Fishbone deforestation pattern affecting environment

Rondonia is a state in the Amazonian region where the establishment of rural development projects has resulted in the construction of orthogonal road networks. Deforestation along the rapidly expanding network of highways and local roads has created a unique fishbone pattern.

Somnath Baidya Roy, a professor of atmospheric sciences at Illinois, is studying the atmosphere dynamics of fishbone deforestation, and will present his findings at the American Geophysical Union meeting in San Francisco, Dec. 11-15.

“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.”

Whether there has been a change in the overall amount of precipitation has not been established, but there is definitely evidence for the redistribution of precipitation. Roy attributes this redistribution to “vegetation breezes” that are similar to lake and sea breezes.

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 uses a high-resolution computer simulation model to study the effects of deforestation on climate, and the effects that climate change has on the landscape, a process known as “feedback cycle.”

Recent studies have indicated that fishbone deforestation can trigger up to 15 millimeters more rain over pastures, stimulating an increased growth of vegetation 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.”

If the deforestation had resulted in less rainfall, leading to a decrease in plant growth, this would be referred to as a “positive” feedback-cycle.

Roy’s model is high-resolution, resulting in very detailed data. The drawback to this model is that it cannot be carried out for prolonged periods, unlike more conventional climate models, which provide coarser data but can be carried out continuously.

“Our next goal is to correlate my model with other climate models,” Roy said, “so that we may study the longer term aspects of fishbone deforestation, while maintaining the high-resolution.”

Editor’s note: To reach Somnath Baidya Roy, call 217-244-1123; e-mail: sbroy@uiuc.edu.