318 



Interior West — (^nr Livini; Resources 



For further information: 



David L. Peterson 



National Biological SeiA'ice 



Cooperative Park Studies Unit 



University of Washington 



Seattle. WA 98195 



Woodman, J,N. 1987. Potential impact of carbon dioxide- Woodward. A., M.B. Gracz. and E.S. Schreiner. 1991. 



induced climate changes on management of Douglas-fir 

 and western hemlock. Pages 277-283 in W.E. Shands and 

 J.S. Hoffman, eds. The greenhouse effect, climate change, 

 and U.S. forests. The Conservation Foundation. 

 Washington, DC. 



Climatic effects on establishment of subalpine fir (Al'ies 

 lasiociirpa) in meadows of the Olympic Mountains. The 

 Northwest Environmental Journal 7:353-354. 



Southwestern 

 Sky Island 

 Ecosystems 



by 



Peter Warshall 



University of Arizona 



The "'sky islands" of Arizona and New 

 Mexico in the southwestern United States 

 form a unique complex of about 27 mountain 

 ranges whose boundaries, at their lowest eleva- 

 tion, are desert scrub, grasslands, or oak wood- 

 lands (Figs. 1 and 2; Table 1). Since the last 

 glaciation, these forested mountain ranges have 

 become relatively isolated from each other 

 Expanding desert grasslands and desert scrub in 

 the valleys ("the sea" between the sky islands) 

 have limited genetic interchange between popu- 

 lations and created environments with high evo- 

 lutionary potential. The resulting sky island 

 ecosystems support many perennial streams in 



Galiuro 

 Mts. 



ARIZONA 



Pinalehos Mis. 



Catalina Mts. 



NEW MEXICO 



Rincon Mts. 



"OS, 





Sierrita 

 Mts. 



'*% 



Whetstone 



Chiricahua Mts 



Animas Mis. 



Sierra de 

 Sierra Pini'os Mis. 



Cubila Mis, 



Azul Mts. 



San Jose 

 Mts. 



Ajos Mts. 



Sierra 

 Manzanal Mts. 



San Luis 

 Mts. 



Pulpito 

 Mis. 



San Antonio 

 Mts. 



Aconchi Mts. 



Purica 

 Mts. 



Oposura 

 Mts. 



Tigres 

 Mts. 



CHIHUAHUA 



Huachinera 

 Mts. 



Sierra Madre Occidental Mts. 



SONORA 



I [ Mountain range 



Fig. 1. Sky island mountain ranges of Arizona, New Mexico, and adjacent Sonora and Chihuahua 

 (Marshall 1957). All of the labeled mountain ranges have pine-oak woodland. 



an arid climate, have a high number of endemic 

 species, and harbor most game species as well 

 as most threatened and endangered species in 

 the Southwest. 



The southwestern sky island "archipelago" 

 is unique on the planet. It is the only sky-island 

 complex extending from subtropical to temper- 

 ate latitudes (compared to the Great Basin, the 

 Venezuelan, and the African sky islands) with 

 an exceptionally complex pattern of species of 

 northern and southern origins. The "continents" 

 that have been the main sources of species for 

 the archipelago are the Sierra Madre of Mexico 

 and the Rocky Mountains of the United States. 

 although the flora has been influenced by the 

 Califomian, Sonoran, Intermountain, Cordil- 

 leran, and SieiTa Madrean Floristic Provinces 

 (S. McLaughlin, University of Arizona, unpub- 

 lished data). 



The ecosystems of each mountain range are 

 of major interest to resource managers con- 

 cerned with preserving each sky island's unique 

 biogeography and biological diversity as well as 

 to the public for recreation. Land uses some- 

 times conflict on the sky islands: camping, rock 

 climbing, car-based tourism, military maneu- 

 vers, hunting, fishing, exotic grass and fish 

 stocking, grazing, water-supply withdrawals, 

 timber and fuelwood extraction, bird watching, 

 critical habitat for threatened and endangered 

 species, skiing, summer homes, mining, scien- 

 tific research, sacred Native American cere- 

 monies, and archaeological sites. 



Most American sky islands are within the 

 Gila River basin. About 15 additional sky 

 islands are in Mexico and will not be discussed 

 here. Nevertheless, the cross-border manage- 

 ment of sky islands is important for such tasks 

 as reintroduction of the Mexican wolf (Canis 

 lupus baileyi). maintenance of disjunct popula- 

 tions of rare plant species, and migration of the 

 Mexican pronghorn (Antilocarpa americana 

 me.xicana), if it still occurs. 



Status of Information 



The floras of the largest sky islands of 

 Arizona have been inventoried (S. McLaughlin, 

 University of Arizona, unpublished data), 

 including most insular, endemic, and rare 

 species. Certain inventory gaps (e.g., the 

 Baboquivari, Galiuro. Santa Rita. Whetstone, 

 and Patagonia mountains) exist. In addition, the 



