Tehuacán-Cuicatlán Biosphere Reserve, Biosphere reserve and UNESCO World Heritage Site between Puebla and Oaxaca, Mexico.

The Tehuacán-Cuicatlán Biosphere Reserve covers 490,186 hectares across 51 municipalities in Puebla and Oaxaca, between the Sierra Madre de Oaxaca and the Sierra Mixteca. Its valleys run northwest to southeast and hold xerophytic scrub, tropical dry deciduous forest, pine-oak forest and pockets of cloud forest. The reserve includes one of the world's densest stands of columnar cacti, with 45 of Mexico's 70 species, alongside barrel cacti and spiny clumps on rocky slopes.

Occupation of the Tehuacán-Cuicatlán valley goes back about 12,000 years. Fossil maize found by MacNeish in the Coxcatlán Cave, Puebla, dates to around 5000 BC, and the valley holds the earliest known irrigation works in Mesoamerica: terraces, canals, wells, aqueducts and dams. Otomanguean-speaking peoples lived here in pre-Columbian times, and eight indigenous groups remain. The reserve was declared on 11 September 1998 by President Ernesto Zedillo.

The reserve's name joins Cuicatlán and Tehuacán, where its administrative offices sit. Eight indigenous groups live within its bounds: Mixtecs, Cuicatecs, Ixcatecs, Nahuas, Chocholtecs, Popolocas, Chinantecs and Mazatecs. The 1998 declaration lets residents keep their existing economic activities provided they do not harm the area.

The Helia Bravo Hollis Botanical Garden serves as the main entry point, from which visitors can explore the surrounding area. Guided tours from nearby cities are available and help visitors learn about the different zones and walking routes.

Mexico holds 70 columnar cactus species, and 45 of them grow in this central part of the country, forming one of the world's densest columnar cactus forests. Nine plant communities here are mostly endemic to the reserve. The tall vertical stems visible on the slopes are these cacti.