A new study warns that if timber harvest continues unchecked in the Mexican cloud belt forests, millions of monarch butterflies who spend their winter there would face imminent threat in the coming few decades. To assess the effects of logging, researchers from Virginia-based Sweet Briar College analysed aerial images of the forests that were taken over 28 years. The researchers found that in 1971, the forests were extremely lush, but by 1999 more than 40 per cent of this green canopy was reduced to semi-altered forests. "Our findings reflect the limitations of government mandated protection decrees as deterrents to habitat degradation,' the researchers said.