Extreme weather earlier this year decimated large swaths of sensitive forest habitat where monarch butterflies winter in Mexico, according to a study released on Tuesday.

Storms in March destroyed 54 hectares (135 acres) of the core of Mexico's Monarch Butterfly Biosphere Reserve, located at the border of the states of Mexico and Michoacan. That's more than four times more habitat destruction than illegal logging, which declined 40 percent this year.

It was the worst weather damage since 2009-10 when storms destroyed more than 100 hectares of forest.

While the loss constitutes a small percentage of the of the 13,551-hectare (34,000-acre) area of the reserve's core, scientists said the second major weather event in five years is troubling.

"It's worrying because this may indicate that the weather will continue to become more extreme," said Omar Vidal, director-general of the Mexican arm of the World Wildlife Fund, which issued the study alongside Mexico's National Autonomous University, the National Commission for Natural Protected Areas and others.

"It's a large amount of trees, it's a large amount of forest, so essentially we're losing habitat for the monarch in this sanctuary," he added. "We need to restore areas that have been deforested, either by illegal logging or violent winds, so that the monarch continues visiting these areas in the long run."

The storms combined high winds, rain and freezing temperatures, causing millions of butterflies to die.

Alejandro Del Mazo, the attorney general for environmental protection, said the storms killed about 6.2 million butterflies, or about 7.4 percent of the estimated 84 million butterflies that wintered in Mexico.

In one of Mother Nature's greatest migrations, the black and orange monarch travels every November 3,400 miles (5,500 kilometers) from Canada and the United States to biosphere reserve to hibernate for five months.

There were an estimated 1 billion monarch butterflies two decades ago. The destruction of forest habitat in Mexico and loss of milkweed plants in the United States where the butterflies lay their eggs have contributed to a drastic decline in their population. Monarch larvae only eat milkweed plants.

Surveys earlier this year suggested monarch numbers could soon rise to 150 million. Conservations attributed the rise to favorable weather at the time and the planting of more milkweed.

Conservationist have tried to encourage poor communities in the area that money brought in by tourism is more valuable than illegal logging.

cw/sms (AP, Reuters)