First view of a world without fire

The natural vegetation covering the globe looks like it does because of the climate, doesn’t it? Forests are found where water is abundant and it is not too cold, deserts are found where it is dry. This is what our intuition tells us – but it is not always true.

New research carried out by Bond, Woodward and Midgley from University of Cape Town, University of Sheffield and the South African National Biodiversity Institute of and published in the February 2005 issue of ’New Phytologist’ has shown that a potent force overrides climate in shaping vegetation – fire.

Much of the world is covered by vegetation that seems out of place, for example in Mediterranean regions of South Africa low shrublands are found where rainfall is great enough to support forests. We also know, from satellite imagery, that wildfires are a global phenomenon occurring on all vegetated continents. Bond et al. suspected that fires are common in areas where vegetation does not “fit” the climate. If true, this suggests that fire has a major effect on the ecosystems of the world. So, how different would the world look if we could ’switch fire off’?

A new type of ecosystem model, Dynamic Global Vegetation Models (DGVMs) – developed to answer questions on the link between global climate change and vegetation, was used to simulate a world without fire for this research.

Dr William Bond, University of Cape Town, explains: “For the first time, we have a global estimate of the importance of fire in shaping the natural world: without fire, the extent of closed forests would more than double (from 27% to 56% of the vegetated surface of the world), tropical grasslands and savannas would shrink to less than half (48%) of their current extent and temperate grasslands and shrublands, including the shrublands of Mediterranean climate regions, would shrink to 60% of their current extent.”

“Fires destroy property and livelihoods and affect local air quality, but perhaps more importantly, fires destroy above-ground vegetation on a huge scale – burning the critical carbon sinks which form such a fundamental part of the world’s attempts, through the Kyoto protocol, to slow the rate of carbon dioxide increase in atmosphere. Human influences on fire are near universal. We suppress fires in some regions and ignite them in others. However the fire-maintained ecosystems identified in our research have been burning for millions of years and include some of the most biodiverse regions of the world. We need to balance the necessity of using fire in these ecosystems with protecting forests from indiscriminate burning. This issue requires urgent and focused attention from the ecological and geochemical communities if we are to manage the effects of global change on our planet.”

Fire changes vegetation quickly, directly and fundamentally – it is now clear from this research that a fundamental understanding of landscape fires is necessary for comprehending the way much of the world works and for projecting the effects of changing human land use and climate on vegetation. Thus, understanding direct climate effects on our biosphere is far from enough for projecting intensifying global change impacts into the future.