Employees of a German logging company stand next to a felled tree in northern Republic of the Congo.

"There are very few of these trees targeted by the logging companies [in a given area]," said ecologist Nadine LaPorte.

"You'll see one tree per hectare (2.5 acres). To get to this one tree, you have to also fell the trees around [it]."

LaPorte and her colleagues used high-resolution satellite imagery to document the disturbances created by tree-felling and skid trails, the temporary paths made by loggers for dragging felled trees.

Gaps created by tree-fall ranged from 2,000 to 6,500 square feet (200 to 600 square meters) in size and, together with skid trails, accounted for 9 percent of the area in which logging occurred, the study showed.

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