Biodiversity in the Madrean Archipelago of Sonora, Mexico Thomas R. Van Devender, Sergio Avila-Villegas, and Melanie Emerson Sky Island Alliance, Tucson, Arizona Dale Turner The Nature Conservancy, Tucson, Arizona Aaron D. Flesch University of Montana, Missoula, Montana Nicholas S. Deyo Sky Island Alliance, Tucson, Arizona Introduction open to incursions of frigid Arctic air from the north, and the Sierra Madres Oriental and Occidental create a double rain shadow and Flowery rhetoric often gives birth to new terms that convey images the Chihuahuan Desert. Madrean is a general term used to describe and concepts, lead to inspiration and initiative. On the 1892-1894 things related to the Sierra Madres. In a biogeographical analysis of expedition to resurvey the United States-Mexico boundary, Lieutenant the herpetofauna of Saguaro National Monument, University of Arizona David Dubose Gaillard described the Arizona-Sonora borderlands as herpetologist and ecologist Charles H. Lowe was probably the first to “bare, jagged mountains rising out of the plains like islands from the use the term ‘Madrean Archipelago’ to describe the Sky Island ranges sea” (Mearns 1907; Hunt and Anderson 2002). Later Galliard was between the Sierra Madre Occidental in Sonora and Chihuahua and the the lead engineer on the Panama Canal construction project. Mogollon Rim of central Arizona (Lowe, 1992). Warshall (1995) and In 1951, Weldon Heald, a resident of the Chiricahua Mountains, McLaughlin (1995) expanded and defined the area and concept. coined the term ‘Sky Islands’ for the ranges in southeastern Arizona (Heald 1951). Frederick H. Gehlbach’s 1981 book, Mountain Islands and Desert Seas: A Natural History of the US-Mexican Borderlands, Biodiversity provided an overview of the natural history of the Sky Islands in In 2007, Conservation International named the Madrean Pine-oak the southwestern United States. The ‘desert seas’ in the valleys are Woodlands as a global biodiversity hotspot. This was a very large desert grassland and Chihuahuan desertscrub in the north, Sonoran area that included the Sierra Madre Oriental in eastern Mexico, the desertscrub to the west, and foothills thornscrub in the south. Variants Sierra Madre Occidental (SMO) in western Mexico, and the Sky Is- of the term include Sky Island region (McLaughlin 1995; Gottfried land ranges north of them into Texas, New Mexico, and Arizona. The and others 2005; Skroch 2008), sky-island ranges (Felger and Wilson Sierra Madre Occidental extends in western Mexico from Zacatecas 1995, Fishbein and others 1995), and sky island bioregion (Fishbein and and Jalisco north to Chihuahua and Sonora. The southwestern United others 1995; Skroch 2008). Today we mostly use ‘Sky Island Region’ States is famous for its diversity of animals and plants, and in many with capital letters. The best name in Spanish is Islas Serranas, rather groups diversity increases southward in Sonora into the Sierra Madre than the literal translation Islas del Cielo, because cielo means both Occidental and the New World tropics. ‘sky’ and ‘heaven.’ The analogy to oceanic islands (Warshall 1995) Species richness is enhanced in the Sky Island Region for many is limited because Sky Islands differ from true insular areas in high reasons. The western half of North America is mountainous, with species diversity, low local and regional endemism, and low percent- topographically diverse habitats and vegetation zoned along eleva- ages of non-native species (McLaughlin 1995). While any isolated tional-climatic gradients. Biotic communities are concentrated in area is a potential area for speciation in small populations, there are small geographic areas compared to the eastern United States where relatively few species restricted to the Sky Island Mountains. vegetation mostly changes along a north-south latitudinal gradient. The term ‘Madrean’ comes from the Sierra Madre. The Mexican The Madrean Archipelago is a convergence zone for five biotic Plateau is a vast area of grasslands and desertscrub between the provinces (fig. 1). The Rocky Mountains and Colorado Plateaus to the Rocky Mountains in New Mexico and ca. 1,300 km to the south the north have temperate climates. In the mid-continent, the grasslands of Trans-Mexican Volcanic Belt in south-central Mexico. The Plateau is the Great Plains extend from Canada south to New Mexico, Texas, and the Mexican Plateau. In the south, a mosaic with desert grassland in the valleys and Chihuahuan desertscrub on adjacent limestone slopes extends westward into southeastern Arizona and northeastern Sonora. In: Gottfried, Gerald J.; Ffolliott, Peter F.; Gebow, Brooke S.; Eskew, Lane On the western edge of the Sky Island Region, Sonoran desertscrub G.; Collins, Loa C., comps. 2013. Merging science and management in surrounds Sky Island ranges. In the south, more tropical oak wood- a rapidly changing world: Biodiversity and management of the Madrean lands and pine-oak forests are in the Sierra Madre Occidental and Archipelago III; 2012 May 1-5; Tucson, AZ. Proceedings. RMRS-P-67. Sky Island mountaintops. In the lowlands, foothills thornscrub (FTS) Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky and tropical deciduous forest are present. The transition between the Mountain Research Station. New World tropics and the northern temperate zone is at about 29°N in 10 USDA Forest Service Proceedings RMRS-P-67. 2013 Biodiversity in the Madrean Archipelago of Sonora, Mexico Van Devender, Avila-Villegas, Emerson, and others B C A Figure 2—(A) The U.S.-Mexico Boundary and Gadsden Purchase Figure 1—Map of the biotic convergence in the Madrean Archipelago Surveys of 1848-1857 went through Guadalupe Canyon (photo by T. (map by Nick Deyo). R. Van Devender). (B) Arthur C.V. Schott and (C) Charles Wright were expedition botanists. east-central Sonora. The northern limits of FTS in Sonora are at about 30°11’N east of Sinoquipe in the Río Sonora Valley and 30°26’N at B Presa Angostura on the Río Bavispe at the southern end of the Sierra El Tigre. FTS does not reach Arizona, but the distributions of quite a few FTS species cross the border into southern Arizona in desert grassland or oak woodland. Sky Island Bioblitzes Today the term ‘bioblitz’ is popular, meaning an intensive effort in a short period to document the diversity of animals and plants in an area. The first bioblitz in the southwestern United States was the 1848-1855 survey of the new boundary between the United States and Mexico after the Treaty of Guadalupe Hidalgo of 1848 ended the Mexican-American War. The border between El Paso, Texas, and A the Colorado River in Arizona was surveyed in 1855-1856, following the Gadsden Purchase in 1853. Besides surveying and marking the border with monuments, these expeditions made extensive animal and plant collections, often by army physicians. Botanists John M. Figure 3—(A) The second U.S.-Mexico Boundary Survey in 1892- 1894 was led by Edgar A. Mearns. (B) The Arizona-Sonora Boundary Bigelow, Charles C. Parry, Arthur C. V. Schott, Edmund K. Smith, is between the Sierra San José and the Huachuca Mountains (photo George Thurber, and Charles Wright (fig. 2) and zoologist John H. by T. R. Van Devender). Clark collected between the Santa Rita Copper Mines (= Silver City), New Mexico and Santa Cruz, Sonora in the modern Arizona-Sonora borderlands. On the second United States-Mexico Boundary Survey in 1892-1894, Edgar A. Mearns (fig. 3) collected 30,000 animal and plant collections were published in the book Río Mayo Plants (Gentry plant specimens. The mammals were published in the book Mammals 1942). In the 1970s, 80s, and 90s, Paul S. Martin led expeditions from of the Mexican Boundary of the United States (Mearns 1907). In the University of Arizona, which retraced Gentry’s travels, explored 1890, Norwegian Carl S. Lumholtz led an anthropological expedition new areas, and resulted in a revision of the Río Mayo flora (Martin through northeastern Sonora. He published a popular travelogue in and others 1998). This large area includes the Sierra Madre Occidental 1902. Sweden’s Carl V. Hartman was a botanist in charge of general in eastern Sonora and western Chihuahua. biological collections (fig. 4). Studies of the flora and fauna of the Yécora area in the SMO in eastern Sonora provide baseline information needed to compare Río Mayo-Yécora Baseline biotas in the Madrean Archipelago with the mainland Sierra Madre Occidental, putting the biodiversity of Sky Island ranges in regional In the 1930s, Howard Scott Gentry was a recent graduate from the context. Mexican Federal Highway 16 (MEX 16), one of the few University of California at Berkeley. In search of employment, he highways that crosses the SMO, provides a west-to-east elevational went to the New World tropics in the Álamos area in southern Sonora, transect from the Río Yaqui (180 m) east to the Chihuahua border, in hopes of selling biological specimens to museum collections. His 42 km east of Yécora (fig. 5). USDA Forest Service Proceedings RMRS-P-67. 2013 11 Van Devender, Avila-Villegas, Emerson, and others Biodiversity in the Madrean Archipelago of Sonora, Mexico C A B Figure 4—The Lumholtz Expedition. (A) Carl S. Lumholtz. (B) Botanist Carl V. Hartman. (C) Sketch of the church in Bacadéhuachi in Lumholtz (1902). de Yécora region on 36 fieldtrips from 1995 to 2008. This flora with 1,776 taxa in 3,300 km2 is very diverse, ca. 30% more diverse than the Huachuca Mountains in southeastern Arizona (Reina-G. and Van Devender 2005). There are 2,125 observations of 301 species of birds from the Municipio de Yécora in the Madrean Archipelago Biodiversity Assessment (MABA) database (http://www.Madrean.org). Borderlands Exploration Higher Sky Island mountain ranges such as the Sierras de los Ajos, Elenita, Marquita, and Tigre have extensive pine-oak forest and mixed-conifer forests on the highest peaks (fig.