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[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.] African reforestation As outlined in the Part I [http://bravenewclimate.com/2010/01/05/boverty-blues-p1/], 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. Full: http://bravenewclimate.com/2010/02/04/boverty-blues-p2/ ________________________________________________ Send list submissions to: [email protected] Set your options at: http://lists.econ.utah.edu/mailman/options/marxism/archive%40mail-archive.com
