The Characteristics of the Overwintering Habitat
The oyamel forests of Mexico are remnants of boreal forests that advanced south with periods of glaciation. When the glaciers retreated, they were left as high elevation survivors, existing as isolated islands at 2400-3600 meters (7,800 – 11,700 feet).
In Mexico, forests cover one third of the land area, and more than half of this forested area is considered primary forest, one of the most diverse types of forests in the world.
The monarch butterfly overwintering habitat is described as a temperate forest, composed by oyamel (sacred fir) and pine (smooth-bark Mexican pine), with the scarce presence of the Mexican cedar tree and other tree species. The distribution of the species varies with the altitude, being the oyamel trees the ones who are adapted to the top of the Mountains (elevation between 2,400 and 3,900 meters). The oyamel forests are small, isolated areas that are distributed along the Transvolcanic Belt of Central Mexico. Descending to the base of the mountains, the oyamel and Mexican pine trees mixed together, creating a unique and beautiful pine-oyamel forest.
The Monarch Butterfly Biosphere Reserve protects the remnant islands of the oyamel forest (inside the core zone) and the pine-oyamel forest (inside the core and buffer zones). The main threat to the conservation of the oyamel and pine-oyamel forest is the rapid forest degradation due to different practices:
- Commercial (legal or illegal) logging
- Wood harvesting for domestic use
- The agricultural practices that have left unused, degraded lands in the foothills of the overwintering sites.
- Forests fires
- Climate change
Zones of the Monarch Butterfly Biosphere Reserve (CONANP, 2001)
The distribution of this type of forest is very limited, and the extent and quality of this forest is constantly decreasing with the direct consequence the loss of local biodiversity—that includes several endemic species. Some of the endemic species are listed by IUCN as threatened or endangered.
Therefore, the loss of the oyamel and pine-oyamel forest not only jeopardizes the survival or the migratory monarch butterfly, but also many other endemic species who depend of this unique ecosystem.
The Monarch Butterfly Biosphere Reserve was established in the year 2000, protecting 56,259 hectares of oyamel and pine-oyamel forest.