Biodiversity and management of the Madrean Archipelago: The Sky Islands of southwestern United States and northwestern Mexico

-Previous work on biogeographic isolation has concerned itself with oceanic island chains, islands associated with continents, fringing archipelagos, and bodies of water such as the African lake system which serve as "aquatic islands". This paper reviews the "continental islands" and compares them to the Madrean sky island archipelago. The geological, hydrological, and climatic context for the Afroalpine, Guyana, Paramo, low and high desert of the Great Basin, etc. archipelagos are compared for source areas, number of islands, isolating mechanisms, interactive ecosystems, and evolutionary history. The history of scientific exploration and fieldwork for the Madrean Archipelago and its unique status among the planet's archipelagos are summarized. In 1957, Joe Marshall published "Birds of the Pine-Oak Woodland in Southern Arizona and Adjacent Mexico. " Never surpassed, this elegant monograph described the stacking of biotic communities on each island mountain from the Mogollon Rim to the Sierra Madre. He defined the Madrean archipelago as those island mountains with a pine-oak woodland. In 1967, Weldon Heald (1993), from his home in the Chiricahuas, coined the addictive phrase-"sky islands" for these insular mountains of the North American borderlands. Weldon Heald's catch phrase immortalized Joe Marshall's meticulous observations. Today's conference is the first solely dedicated to understanding Madrean sky island biology, beauty, and needs for management and conservation. There are about 40 sky islands (fig. 1) between the Mogollon Rim and the Sierra Madre Occidental (Warshall, in press). Mt. Graham on the Pinaleno mountains is the tallest peak (10,712 feet). Relief between valleys and peaks ranges from 1250 to 6750 feet (McLaughlin, 1992), but is typically between 3000 and 5000 feet. The Madrean region has exceptional species richness, super-species complexes, unusual neoendemics and archeoendemics, an exceptional mixture of species from the Nearctic and Neotropic regions, important influences from the eastern (North 10ffice of Arid Lands Study, Col/ege of Agriculture, University of Arizona, 845 N. Park, Tucson, AZ 85719. 6 American Prairies Province of Takhtajan, 1986) and western biogeographic provinces, a wealth of genetically unique cultivars in the Sierra Madre Occidental, and a myriad of mysteries concerning the distribution of disjuncts, species "holes," and species II outliers" on individual mountains (e.g., Ramamoorthy, 1993). The northernmost sky islands are the only place in North America where you can climb from the desert to northern Canada in a matter of hours (Warshall, 1986). The sky islands pose numerous puzzles about vertical migration strategies used by plants and animals both annually and over glacial time periods. These interests in ecology and evolution mix with the other citizen interests in skiing, grazing, hunting, fishing, escaping the heat, summer homes, telescopes and radio towers, bird watching, rock-climbing, military practice maneuvers, fuelwood cutting, camping, mining, sacred Native American values and ceremonies, archaeological sites, as well as preservation of sky island habitat for threatened and endangered species. Underpinning all these interests is the exceptional beauty of the sky islands-their layering of peaks in a dusty sunset, lines of vibrant riparian along arid yellow slopes, the contrast of snow and desert, the baffling complexity of erratic ridge lines, the power of fires, and the subtle tones of blue-gray limestonE! , speckled granite, and pastel volcanics.