A mission for monarchs: masses of autumn-colored monarchs cluster together as they overwinter in Mexico. Depletion of the forest there has many concerned for the butterfly's future

American Forests, Summer-Autumn, 2004 by Will Clattenburg

Jose Luis Alvarez insists that he is, first and foremost, a tree man. His nursery, Vivero Hacienda La Cruz, is located on one of the most fertile grounds in the central-Mexican state of Michoacan. Here, where the springs flow and the rich dark soil provides a secure bedding for seeds and seedlings, Alvarez produces thousands of trees that go towards repopulating the surrounding mountains and valleys.

Alvarez, 51, was not always a tree planter. He grew up in Juarez and spent several years abroad before returning to Mexico to settle permanently with his family. "I traveled throughout Mexico, looking for a place where I could buy a ranch," he says. "It had to have certain requirements ... and it had to be within my means." He eventually picked La Cruz in Michoacan, a colonial ranch close to Santa Clara de Cobre. The surrounding forests played a large part in influencing his decision. Only four years after he settled in La Cruz, Alvarez was helping local people replant trees.

Now he raises trees both for commercial plantings and for reforestation. He plants many trees on land owned by indigenous community groups called ejidos, made up of 200 to 300 individuals or ejidatarios. Through his efforts, the ejidatarios learn to make better use of their land, and the wildlife thrives.

Perhaps no species of wildlife benefits more than the monarch butterfly, a species beloved throughout North America. Tree plantings preserve the monarchs' winter quarters and allow the autumn-colored insects to maintain their yearly migration from the eastern United States and Canada to the pine and oyamel fir forests of central Mexico.

To witness the great monarch migration is to witness one of nature's most spectacular sights. The butterflies arrive in Mexico at the beginning of November, around the time of the present day holiday of Los Dias de Muertos, or Day of the Dead. This is fitting, considering the Aztecs used to believe monarchs represented the spirits of slain warriors.

No one knows for sure what triggers the butterflies to fly south at this exact time every year, stopping at the same exact spots as did previous generations, but Alvarez offers a couple of theories.

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"Some scientists believe that the monarchs sense the inclination of the earth by the changing autumn light," he says. "Others say that the monarchs have certain chemicals in their body that attract them to Mexico."

Their flight covers almost 3,000 miles, and by the time they reach the homestretch, approximately a million butterflies fly side by side. Not a single individual in this butterfly caravan has ever been to Mexico, yet they never get lost and succeeding generations always come back.

Once the monarchs nestle safely in the pine and fir forests of central Mexico, they take up residence for six months. During this time they mate and build crucial fat reserves for their home journey, not a bad life by any standard. Oyamel firs aid in the fattening process by providing monarchs with a cool environment and protecting them from the slightly wet atmosphere.

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Butterflies cluster in thick, seething groups around the branches and trunks of these fir trees, and will even land on naturalists and photographers who pause for longer than a few seconds. At the end of six months, the monarchs resume their flight, this time spreading their wings to ride the northern breezes to Texas, where several lay their first eggs.

Shortly after laying an average of 100 to 300 eggs, one group of returnees passes away, leaving the surviving larvae to fend for themselves. Endowed with an insatiable appetite for milkweed, and almost always in close proximity to the plant, these larvae eventually turn into butterflies and continue flying north. Three generations of butterflies come and go before the monarchs ride the wind currents back to Mexico.

Deforestation could cancel the monarchs' plans. Even the loss of a few trees from the canopy hurts overwintering butterflies. Alvarez first learned about the monarchs' plight while trying to reforest the scarred paths of loggers. In January 2002, the danger to the butterflies became impossible to ignore when 80 percent of some colonies in Michoacan died in a severe snowstorm. Holes in the canopy had left the roosting insects prey to the frosty nights.

Alvarez, who modestly says his expertise is trees not butterflies, demonstrates the difference in tree cover with his hand. Holding his fingers upward and closed, he explains, "The butterflies need a closed canopy, like this."

Now he spreads his fingers in five directions. "This is an open canopy: If it rains, the water freezes the butterflies and they fall like cardboard." Open canopies present another big disadvantage: they let in more light, which triggers monarchs to fly when they should be resting. By flying at unnecessary times, monarchs deplete their fat reserves and are unable to make the return journey to the United States. If fewer butterflies make it to the U.S., fewer will return to Mexico.