LAND DEGRADATION & REHABILITATION, VOL 5, 71-78 (1994)

LOCAL FACES, GLOBAL FLOWS: THE ROLE OF LAND USE AND LAND COVER IN GLOBAL ENVIRONMENTAL CHANGE

B. L. TURNER I1 George Perkins Marsh Institute and Graduate School of Geography, Clark University, 950 Main Street, Worcester,

Massachusetts, 01610-1477 USA

ABSTRACT The emergence of land-use and land-cover change (LUCC) as one of the major themes within the global environmen- tal change research community poses a series of difficult but not insurmountable problems. LUCC takes place incrementally through the operation of sets of human and biophysical forces largely specific to the locale in question, but cumulatively LUCC contributes significantly to global environmental change. Linking LUCC to global change requires the cooperation of the natural and social sciences to bridge the local to global dynamics involved. The International Geosphere-Biosphere Programme and the Human Dimensions of Global Environmental Change Programme are undertaking the development of an international research project with such aims in mind, This project seeks to improve understanding of LUCC dynamics by balancing the need for a nuanced understanding at the local level with the need from improved regional and global LUCC models. The rudiments of this effort and some of problems confronting it are outlined here.

KEY WORDS Land use Land cover Global change Integrative assessment

INTRODUCTION

This collection of papers and the symposium that spawned it testify to the recognition by the Australian Academies of Science and Social Sciences of the changes that humans have produced and continue to produce in the terrestrial ecosystems of the earth. These changes are of no small consequence as they affect local environmental habitability, but they also contribute to global environmental change, both in the world-wide condition of the states or faces of the earth and in the biogeochemical cycles that sustain the biosphere. Changes in these flows, of course, have the potential to trigger climate change with its feedbacks on terrestrial ecosystems (Henderson-Sellers, this issue).

KINDS O F CHANGE

Human activities contribute to two major kinds of changes that are global or potentially global (Figure 1). The first involves aspects of the biosphere that operate as fluid global systems, notably the oceans and atmosphere, through the global biogeochemical cycles that drive them. The term global environmental change was originally restricted in its application to systemic changes of this sort (Turner, et al., 1990b), in which the source of change may be concentrated spatially, but still be of great magnitude. Subsequently, however, the meaning of global change has been expanded by the international research community to include other modifications, alterations and transformations, such as a loss of biodiversity or soil fertility, that become global problems by altering the states or faces of earth or by altering those flows that operate over a less than global range (Brookfield, 1989). Usually, such cumulative change merits the title of global change only when it attains a global distribution (Turner, et al . , 1990b).

Human activities can contribute to either of these forms of change or to both at once. Industrial production and energy consumption have both systemic and non-systemic effects. The same is true of land use and land cover change, the other principal cluster of proximate human causes of environmental

CCC 0898-5812/94/020071-08 0 1994 by John Wiley & Sons, Ltd.

Received 29 March 1994 Revised 10 May 1994

72 B. L. TURNER I 1

Systemic Point or areal sources of sufficient maqnttude have

impact on a global biogeo- chemical system ( e g , industrial emissions and atmospheric carbon)

*

.- -- .._ /- r\ I,,, j Areal repeated change to reach of some kind

Cumulative

L -..,’ -*.. ._ .//’ ‘ - ’ biodiversity loss) /

1 a sufficient magnitude to 1 create worldwide concern / (e g., deforestation and

Figure 1. Forms of global change

change. Deforestation, for example, is a form of cumulative change that drives further cumulative changes (e.g. loss of diversity) and also contributes to systemic change through its role as a source of atmospheric carbon. Although in recent years land cover change has come to appear less important as a source of atmospheric C 0 2 than it once was believed to be, its role in other global systems is indeed important (Henderson-Sellers, this issue).

CHANGE IN LAND USE AND COVER

The globally cumulative and systemic effects of land transformations are relatively well documented. Moving from the local, non-systemic issues to globally systemic issues, we know, for example, that

0 local to regional land degradation-contributing to declines in net primary productivity, crop yields, soil and groundwater and soil nutrients-is largely the product of land use/land cover change, as is a loss in biodiversity

0 one-half of the ice-free surface of the earth is substantially altered in these and other ways 0 over the past 300 years, the area of the earth’s surface under cultivation has grown from roughly the size

of Argentina to roughly the size of South America 0 land use accounts for most of the 20-40 per cent of potential terrestrial productivity exploited by

humans 0 over the past 150 years, the net flux of carbon dioxide to the atmosphere from land use and land cover

changes is equivalent to that contributed by fossil fuel sources 0 land use is responsible for most of the methane released to the atmosphere by human activities.

There are few dimensions of global environmental change to which land use and land cover are not important. It is this understanding that prompts the Australian and international science communities to promote major new research initiatives on land use and land cover change. Some of the issues raised in these initiatives and the form that one interdisciplinary and international project might take are the subjects of the remainder of this paper.

DEFINITIONS AND DYNAMICS

These initiatives have emerged from both the natural and human sciences, which, historically, have not shared the same interests in the land. The former have been principally concerned with land cover, the latter with land use. Emerging interdisciplinary efforts [e.g. the International Geosphere-Biosphere

LAND COVER AND USE IN GLOBAL ENVIRONMENTAL CHANGE 73

Climate Change

Physical System

(physical maintenance) - (modification) I 1

Land cover #2

Land cover #1

Land cover #3 t (conversion) - r I

Proximate sources

t t

(env. impacts on DF's)

Figure 2. Linkages between human causes and land use and cover. Source: Turner, et a[. (1993: 26)

Programme (IGBP) and the Human Dimensions of Global Environmental Change Program (HDP); see Turner, et al . , 1993; Turner el al. , 19941 distinguish the two terms as follows: (i) land cover refers to the physical attributes of the surface of the earth, such as cropland, forest, grasslands, wetlands or tundra; (ii) land use, by contrast, refers to the purposes for which humans manage covers, such as agroforestry, wheat farms, ranching, national parks, settlement and slash and burn cultivation.

As repeatedly demonstrated in this issue, humankind cannot sustain itself without altering, or even transforming, the surface of the earth. Any significant changes in land use affect land cover (Figure 2). Cover changes, moreover, react locally on land uses while also contributing to wider processes of change, such as climate warming. The land uselland cover dynamic is, therefore, central to the human responses to global change.

Understanding the land uselland cover dynamic in all of these aspects requires the contributions of both the natural and human sciences. Land uses are the product of the pre-existing environment and the socio-economic subsystem exploiting it (Figure 2). Use of the land generates immediate cover conse- quences (e.g. weed invasion) and globally systemic ones (e.g. methane from wet rice) to which the management strategy may have to adjust. Such adjustments affect the socio-economic dynamics that produced the original uses, sometimes leading to different uses. Alternatively, changes in the socio- economic dimensions alone may trigger land use and land cover changes.

This brief assessment leads to a simple conclusion. The study of land cover in global change is inadequate without consideration of the human dimension just as that of land use is lacking without an examination of the environmental dimension (Blaikie and Brookfield, 1987). It is precisely this recog- nition that has joined the natural and human sciences in efforts throughout the world dealing with global environmental change.

74 B. L. TURNER I I

HUMAN CAUSES OF LAND USE/LAND COVER CHANGE

A long tradition of study has established the broad patterns of land use/land cover changes wrought by human action (e.g. Wolman and Fournier, 1987; Richards, 1990; Meyer and Turner, 1994; Turner, et af., 1990a). Since 1700, human activity globally has reduced the forest area by 15 per cent, increased cropland by 390-460 per cent, but hardly changed the net world extent of grasslands, though it has modified their condition dramatically through overgrazing and the spread of exotic flora.

Individual case studies inform us of the details of human-land interactions in particular places. For example, the tropical forests of most of the Yucatan peninsular region may be no older than 500-800 years, having recovered after an extended period of clearance by the ancient Maya (Turner and Butzer, 1992). We can correlate changes in land use and population with this deforestation (Figure 3). The tree cover of New England has returned after major deforestation in the 18th and 19th centuries (Foster, 1993), even though the population of the region has continued to rise. Many other examples could be given, some of the better ones drawn from work in Australia. Taken together, such studies offer much information of the kind needed to parameterize land cover models. Importantly, however, individual studies are difficult to compare other than in a qualitative way.

Far less common are land use/land cover studies that are part of an orchestrated set based on common protocols which follow a common purpose, use the same definitions and measures, and generate comparative results. The recent Project on Critical Environmental Zones (PROCEZ) of the George Perkins Marsh Institute (Kasperson, et a l . , in press) and on the ongoing Population Growth, Land Transformations, and Environmental Change (PLEC) programme, headed by Brookfield of the Austra- lian National University, are examples of attempts to draw on the kind of understanding provided by co- ordinated case studies. The latter project is in mid-course; the former is completed and is used here to illustrate several points. PROCEZ involved interdisciplinary teams in nine regions examining the degree to which human-induced changes have jeopardized the sustained use of the regional environment and the kinds of responses taken to these changes (Cocks and Walker, this issue). The case histories identified complicated mosaics of human causes giving rise to the land use/land cover changes in each region. The same classes of causes were apparent in almost every case-population, consumption (affluence), technological change (the so-called PAT variables), political economy, political structure and belief/ attitudes-but the way they interacted and their relative importance varied appreciably. Interestingly though, almost every regional interpretation emphasized the primacy of political economy and structure over the PAT variables, which typically prevail in cross-regional and global aggregate analyses (e.g. Billsborrow and Okoth-Ogendo, 1992; Rudel, 1989). Whether these results reflect the biases of the investigators (in either kind of study), differences in studies using quantitative versus qualitative analyses, or the spatial scale and level of detail of the case studies cannot be determined at this time. It is important to recognize that PROCEZ was constrained by the inability to obtain standardized, quantitative data on human causes, an issue to which we will return.

Case studies provide the richness of detail absent from more general approaches and should always be used to inform the latter. Comparative case studies, in addition, have the potential to provide statistical inputs into modelling and projecting efforts, a role that many of the land use/land cover community favour. Several tensions are involved in such linkages. Among these are contending positions

0 on the usefulness of case studies for modelling approaches 0 on the usefulness of models for assessing real world problems 0 on the appropriateness of empirical based versus theory based approaches to case studies 0 among some social scientists, over the usefulness of current land use/land cover models, based largely

on non-integrated economic sectors, and the need for georeferenced, integrative outputs that, for example, would provide the total land use and land cover for an area.

In summary: (i) we have subtantial knowledge of the broad relationships between human activity and land use/land cover change over the long term and at the global scale; (ii) we have an in-depth

LAND COVER AND USE IN GLOBAL ENVIRONMENTAL CHANGE 75

76 H. L. ’TURNER 11

understanding of these relationships for specific locales and regions from detailed case studies; (iii) we have not been able to conceptualize these relationships in a manner useful for the goals of the global change research community, specifically those of modelling and projecting land use/land cover changes at the spatial scales required by the global change agenda: and (iv) different views exist on the relative usefulness of case studies and global/regional modelling and on the relation of the two.

LAND USE/LAND COVER CHANGE CHALLENGE

The IGBP and the HDP have joined to seek a new interdisciplinary understanding of land use/land cover change that better meets the needs of the global change community through the development of an international core research project on Land Use/Cover Change (LUCC) (Turner, et af., 1993; Turner, el al . , 1994). The ultimate aim of LUCC is to improve the modelling and projection of global land use and land cover change through the use of a subglobal approach sensitive to local and regional variations in the relationships of human and biophysical drivers, land uses and land cover.

To reach this goal requires (i) the identification of the clusters of drivers that combine to change land use (hence, land cover) in different socio-economic and environmental settings (or what we may call ‘cause to cover settings’); (ii) the identification of a set of competing theories that explain use/cover change (Powell, this issue); and (iii) the development of a means of coupling land useiland cover models of different spatial and temporal scales. These requirements entail (a) the development of a protocol to study land use/land cover dynamics in critical and characteristic settings (e.g. where most change or the most important kind of change is taking place and where conditions typify major land uselland cover dynamics, respectively); (b) use of these findings to inform new models developed and (c) from refine- ments in existing models and (d) from the case studies themselves (both of them capable of handling economies of various degrees of market development and of delivering outputs in terms of regionally integrated and georeferenced land uses and land covers).

To accomplish such lofty goals and difficult tasks requires the research community to co-operate in ways to which it is unaccustomed. We are all familiar with the supposed problems that arise between natural and social scientists. Such problems may be exaggerated and involve mostly the outcomes to which a particular effort should be directed, at least as judged by our negotiations to date. These negotiations, however, have largely involved individuais who share a ‘science view’ of research. Perhaps more difficult to resolve are the divisions within the social sciences, where major tensions surface over the very nature of, and therefore the appropriate methods for, understanding (Turner, 1991).

Another impediment to the LUCC task is the scale of co-operation involved. The LUCC effort requires international co-operation not only in data measurement and collection, but in undertaking case studies following a common protocol to facilitate the kinds of comparative assessments required. Not only are comparative case studies expensive to undertake, but the kind proposed entail a ‘big science’ approach, one with which the social sciences are not overly familiar and of which many practitioners are intuitively suspicious.

Possibly the most important challenges confronting LUCC are conceptual issues about integrating spatial scales and about disaggregating sectors through georeferencing. The former is a longstanding concern, often referred to as the ‘micro-macro’ problem. It has been repeatedly shown that analysis of an issue at one scale leads to a different set of outcomes than at another scale (e.g. Meyer, et af., 1992), as in PROCEZ. However, the reasons for this result have not been well articulated. The physical sciences have identified the spatial and temporal scales at which various processes operate, hence offering a structure on which cross-spatial analysis of their interactions and consequences might be framed (e.g. Clark, 1987). The social sciences have not yet produced anything similar for social processes.

The micro-scale (case study) researcher not only is likely to accept the notion that analyses cannot be transferred across scales, but also objects to the use of global models to understand particular regions or locales, especially where these areas are outside cohesive market or pure subsistence economics. For this group, if LUCC modelling is to proceed, we must begin at ground zero, so to speak, reconceptualizing the

LAND COVER AND USE IN GLOBAL ENVIRONMENTAL CHANGE 77

models to account for the significant kinds of local government policy for the use and cover outcomes at very small spatial scales (e.g. small drainage systems or countries). Unfortunately, such reconceptualiza- tions are not only time consuming, but may require more comparative data than exist.

The macro-scale researcher (global modeller) is likely to recognize these data problems and to have undertaken sufficient trials to know that the data problems hinder detailed analysis and that simple market based formulations focusing on PAT variables provide the most robust explanations and pro- jections to date. This cluster of researchers is prone to seek to elaborate existing global models to bring them down to the regional levels.

The second impediment may be easier to overcome, indeed as a logical outgrowth of the analytical use of geographical information systems. Land use per se has not been central to modelling in the social sciences, particularly in economics where the focus has been on sector and product modelling. Few economic models integrate sectors, but treat livestock, timber and agricultural production independently. These models determine changes in any one product (e.g. timber offtake), but rarely integrate products and translate them into land uses, such as pasture, forest reserves and cotton land. Moreover, social science models of these kinds rarely georeference beyond the large bounds of the unit of analysis (by state, region or province). The locational attributes of different uses have not been central to modelling efforts.

These circumstances are beginning to change. Integrative sector models are improving, as illustrated in the MINK project (Rosenberg, 1993) and georeferenced use/land cover outcomes are emerging from some global models, such as the IMAGE models (Alcamo, 1994). These improvements notwith- standing, much remains to be done before land use/land cover models can capture georeferenced land use/land cover outcomes by region and can be 'summed' to cover the globe or significant portions of it (Figure 4).

These goals and tasks are daunting and will no doubt consume a decade or more of research. I am convinced, however, that significant improvements can be made towards the objectives discussed. Not to confront them will merely perpetuate the current situation; not providing the research and policy community with the best that science could offer (Chisholm, this issue). And surely we need the best if we are to live with global change in a satisfactory way?

Current Dominant Approach

I LIVESTOCK ~ SECTOR

AGRICULTURE 1 SECTOR !

I

T S ' I E M C B T ' - E o R R

i TOTAL FOREACH I

t SECTOR FORENTIRE '

independent sector models leading t o undi f fe rent ia ted areal

Required LUCC Approach

outputs

Integrated sector models

Figure 4.

leading t o

Sector to land use based

pasture

georeferenced land-use results

models.

78 H. L. TURNER I I

REFERENCES

Alcamo, J. (ed.) 1994. IMAGE 2.0: Integrated Modeling of Global Climate Changes, Kluwer Academic, Dordrecht. Billsborrow, R. E. and Okoth-Ogendo, H. W. 0. 1992. ‘Population driven changes in land use in developing countries’, Ambio, 21,

Blaikie, P. and Brookfield, H. C. 1987. Land Degradation and Society, Methuen, London. Brookfield, H. C. 1989. Sensitivity to Global Change: a new task for oldlnew geographers, Norma Wilkinson Memorial Lecture,

University of Reading, Reading. Clark, W. C. 1987. Scale relationships in the interaction of climate, ecosystems, and society, pp. 337-378 in K. C. Land and S. H.

Schneider (eds.) Forecasting in the Social and Natural Sciences, D. Reidel, Dordrecht. Foster, D. R. 1993. Land-use history and forest transformations in central New England, pp. 91-1 10 in M. J . McDonnell and S. T.

A. Pickett (eds.) Humans as Components of Ecosystems, Springer-Verlag, New York. Kasperson, J . X . , Kasperson, R. E. and Turner 11, B. L. (eds.) Regions at Risk: comparisons of threatened environments, United

Nations University, Tokyo, in press. Meyer, W. B. and Turner TI, B. L. 1993. ‘Human population growth and global land-uselcover change’, Annual Review of Ecology

and Systematics, 23, 39-61. Meyer, W. B. and Turner, 11, B. L. (eds) 1994. Changes in Land Use and Land Cover: a global perspective, Cambridge University

Press, Cambridge. Meyer, W. B., Gregory, D., Turner 11, B. L. and McDowell, P. F. 1992. The local-global continuum, pp. 255-279 in R. F . Abler,

M. G. Marcus, and J . M. Olson (eds.) Geography’s Inner Worlds: pervasive themes in contemporary American geography, Rutgers University Press, New Brunswick.

Richards, J . F. 1990. Land transformation, pp. 163-178 in B. L. Turner TI, et al. (eds.) The Earth as Transformed by Human Action, Cambridge University Press, Cambridge.

Rosenberg, N. J . (ed.) 1993. ‘Towards an integrated assessment of climate change: the MINK study’, Climatic Change, 24(1-2) (Special Issues). 1-173.

Rudel, T. K. 1989. ‘Population, development, and tropical deforestation: a cross national survey’, Rural Sociology, 54, 327-338. Turner 11, B. L. 1990. The rise and fall of Maya population and agriculture, loo0 B.C. to present: the Malthusian perspective

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Turner, 11, B. L. and Butzer, K. W. 1992. ‘The Columbian Encounter and Land-use Change’, Environment 43(8), 16-20. Turner 11, B. L., Clark, W. C., Kates, R. W., Richards, J. F., Mathews, J. T. and Meyer, W. B. (eds.) 19YOa. The Earth as

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Turner 11, B. L., Kasperson, R. E., Meyer, W. B., Dow, K., Golding, D., Kasperson, J. X., Mitchell, R. C. and Ratick, S. J. 1990b. ‘Two types of global environmental change: definitional and spatial-scale issues in their human dimensions’, Global Environmental Change: Human and Policy Dimensions, 1, 14-22.

Turner 11, B. L., Moss, R. H. and Skole, D. L. (eds.) 1993. Relating Land Use and Global Land-cover Change: a proposal for an IGBP-HDP core project (IGBP Report No. 24 and HDP Report No. 5 ) , IGBP, Stockholm.

Turner 11, B. L., Meyer, W. B., and Skole, D. L. 1Y94. ‘Global land-uselland-cover change: toward an integrated program of study’, Ambio XXIII, 91-95.

Wolman, M. G. and Fournier, F. G. A. (eds.) 1987. Land Transformation in Agriculture, Wiley, Chichestcr.

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