A Brief History of Savanna Studies

*Until the mid-1980s, savanna studies were based on the concepts of ecology first developed in Europe and North Amercia between about 1910 and 1940. Plant communities were seen as 'organisms', or ecosystems, the equilibrium state of which would be determined by one prime external ecological or abiotic factor, such as climate, geology, soil or fire. Unfortunately, there was strong disagreement over which factor controlled savannas. British foresters working in West Africa thought savannas were anthropogenic (human-created) communities, forged out of the forest by cutting and burning. In contrast, German scientists working in South West Africa (Namibia) and South America tended to view savannas as a climatically-determined vegetation type, while the French in Indochina (Laos, Cambodia and Vietnam) saw savannas as essentially fire climaxes. There were also other more idiosyncratic explanations, certain geographers, for example, arguing that savannas were primarily determined by geomorphology (the age of the land surface) and soils. In truth, however, there was very little real debate or discussion between the different Schools of thought, and savanna studies soon became somewhat nationalisitic, regionally constrained, and ultimately outdated in relationship to the more general advances being made in the ecological sciences.

*Since 1984, however, savanna studies have been revolutionized and they have become increasingly interdisciplinary and international in character. It is now thought that all savannas are determined by the complex interplay of at least six main ecological determinants. These are: PAM (plant available moisture), PAN (plant available nutrients), fire, herbivory, major historical anthropogenic (human) events, and, at certain locations, special regional factors, such as frost and wind. PAM and PAN are seen as the prime determinants of savanna form, which is then modified by fire, herbivory, and any other relevant special local factor. Historical events, such as the abandonment of human settlement or enhanced global warming, may trigger savannas into a totally new ecological state. The relationships between this complex of variables are now analysed multivariately, using models or hierarchy theory, and the PAM/(P)AN Plane (a two-dimensional plane in which the axes are defined by measurements of PAM and PAN) can be used to make basic international, national, and regional savanna comparisons.

*Perhaps even more importantly, savannas are no longer seen as being simple equilibrium systems, but rather they are regarded as a vegetation type which is constantly under a regime of change, with their biology driven by both gradual and catastrophic variation in the six ecological determinants. Some scholars think of savannas as ever moving between what are called 'multiple equilibrium sates', such as open grassy savannas, wooded savannas, and woodlands. Others, however, including the author, are of a more radical disposition and regard savannas as being intrinsically non-equilibrium systems, in which every savanna organism responds individualistically to changes in the ecological determinants.

*These new approaches place savanna studies at the centre of ecology and the discussion of global environmental change, the six ecological determinants linking savannas directly with both world-scale and local-scale environmental fluctuations. Fundamentally, savanna studies have at last come of age.


*SOME FURTHER READING

Fairhead, J. and M. Leach 1996. Misreading the African Landscape: society and ecology in a forest-savanna mosaic. Cambridge: Cambridge University Press.

Mistry, J. 2000. World savannas: ecology and human use. Harlow, Essex: Prentice Hall (Pearson Education).

Scholes, R.J. and B.H. Walker 1993. An African savanna: synthesis of the Nylsvley study. Cambridge: Cambridge University Press.

Solbrig, O. (editor) 1991. 'Savanna modelling for global change.' Biology International (Special Issue) 24. Paris:IUBS.

Stott, P. 1991. 'Recent trends in the ecology and management of the world's savanna formations.' Progress in Physical Geography 15, pp. 18-28.

Stott, P. 1994. 'Savanna landscapes and global environmental change.' Pp. 287 - 303 in N. Roberts (editor) Global environmental change. Cambridge, Mass.: Blackwell.

Sullivan, S. 1996. 'Towards a non-equilibrium ecology: perspectives from an arid land. Journal of Biogeography 23, pp. 1 - 5.