54, November/December 2003
Fire Ecology I
Earth is a fire planet. The combustion of fire on the face of earth is based on the same phenomena as the combustion in our cells, only writ large across the landscape. Fire certainly predates human presence on the planet, due to the agencies of lightning and volcanic action; yet it is through millenia of human activities that fire has become so predominantly entrenched as the most important global disturbance, in terms of the total area and number of biomes that it affects.
The focus of this issue of the Arid Lands Newsletter is on "fire ecology, past and present." The questions proposed for consideration concerned the extent of our knowledge of dryland fire regimes, our understanding of prehistoric and historic human uses of fire and their contribution to such regimes, and our knowledge of specific effects of fire on the surrounding ecosystem. The articles submitted in response to these questions do not fall into any particularly neat pattern. In geographic terms they range from Africa and Mediterranean Europe to Australia and South Asia; in ecological terms they span the gamut from seasonally dry deciduous tropical forest to stark desert. Two of them focus on specific effects of fire on, respectively, flora and ecosystem nutrient capital; three focus on broader-scale issues of fire regimes, human fire use, and fire management. They do not necessarily reach the same conclusions and in some cases seem to directly contradict each other. Taken as a whole, however, they point to two important conclusions: first, that the connection between humans and fire is inescapable and must be taken into account in any formulation of policy regarding fire; and second, that while fire is a global phenomenon, like so many other such phenomena its expressions are local and must be studied, understood and managed on a firm underpinning of local knowledge.
In the first article, Douglas Bird and colleagues present data from their study of the resource use and fire regimes among the Mardu Aboriginals of Australia's Western Desert. This study--the first quantitative analysis of the relationship between Aboriginal foraging and burning strategies--indicates that Mardu women are important hunters whose regular, controlled use of fire during hunting may positively affect the biodiversity of vegetation and small animals in the region. This suggests that, as the authors state, "incorporating women's hunting goals into fire policy will be critical for current conservation efforts in the Western Desert."
Turning next to Africa, Navashni Govender outlines the history and evolution of fire management practices in South Africa's Kruger National Park. The Park's grasslands and savanna comprise one of the largest natural protected areas in the world; as such, what is learned here has application not just to other African savannas but also to other savanna biomes and protected areas around the world. Current fire management policy in Kruger National Park has evolved to simulate "as closely as possible the intensity, spatial and temporal heterogeneity of a natural fire regime, taking into account the importance and reality of anthropogenic fires in this system and thereby achieving its mandate of maintaining biodiversity in all its facets and fluxes."
Oliver Rackham weighs in with an overview of fire in the European Mediterranean, based both on his knowledge of the historical record and on his more than 30 years of research in the region. Many Mediterranean ecosystems are naturally fire-prone, and humans have set extensive occupational fires in the region since at least the Middle Ages. Ironically, Rackham's experience is that fires in the region may have increased since the widespread rural depopulation of the European Mediterranean in the 20th Century: "There is now much more to burn than when the countryside was densely populated and used." Like Bird's article, this one suggests that human manipulation of fires, as traditionally practiced for agricultural or other human ends, may have beneficial effects on the overall health of ecosystems.
In a more specifically focused article, Maria Carmen del Cobo and Jose Antonio Carreira report on a study they conducted on the connection between fire, soil nutrient capital depletion, and potential desertification in a semiarid Mediterranean shrubland. Their research indicates that in a fire-prone habitat such as this, long-term ecosystem health relies upon a balance between fire-related nutrient outputs and succession-related nutrient inputs to ecosystem nutrient capital. However, if fire frequency breaches a certain threshold, this balance may be upset, leading to long-term soil nutrient depletion, slower vegetation recovery, increased erosion and eventual desertification.
Finally, Sonali Saha and Ankila Hiremath report on fire's effects on tree regrowth and vegetation community composition in two deciduous tropical forests in India. Their research indicates that current fire regimes in these two study sites are potentially leading to loss of biodiversity by favoring dominance of trees that can resprout freely after fires over those than can resprout from the base alone or that can grow from seed alone. Yet, humans have existed in these areas for millenia and have most likely used fire for just as long, so the interesting question is why this growing imbalance of tree species within the forests is occurring now. Although they do not focus on this issue, the authors do state that "it is also likely that fire-return times have decreased significantly as local population densities have increased in the last four or five decades." As with Cobo and Carreira, then, the issue seems to be that once a certain threshold of fire frequency is breached, long-term balances are upset in a way that is detrimental to biodiversity and overall ecosystem health.
Thus we are brought full circle to the points that humans and fire are inextricably linked in ways that must be recognized for any fire management policy to be effective, and that fire, while a global phenomenon, expresses itself locally and must be understood locally. As fire historian Stephen Pyne states in his book Smokechasing (2003, p. 8-9; see review in this issue), "By far the greatest proportion of fire on the planet and virtually all its fire regimes result from human tinkering. This fidgeting and tweaking are ecological acts." And, as a result, "The pressing issue before fire management is not whether fire has existed previously, but in what ways--according to what regimes and by what means--and what its various presences might signify for a particular landscape today." (ibid., p. 10).
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