Expansion of avocado monoculture threatens the overwintering habitat of monarch butterflies in central Mexico

Avocado (Persea americana Mill.) has become the main cultivated crop in the highlands of central Mexico. However, avocado monoculture has triggered the loss of conifer forests, even within protected areas, such as the Monarch Butterfly Biosphere Reserve that hosts the overwintering sites of the migratory monarch butterflies (Danaus plexippus Linnaeus). This study modeled avocado monoculture expansion from 2006 to 2024 and suitable areas for avocado cropping under current climate and climate change (low and high emissions) scenarios in pine-oak, mixed-conifer, and sacred fir forests. As a result, 1345 ha of avocado orchards covered the protected area in 2024; most came from the conversion of former traditional croplands and 337 ha from pine-oak forests. Under the current climate, suitable areas were found in 5076 ha, of which avocado orchards already occupied 27 % and 50 % covered by forest. Under the low-emission scenario, 3576 ha were suitable by 2050 and 5133 ha by 2070; under the high-emission scenario, they amounted to 5038 ha by 2050 and 10,395 ha by 2070. In both climate change scenarios, suitable areas moved to higher elevations. Pine-oak forest was the most affected by the expansion of avocado monoculture. Although sacred fir and mixed-conifer forests, the overwintering habitats of monarch butterflies, were not directly affected, the projected expansion of avocado cropping represents a threat due to the reduction of nectar sources and the use of pesticides in new orchards. Therefore, the preservation of conifer forests and better avocado cultivation practices are crucial to ensure this migratory phenomenon.