Global land use models
Contents
Introduction
Global land-use models address the allocation of land to specific land-use (Global land use models) types. They are used to understand the dynamics of land-use change but also to project the future development of land-use patterns.
Land supplies a multitude of goods and services to human societies – and the demand for these is changing with demography, wealth, and lifestyles. However, land is available in limited stocks only and thus, food-, fiber-, and timber production, recreation, nature conservation, infrastructures, and settlements compete for suitable land. The historical development, cultural background, political and institutional conditions, trade regimes, and most of all the land’s suitability for specific land-use types constrain this competition. Their interaction determines the spatial land-use pattern and the spatial extent of the area under cultivation. Land suitability, however, is not distributed evenly over space but forms heterogeneous patterns, complicating the competition for suitable land (see Land-use and land-cover change).
Societal and environmental conditions change, modifying the global land-use pattern as a consequence. Well-known examples for these global land-use changes are tropical deforestation and agricultural expansion, intensification, and specialization.
Global Modeling Approaches
To analyze this complexity and to project the future development of land-use patterns as integral parts of the Earth System, land-use models are being developed and employed.
The global scale is of special interest for analyzing land-use change processes. Many of the drivers and also many consequences of land-use change are of global extent and so-called globalization increasingly allows the shifting of land requirements from one region to another. These changes can only be addressed in a global framework. However, global approaches require high levels of generalization and aggregation, both spatially and conceptually. Thus, specific methodologies are needed for global approaches that differ significantly from smaller-scale approaches: Global land-use models implement other processes than smaller-scale approaches. They can – in principle – cover feedbacks to world market prices or inter-regional competition and can, thus, determine total area demand, which often is an input to smaller-scale models. On the other hand, several processes that are often considered in small-scale land-use models, such as effects of land tenure or management, cannot be included in the global level. Some processes are only analyzed at local scales that cannot be generalized or extrapolated to other regions. It is also hard to find adequate data for these local processes at the global scale. The lack of suitable global data sets and the special requirements of global-scale modeling approaches partially explain the small number of global-scale land-use models available.
The complexity of global land-use change processes is often much reduced by excluding inter-sectoral competition: That is, most global land-use models focus on agriculture or forestry only. Rarely, agriculture and forestry are addressed in the same model. Recreation, infrastructure, and settlements are completely ignored in global land-use models. Methodologically, the complexity is often reduced by employing only disciplinary methods in the models, ignoring the interdisciplinary character of land-use dynamics. Based on their disciplinary background, three types of large-scale modeling approaches can be recognized:
- geographic land-use models;
- economic land-use models; and
- integrated land-use models, which combine both approaches.
At the global scale, no geographic land-use model exists and most economic land-use models are not designed or employed to analyze land-use dynamics, although they allocate land in monetary terms to specific production types. Nonetheless, all three methodologies can be principally employed at the global scale to analyze and project global land-use dynamics. Most global-scale land-use models that are specifically designed to analyze and project land-use changes are integrated models, i.e., they are based on geographic and economic modeling approaches.
Geographic Modeling Approaches
Geographic approaches focus on spatial patterns of land-use change processes. They allow the flexible inclusion of behavioral patterns that affect the spatial allocation of land. Geographic modeling approaches require external projections of area- or commodity demand. These external demands are consequently not affected by the spatial limitations in their production, which can strongly affect demand via the price mechanism. Geographic approaches comprise empirical-statistical as well as rule/process-based models.
So far, there is no global geographic land-use model. These models are developed for and applied at [[region]al] to continental scales. The methodologies, however, is in principle applicable at the global scale as well and are partly used in integrated models. Examples of large-scale geographic land-use models are the CLUE models.
Economic Modeling Approaches
Economic land-use models on the contrary are concerned with the interaction of commodity demand, production, and trade, but largely ignore the spatial heterogeneity of land suitability. The variations in land suitability, however, largely determine the production inputs needed (e.g. land, chemicals, labor) and, thus, production costs. They also limit the total production potential. Usually, economic large-scale land-use models are partial or general equilibrium models.
Several global-scale economic models exist – but even if these include land as a primary production factor, the vast majority is not designed to analyze the allocation of land but focuses on changes in market structures of land-intensive goods or land-use emissions. Their methodologies are, however, employed in integrated models. Examples of economic global land-use models are the GTAP models and the AgLU model.
Integrated Modeling Approaches
These disciplinary shortcomings can only be overcome by integrating geographic and economic methodologies – a challenge yet to be fully met. Few models attempt to integrate over these disciplinary boundaries, but these models are usually specifically designed to address global land-use dynamics. Such integration is hampered by the strong differences in thematic, spatial, and temporal scales. First approaches to integrate economic and geographic methodologies and data are promising, but are often inconsistent and/or incomplete. Commodities and land are included in monetary terms only and often cannot be simply mapped to physical units as hectares or metric tones. Examples of integrated global land-use models are the coupled IMAGE-GTAP/LEI model and the FARM model.
Outlook
Global land-use change is of crucial importance for future food security, biodiversity (Biodiversity and ecosystem services), terrestrial biogeochemical cycles, climate, freshwater availability, and soil degradation. Global land-use change is a crucial link between human societies and the natural environment. Our understanding of the role of land-use change in the Earth System and our ability to project future land-use patterns significantly determine our ability to assess the scope and to manage the impacts of global change. Despite this importance, available tools to address global land-use change are strongly limited in their abilities. A new generation of large-scale land-use models needs to address the competition for land between different sectors, the interaction of spatial expansion and intensification, the role of different management types, as well as feedbacks between society and environment.
Further Reading
- Burniaux, J.M., Lee, H.L. 2003. Modelling Land Use Changes in GTAP.
- Darwin, R., Tsigas, M., Lewandrowski, J., Raneses, A., 1996. Land use and cover in ecological economics. Ecological Economics 17: 157–181.
- Foley, J. A., DeFries, R., Asner, G. P., Barford, C., Bonan, G., Carpenter, S. R., Chapin, F. S., Coe, M. T., Daily, G. C., Gibbs, H. K., Helkowski, J. H., Holloway, T., Howard, E. A., Kucharik, C. J., Monfreda, C., Patz, J. A., Prentice, I. C., Ramankutty, N., Snyder, P. K. 2005. Global consequences of land use. Science 309:570-574.
- Global Land Project. 2005. Science Plan and Implementation Strategy. IGBP Report No. 53/IHDP Report No. 19, IGBP Secretariat, Stockholm.
- Heistermann, M., Müller, C., Ronneberger, K. 2006. Land in Sight? Achievements, Deficits and Potentials of Continental to Global Scale Land-Use Modeling. Agriculture, Ecosystems and Environment, 114(2-4): 141-158.
- Hertel, T.W. (Ed.) 1997. Global Trade Analysis. Cambridge University Press, Cambridge. ISBN: 0521561345
- van Meijl, H., van Rheenen, T., Tabeau, A., Eickhout, B. The impact of different policy environments on land use in Europe. Agriculture, Ecosystems and Environment, 114(1): 21-38.
- Meyer, W. B., Turner, B. L. 1994. Changes in Land Use and Land Cover: A Global Perspective. Cambridge University Press, Cambridge England; New York, NY, USA. ISBN: 0521470854
- Sands, R., Leimbach, M. 2003. Modeling agriculture and land use in an integrated assessment framework. Climatic Change 56: 185–210.
- Turner II, B. L., Clark, W. C., Kates, R. W., Richards, J. F., Mathews, J. T., Meyer, W. B. 1990. The Earth as Transformed by Human Action: Global and Regional Changes in the Biosphere Over the Past 300 Years. Cambridge University Press with Clark University, Cambridge; New York. ISBN: 0521446309
- Verburg, P.H., de Koning, G.H.J., Kok, K., Veldkamp, A., Bouma, J. 1999b. A spatial explicit allocation procedure for modelling the pattern of land use change based upon actual land use. Ecological Modelling 116(1): 45–61.
- Verburg, P.H., Soepboer, W., Veldkamp, A., Limpiada, R., Espaldon, V., Mastura, S.S.A. 2002. Modeling the spatial dynamics of regional land use: The CLUE-S model. Environmental Management 30, 391–405.
