An updated version of NAFTA includes measures that crack down on the trade of illegally harvested wood, while also promoting sustainable forestry in the U.S., Mexico, and Canada.

The language is a significant leap for protection of rainforests in the Amazon and elsewhere, according to Alexander von Bismarck, head of the advocacy group Environmental Investigation Agency and member of a U.S. Trade Representative advisory committee on environmental issues.

“We continue to lose the Amazon, the biggest forest...