The Vegetation of Sonora, Mexico

The New World tropics reaches its northern limit in Sonora, not as often stated at the Tropic of Cancer (23.37°N) just north of Mazatlán, Sinaloa. The northernmost tropical deciduous forest (TDF) is in Sonora (28.6˚N), 680 kilometers north-northwest of Mazatlán and 300 km south of the Arizona border.

The Sierra Madre Occidental (SMO) in northeastern Sonora reaches its northern limit in the Sierra de Huachinera (30.25°N; Fig. 1). Between the SMO and the Mogollon Rim in central Arizona, there are 55 isolated Sky Island mountain ranges, or complexes of several ranges, connected by oak woodland corridors in the Madrean Archipelago, 32 of them in northeastern Sonora (Deyo et al. 2013; Van Devender et al. 2013a). These Sky Islands, crowned with oak woodland or pine-oak forest, emerge from lowland ‘seas’ of desert grassland, foothills thornscrub, or tropical deciduous forest.

Sonora, with an area of 184,934 km², is the second largest state in Mexico after Chihuahua. The state of Sonora has a diverse physiography, from the heights of the SMO in eastern Sonora, and the isolated Sky Island mountains in northeastern Sonora, westward to the western lowlands and the Gulf of California. The vegetation of Sonora is equally diverse (Fig. 2). Rzedowski’s (1978) Vegetación de México provided a general classification for the country of Mexico. Brown & Lowe (1982a, 1982b) presented a more specific classification of the vegetation for the southwestern USA and northwestern Mexico, including Sonora. Martínez-Y et al. (2010) and Van Devender et al. (2010) summarized the vegetation of Sonora. The vegetation from the coast of the Gulf of California to the crest of the Sierra Madre Occidental in southern Sonora is described in Gentry’s Río Mayo Plants: The Tropical Deciduous Forest and Environs of Northwest Mexico (Martin et al. 1998). Van Devender & Reina-G. (2005) described the same tropical-to-montane vegetation on the western slopes of the SMO in the Municipio de Yécora in eastern Sonora. González-E. et al. (2012) provided an overview of the floristic subprovinces of the Sierra Madre Occidental and defined the Madrean Tropical subprovince in Sonora.