Several recent papers and presentations by Mark Cochrane, Dan Nepstad, and their colleagues at the Woods Hole Research Center, IPAM, and IMAZON have dramatically altered the way I think about two major issues: forest fires and the environmental impact of logging. Maybe they will have the same effect on you.
Until Cochrane and Nepstad came along I believed forest fires were spectacular events but had limited long-term consequences. I was convinced that while selective logging, as typically applied in Latin America, often degrades forests it does not completely destroy them. For that to happen farmers had to follow the loggers into an area. It turns out I was wrong.
Traditional selective logging dries out forests by opening the canopy and creates a lot of flammable debris. Nearby farmers and ranchers can provide one potential source of ignition, although there are others as well.
What these researchers have shown is that after a forest burns once, it becomes more susceptible to burning again; only the second fire is much more intense and destructive. Forests recuperate much slower to the second round of fires and ultimately you have nothing left. Large parts of the Brazilian Amazon that appear on the satellites as ’deforested’ may not have been willfully cleared by anyone. They are simply forests that ’accidentally’ burned one time too many. This may also be one of the main explanations for why Brazil’s official deforestation estimates shot up between 1993 and 1995.
If you want to read a less prosaic and more scientific version of this story, a good place to start is Cochrane et. al.’s ’Investigating Positive Feedbacks in the Fire Dynamic of Closed Canopy Tropical Forests’. Cochran’s paper brings together technical information from experimental plots, landowner interviews, and satellite imagery focusing on Brazil’s so-called ’arc of deforestation’. Although in theory it covers both the western and the eastern Amazon, most of the data come from the drier east, where it rains less than 1,800 mm each year. The authors conclude that ’Left unchecked the current fire regime will result in an inexorable transition of the entire affected area to either scrub or grassland’. They estimate that Para and Mato Grosso alone have thirty million hectares of forest that could be lost through this process.
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