MAROANSETRA, Madagascar — Exploiting a political crisis, Malagasy timber barons are robbing this island nation of its sylvan heritage, illegally cutting down scarce species of rosewood trees in poorly protected national parks and exporting most of the valuable logs to China.

For a decade or more, this illicit trade existed on a small scale. But in the past year, it has increased at least 25-fold, according to environmental groups that have been tracking the outgoing shipments. They estimate the value of trees felled this past year at $167 million or more.

This accelerated plunder of the rainforest coincided with a military coup in March 2009. Andry Rajoelina, the mayor of Antananarivo, Madagascar’s capital, was installed as president, and he has since led a weakened and tottering government that is unable — and perhaps unwilling — to stop the trafficking.

“The government does nothing because it shares in the money,” said Ndranto Razakamanarina, president of an association of Malagasy environmental groups and a policy officer with the World Wildlife Fund. “Many of the ministers think they’ll be in office only three or six months, so they decide to make money while they can. The timber mafia is corrupt, the ministers are corrupt.”