Monarch butterflies roost in huge numbers during the winter only in oyamel fur trees in the mountains of central Mexico. The fur's dense foliage provides insulation from freezing temperatures. And unlike other trees, monarchs can easily cling to the fir's tiny needles with their claws.
But as temperatures rise with global warming, oyamel furs won't be able to survive where they are growing now. People will have to plant the oyamels at higher elevations, so the butterfly reserves will be ready for changed conditions.
That's just what Mexican conservationists are planning for now.
Find out more here.
Photos of my trip to the wintering areas in 2015.