Global Land Resources & Population Supporting Capacity
Hari Eswaran1, Fred Beinroth2, and Paul Reich1
1USDA Natural Resources Conservation Service, Washington DC and
2Department of Agronomy and Soils, University of Puerto Rico, Mayaguez, PR.
Anticipated advances in biotechnology and sustainable land management in combination with the availability of high quality lands suggests a level of food production that will sustain twice the current global population. However, lack of political will, insufficient investments in modern agriculture, and a general apathy to the tenets of sustainable land management threaten food security in Third World countries and in some, contribute to poverty and famine. From a global land-productivity point of view the specter of Malthusian scenarios seems unwarranted. Sadly, however, local and regional food shortages are likely to continue to occur unless mechanisms for equitable food distribution, effective technical assistance and infusions of capital for infrastructure development are implemented in some developing countries.
Keywords: Land resource quality, land resource stress, food security
Published in: Eswaran, H., F. Beinroth, and P. Reich. 1999. Global land resources and population supporting capacity. Am. J. Alternative Agric. 14:129-136.
There are many debates concerning the quality and quantity of natural resources required for sustaining human life (Durning, 1989, Durham, 1992). Perceptions of an acceptable quality of life determine the range of opinions. The world population is currently about 6 billion people of which about 2 billion are malnourished and an equal number live below the poverty level. The latter two categories include socially or economically disadvantaged people who eke out a living from a plot of land that in many cases does not belong to them. As pressure for land increases, these land-less groups move to more fragile ecosystems, often permanently destroying them to survive (Stewart et al., 1990). This group of land users is not amenable to modern conservation practices or technologies, is not receptive to or is unable to practice sustainable technologies, and in general does not contribute to the food and fiber needs of society as a whole. In many countries, this group is comprised of the forgotten persons, ignored by the bureaucracy and disowned by the affluent of the nation. However, in their struggle to survive, their long-term impact on soil resources and environment in general may be so detrimental that in reality they may control the quality of life of a nation as a whole (Eswaran et al., 1995). Pimentel et al. (1994) posed the question, "Does human society want 10 to 15 billion humans living in poverty and malnourishment or 1 to 2 billion living with abundant resources and a quality environment?" This reflects the opinion of other supporters of the Malthusian concept (Ehrlich et al., 1993; Brown, 1994) and suggests that the limits of the land resource are being reached. We already have exceeded the second option three fold. Our question today is, how many more people can the earth's land resources support so that most persons can enjoy an acceptable quality of life?
There have been several assessments of the population supporting capacity of earth. According to Buringh (1989) between 11 to 12 % of the land surface is generally suitable for food and fiber production, 24 % is used for grazing, forests occupy about 31 % and the remaining 33 % has too many constraints for most uses. A more recent assessment by the Food and Agriculture Organization (FAO, 1995) provides similar estimates. Lal (1989) estimates that to sustain the human population at an acceptable level, about 0.5 ha of cropland per capita is needed. Others also have used per capita land as an index of sustainability, food security, or carrying capacity. Generally, total land area is used, and this results in erroneous or misleading conclusions. Per capita arable land is a better indicator, and the reciprocal of this number is an estimate of the carrying capacity. The index that is sought should reflect the ability of a unit of land to support a number of persons, and in this paper, the term carrying capacity is used in this sense.
The oft-repeated challenge is to find means to feed and clothe the population without degrading the land and water resources. A first step is to obtain a better estimate of the quality of land resources and the population supporting capacity of this resource base. In the absence of reliable national resource inventories for most countries of the world coupled with less information on the quality of the resource base, it is inevitable to use available information, such as global level data, to make regional or national assessments.
The impetus for this study resulted from the conclusion of a meeting (Greenland et al. 1998) on "Land Resources: On the Edge of the Malthusian Precipice?" The concluding report indicates that, "if all the resources are harnessed and adequate measures taken to minimize soil degradation, sufficient food to feed the population in 2020 can be produced, and probably sufficient for a few billion more." We decided to evaluate the quality of global land resources and attempt to estimate the population supporting capacity. Interaction with other resources or other aspects of human needs are not considered in this preliminary appraisal. Previous attempts to answer this question have been limited by the absence of reliable databases and spatial analysis technology such as Geographic Information Systems. The purpose of this paper is to make an assessment of population supporting capacity based only on land area stratified by productive potential. It should be considered as a first step in the process towards a better assessment that provides for land degradation, changes in dietary patterns, contributions of technology, and energy inputs in agriculture. The present analysis is based on better databases that have become available recently and hence, unlike previous estimates, is more science-based.
Each country has land of differing capabilities determined by the quality of the soil and its performance under the prevailing climate. The Food and Agriculture Organization Database (FAO, 1997; WRI, 1997) provides country assessments on quantity of arable land and other indicators for national and global assessments. Until recently, databases that provide such information were not readily available or accessible in a digital format. The FAO/UNESCO Soil Map of the World (FAO, 1971-1981), which is now digitally available (FAO, 1991), provides for the first time a digital database of global soil resources. The authors compiled a global climate database, comprising data from about 25,000 stations, and, using a water-balance model, the soil moisture and temperature regimes were computed. Using GIS, the soil climate information was overlaid on the soil map.
The combination of soil and climate information was used to empirically assign the derived polygons (Wang et al., 1990) to one of 25 major land resource stress classes (details of the method will be published by Eswaran et al., 1999). Knowing the properties of the soils and the major stresses they experience, nine land quality classes are created using the matrix in Table 1. As management inputs are not considered, these reflect the inherent land quality. Table 2 explains the terms, and Table 3 elaborates on the 9 classes.
This is a universal classification and several assumptions were made:
Some, such as Smil (1987), have argued that a country with less than 0.07 ha of arable land per person cannot feed its population in the absence of very intensive agriculture. This is equivalent to a population supporting capacity of about 14 persons per ha of land, which itself is perhaps an unrealistically high number. The energy inputs required to produce at this level would be excessively high for any meaningful output. There are countries, which have per capita land numerically close to 0.07, however, this does not imply that their agriculture is designed to support 14 or more persons. Nevertheless, the 0.07 ha estimate is now used by United Nations organizations as a threshold mark for evaluating the land’s carrying capacity.
From the global soil map and soil climate GIS information used in this study, about 38.5 million km2 or 29.45% of the earth’s ice-free land surface is too dry for sustainable human habitation (Beinroth et al., 1994). Advanced water and energy supply and irrigation techniques have enabled some use of these arid lands. About 20.2 million km2 or (15.46%) of the land occur in the cold tundra zone, which are not easily amenable to normal agriculture. Most of these lands are included in the land quality Classes VIII and IX. There are other constraints, which prevent the use of soils for agriculture. Saline and alkaline soils, for example, occupy 3,105,000 km2 or 2.4% of the land surface, and soil acidity affects 18,420,100 km2 or 14.1% of the total land (Eswaran et al. 1997a). There are sloping lands, sandy soils, soils with low water and/or nutrient-holding capacity, soils with high organic matter (peats), etc. Some limitations are considered permanent or cannot be corrected by low to medium level inputs and in general, such soils are included in Classes VII, VIII, and IX. In the other classes, the limitations can normally be corrected; Class I land has the fewest number of constraints for agricultural use.
The global distribution of the tundra (Class IX) and the deserts (Class VIII) are shown in Figure 1. Many soils in desert regions are irrigated but these are considered unsustainable. The contiguous areas of prime lands (Class I) in the world are in the United States, Argentina, Uruguay, and southern Brazil. Large areas are also present in Europe and in northern China. In Africa, only South Africa has a significant amount of Class I land. By definition, such lands are absent in the tropics, which explains the general low productivity of tropical soils. Class II and III lands are extensive in the tropics and in the temperate areas. Most of these lands are under some form of agriculture and irrigated, when possible, in the semi-arid parts. A major part of Class IV, V, and VI lands, particularly the Class V lands are in the tropics. In the Amazon basin, Central Africa, and in South East Asia, these form the large tracts of forests. Land clearing and shifting cultivation is gradually invading these regions. Use of these lands for low-input agriculture promotes land degradation and even desertification. As is evident in the map, countries with large areas of Class IV or poorer quality lands have few alternatives but to exploit them. With medium and high input levels, they can be managed and are productive (Buol and Eswaran, 1994). From the point of view of ecosystem integrity there is an obligation for the more fortunate countries to help in the wise use of the fragile lands of the poorer countries.
Only a few countries implement science-based land use planning. The former Soviet countries and other centrally managed economies developed good land use systems, as exemplified by Albania. In Albania, the flat valley bottoms were reserved for agriculture, the lower hill-slopes for housing and infrastructure, and the steeper hilly terrain for forestry. The land productivity was low, however, due to absence of inputs or poor management. With democratization and removal of societal controls, misuse of land is now the rule. In the more liberal societies, economic forces (constrained to some extent by zonation laws and ownership rights) frequently drive land use, which results in haphazard development of land exploited for agriculture. In the developing countries of the latter group, land-less people have been forced to exploit fragile agro-ecosystems.
Mismanagement of land and misuse of fragile lands have prompted global inquiries on the extent of degraded land. Oldeman et al. (1991) suggest that about 17 % of the global land area is degraded by human interventions. The consequences of land degradation not only affect the performance of the land for food and fiber production but also have grave consequences for the environment including biodiversity. Another resource, not addressed in the present assessment is water, which is closely related to the production potential of land. Water constraints are already slowing food production in some countries of the world. The 2.4 million km2 of global irrigated land have been largely responsible for meeting the food needs of the burgeoning population. Some countries, such as India and Pakistan, rely heavily on irrigated lands to meet a major part of their respective requirements. Also many countries have reached or are nearing the limits of the land that can be irrigated due to lack or scarcity of water, costs of infrastructure development, environmental concerns, and the rapid rates of salinization of irrigated lands.
The area of land in each Land Quality Class is given in table 4. Class I land only occupies about 3.1 % of the ice-free land surface. Together with Class II and III lands, the 12.6 % of land represent the total land area that is generally free of constraints for most agricultural uses. They are, however, unequally spread around the globe with a larger portion in the temperate countries of the world. Class I and II lands generally have good resilience, are highly productive, and benefit from conservation technologies that are directed to preserving the favorable attributes. Many countries have very small areas of either Class I or II lands, or have utilized all available I, II, and III lands and consequently have to use more inferior lands.
Class IV, V, and VI land occupy a significant part of the earth’s surface (36.8 million km2) and also support more than 50% of the world’s population. In the tropics, such as in parts of Asia, these are also the lands that approach the threshold of 0.07 hectares per person per capita land. At low levels of input, though their performance is low, adequate supply is still possible, as there is a large area of such lands. However, degradation of the resource base will slowly reduce its capacity unless additional land management practices such as agroforestry (Sanchez et al., 1998) are introduced.
Because of population pressures and the desire to provide land for the land-less, countries consciously use poorer quality lands to achieve regional equity within the country. Where irrigation could be established, some Class VIII lands have been brought under agriculture, particularly in North Africa and the Near East. Actual land use is not estimated in this assessment. In fact, from a sustainable agriculture point of view, Classes IX, VIII, and VII are not recommended for agriculture, though small areas may currently be used. Table 4 also provides the cumulative percentages of land from Class I through VI. These percentages provide an estimate of the land as they are successively consumed.
Fischer and Heilig (1998) estimate that the available land area with some potential for rainfed crop cultivation is about 5.55 million km2 in developing countries. They do not provide an estimate for global land area available for cultivation. In our estimate (Table 4) the total global land area suitable for cultivation is 60.2 million km2. WRI (1997) estimates that about 49.77 million km2 were under cultivation (or 'domesticated land' as they refer to) in 1995. This suggests that the amount of available land, globally, for future cultivation is only about 10 million km2 some of which must be shared with forestry, wilderness and for urban use. Thus the amount of land available for agricultural use is expected to correspond to the estimate of Fischer and Heilig (1998).
Land has been and will continue to be used for purposes including forestry, recreation, and urban needs. Ideally, partitioning land for its multiple uses should be based on societal values and economic considerations. Table 5 is an empirical partitioning of land based on its quality and its potential uses. There is always strong competition for land for its multiple uses and usually economic factors determine the final land use. In societies with strong social commitments, the economic forces are frequently required to compromise or look for other options. In many parts of the world, Class I land is under siege and the rate of consumption for non-agricultural uses is very high. Globally, about 50% of Class I land may still be used for agriculture. Based on the amount of land used for grain crop production (Table 5), the population supporting capacity is discounted proportionately. The adjusted population supporting capacity is shown in Table 6. Class I and II lands together would be able to support about 9 billion persons.
The optimal population supporting capacity of each land quality class is shown in Table 6. The optimal proportions for each of the land use classes will vary with the country and determined by the socioeconomic demands. However, if environmental considerations and biodiversity, as expounded by Szaro and Johnston (1996) are emphasized, then one has to provide for these aspects of humanity. The values in Table 6 are empirically derived but based on expert judgement on the productivity of soils and other considerations. The idealized population supporting capacity for each land quality class in Table 6 is the best estimate at this time and is derived from estimates of per capita arable land and gross domestic product (GDP), using data cited by WRI (1997) and relating these to the general land quality. The per capita arable land is an estimate of intensity of land use and the per capita GDP was used as an estimate of levels of input. Countries were assigned to one of the three levels of inputs of FAO (1976) using a GDP of < $1,000 to indicate low levels of input, $1,000 to 10,000 a medium level and >$10,000 a high level of input. In the absence of land resource specific data, these proxies provide the basis for assessment. The quality of such an assessment becomes enhanced with better databases, which may not be forthcoming in the next few decades particularly in developing countries. The adjusted population supporting capacity is then calculated using the empirical proportions of agricultural lands in Table 5.
Table 7 provides the final estimates. Land quality classes VII, VIII, and IX are excluded, as they are considered unsustainable to attempt to use these lands for grain crop production. Irrigation of deserts is also ignored in this study. Class I, II, and III lands together, would be able to support about 3.2 billion persons under a low-input scenario and about 4.6 billion persons under a medium-input scenario. Most of these lands are in the part of the world with a temperate climate. Land quality classes V and VI are the most extensive of the nine classes. They occupy large areas in the tropics but their contribution to the total population supporting capacity is low. Classes I to VI land cumulatively can support about 6.2 billion people, which is close to the current world population, under low-input technologies. With medium input technologies, this increases to about 8.7 billion persons. Uniform high-level technology input across the globe will not materialize in the next millenium. Thus, the realistic level is an intermediary situation between the medium- to high-level input in Table 7. This suggests that it would not be unrealistic to expect the global land resources of being able to support a population between 9 to 20 billion persons. There will be an adequate supply of grains to feed the 9 billion persons who will inhabit the earth in the year 2025; this does not imply that all will be fed.
Other refinements can be made in this process of evaluating the population supporting capacity of global land resources. Degradation state and levels of technology in different countries were not considered in this assessment. Country level estimates, which will be made in a follow-up study, will include some aspects of these additional controls of population supporting capacity.
Land is a limiting resource in many countries, particularly considering the fact that there are only about 5 million km2 available for future sustainable land use. With time the situation will worsen due to soil degradation, which reduces the performance of the soil. Exponential growth of urban centers consumes large areas of prime land as the centers originally developed on lands that had potential to feed the community. Those countries, which have opted for large scale irrigation programs to complement their food producing capacity, are generally at risk due to salinization and or alkalization which slowly but surely accompany irrigation in arid and semiarid environments. In the drier countries of the world, supply of water may become a limiting factor before the inability of the land to produce is felt (Postel, 1989). Waterways traversing nations, or even states as in India, become sources for conflict when limits of the resource are reached. Further, the increasing requirements of non-agricultural water use will inflate prices, resulting in stringent irrigation policies that will be reflected in efficiencies of production. Inadequacies or inefficiencies of irrigation (World Bank/UNDP, 1990) continuously reduce the effective amount of land that can be used for food production.
The land resources provide about 96% of world food, and the remaining food comes from rivers, lakes, and seas (Pimental and Hall, 1989). For the global land resource to continue to produce and feed and clothe the population, using only the bare minimum of land for this purpose, a number of conditions must be in place:
From a global land-productivity point of view the spectre of Malthusian scenarios seems unwarranted. Sadly, however, local and regional food shortages, particularly in Asia, are likely to continue to occur and the population succumb to Malthus’ nightmare (Malthus, 1798) unless mechanisms for equitable food distribution, effective technical assistance and infusions of capital for research and infrastructure development are implemented (Swaminathan, 1986). The current trend of the globalization of the world economy and international agreements such as the Global Agreement on Trade and Tariff offer some hope that global food security can be achieved. This initial assessment, at least from the distribution of land resources, supports the earlier study of Eswaran et al. (1997b) that many countries in Africa have the potential to be food exporters if the systems are permitted to do so.
The conclusion of this study is that famine and starvation of people of some countries are not the result of the innate inability of global land resources to produce the necessary food but because of an absence of political will in most countries. In most cases, poverty, starvation, and famine are generally due to inadequate natural resource endowments and the lack of capital to mitigate these constraints. Endemic poverty or inability to feed the increasing population occurs mostly in those countries where the poor quality of land prevents even a subsistence form of agriculture. Knowing the ability of each country will help the development of appropriate strategic plans by both the countries themselves and also the global community. Such studies will also help countries develop land use plans that are environmentally sound and also enable international donors to mount a strategic program to ensure food security in all nations.
Beinroth, F.H., H. Eswaran, P.F. Reich, and E. Van den Berg. 1994. Land related stresses in agroecosystems. In: (Eds. Virmani, S.M., J.C. Katyal, H. Eswaran, I.P. Abrol) Stressed Ecosystems and Sustainable Agriculture. Oxford & IBH Publ. Co. New Delhi, India. 131-148.
Brown, L.R. 1994. Facing food security. In: L.R. Brown, C. Flavin, and S. Postel. (Eds.) State of the World. Earthscan Publ. London.
Buringh, P. 1989. Availability of agricultural land for crops and livestock production. In: L. D. Pimental and C.W. Hall (eds.) Food and Natural Resources. Academic Press, San Diego. 69-83.
Buol, S.W. and H. Eswaran. 1994. Assessment and conquest of poor soils. In (Ed. J.W. Maranville, V.C. Baligar, R.R. Duncan, and J.M. Yohe.) "Adaptation of plants to soil stresses". INTSORMIL Publication 94-2, Univ. of Nebraska, Lincoln, NE. 17-27.
Durham, D.F. 1992. Cultural carrying capacity. Focus. 2:5-8.
Durning, A.B. 1989. Poverty and the environment: Reversing the downward spiral. Worldwatch Institute, Washington DC.
Ehrlich, P.R., A.H. Ehrlich, and G.C. Daily. 1993. Food security, population, and the environment. Population Dev. Res. 19:1-32.
Eswaran, H., S.M. Virmani, and I.P. Abrol. 1995. Issues and challenges of dryland agriculture in Southern Asia. In: (Eds. A.S.R. Juo and R.D. Freed. Agriculture and the Environment: Bridging Food Production and Environmental Protection in Developing Countries). ASA Special Publication No. 60. American Society of Agronomy, Madison WI. 161-180.
Eswaran, H., P. Reich, and F.H. Beinroth. 1997a. Global distribution of soils with acidity. In: Moniz, A.Z., A.M.C. Furlani, R.E. Schaffert, N.K. Fageria, C.A. Rosolem, and H. Cantarella. "Plant-Soil Interactions at Low pH: Sustainable Agriculture and Forestry Production". Proc. 4th. Inter. Symp. On Plant-Soil Interactions at Low pH, Belo Horizonte, Minas Gerais, Brazil, 159-164.
Eswaran, H., R. Almaraz, P. Reich, and P. Zdruli. 1997b. Soil quality and soil productivity in Africa. J. Sustainable Agric. 10:75-94.
Eswaran, H., R.W. Arnold, F.H. Beinroth, and P.F. Reich. 1999. A global assessment of land quality. In preparation.
FAO. 1971-1981. FAO/UNESCO Soil Map of the World, 1:5 million. Vols. 1-10. FAO/UNESCO, Rome, Italy.
FAO. 1976. A framework for land evaluation. FAO Soils Bulletin No. 32. Rome, Italy: FAO, 72 pp.
FAO. 1991. The digitized Soil Map of the World. World Soil Resources Report 67/1 (Release 1.0), Food and Agricultural Organization, Rome.
FAO. 1995. Agriculture towards the year 2010. Food and Agriculture Organization of the United Nations, Rome, Italy.
FAO. 1997. FAO Production Yearbook. Rome, Italy.
Fischer, G., and G.K. Heilig. 1998. Population momentum and the demand on land and water resources. In: Greenland, D.J., P.J. Gregory, and P.H. Nye. 1998. (Eds.) Land Resources: On the Edge of the Malthusian Precipice? CAB International, New York. 8-29.
Greenland, D.J., and I. Szabolc. 1994. (Eds.) Soil Resilience and Sustainable Land Use. CAB International, Wallingford, UK.
Greenland, D.J., P.J. Gregory, and P.H. Nye. 1998. (Eds.) Land Resources: On the Edge of the Malthusian Precipice? CAB International, New York. 180 pp.
Lal, R. 1989. Land degradation and its impact on food and other resources. In: D. Pimental and C.W. Hall (eds.) Food and Natural Resources. Academic Press, San Diego. 65-68.
Oldeman, L.R., R.T.A. Hakkeling, and W.G. Sombroek. 1991. World map of the status of human-induced soil degradation: an explanatory note. Wageningen, Netherlands: International Soil Information and Reference Centre. 34 pp.
Malthus, T.R. 1798. An Essay on the Principle of Population as it Effects the Future Impairment of Society. St. Paul’s Churchyard, London.
Pimental, D., and C.W. Hall. 1989. Food and Natural Resources. Academic Press, San Diego, USA.
Pimental, D., R. Harman, M. Pacenza, J. Pecarsky, and M. Pimental. 1994. Natural resources and an optimum human population. Population and environment, 15:347-369.
Postel, S. 1989. Water for agriculture: facing the limit. Worldwatch Paper No. 93, Worldwatch Institute, Washington DC.
Sanchez, P.A., R.J. Buresh, and R.R.B. Leakey. 1998. Trees, soils, and food security. In: Greenland, D.J., P.J. Gregory, and P.H. Nye. 1998. (Eds.) Land Resources: On the Edge of the Malthusian Precipice? CAB International, New York. 89-101.
Smil, V. 1987. Energy, Food, Environment: Realities, Myths, Options. Oxford Univ. Press, New York.
Stewart, B.A., R. Lal, S.A. El-Swaify and H. Eswaran. 1990. Sustaining the soil resource base of expanding world agriculture. Proc. Symposium on "Global Soil Changes and their dynamics in a changing environment". 14th. Int. Congress Soil Science., Kyoto, Japan.
Szaro, R.C., and D.W. Johnston. 1996. Biodiversity in managed landscapes. Oxford Univ. Press. New York.
Swaminathan, M.S. 1986. Building national and global nutrition security systems. In: M.S. Swaminathan and S.K. Sinha (Eds.) Global Aspects of Food Production. Tycooly Int., Oxford, England. 417-449.
Tinker, P.B. 1998. The environmental implications of intensified land use in developing countries. In: Greenland, D.J., P.J. Gregory, and P.H. Nye. 1998. (Eds.) Land Resources: On the Edge of the Malthusian Precipice? CAB International, New York. 163-173.
Wang, F., G. Barent Hall, and P. Subaryono. 1990. Fuzzy information representation and processing in conventional GIS software: database design and application. International J. Geographic Info. System 4: 261-283.
Wetenschappelijke Raad Regereingsbeleid. 1994. Persistent risks: Four perspectives for rural areas in the European Community. Publ. Netherlands Scientific Council for Government Policy, 144 pp. The Hague, The Netherlands.
World Bank/UNDP. 1990. Irrigation and Drainage Research: A Proposal for an Internationally Supported Program to Enhance Research on Irrigation and Drainage Technology in Developing Countries. World Bank. Washington DC.
WRI. 1997. World Resources 1996-1997. World Resources Institute. Washington DC.