The Monarch Butterfly Biosphere Reserve () is a World Heritage Site containing most of the overwintering sites of the eastern population of the monarch butterfly. The reserve is located in the Trans-Mexican Volcanic Belt pine-oak forests ecoregion on the border of Michoacán and State of Mexico, 100 km (62 miles), northwest of Mexico City. Millions of butterflies arrive in the reserve annually. Butterflies only inhabit a fraction of the 56,000 hectares of the reserve from October–March. The biosphere's mission is to protect the butterfly species and its habitat.
Most of the overwintering monarchs from eastern North America are found here. Researchers discovered these areas in 1975. Presidential decrees in the 1980s and 2000 designated these still privately held areas as a federal reserve. The Reserve was declared a Biosphere Reserve in 1980 and a World Heritage Site in 2008. The reserve remains predominantly rural. Reserve administrators continue to be concerned with deleterious effects of illegal logging and tourism. Conservation efforts sometimes conflict with the interests of local farmers, community-based landowners, private land owners and indigenous people.
History
The region that comprises the reserve was over-logged during the colonial period of the 19th century. The post-Mexican Revolution saw an increase in restitution for these actions in the form of land grants among the Indigenous populations. The region has remained mostly rural, noted for communities of Otomi and Mazahua. These communities have "traditionally preserved upper mountain ranges as communal lands for... collective use, including sustainable forest exploitation, while the lower hills were divided into family plots where households grew crops in traditional food gardens" (see below: Conservation).
Initial protection for the monarch butterfly overwintering areas was decreed in 1980 by President José López Portillo after decades of extensive research on the migratory patterns of the monarch butterfly. In the late 1980s reserve management was delegated to the Secretariat of Urban Development and Ecology.
In 1986, poet and founder of the Group of 100 Homero Aridjis convinced President Miguel de la Madrid to give the overwintering sites special protection, and the resulting presidential decree, published October 9, 1986, designated Sierra Chincua, Sierra El Campanario, Cerro Chivatí-Huacal, Cerro Pelón and Cerro Altamirano as protected areas for the migration, hibernation and reproduction of the monarch butterfly as part of the Monarch Butterfly Special Biosphere Reserve covering . A "total and permanent ban on logging and use of the vegetation and wildlife" was decreed in the core zones, . The buffer zones, were to "protect the core zone from outside impact, and productive economic activities were allowed, within environmental norms."
In September 2000, the Monarch Butterfly Biosphere Reserve was enlarged to cover , with core zones of and buffer zones of . In 2008, when Homero Aridjis was Mexico's ambassador to UNESCO, he convinced the World Heritage Committee's 21 members to unanimously agree to list the Monarch Butterfly Biosphere Reserve as a World Heritage Site, in the category of natural sites.
In February 2014, the Group of 100 and Make Way For Monarchs addressed a letter to President Enrique Peña Nieto, President Barack Obama and Prime Minister Stephen Harper asking them to discuss the future of the monarch butterfly at the North American leaders' Summit to be held in Toluca, state of Mexico on February 19–20. The letter said, "Plummeting from a high of 1.1 billion monarch butterflies overwintering in central Mexico´s high-altitude oyamel fir forests in 1996 to a pitiful 33 million thinly scattered over seven sites during the current 2013–2014 season, the extraordinary monarch butterfly migratory phenomenon is now officially endangered. In past years, the decline in butterfly numbers was blamed on logging in Mexico's Monarch Butterfly Biosphere Reserve, out-of-control ecotourism and devastating climate events such as the 2002 winter storms in the state of Michoacan and the severe 2011 drought in Texas.
However, monarch butterfly experts now largely agree that a major cause of the dramatic drop in monarch numbers is the huge increase in land planted with genetically modified, herbicide-resistant soybean and corn crops (93% of total soybean acreage and 85% of corn acreage in 2013) in the U.S. Corn Belt. Relentless spraying of herbicides on the fields has destroyed the once abundant milkweed plants, the only plants that monarch caterpillars can eat. The monarch butterfly is literally being starved to death. Sharing the blame is continued degradation of the monarchs' overwintering habitat in Mexico, where small-scale illegal logging is still rampant."
The joint statement released by the three leaders at the end of the meeting stated that "We will continue to collaborate in the protection of our region's biodiversity and to address other environmental challenges, such as wildlife trafficking and ecosystems at risk. Our governments will establish a working group to ensure the conservation of the Monarch butterfly, a species that symbolizes our association." In June 2014, Obama established a Pollinator Health Task Force, one of whose stated goals is to "increase the Eastern population of the monarch butterfly to 225 million butterflies occupying an area of 6 hectares in the overwintering grounds in Mexico, through domestic/international actions and public/private partnerships, by 2020."
In June 2016, more than 200 scientists, writers and artists signed a letter written by Homero Aridjis, Lincoln Brower and Ernest Williams and addressed to Mexican President Enrique Peña Nieto, U.S. President Barack Obama and Canadian Prime Minister Justin Trudeau in advance of the North American Leaders' Summit in Ottawa later that month, urging the three countries to work together to mitigate the loss of the butterflies' breeding habitat and to terminate all logging in the Monarch Butterfly Biosphere Reserve in Michoacán and the State of Mexico.
In 2020, there were nine monarch colonies in the Biosphere Reserve, occupying . As scientists estimate there could be as many as 50 million monarchs in a hectare, the 2020 population only reached 105 million. Monarchs wintering in central Mexico's forests in 2024-2025 occupied , almost doubling the occupied during the previous winter.
Another notable piece of context regarding the MBBR is the disappearance of Homero Gómez González in January 2020, who was an important figure in the conservation of the butterfly. Gonzalez-Duarte points out that a disappearance creates fear and terror amongst the community by preventing mourning. Media coverage of this event followed the narrative that loggers were to blame for the disappearance of the environmentalist. Gonzlez-Duarte challenges this narrative and attributes the disappearance to growing violence and an increased presence of organized crime.
As of 2023, one of the larger known overwintering sites was in the Joya Redonda Monarch Butterfly Sanctuary, located southeast of Mexico City, in the foothills of the volcanoes Popocatépetl and Ixtaccíhuatl in the state of México's municipality of Atlautla. Clusters of monarchs roost in the sanctuary's oyamel fir trees each winter. Although area residents had earlier seen small numbers of monarchs, more butterflies began to establish colonies in Atlautla during the early 2000s as deforestation to the northwest destroyed old hibernation grounds within the Monarch Butterfly Biosphere Reserve. Assisted by local volunteers, the Joya Redonda's colonies increased tenfold in one year. During the 2021–2022 season, only four colonized trees existed; during the following season, there were 42. At the time, tourists were charged 100 pesos (around U.S. $5.50) for access to the sanctuary.Multiple sources:
Ecosystem Geography and forest cover
The reserve extends from the mountainous forests of eastern Michoacán to western Mexico State 100 km northwest of Mexico City. The reserve in Michoacán contains the highest elevations in the state, including peaks that reach 2,700 masl (metres above sea level). The climate is classified as being temperate and somewhat moist with a rainy season in the summer. The average maximum temperature is 22 °C (71 °F). Sub-climates exist in this area: cool and semi moist, semi cold and semi moist, and cold and semi moist.
The reserve is characterized by outcroppings of basalt forming fissures, faults and cliffs in a northeast–southwest orientation. Rock formations have replaced older ones such as volcanic cones and old lava beds. The soil is highly permeable, resulting in little surface water. There are some small ponds and arroyos. The forests of pine and of drought-resistant oyamel fir trees provide microclimates that provide shelter when temperatures fall to freezing and/or there are winter rains. Scientists are concerned that the oyamel habitat in the reserve will shrink or disappear by the end of the 21st century, mainly due to climate change.
This area is predominantly covered in forests. The composition of the forest varies with altitude: holm oak up to 2900 masl holm oak and pine between 1500 and 3000 masl oyamel fir between 2400 and 3600 masl.
Below 2400 masl, there are small areas with junipers, cedars, and meadows. Areas have been modified by agriculture and human settlements.
Fauna The wildlife in the area ranges from the sub-tropical to the sub-arctic including a number of species that are endemic only to this area. These include white-tailed deer (Odocoileus virginianus), coyotes (Canis latrans), long-tailed weasels (Neogale frenata), grey foxes (Urocyon cinereoargenteus), rabbits (Sylvilagus spp.), ravens (Corvus corax), turkey vultures (Cathartes aura), great horned owls (Bubo virginianus), as well as various types of hummingbirds, reptiles and amphibians.
There are fourteen major butterfly colonies located in these rugged forested mountains, which account for more than half of colonies of the monarch butterfly's eastern U.S./Canada population. It is estimated that up to a billion individuals spend winter here in any given year. These colonies are dense, with between six and sixty million butterflies per hectare. The reserve areas are found in the municipalities of Ocampo, Angangueo, Zitácuaro and Contepec in Michoacán and Donato Guerra, Villa de Allende and Temascalcingo in the State of Mexico. They are divided into five principal zones or nuclei.
Eight of the fourteen colonies are in the protected area. The colonies proper cover only 4.7 hectares, but the protected biosphere area covers 56,259 hectares. Five colonies are open to visitors: Sierra Chincua and El Rosario in Michoacan, and La Mesa, Piedra Herrada and El Capulin in the State of Mexico. There are other colonies near San José Villa de Allende and Ixtapan del Oro, but they are not actively promoted for tourism because of the risk of harm to these butterfly colonies. El Rosario is the largest sanctuary in Michoacán, where the butterflies cover about 1,500 trees.
While the Biosphere still has problems with infrastructure, especially with trash around parking and merchant areas, a number of improvements have been recently made, most notably in the sanctuary of El Rosario. These include well-defined footpaths with security patrols and stone/or concrete steps in steep places to help against erosion. Horsepaths were also eliminated for erosion reasons. Only two areas have significant installations. In the Sierra Chincua there is a research facility dedicated to the monarch butterfly and a nursery for reforestation efforts. Cerro El Companario has facilities for tourism.
Conservation
Migratory patterns and conservation efforts