Madrean pine-oak woodlands
The Madrean pine-oak woodlands are found at higher elevations in Mexico's major mountain ranges, the Sierra Madre Occidental, the Sierra Madre Oriental, the Trans-Mexican volcanic belt, the Sierra Madre del Sur, the Sierra Madre de Oaxaca, the Peninsular Ranges of the Baja California Peninsula, and there are also approximately 27 enclaves in southern Arizona and New Mexico and in western Texas, where they are known as the "Madrean sky islands". The major Madrean "sky island" ranges in Arizona are the Dragoon Mountains, Chiricahua Mountains, Pinaleño Mountains, Santa Catalina Mountains, Rincon Mountains, Santa Rita Mountains and Tumacacori Highlands. In New Mexico the Sacramento Mountains and Guadalupe Mountains which extend into Texas, as well as, the Davis Mountains and Chisos Mountains are also forested sky islands.
Conservation International estimates the woodlands' original area at 461,265 km². The woodlands are surrounded at lower elevations by other ecoregions, mostly tropical and subtropical deserts and xeric shrublands, forests, and grasslands. Woodland areas were isolated from one another and from the pine-oak woodlands of the Sierra Madre Occidental to the south by the warming and drying of the climate since the ice ages.
The pine-oak woodlands are composed of stands of oak (Quercus), pine (Pinus), douglas-fir (Pseudotsuga) and fir (Abies). The trees generally occur in mixed stands, though monospecific stands are sometimes found. The pine-oak woodlands are home to one-quarter of Mexico's plant species, and Mexico is home to 44 of the 110 species of pine and over 135 species of oak, over 30 percent of the world's oak species. Plant species derived from Madrean ancestors, known as the Madro-Tertiary flora, are an important element of the California chaparral and woodlands ecoregion.
The World Wildlife Fund recognizes several distinct pine-oak woodlands ecoregions, based on geographic distribution and species mix.
- Sierra Juárez and San Pedro Mártir pine-oak forests of the Sierra de Juárez and Sierra de San Pedro Mártir ranges of the northern Baja California peninsula.
- Sierra de la Laguna pine-oak forests of the Sierra de la Laguna in the southern Baja California peninsula.
- Sierra Madre Occidental pine-oak forests extend along the Sierra Madre Occidental range from the Rio Grande de Santiago in Mexico's Jalisco state through Nayarit, Sinaloa, Durango, Sonora, and Chihuahua, and include the Madrean Sky Islands of Arizona and New Mexico.
- Sierra Madre Oriental pine-oak forests extend along the Sierra Madre Oriental ranges of Texas and Mexico, from mountaintop enclaves in west Texas through Coahuila, Tamaulipas, Nuevo León, San Luis Potosí, Querétaro and Guanajuato.
- Trans-Mexican Volcanic Belt pine-oak forests
- Sierra Madre del Sur pine-oak forests
- Sierra Madre de Oaxaca pine-oak forests
- Madrean Pine-Oak Woodlands (Conservation International)
- "Sierra Juarez and San Pedro Martir pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.
- "Sierra de la Laguna pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.
- "Sierra Madre Occidental pine-oak woodlands". Terrestrial Ecoregions. World Wildlife Fund.
- "Sierra Madre Oriental pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.
- Sierra Madre Occidental Pine-Oak Forests images at bioimages.vanderbilt.edu (slow modem version)
- "Trans-Mexican Volcanic Belt pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.
- "Sierra Madre del Sur pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.
- "Sierra Madre de Oaxaca pine-oak forests". Terrestrial Ecoregions. World Wildlife Fund.