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Thursday, September 2, 2010

80% of tropical agricultural expansion between 1980-2000 came at expense of forests


More than 80 percent of agricultural expansion in the tropics between 1980 and 2000 came at the expense of forests, reports research published last week in the early online edition of the Proceedings of the National Academy of Sciences (PNAS).

The study, based on analysis satellite images collected by the United Nations Food and Agricultural Organization (FAO) and led by Holly Gibbs of Stanford University, found that 55 percent of new agricultural land came at the expense of intact forests, while 28 percent came from disturbed forests. The remainder came from shrub lands.

"This finding confirms that agricultural expansion did not arise largely from previously cleared land and that agricultural expansion indeed has been a major driver of deforestation and the associated carbon emissions," write the authors. "This study confirms that rainforests were the primary source for new agricultural land throughout the tropics during the 1980s and 1990s."

Total agricultural land increased by 629 million hectares (ha) in developing countries the 1980s and 1990s, including a net rise of than 100 million ha in tropical regions. Much of the expansion occurred in Brazil, Indonesia, and Malaysia, countries that now produce 40 percent of the world's of sugarcane, soybeans, and palm oil, but have experienced high rates of forest loss. Conversion of these forests generated substantial greenhouse gas emissions.

"This has huge implications for global warming, if we continue to expand our farmland into tropical forests at that rate," said Gibbs in a statement. "Every million acres of forest that is cut releases the same amount of carbon into the atmosphere as 40 million cars do in a year."

Gibbs and colleagues found "cropland expansion was faster in the 1980s than in the 1990s" but "pasture showed the opposite trend" with the largest increases occurring in South America. The area of agricultural land converted from intact rainforests in Latin America was 13 percent higher in the 1990s than the 1980s.

"We are seeing mounting tension between growing the food, feed and fuel and keeping forests standing," Gibbs told

The scientists found little evidence that agricultural lands converted from forest areas were being abandoned long enough to enable forest regeneration during the study period.

"We estimate that less than 5% of previously agricultural land later supported natural vegetation during the 1980s and 1990s," the authors write.

The paper also cautions that the trend of agricultural expansion at the expense of forests is likely to continue.

"If the agricultural expansion trends documented here for 1980–2000 persist, we can expect major clearing of intact and disturbed forest to continue and increase across the tropics to help meet swelling demands for food, fodder, and fuel," the authors write. "Indeed, recent studies confirm that large-scale agro-industrial expansion is the dominant driver of deforestation in this decade, showing that forests fall as commodity markets boom."

Nevertheless the authors are guardedly optimistic about the future for tropical forests. They highlight the emergence of reducing emissions from deforestation and forest degradation (REDD), an approach that could see tropical countries compensated for protecting forests. Under some proposals, farmers and ranchers might receive carbon payments to incentive expansion on grasslands and degraded agricultural lands instead of on forest lands. Further the consolidation of the drivers of deforestation from hundreds of millions of rural poor to a limited number of corporations is presenting new opportunities for activists to confront forest destroyers.

"The good news is that we are seeing the tides change in Brazil where roughly one fourth of tropical agricultural expansion occurs," said Gibbs via email. "It's encouraging to see that deforestation rates have been declining since 2004 while production of soy, sugarcane and cattle are increasing."

"Brazil has stepped up enforcement of environmental laws and also reduced credit access to known deforesters. However, the soy moratorium led by Greenpeace and others have also substantially contributed by using consumer-driven market pressure to forge partnerships with industry and ensure that soy farms and more recently, cattle operations, are not leading to new deforestation."

"It is important to remember though, that we are in global economic slump. The real question is whether the Brazilian government and moratoriums will be strong enough safeguards when prices soar again."

"Continued pressure from activist groups combined with international climate agreements could provide a real opportunity to shift the tide in favor of forest conservation rather than farmland expansion."

Regional findings

  • Nearly 60% of new agricultural land was derived from intact forests, and another 35% came from disturbed forests
  • Between 1980 and 2000 cropland area increased by ∼50% in East Africa and by ∼25% in West Africa. In Central Africa the total cropland area declined.

  • Southeast Asia relied on intact forests for nearly 60% of new agricultural land and on disturbed forests for more than 30%.
  • The area of tree plantations increased from roughly 11 million ha to 17.4 million ha between 1980 and 2000
  • Oil palm was responsible for more than 80% of the expansion in plantation area by the 1990s
  • Cattle pastures increased by ∼35 million ha in South America and ∼7 million ha in Central America between 1980 and 2000
  • Cropland areas increased by ∼5 million ha in South America between 1980 and 2000, more than double the increase in Central America.
  • Sugarcane and soybeans are responsible for the majority of the increase in South America, whereas there were few changes in crop types across maize-dominated Central America
  • The area of agricultural land coming from intact rainforests was 13% higher in the 1990s than the 1980s

Gibbs HK, Ruesch AS, Achard F, Clayton MK, Holmgren P, Ramankutty N, Foley JA (2010) Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s. PNAS

Global demand for agricultural products such as food, feed, and fuel is now a major driver of cropland and pasture expansion across much of the developing world. Whether these new agricultural lands replace forests, degraded forests, or grasslands greatly influences the environmental consequences of expansion. Although the general pattern is known, there still is no definitive quantification of these land-cover changes. Here we analyze the rich, pan-tropical database of classified Landsat scenes created by the Food and Agricultural Organization of the United Nations to examine pathways of agricultural expansion across the major tropical forest regions in the 1980s and 1990s and use this information to highlight the future land conversions that probably will be needed to meet mounting demand for agricultural products. Across the tropics, we find that between 1980 and 2000 more than 55% of new agricultural land came at the expense of intact forests, and another 28% came from disturbed forests. This study underscores the potential consequences of unabated agricultural expansion for forest conservation and carbon emissions.

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