The paper ends with conclusions on the potentials andrisks of further improvements in the HANPP intensity of biomassproduction and an outlook at possible future global developments.

2. Methods and Data

The results of HANPP calculations strongly depend on the respectivedefinition used, and definitions vary considerably between studies (Erbet al., 2009b; Haberl et al., 2004, 2007).We here use data from six studiesthat defined HANPP as the difference between the NPP of potential veg-etation (NPP0) – the vegetation that would prevail in the absence of landuse – andNPPt; that is, the fraction of theNPP that remains in ecosystemsafter harvest (NPPh). NPPact denotes the NPP of the currently prevailingvegetation (Haberl et al., 2004, 2007). The difference between NPPactand NPP0, that is the NPP change resulting from land conversion, isdenoted as ΔNPPLC. Accordingly HANPP can be defined as follows:

(1) HANPP=NPP0−NPPt with(2) NPPt=NPPact−NPPh and(3) ΔNPPLC=NPP0−NPPact

Two processes contribute to HANPP: (1) the change in NPP resultingfrom land conversion (ΔNPPLC) and (2)withdrawal or destruction of bio-mass during harvest (NPPh). We here discuss not only HANPP, but alsoits components, in particular NPPact and NPPh. We only refer to data foraboveground NPP, as data on belowground NPP were not available forall underlying studies.In addition to HANPP and its components, we are also interested inchanges in yields and area-efficiency; that is, in the amount of biomassgained per unit area and year. We define HANPP intensity (HANPPi) asthe HANPP per unit of harvest5:

5 A more comprehensive intensity indicator would be HANPP per unit of used extrac-tion (instead of NPPh which also includes biomass fractions not further used). The shareof used extraction inNPPh varies considerably across countries and over time. In particularin countries with high deforestation rates, the difference between NPPh and used extrac-tion can be large. As not all of the six case studies provide information on used extraction,we had to restrict our comparison to HANPP per unit of NPPh.

(4) HANPPi=HANPP/NPPh.

The inverse of HANPP intensity has been interpreted as ameasure of land use efficiency: If ΔNPPLC is low (it may even be-come negative), most or all HANPP results from harvesting bio-mass (NPPh) which means that little or no productivity potentialis foregone due to land management (Krausmann and Haberl,2007).

We use data from six published case studies which provide com-parable data on the development of aboveground HANPP and its com-ponents over decadal to centennial periods of time. Table 1 gives anoverview of the case studies.

The six countries are quite different with respect to their bio-geographic and socio-economic conditions (Table 1): Austria andHungary are two neighboring central European countries with tem-perate climate. Austria is dominated by the Alps and has a highshare of woodlands. In contrast, Hungary is characterized by fertileplains used for crop production but a more continental climatewith lower average precipitation. The United Kingdom (UK) is situ-ated in north-west Europe. It also has a temperate climate which isfavorable for crop production in its southern part, while large areasin the north are only suitable for extensive grazing. Spain in south-western Europe is characterized by a Mediterranean climate; aver-age annual precipitation is low and large parts of the country areconsidered semi-arid and feature a high share of irrigated cropproduction.

In addition to the industrialized European countries, two non-European countries with much lower income were included. ThePhilippines are an archipelago comprising of over 7000 islands.They are located in the Western Pacific Ocean and have a hotand humid tropical maritime climate. A large share of the landhas been deforested and is used for agriculture. South Africa (ab-breviated RSA for ‘Republic of South Africa’) is the southern-mostcountry of Africa. It is mostly characterized by a subtropical semi-arid climate. Only a small percentage of the land is used for cropproduction.

In contrast to Austria, the United Kingdom and Hungary, wherepopulation grew only modestly in the 20th century, the Philippines,South Africa and Spain experienced high population growth(Table 1). At the turn of the 21st century, only South Africa with apopulation density of 36 inhabitants per km² can be consideredsparsely populated; all other countries are densely populated withpopulation densities above 80 cap/km². South Africa is also the onlycountry with a comparatively low HANPP. The aboveground HANPPof all other countries is far above the global average level of 29% in theyear 2000 (see also Haberl et al., 2007; Krausmann et al., 2009).

The six case studies provide data on aboveground HANPP and re-lated parameters for different periods of time in the 20th century. ForAustria, the UK and the Philippines the data cover a period of time ex-ceeding one century. The studies for Spain, Hungary and South Africacover the second half of the 20th century. We here focus on changesin the 20th century.

All six studies used the basic definition of HANPP outlinedabove. However, there were some differences with respect tothe inclusiveness of the definition of NPPh. Five of the six casestudies (all except the Austrian one) used a comprehensive con-cept of NPPh that includes not only biomass harvested for furthersocioeconomic use (such as crops or timber), but also all biomassdestroyed during the harvest process, even if the biomass is notfurther used by society. Examples of such by-flows are residuesremaining in the field or bark and twigs of felled trees notremoved from the forest. The methods and data sources used toquantify HANPP were also similar in all cases but the Austrianone. These five studies combined statistical data on land use/land cover and biomass harvest with information on actual andpotential productivity derived from a dynamic global vegetation

Table 1Overview of the national HANPP studies used in this paper and socio-economic and bio-geographic characteristics of the six countries. Sources: Population growth and populationdensity are based on Maddison, 2008; GDP per capita in constant 2005 USD and average annual precipitation are from World Bank, 2011; annual temperature means were calcu-lated from Hijmans et al., 2005.

Country Observedperiod

Reference GDP/cap (PPP)2005 [USD/cap/yr]

Population density2005 [cap/km2]

Population growth1910–2005 [%]

Precipitation[mm/yr]

Temperature[°C]

HANPP in the year2000 [% of NPP0]

Austria 1830–1995 Krausmann, 2001 33.377 101 23% 1110 5.6 51%United Kingdom(UK)

1800–2005 Musel, 2009 32.731 249 35% 1220 8.4 68%

Philippines 1910–2003 Kastner, 2009 2.927 295 890% 2348 25.4 62%Spain 1955–2003 Schwarzlmüller, 2009 27.377 80 103% 636 13.1 62%Hungary 1961–2005 Kohlheb and Krausmann,

200916.955 108 26% 589 10.4 71%

South Africa(RSA)

1961–2006 Niedertscheider et al., inpress

8.597 36 616% 495 17.0 21%

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model (LPJ).6 The Austrian study, published much earlier than theother studies, applied a less inclusive definition of NPPh that onlyincluded the extraction of biomass used by society. Moreover, theNPP0 used in this study was based on a simple static productivitycalculation based on temperature and precipitation as well asdominant plant species making up potential vegetation. There-fore, the comparability of the Austrian results is limited, as willbe discussed below.

All data used in this article were taken from original publications(Table 1); in addition, auxiliary data were taken from databases andliterature cited below. In order to enhance comparability, NPP dataare presented as carbon flows per unit area and year (kg C/m2/yr).7

Original data given in dry matter were converted by assuming a Ccontent of dry matter biomass of 50%. Data for Hungary and Austriawere originally presented in Joule gross calorific value (GCV). Thesedata were converted to kg C by assuming an average GCV of18.5 MJ/kg and a carbon content of 50% per kg dry matter (Haberlet al., 2007). In the case of Hungary, the original HANPP calculationdid not include unused crop residues as part of NPPh. To assure con-sistency with the other case studies and to enhance comparability,these flows were extrapolated from data on commercial harvestusing region specific harvest factors from Haberl et al. (2007). This in-creased overall HANPP in Hungary by 15 to 40% compared to the pub-lished data.

Obviously, using only six case studies (four of which are Europeancountries) in order to detect general temporal trends of HANPP can-not lead to comprehensive results valid at the global scale. However,to our knowledge these case studies are the only national long-termstudies of HANPP which have been published so far, and a compara-tive discussion of their results sheds light on very generic temporaltrends visible in all (or most) of the countries investigated. Secondly,despite the strong European bias, the case studies do cover a widearray of biogeographic and economic conditions, allowing for a com-parison of very different framework conditions of HANPP develop-ment during the 20th century.

3. Comparison of National HANPP Trends

Fig. 1 shows the development of HANPP and key components ofHANPP in the six countries. In the UK and the Philippines, HANPP in-creased considerably during the first half of the 20th century (Fig. 1a).It peaked in the 1960s and has since stabilized (Philippines) or even

6 HANPP calculations are based on statistical data on land use, agriculture and forestryharvest and livestock. The quality of these data, thus, is relevant for the robustness of the cal-culated HANPP values. All case studies used national and international data sources of highquality and standardization. Data were cross checked, validated with national experts andin the case of the Philippines also a sensitivity analysis has been performed. It can thereforebe assumed that the general patterns of HANPP across countries and in particular the longterm trends, which this paper is concerned with, are robust.

7 NPP flows such as those in Fig. 1 are presented as national averages: the total na-tional NPP flow divided by the total national land area.

declined (UK). In Spain andHungary, HANPP also declined in the secondhalf of the 20th century. In these four countries, HANPP was high andamounted to 60–70% of NPP0 in the year 2000. In Austria, HANPP wassomewhat lower and comparatively stable throughout the observed pe-riod. South Africa is characterized by a stable, low level of HANPPthroughout the observed period.

Fig. 1b shows that the average productivity of the vegetation(NPPact per unit area and year) slightly declined in the UK and thePhilippines during the first half of the 20th century. Around mid-century, the trend reversed and productivity began to increase.Spain, Hungary and Austria also show substantial increases in NPPactsince the 1960s. In the four decades between 1960 and 2000, growthof NPPact ranged from 12% in Austria to 44% in the UK.

In parallel to NPPact, we find a significant growth in the amount ofbiomass harvested (NPPh). The growth of NPPh in the four decadessince 1960 ranged from 28% in Austria to 54% in Spain. In Hungary,both NPPact and NPPh increased to a very high level in 1989. Withthe collapse of the agricultural production system of the plannedeconomy in Hungary, agricultural productivity and harvest plum-meted. In the decade after the regime change, both parametersshowed strong oscillations. In South Africa, the pattern is quite differ-ent: The level of all flows is much lower than in the other six coun-tries. NPPact declined until 1980 and shows a dramatic peak in 2000that can be explained by climatic anomalies (see below). NPPh grewby 26% in the last 40 years.

With the exceptions of the Philippines, all countries show a con-siderable decline in HANPP intensity (the ratio of HANPP overNPPh) – that is, a growing HANPP efficiency of biomass production.Improvements of aggregate HANPP intensity were largest in Spain,Hungary and the UK, where HANPP intensity in the year 2000 wasaround 40% lower than in 1960 (Fig. 1d). In the UK and Hungary,HANPP intensity even reached a level of one or below one, whichmeans that NPPh roughly equals HANPP and ΔNPPLC is at or belowzero. This is the case when land use does not reduce the land's pro-ductivity compared to the NPP of potential vegetation (NPP0). In thePhilippines, HANPP intensity did not change significantly during the20th century.

4. Discussion

4.1. Comparability of Six Cases

As outlined in the Methods and Data section, all case studies usedthe same general definition of aboveground HANPP, but there weresome deviations in the Austrian case. For Austria, the definition ofNPPh was less inclusive (i.e. only used biomass extraction was con-sidered) and a different, static method was used to estimate NPP0(and therefore also the productivity of forests and natural grass-lands). This less inclusive definition of NPPh results in a substantialunderestimation of NPPh and thus lowers HANPP values. However,we do not believe that this strongly affects the temporal trend of

a) HANPP in % of NPP0

Austria PhillippinesUK SpainHungary RSA

b) NPPact

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Austria PhillippinesUK SpainHungary RSA

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AustriaPhillippinesUKSpainHungaryRSA

d) HANPP intensity (HANPP per unit of NPPh)

kg H

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Ph

AustriaPhillippinesUKSpainHungaryRSA

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Fig. 1. Development of HANPP and its components in Austria, Hungary, the Philippines, South Africa (RSA), Spain and the United Kingdom (UK). (a) HANPP in % of NPP of potentialvegetation (NPP0), (b) NPP of the currently prevailing vegetation (NPPact) in kg C/m2/yr, (c) Harvested NPP (NPPh) in kg C/m2/yr and (d) HANPP intensity (HANPP/NPPh). Sources:Calculated from the studies referenced in Table 1.

132 F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

HANPP and its components. The effect of the use of a static approachto estimate NPP0, as opposed to the LPJ results that consider changesin climate and atmospheric CO2 concentration which are underlyingthe other case studies, is less straightforward. However, becauseNPP0 is not only used as a reference state for calculating aggregateHANPP, but also underlies the calculation of NPPact of forests and nat-ural grasslands, we assume that the general trend should be largelyvalid.

Another issue that requires explicit consideration is the stark in-crease in NPPact in South Africa around the year 2000. This peak is re-lated to unusually strong rainfall in South Africa's drylands duringthat period. After a period of precipitation events above average dur-ing the La Nina period in 1999/2000, biomass productivity in hugeparts of the RSA increased considerably. It is estimated that in severalregions of Southern Africa biomass production rose by around 40%(Anyamba et al., 2002). These patterns during La Nina events weremost significant in the westerns parts of South Africa, the Karoo(Nicholson and Selato, 2000). In any case, the values for South Africaaround the year 2000 have to be interpreted with care.

4.2. What Drives HANPP Trajectories?

At the beginning of the 21st century, the aboveground HANPP wasvery high in four of the six countries. Despite considerable differencesin climate and land use, the aggregate level of HANPP in Spain, Hungary,the UK and the Philippines was similar; that is, within a range of 60%and 70%. Austria's HANPP was a bit lower, but at 50% still far above

the global average. If a more inclusive definition of HANPP had beenused, the Austrian level would have been closer to that of the otherfour densely populated countries. HANPP is much lower in the onlysparsely populated country in our sample, South Africa. This is in linewith a recent cross-country analysis which has shown that populationdensity has a strong effect on a country's level of HANPP. Typically,sparsely populated countries have a low level of HANPP, whereasHANPP is high in countries with high population density (Krausmannet al., 2009).

The HANPP trends (Fig. 1) bear some noteworthy similarities thatmay suggest a general pattern: In two of the three cases for whichcentennial data are available, HANPP increased in the first half ofthe 20th century. This growth came to a halt or was even reversedin the second half of the 20th century. In all six countries, harvest(NPPh) increased substantially in the second half of the 20th century,but HANPP stabilized (Philippines, South Africa) or even declined(all European cases). A comparison of HANPP trends and thedevelopment of GDP per capita (Fig. 2) shows that economic growthis not related to increases in HANPP. GDP is growing in all six coun-tries at an average annual rate between 1.5% (Hungary) and 3.4%(Philippines). In contrast, annual growth rates of HANPP are nega-tive or small and range between−0.1% (Austria, UK) and 0.8% (Phil-ippines). Consequently, HANPP per unit of GDP is falling rapidly in allcountries (Table 2). HANPP behaves similar with respect to popula-tion growth: While it has been shown that there is a strong positivecorrelation between population and biomass harvest as well asbiomass use across countries and over time (Krausmann et al.,

Fig. 2. Development of HANPP in relation to GDP and population. Indexed (1961=1) development of GDP (1990 intl. Geary Khamis $ per capita and year), Population, HANPP (%),HANPP per capita and year and HANPP per $ GDP and year.Sources: Maddison (2008) (GDP and Population) and own calculations (all others).

Table 2Changes of HANPP per capita and year, HANPP per unit of GDP and year and Harvest (NPPh) per capita and year in the periods 1910–1961 and 1961 to 2005. Sources: own calcu-lations based on Maddison (2008) for GDP and population.

HANPP per GDP HANPP per capita Harvest per capita

1910–1961 1961–2005 1910–1961 1961–2005 1910–1961 1961–2005

Austria −51% −71% −51% −15% 20% 12%Philippines −71% −71% −71% −54% −50% −54%UK −56% −64% −56% −15% −16% 32%Spain −84% −29% 19%Hungary −48% −2% 22%RSA −65% −55% −49%

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134 F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

2009; Steinberger et al., 2010), our data indicate that HANPP is notgrowing in line with population (Fig. 2): Population numbers are in-creasing in all cases, but HANPP remains stable or is even declining inthe observed time periods. The only exception is the Philippines,where HANPP is growing in the first half of the 20th century, but at amuch slower pace compared to population. As a result, per capitaHANPP is declining considerably in all countries (Table 2). Biomass har-vest per capita, in contrast, is even increasing in the four Europeancountries (Table 2). This indicates a decoupling of biomass harvestand HANPP. To understand the decoupling of HANPP from economicgrowth and population growth we need to discuss the changes in theland use and biomass production systems that underlie HANPP inmore detail.

An explanation of these perhaps counter-intuitive findings needsto start with the recognition that HANPP measures the combined im-pact of land-use change and biomass harvest on trophic energy avail-able in terrestrial ecosystems (see Methods and Data section). Thesetwo factors directly determine HANPP, but the interrelations betweenthe two factors and their combined effect on HANPP are complex (Erbet al., 2009b; Krausmann et al., 2009). In order to explain the devel-opment of HANPP in the six case studies, we start with a closerlook at the underlying changes in land cover. Table 3 shows the de-velopment of the share of forests and cropland of each country'stotal land area.

As Table 3 shows, forest area increased everywhere except in thePhilippines throughout the observed period. Cropland areas declinedin Austria, continuously increased in the Philippines, and increased inthe first half of the 20th century in the UK, while they decreased inthe second half of the 20th century in all countries except the Philip-pines. The Philippines are the only country with a massive deforesta-tion over the 20th century: forest cover fell from 62% in 1910 to only23% in the year 2000. The shift from agricultural land back to forestsin recent decades has been observed in many now industrializedcountries and is often referred to as ‘forest transition’ (Kauppi et al.,2006; Mather and Fairbairn, 1990; Mather and Needle, 1998;Meyfroidt et al., 2010).

Declining farmland areas and growing forest areas are likely to re-sult in a decline of HANPP because HANPP per unit area is muchhigher on croplands, where aboveground HANPP is mostly above90%, than in forests where HANPP levels are usually far below 40%(Haberl et al., 2007). Moreover, on cropland, the HANPP level perunit area and year is more or less independent of the yield level asNPPact and NPPh usually grow in parallel; that is, increases in plant

Table 3Development of forest land and cropland in the period 1910 to 2000. Data were derivedfrom HANPP studies referenced in Table 1.

1910 1930 1960 1980 2000 Δ1910–1960 Δ1960–2000

[% of total national territory] [% during period]

(a) Share of forest landAustria 40% 41% 42% 44% 47% 5% 13%Hungary n.d. n.d. 14% 17% 19% 33%Philippines 62% 56% 40% 28% 23% −35% −42%RSA n.d. n.d. 8% 8% 8% 5%Spain n.d. n.d. 20% 21% 22% 13%UK 4% 5% 7% 9% 11% 76% 64%

(b) Share of croplandAustria 23% 21% 18% 17% 14% −22% −21%Hungary n.d. n.d. 60% 58% 52% −15%Philippines 12% 19% 26% 33% 32% 114% 23%RSA n.d. n.d. 11% 11% 9% −14%Spain n.d. n.d. 43% 41% 36% −15%UK 25% 24% 30% 29% 27% 19% −10%

n.d. … no data.

growth are largely matched by increases in NPPh (see below). Thegeneral rule of thumb according to which increases in forest land re-sult in decreases of HANPP whereas increases in farmland driveHANPP upwards may not hold, however, in arid regions. In these re-gions, irrigation may lead to a very large increase of NPPact over NPP0and HANPP can even become negative, see for example the maps inHaberl et al. (2007).

When comparing the development in the Philippines to that in theEuropean countries, we also need to consider their differences interms of their respective stage in the socio-ecological transitionfrom agrarian to industrial society (Fischer-Kowalski and Haberl,2007), as well as the extremely strong population growth observedin the Philippines (see Table 1). While the European countries haveall completed their agrarian–industrial transitions, the transition isstill on-going in the Philippines. High levels of HANPP in the Europeancases in the early points in time were a legacy of deforestation pro-cesses that had mostly occurred before our observation periodsstarted (e.g., Bork et al., 2001).

The UK is a special case due to its low initial forest cover in the be-ginning of the 20th century. Despite very strong growth of forest area,HANPP increased in the UK in the first half of the 20th century, drivenby an increase in cropland. In the UK, cropland increased at the ex-pense of grasslands that were used relatively extensively in the be-ginning of the 20th century. The area of cropland grew due to thefood production campaigns of the First, butmost noticeably, the SecondWorldWar, when areas of grasslandwere plowed up for arable cultiva-tion (Martin, 2000; Sieferle et al., 2006).

Perhaps unexpectedly, the expansion of settlement/infrastructureareas into agricultural land, observed in all six case studies (notshown), did not result in HANPP growth, sometimes rather in a re-duction. This can be explained as follows: Soil sealing results in aHANPP of 100%, but settlement and infrastructure areas are usuallyaccompanied by areas such as gardens and parks with an oftenquite high NPPact and mostly low NPPh. These areas are often irrigatedand fertilized. As a result, HANPP on these areas is usually much lowerthan on intensively used croplands. Moreover, infrastructure areasmostly grow at the expense of cropland, and therefore their growthmay even reduce HANPP, at least if the cropland is not shifted some-where else, i.e. if cropland areas are shrinking, as observed in mostcountries.

As shown in Fig. 1c, NPPh grew massively in all six countries. Inparticular in the second half of the 20th century, these increases inharvest did not translate into further increases in HANPP. This waslinked to a surge in average NPPact in the same period (Fig. 1b). As dis-cussed above, the reforestation of agricultural areas with low produc-tivity contributed to some extent to the increases in NPPact thatcounteracted further increases in HANPP. But the growth of NPPacton agricultural land was even more important, as it allowed to greatlyincrease harvests without increasing HANPP. NPPh is related to agri-cultural yields and can therefore be interpreted as an indicator of‘output intensification’ (Lambin et al., 2000).

Agricultural intensification is therefore important for understand-ing HANPP trajectories.

Beginning after World War II, the industrialization of agricul-ture, and the so called ‘green revolution’ in the developing world(Evenson and Gollin, 2003; Tilman, 1998), helped to rapidly in-crease agricultural yields and biomass harvests. Agrochemical in-puts, irrigation and a spatial reorganization of land use allowed formassive increases in the NPP of agricultural ecosystems. Fig. 3shows that fertilizer use per unit of cropland multiplied in all coun-tries in the two decades after 1960 and reached very high levels inthe UK, Austria and Hungary. In these countries, fertilizer consump-tion declined since the 1980s, when pressures from environmentallegislation and economic drivers triggered a more efficient use ofagrochemicals (e.g. Krausmann et al., 2003). The massive declinein Hungary is a result of the collapse state planned agricultural

Fer

tiliz

er u

se [

kg/h

a cr

opla

nd]

AustriaHungaryPhilippinesSouth AfricaSpainUnited Kingdom

-

100

200

300

400

1961

1966

1971

1976

1981

1986

1991

1996

2001

2006

Fig. 3. Mineral fertilizer use (pure nutrient of nitrogen, phosphorus and potassium fer-tilizer) in the six case studies.Source: Own calculations based on IFA (2011) and FAO (2011).

135F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

production system and is also reflected in a drastic decline in NPPhand NPPact (Fig. 1).8

Fertilizer input per unit of agricultural land in the RSA reached amaximum in 1981. The decline in the 1980s was linked to the eco-nomic crisis of Apartheid (trade embargo, disinvestment), which con-siderably impeded agricultural modernization (visible also in a lowNPPh on cropland after 1978). The slowdown of agricultural perfor-mance can be directly related to the removal of governmental subsi-dies as well as to the rising costs for fossil fuels and mineralfertilizers. In Spain and the Philippines, where agricultural industrial-ization progressed at a much slower pace, growth in fertilizer usecontinued to grow and is approaching Central European levels.9 Inarid Spain, irrigation was also an important driver for increases inharvest and NPPact. According to data reported by the FAO (2011)the amount of irrigated cropland in Spain increased from 9 to 22%since 1961.

Fertilization and irrigation result in stark increases in NPPact andNPPh of agricultural areas but hardly affect HANPP on these areas, asthe additional plant growth is subsequently harvested and theamount of NPP remaining in the ecosystem (NPPt) remains approxi-mately at the same level. Moreover, the industrialization of agricul-ture accelerated the shift of agricultural land to forests discussedabove: Capital intensive crop and livestock production systems wereconcentrated on the best farmland and land of marginal productivitywas increasingly taken out of production and became available for re-forestation, a process which has also termed agricultural adjustmentto land quality (see Krausmann, 2006; Mather and Needle 1998). Thiscontributed to the observed increases in average productivity in thefour European countries. Yet another side effect of productivity growthwas the implementation of political measures to prevent overproduc-tion, e.g. subsidies for letting land lie fallow. This land is then not har-vested and thus also contributed to a reduction of HANPP.

The aggregate effect of the changes in land cover and in the inten-sity of land use was the observed stabilization or even a decline inHANPP in the second half of the 20th century in spite of massive in-creases in harvested NPP. Conveyed differently, the stabilization ofHANPP can be seen as a result of considerable reductions of HANPPintensity: The industrialization of agriculture boosted NPPact on culti-vated land and reduced ΔNPPLC. This allowed for reductions of the

8 The high HANPP values in Hungary in the years 1993, 2000 and 2003 are due tostrong fluctuations of NPPact and NPPh related to weather extremes. In these years, se-vere drought periods, often in combination with floods and inland inundation in otherparts of the year, had devastating effects on agricultural harvest. It can also be as-sumed, that after the collapse of the planned agricultural production system was morevulnerable to external effects such as extreme weather events.

9 The high level in the UK is probably to some degree an artifact because fertilizer isalso applied to intensive grassland and not only to cropland in the UK. This is of lesssignificance in Austria and Hungary.

amount of HANPP per unit of harvested biomass. As shown inFig. 1d, HANPP intensity declined considerably in the four industrial-ized countries throughout the second half of the 20th century. InHungary and the UK, two countries with a very high share of croplandor intensively cultivated grassland, average NPPact even surpassedNPP0 and HANPP intensity reached values below one. Only in SouthAfrica and the Philippines we find little evidence of significant reduc-tions in aggregate HANPP intensity. While in South Africa this can beexplained by extensive land use practices, for the Philippines it war-rants a closer look. The apparent lack of improvements in HANPP in-tensity is largely due to the definition of HANPP intensity, whichincludes biomass destroyed/burnt without direct socioeconomic useinto NPPh. Relating total HANPP to biomass extracted for further so-cioeconomic use would be a more comprehensive intensity measure.For the Philippines such a measure shows significant improvementsin HANPP intensity: the value decreased from 8.7 in 1910, over 3.7in 1960, to 2.7 in 2003. These efficiency gains can be mainly explainedby the fact that compared to other ways of biomass appropriation, theuse of fire for land clearing has lost significance during the 20th cen-tury (Kastner, 2009) and consequently HANPP per used biomass ex-traction declined while HANPP per total NPPh did not change much.

The improvements in HANPP intensity in the last decades came,however, at a considerable cost. Irrigation, fertilization and generalintensification of land use not only boosted agricultural output, butthe industrialization of agriculture increased the direct and indirectenergy requirements of agriculture (e.g. mechanization and fertilizeruse/Fig. 3). As a result, the energy return on investment (EROI) of ag-ricultural production systems declined (Krausmann et al., 2003;Pimentel et al., 1990), while greenhouse gas emissions from agricul-ture increased (Smith et al., 2008).10 Intensive agricultural produc-tion also entailed a plethora of environmental pressures: Leachingof plant nutrients into ground and surface water, soil erosion, deple-tion of ground water reserves, release of toxic agrochemicals andmany more (IAASTD, 2009).

Population growth and economic development drive the demandfor biomass. More people need more food, and increasing incomedrives up the consumption of biomass-intensive animal products(Erb et al., 2009a). The substitution of fossil fuels for fuelwood is usuallyoffset by an increase in timber demand during industrial development(Krausmann et al., 2009; Steinberger et al., 2010). Our six case studiesnevertheless suggest that population and economic growth andHANPP are largely decoupled during industrialization (Haberl andKrausmann, 2001). The major underlying factor of this decoupling arethe technological changes in agriculture discussed in the previous sec-tion. Another factor that needs to be taken into account when nationalHANPP trends are discussed, however, is international trade.

4.3. Biomass Trade and Embodied HANPP

The amount of biomass traded internationally is increasing rapidly.At the global scale, biomass exports grew by a factor of 6 from 1961 to2008 and currently amount to 1.6 Gt (Gigatons, 1 Gt=109 t=1 Peta-gram or Pg) of fresh weight per year (FAO, 2011). It has been shownthat biomass trade may considerably decouple domestic biomass con-sumption from domestic HANPP, because HANPP only considers effectson national territory and biomass trade may shift burdens abroad (Erbet al., 2009b). The ‘physical trade balance’ (defined as importsminus ex-ports; Dittrich and Bringezu, 2010) of the six countries included in thisstudy is shown in Fig. 4. According to these data, net biomass importsare large but slightly falling in the UK, increasing in Spain and in the

10 Krausmann (2004), for example, has shown that due to the massive increase in di-rect and indirect energy input the overall energy efficiency of agriculture (ratio of en-ergy output to input) in different Austrian regions declined from 3–6 in the 19thcentury to around 1 in 1995. Cusso et al. (2006) found a similar trend for Spanish casestudies, where the energy efficiency of agriculture fell from 1.7 to 0.2.

net b

iom

ass

trad

e in

kg/

m²/

yrAustria PhillippinesUK SpainHungary RSA

-0.04

-0.02

-

0.02

0.04

0.06

0.08

1961

1966

1971

1976

1981

1986

1991

1996

2001

2006

Fig. 4. Development of net biomass trade from 1961 to 2008 in kg C/m²/yr in the sixcountries. Negative net trade means net exports, positive net imports.Source: Calculated based on FAO (2011).

NPP of potentialvegetation (NPPO)

P a

s %

of N

PP

O

Harvest (NPPh)

136 F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

Philippines, about balanced andmore or less stable in Austria and SouthAfrica, and falling in Hungary. These data suggest that growing importsmay have contributed to the stabilization or decline of HANPP in Spainand the Philippines but rather not in the other four countries.

However, the physical trade balance of biomass does not provide afull picture in the context of HANPP. The reason is that the HANPP re-lated to each unit of traded biomass is strongly dependent on its quality(e.g., grain vs. meat or cheese) as well as on regional differences inyields and conversion efficiencies (Erb et al., 2009b). The measure ofembodied HANPP (eHANPP) has been introduced to correct for suchdistortions (Erb et al., 2009c; Haberl et al., 2009). eHANPP corrects na-tional HANPP for the HANPP embodied in traded biomass products,similar to the ‘virtual water’ concept (Hoekstra andHung, 2005). Unfor-tunately, no eHANPP time series are currently available — at presentthere exists only one global eHANPP dataset for the year 2000 (Erbet al., 2009c). Results for the six countries in our analysis are reportedin Table 4.

As Table 4 shows, eHANPP was almost twice as large as HANPP onnational territory in the UK in the year 2000. This suggests that im-ports play a substantial role in supplying the UK with biomass-based products and are probably quite important for the decouplingbetween population, economic growth and HANPP. In the Austriancase, the eHANPP related to biomass imports is substantial, despitean almost balanced physical trade balance. By contrast, Hungary andSouth Africa are even ‘net exporters’ of eHANPP, i.e. the HANPP ontheir respective territories is larger than the eHANPP related to theproducts consumed in their national economies.

Table 4HANPP on national territory, HANPP embodied in traded biomass, eHANPP (the sum ofHANPP on national territory and HANPP embodied in trade) and the ratio of eHANPP toHANPP for the six countries in the year 2000. Negative values of HANPP embodied intraded biomass indicate net exports. Data source: Erb et al. (2009c).

HANPP onnational territory[1000 t C/yr]

HANPP embodiedin traded biomass[1000 t C/yr]

eHANPP[1000 t C/yr]

RatioeHANPP/HANPP

Austria 22 7 29 1.34Hungary 36 −5 31 0.87Philippines 166 16 181 1.09RSA 184 −15 168 0.92Spain 113 65 177 1.57UK 71 65 136 1.91

5. Conclusions and Outlook

Based on the evaluation of data for six case studies we assume thatHANPP increases with population during early periods of industriali-zation (Fig. 5). When fertile land is abundant, growth in the demandfor food and feed is met by the expansion of agricultural land. This re-sults in deforestation and productive woodlands are replaced by lessproductive agricultural ecosystems. In this phase, population growth(or export production) outgrow any improvements in yields anddrive an increase in HANPP, which can reach high levels of morethan 70%. The industrialization of agriculture changes this trend(Fig. 5). In our case studies massive increases in agricultural yieldsresulted in increases in the NPPact of agricultural ecosystems. Conse-quently growing harvests could be achieved without further increas-ing HANPP, or could even go in parallel with reductions of HANPP.Increasing area productivity reduced the pressure to cultivate landof marginal productivity. Agricultural areas were increasingly takenout of production and reforested, which further contributed to reduc-tions of HANPP. As a consequence, HANPP intensity, that is theamount of HANPP associated with each ton of biomass extraction,declined.

The analysis of six historical case studies has shown that biomassharvest can be decoupled from HANPP. This development may beseen as promising with respect to the forecasted growth of globalpopulation and the corresponding surge in the demand for food,feed and fuel. Indeed, data on national HANPP for 175 countries inthe year 2000 suggest that a considerable share of countries haveland use systems with a high HANPP per unit of biomass extraction(Haberl et al., 2007). In these countries, which are responsible for40% of global HANPP but contribute only 26% of global biomass ex-traction, further improvements in HANPP intensity might be possible.

In spite of such potential efficiency gains, which could help to in-crease global biomass harvest without increasing HANPP, caveatsarewarranted. HANPP is not an all-encompassing indicator of ecologicalpressures resulting from land use and it is not sensible to importantproblem shifts associated with agricultural intensification (cf. Marullet al., 2008). The national case studies have shown that reductions inHANPP intensity result from increased land-use intensity. These in-creases are associated with a reduction of energy efficiency of biomassproduction and considerable ecological costs. The green revolutionwas based on the industrialization of agriculture and entailed a surgein fossil energy and agrochemical inputs. It is clear that further improve-ments in HANPP efficiency are likely to lead to a further increase in

early industrialization

Industrialization of agriculture

NPP of actual

NPP remaining inecosystems (NPPt)

HANPP

NP

P fl

ows

[t/yr

] and

HA

NP

vegetation

Fig. 5. Conceptualization of changes in HANPP and its components during the 20th cen-tury: During early periods of industrialization biomass harvest (NPPh) increased at theexpense of NPP remaining in ecosystems after harvest (NPPt), mostly due to the expan-sion of cultivated areas. This drove increases in HANPP. The industrialization of agricul-ture allowed for increases in harvest by increasing the NPP of the prevailing vegetation.Additional harvest did not result in higher HANPP, but HANPP rather slight reductionsin HANPP can be observed.

137F. Krausmann et al. / Ecological Economics 77 (2012) 129–138

agricultural inputs and aggravate environmental pressures, at least ifthey are based on the currently predominant technologies.

Our analysis of long-term trends of HANPP from six national casestudies indicates that the ecological concept of carrying capacity can-not be applied to human societies in a straightforward manner, atleast since the Neolithic revolution. By means of technology, humansare able to drastically increase the capacity of terrestrial ecosystemsto supply food and fuel for human use and to decouple human popu-lation and economic growth fromHANPP. This does, however, notmeanthat there are no limits for growth. Expanding the capacity of the earthto provide human society with biomass comes at considerable ecologi-cal costs and the long term sustainability of the achieved gains inHANPP efficiency is questionable. An analysis of HANPP and related pa-rameters can help to better understand the dynamic relation of popula-tion and resource use and the processes involved in these transitions.

Acknowledgments

This work has been funded by the Austrian Science Funds (projectsP20812-G11 and P21012-G11) and by the EU-FP7 project VOLANTE. Itcontributes to the Global Land Project (www.globallandproject.org).

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