Encompassing Mexico’s main mountain chains, and isolated mountaintop islands in Baja California and the southern United States, the Madrean Pine-Oak Woodlands is an area of rugged mountainous terrain, high relief, and deep canyons. A quarter of all Mexico’s plant species are found here, many of them found nowhere else on Earth. The pine forests of Michoacán provide famous overwintering sites for the annual migration of millions of monarch butterflies. Unfortunately, the destruction of pine forests due to excessive logging is the leading cause of habitat loss in this region.