This is the second of a two part post by Geoff Russell. Part I sketched the quantitative features of the global fire regime, biomass flows, while this part looks primarily at Africa.
Boverty was defined in the previous post as the human impact of too many bovines overwhelming the local biosphere’s ability to feed them … the bovines are usually cattle and more than a few African countries have boverty induced poverty. Their livestock is a millstone around their necks and helping to keep them poor.
Western aid organisations, particularly those run by BBQ obsessed Australians, seem dominated by people haven’t woken up to the simple fact that the foods they grew up on when the planet had half its present population haven’t been sustainable globally for a very long time. Even in Australia, with its vast landmass and small human population, the production of these foods has driven and continues to drive water shortages, environmental degradation and biodiversity loss. Advocacy of such foods in Africa will benefit few and damage prospects of long term food security.
As outlined in the Part I, many grasslands on the planet are not the product of natural forces, but were cleared by people and kept as grasslands for livestock grazing by annual or occasional conflagrations. This is global burning on a massive scale as shown in the NASA firemaps presented in Part I. The continent with the most deliberate human burning is Africa. Over 200 million hectares and 2 billion tonnes of dry matter are burned annually in deliberately lit fires. Almost all of these fires are set by livestock herders to stop grasslands becoming forests. By comparison, burning by shifting cultivators for crops covered an area about 10 percent of this size. A recent study in Nature gives an idea of what could happen if the burning stopped. The reforestation potential is massive.
Consider the above image from the Nature article. The vertically hatched area has an average rainfall over 780mm and would, according to Sankaran and the large number of other authors, revert to some kind of forest if given half a chance. Its status as savanna is anthropogenic and not a product of natural attributes like soil type and climate.
How long can such regrowth go on adding carbon in the form of forests? Most additional carbon would be added during the first 3 decades but forests can go on adding smaller amounts for centuries. It’s worth noting that fire is probably always a suppressor of biomass production. The frequent claim that fire helps regeneration, making it some kind of friend of biodiversity, can be true but is highly misleading. I intend to do a post on this sometime in the future. But despite some plants benefitting from fire, the general impact is to reduce biomass production. Measurements under 2 rainfall regimes and 4 soil types in Africa always recorded higher biomass production in areas not burned.
One way of measuring a country’s fire intensity is to consider the ratio of biomass burned to biomass appropriated. We saw in Part I that Australia burns about 40 percent of what it appropriates. This ratio is the same as in South East Asia, but much higher than the 1 percent of Western Europe.
Both burn ratios pale beside the staggering 150 percent of sub-Saharan Africa where far more is burned than is otherwise appropriated. This is a stunning number. Corey Bradshaw recently wrote a piece on his blog where he summarised a recent paper on Australia’s mammal extinction crisis. His bottom line summary was that we should “Stop burning the shit out of our forests“. In sub-Saharan Africa, they are burning 12 times more biomass from an area 6 times bigger than the 37 million hectares we burn each year. If we are doing as Corey says, then what are the Africans doing? And for what? They reap far less than they burn.
How will global warming compound or alleviate Africa’s problems? The most critical impacts will be changes in rainfall regimes.
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