A better way to cut down the Amazon rainforest?

A better way to cut down the Amazon rainforest?
Rhett Butler, mongabay.com
December 11, 2006

A new study suggests that deforestation that follows a "fishbone" pattern may be less damaging from an environmental standpoint than traditional clear-cutting. The reason? Fishbone deforestation patterns may create conditions that increase precipitation levels which help cleared vegetation recover quicker.

The research, which will be presented this week by Somnath Baidya Roy, a professor of atmospheric sciences at University of Illinois at Urbana-Champaign, at the annual American Geophysical Union meeting in San Francisco, is based on analysis of deforestation in Rondônia, a state in Brazil where the "establishment of rural development projects has resulted in the construction of orthogonal road networks." Deforestation, which typically follows road and highway construction, has progressed in a fishbone pattern (see image below).

Different forms of deforestation in Brazil, courtesy of Google Earth. Fishbone deforestation can also speed forest recovery relative to clear-cutting by creating a larger surface area between deforested areas and remaining forest. This enables seed-dispersers like birds, insects, and mammals to help tree species recolonize cleared areas.

"People often relate tropical deforestation to clear-cuts," Roy said. "Climate models show that clear-cuts, if they happen on a basin-wide scale, will result in decreased rainfall and bring about a drier, more arid landscape. In the case of fishbone patterns, the deforestation is in isolated segments of the landscape, and our models indicate that it results in increased precipitation over these deforested regions."

Roy has yet to determine whether there have been changes in the overall amount of precipitation, but has found evidence that precipitation has been redistributed.

"Roy attributes this redistribution to "vegetation breezes" that are similar to lake and sea breezes," explained a statement from the University of Illinois. "A deforested patch is warmer than the neighboring forests. Warm air is lighter and rises, creating a localized low-pressure zone. Cool air then rushes in to fill the void. Because of this convergence, more cumulus clouds and rainfall occur over the deforested patch."

Roy cites recent studies that show fishbone deforestation can result in up to 15 millimeters more rain over pastures, an increase that stimulates faster vegetation growth in these areas.

"It is very counter-intuitive that in these cases, fishbone deforestation results in a negative feedback-cycle," Roy said. "It's negative because it speeds up vegetation recovery and thus offsets the effects of deforestation."

Overall Brazil has lost some 650,00 square kilometers (250,000 square miles) or 18 percent of the Amazon rainforest since the early 1970s. Most deforestation has resulted from clearing for cattle pasture, agriculture, infrastructure development, and resettlement initiatives. Clearing for pasture is estimated to have been responsible for three-fifths to two-thirds of Amazon deforestation.

This article uses quotes and information from a news release from the University of Illinois at Urbana-Champaign.

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