Quantifying and mapping the human appropriation of net primary production in earth���s terrestrial ecosystems Helmut Haberl*���, K. Heinz Erb*, Fridolin Krausmann*, Veronika Gaube*, Alberte Bondeau���, Christoph Plutzar��, Simone Gingrich*, Wolfgang Lucht���, and Marina Fischer-Kowalski* *Institute of Social Ecology, Klagenfurt University, Schottenfeldgasse 29, 1070 Vienna, Austria ���Potsdam Institute for Climate Impact Research, P.O. Box 601203, 14412 Potsdam, Germany and ��Vienna Institute for Nature Conservation and Analyses, Giessergasse 6/7, 1090 Vienna, Austria Communicated by Hans Joachim Schellnhuber, Potsdam Institute for Climate Impact Research, Potsdam, Germany, May 25, 2007 (received for review June 5, 2006) Human appropriation of net primary production (HANPP), the aggregate impact of land use on biomass available each year in ecosystems, is a prominent measure of the human domination of the biosphere. We present a comprehensive assessment of global HANPP based on vegetation modeling, agricultural and forestry statistics, and geographical information systems data on land use, land cover, and soil degradation that localizes human impact on ecosystems. We found an aggregate global HANPP value of 15.6 Pg C/yr or 23.8% of potential net primary productivity, of which 53% was contributed by harvest, 40% by land-use-induced productivity changes, and 7% by human-induced fires. This is a remarkable impact on the biosphere caused by just one species. We present maps quantifying human-induced changes in trophic energy flows in ecosystems that illustrate spatial patterns in the human domi- nation of ecosystems, thus emphasizing land use as a pervasive factor of global importance. Land use transforms earth���s terrestrial surface, resulting in changes in biogeochemical cycles and in the ability of ecosystems to deliver services critical to human well being. The results suggest that large-scale schemes to substitute biomass for fossil fuels should be viewed cautiously because massive additional pressures on ecosystems might result from increased biomass harvest. biomass global environmental change human impact biosphere land use Ma aterial flows resulting from human activities have become major component of earth���s biogeochemical cycles (1). Human alterations of photosynthetic production in ecosystems and the harvest of products of photosynthesis, often referred to as ������human appropriation of net primary production (NPP)������ or HANPP, have received considerable attention (2���4). NPP is the net amount of carbon assimilated in a given period by vegetation. It determines the amount of energy available for transfer from plants to other levels in the trophic webs in ecosystems. HANPP not only reduces the amount of energy available to other species (2), it also influences biodiversity (5���8), water flows (9), carbon flows between vegetation and atmosphere (10, 11), energy flows within food webs (12), and the provision of ecosystem services (13, 14). Previous studies of NPP harvested to satisfy human needs and wants or foregone because of human-induced changes in eco- system productivity suggested a substantial human impact on the biosphere, thus raising global sustainability concerns (15, 16). Existing global HANPP studies do not make full use of the spatially explicit databases available (12), and their results are quite diverse (2, 5, 16, 17). The estimate presented here is based on the best available global databases and integrates them in a high-resolution geographical information systems (GIS) data set. These data, in combination with a dynamic global vegetation model (DGVM), are used to derive a comprehensive assessment of global HANPP. This study localizes human-induced changes in ecosystems in a grid with 5 geographical resolution ( 10 10 km at the equator) for the year 2000. HANPP results presented here are based on country-level Food and Agriculture Organization (FAO) statistics (161 coun- tries covering 97.4% of global land) on area and biomass harvest on cropland and forests. FAO livestock statistics are used to derive a feed balance for each of these countries to calculate the amount of biomass grazed that is not reported in statistics. Potential NPP is calculated by using the Lund���Potsdam���Jena (LPJ) DGVM (18, 19), a well established biogeochemical pro- cess model of global vegetation. Actual NPP is calculated by using harvest indices to extrapolate NPP on cropland from harvest statistics, whereas LPJ is used in wilderness areas, forests, and grazing areas. On grazing areas, the effects of fertilization, irrigation, and soil degradation on NPP are explic- itly included in the estimate and results are cross-checked against grazing demand. NPP consumed in human-induced fires is calculated in a detailed regional breakdown. Results of HANPP calculations vitally depend on the defini- tion used (2, 20, 21). We define HANPP as the combined effect of harvest and productivity changes induced by land use on the availability of NPP in ecosystems. That is, HANPP is calculated as the difference between the NPP of potential vegetation (NPP0), i.e., the plant cover that would prevail in the absence of human intervention and the fraction of NPP remaining in ecosystems after harvest (NPPt). NPPt is calculated by subtract- ing the amount of NPP harvested or destroyed during harvest (NPPh) from the NPP of currently prevailing vegetation (NPPact) (5, 6). HANPP, thus, is the sum of NPPLC and NPPh, where NPPLC denotes the impact on NPP of human-induced land conversions, such as land cover change, land use change, and soil degradation. One major argument in favor of this HANPP definition is that changes in agricultural technology can result in considerable increases in NPPact over time (22, 23). Harvest increases need Author contributions: H.H., K.H.E., F.K., V.G., and M.F.-K. designed research H.H., K.H.E., F.K., V.G., A.B., C.P., S.G., and W.L. performed research K.H.E., F.K., V.G., A.B., C.P., and S.G. analyzed data and H.H., K.H.E., F.K., W.L., and M.F.-K. wrote the paper. Conflict of interest statement: A.B. and W.L. are employed by the Potsdam Institute for Climate Impact Research, of which H.J.S. is a director. However, H.J.S. was not involved in the work submitted and has formed an independent opinion based on the manuscript submitted. Freely available online through the PNAS open access option. Abbreviations: HANPP, human appropriation of net primary production NPPn, net primary production of n DGVM, dynamic global vegetation model LPJ, Lund���Potsdam���Jena TBFRA, Temperate and Boreal Forest Resources Assessment. See Commentary on page 12585. ���To whom correspondence should be addressed. E-mail: helmut.haberl@uni-klu.ac.at. This article contains supporting information online at www.pnas.org/cgi/content/full/ 0704243104/DC1. �� 2007 by The National Academy of Sciences of the USA 12942���12947 PNAS July 31, 2007 vol. 104 no. 31 www.pnas.org cgi doi 10.1073 pnas.0704243104

therefore not necessarily result in a reduction in NPPt. Thus, it is important to consider NPPLC so as not to neglect techno- logical progress (24). Moreover, we prefer a not-too-inclusive definition of HANPP, in accordance with the fact that a considerable fraction of the NPP of grazing land and forest plantations actually remains in the ecosystem and supplies trophic energy to ecological food webs there. To explore the importance of issues of definition, we use our database to calculate HANPP according to the definition given by Vitousek et al. (2) and compare the results to those obtained with the definition used here. Results Human activities have a substantial effect on global NPP and its pathways through ecological and social systems. Our calculations show (Table 1) that humans appropriated 15.6 Pg C/yr, which represents 23.8% of global terrestrial NPP0 in the year 2000. Because humans mostly use aboveground NPP, it is relevant from a socioeconomic perspective to consider this compartment. Here, we find an even stronger impact: aboveground HANPP amounted to 10.2 Pg C/yr or 28.8% of aboveground NPP0. Overall, biomass harvest contributed 53% to total HANPP, land-use-induced productivity changes contributed 40%, and human-induced fires contributed 7%. A considerable amount of biomass included in NPPh (16% of total HANPP or 3.7% of NPP0) immediately flows back to ecosystems as roots killed during harvest, crop and wood residues remaining on site, or as feces of grazing animals and is, thus, only available for detri- tivorous food chains. Human biomass harvest alone is 12% of total NPP0 and 20% of aboveground NPP0. We find significant alterations in NPP resulting from human- induced land changes ( NPPLC). As shown in Table 1, land use has resulted in an aggregate reduction of global NPP by 9.6%, with large regional variations shown in Fig. 1a. Land use does not necessarily reduce NPP. Irrigated land as well as intensively used agricultural areas can have a higher productivity than the potential vegetation. The spatial distribution of total HANPP is shown in Fig. 1b as the percentage of NPP0 appropriated in each grid cell. Maps of NPP0, NPPact, NPPt, and HANPP in absolute units (g C/m2/yr) are available as supporting information (SI) Figs. 2���5. The maps presented in Fig. 1 show where on earth, and how strongly, humans alter ecological energy flows, thus localizing the intensity of human domination of ecosystems. Cropland and infrastructure areas are used most intensively, resulting in global average HANPP values on these areas of 83% and 73% (Table 2). HANPP is much lower on grazing land (19%) and in forestry (7%). In the global average, areas currently under forestry are Table 1. Global carbon flows related to the human appropriation of net primary production (HANPP) around the year 2000 NPP-related carbon flows Total NPP Aboveground NPP Pg C/yr % Pg C/yr % Potential vegetation (NPP0) 65.51 100.0 35.38 100.0 Actual vegetation (NPPact) 59.22 90.4 33.54 94.8 Human-induced alteration of NPP ( NPPLC) 6.29 9.6 1.84 5.2 Human harvest (NPPh) 8.18 12.5 7.22 20.4 Human-induced fires 1.14 1.7 1.14 3.2 Remaining in ecosystem (NPPt) 49.90 76.2 25.18 71.2 HANPPtotal 15.60 23.8 10.20 28.8 Backflows to nature* 2.46 3.7 1.50 4.2 *On-site backflows of harvested biomass to ecosystems, i.e., unused residues, harvest losses, feces of grazing animals, and roots killed during harvest. Fig. 1. Maps of the human appropriation of net primary production (HANPP), excluding human-induced fires. (a) Land-use-induced reductions in NPP as a percentage of NPP0. (b) Total HANPP as a percentage of NPP0. Blue (negative values) indicates increases of NPPact (a) or NPPt (b) over NPP0, green and yellow indicate low HANPP, and red to dark colors indicate medium to high HANPP. Haberl et al. PNAS July 31, 2007 vol. 104 no. 31 12943 SUSTAINABILITY SCIENCE SEE COMMENTARY