Initially the “Y” in Sayre’s equation referred predominantly to man-made vessels but 1886 marks the first known occasion for its application to a landscape where reference was made to the “stock-carrying capacity of the country.”[iii] While it can be assumed that pastoralists may have commonly had a reasonable idea of how many animals their land might potentially carry, the term became bureaucratically entrenched in the U.S. at a time of agricultural expansion in the late 1800s. Clements[iv] argues that quantitative carrying capacity estimates, assigned to new farming allotments, more easily allowed government to compare and regulate new lands and bankers to more readily capitalise the process.
Once the quantification of maximum livestock numbers was entrenched in farming practice and regulatory structures, it became evident that the concept could equally be applied to native wildlife and by the 1920s, game managers began estimating the number of deer, quail and other game species natural environments might support.[v] Aldo Leopold, for example, advocated a greater awareness of the factors influencing carrying capacity in his 1933 publication, Game Management,[vi] and in so doing, heavily influenced wildlife managers for generations to come.[vii] Consequently, Sayre[viii] argues that carrying capacity approaches to wildlife planning in the twentieth century were responsible for positive outcomes, such as the stabilisation of numbers and distribution of species, but also for ongoing problems such as compromising genetic diversity and ecosystem function through the manipulation of otherwise natural processes.
By the 1940s attention turned to the possibility that carrying capacity could also be applied to human populations and Leopold, again, was at the vanguard. For example, in 1941 he compared the human carrying capacity of America to pre-colonisation levels for indigenous Americans, concluding that, “When we arrived on the scene we raised the carrying capacity of the land for man by means of tools.”[ix] In 1949, William Allan actually performed a carrying capacity analysis of swidden agriculture traditionally practised by the people of Northern Rhodesia in Africa.[x] According to Cohen,[xi] there were various previous carrying capacity calculations world-wide prior to this time, but none that defined the process as a carrying capacity assessment. Allen[xii] utilised three types of data to derive “a method of estimating land carrying capacities for human populations under African conditions and systems of land usage,” and estimated population carrying capacities for various regions with an average of 8 people per square mile.[xiii]
While the application of carrying capacity analysis has differed throughout history, essentially the concept remains unchanged. Kirchner et al.,[xiv] suggest that carrying capacity analysis, applied to wildlife, aims to, “express the capacity of natural areas (ecosystems) to support animal life.” Likewise, in measuring human carrying capacity, areas of land are assessed for the extent to which they can support human life. For example, a carrying capacity estimate may suggest that a particular piece of land might support say, 1000 people. In this example, the answer to the carrying capacity equation is relatively simple - 1000 people - but the complexity lies in the assumptions underpinning the estimation. Consequently, variations in the definition of carrying capacity tend to differ in their exploration of what these inherent constraints entail.[xv] For instance, House and Williams[xvi] define the concept as, “the level of human activity that a region can sustain at acceptable quality of life levels,” inferring a bias towards qualitative societal constraints. Alternately, Whittaker and Likens[xvii] take a more ecologically quantitative view of carrying capacity in describing it as, “the size of the human population that can be supported on a long-term, steady-state basis by the world’s resources without detriment to the biosphere.”
Even though most carrying capacity definitions infer a process for the measurement of causal relationships between a population and its landscape, many only do so from an abstract perspective without the inclusion of summative calculations. Hopfenberg[xviii] states that, “Although models for human carrying capacity exist, they are typically tied to theoretical constructs rather than biologic data,” urging proponents to transition from, “the theoretically derived carrying capacity to an identifiable and quantifiable one.” [xix] In short, qualitative carrying capacity analysis tends to examine population dynamics without ascertaining any actual numerical result while quantitative assessments add calculation to the theory. As such, a qualitative definition of human carrying capacity may be - the ability of a certain area of land to support human life, while a more quantitatively orientated description may be - the maximum number of people that an area of land can support. Quantitative carrying capacity assessment is the primary focus of this research.
[i] SAYRE, N. F. (2008) The Genesis, History, and Limits of Carrying Capacity. Annals of the Association of American Geographers, 98, 120-134.
[ii] Ibid.
[iii] Thomson as per Sayre Ibid., describing the effect of a rabbit plague on the carrying capacity of New Zealand pastures
[iv] Ibid.
[v] Ibid.
[vi] LEOPOLD, A. (1933) Game management, Madison, University of Wisconsin Press.
[vii] SAYRE, N. F. (2008) The Genesis, History, and Limits of Carrying Capacity. Annals of the Association of American Geographers, 98, 120-134.
[viii] Ibid.
[ix] LEOPOLD, A., FLADER, S. L. & CALLICOTT, J. B. ([1941] 1992) The River of the Mother of God: And Other Essays by Aldo Leopold, University of Wisconsin Press.
[x] B, L. (1950) Studies in African Land Usage in Northern Rhodesia. William Allan. African Affairs, 49, 78.
[xi] COHEN, J. (1995) How Many People Can the Earth Support?, New York, W. W. Norton.
[xii] SAYRE, N. F. (2008) The Genesis, History, and Limits of Carrying Capacity. Annals of the Association of American Geographers, 98, 120-134.
[xiii] ALLAN, W. (1965) The African husbandman, Munster, Lit Verlag.
[xiv] COHEN, J. (1995) How Many People Can the Earth Support?, New York, W. W. Norton.
[xv] The validity of various constraints to carrying capacity are explored further in Chapter 6.6.
[xvi] HOUSE, P. W. & WILLIAMS, E. R. (1975) The carrying capacity of a nation: growth and the quality of life, Lexington, Mass., Lexington Books.
[xvii] WHITTAKER, R. H. & LIKENS, G. E. (1975) The Biosphere of Man. IN LIETH, H. & WHITTAKER, R. H. (Eds.) Primary productivity of the biosphere. New York, Springer-Verlag.
[xviii] HOPFENBERG, R. (2003) Human Carrying Capacity Is Determined by Food Availability. Population & Environment, 25, 109-117.
[xix] Ibid.
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