HIGH in the mountains of central Mexico, monarch butterflies arrive by the millions each winter to take refuge, their black and orange wings festooning stands of towering fir trees. But conservationists have grown increasingly concerned as the butterflies in these small patches of forest, some of which were set aside as preserves, compete with the needs of the residents around them.

Now conservationists are trying to help the butterflies by helping the residents. In July, 40,000 trees were planted near El Rosario in the state of Michoacan in an effort to save the fragile habitat where monarchs congregate after their long flight south from the eastern United States and Canada.