Sky islands may sound like some flight of fancy from the tales of Jonathan Swift, yet they are active, vital and interesting ecosystems. Sky islands are actually forested mountain areas that are relatively isolated from one another in regard to flora and fauna. Southwestern sky islands range through New Mexico, Arizona and Northern Mexico.
Within New Mexico there are seven sky island complexes identified by the BLM. These are the Gila Watershed, Peloncillo, Pyramid Mountain, Animas Mountain, Greater Big Hatchet, Cedar Mountain, and Cooke’s Range – Florida Mountains complexes. Within each of these complexes are groups of mountains, ranges, valleys and other land formations which combine to create unique ecological zones.
Since the most recent glaciation, the advance of desert grasslands and scrublands has limited migration – and therefore contact – between various similar species. This further limits diversity among specific populations, yet also encourages evolutionary adaptation. As a result, there exist unique species within each of these ecosystems. Despite being in an arid climate, the sky islands of the southwest support perennial streams, creating an ideal environment that, in general, discourages migration attempts among indigenous species.
Aiding in the creation of the unique ecosystem is a stack of life zones or “biotic communities” ranging from arid to boreal. “By traversing five biotic communities in a few hours,” says Warshall, “bears can feed on Opuntia (prickly pear cactus) fruit in the morning and grass roots growing in semi-alpine meadows in the afternoon.” Some of the biotic communities within the sky islands contain relict areas which are remnants of colder climates.
According to Peter Warshall, in an article published on the USGS website, the southwestern sky islands are unique inasmuch as “it is the only sky-island complex extending from subtropical to temperate latitudes with an exceptionally complex pattern of species of northern and southern origins” (Warshall). Other sky island complexes include the Great Basin and complexes in Venezuela and Africa. A BLM Wilderness survey of the region says “region is ecologically unique because it is the crossroads of the temperate Rocky Mountains and the tropical Sierra Madre Occidental as well as the meeting place of the Sonoran and Chihuahuan Deserts” (BLM - 3). Species located in the region are primarily from sources in the Sierra Madres and Rocky Mountains.
The sky island region contains roughly 250 breeding species of birds. Other animal life abounds, including “jaguar, javelina, coatimundi, black bear, bighorn sheep, mountain lion, elegant trogan, thick billed parrot, Gould’s turkey, sulfur bellied flycatcher and goshawk” (BLM - 3). Additionally, over 400 kinds of plants, as well as many unique reptiles (over 75 identified species), amphibians and invertebrates call the sky islands home.
Despite the “island” status that protects its variant flora and fauna populations, introduction of endemic species is creating hybridized populations among trout, deer, turkeys and other animals. 60 non-native plants have established themselves within the Arizona portion of the sky islands. Additional damage to the population has come in the form of feral exotic animals. Warshall identifies these as two varieties of opossum as well as the European ferret. Species that were once confined to southern islands have been reported farther north recently and appear to be using riparian areas as migratory corridors. These include 15 non-native fish species. This migration may be a result of the fragmentation of habitats due to the building of subdivisions adjacent to sky islands in the Tucson area.
It is clear that, due to the interference and/or indifference of man, the delicate balance of the sky islands is threatened. Current studies show the decline in many native and endangered species. It is essential that the areas be protected from development until proper cataloging of species, particularly of invertebrates, is completed. Without a clear and complete cataloging, the true value of these regions can not be accurately shown.
Bureau of Land Management (BLM). “New Mexico Wilderness Alliance: BLM Wilderness Inventory.” Magee, Greg and Michael Scialdone, ed. CD-ROM. February, 2003 (Ch6. pg3)
Warshall, Peter. “Southwestern Sky Island Ecosystems.” Our Living Resources: A Report to the Nation on the Distribution, Abundance, and Health of U.S. Plants, Animals, and Ecosystems. LaRoe, Farris, Pucket, et al, ed. 1995. U.S. Department of the Interior National Biological Service. <http://biology.usgs.gov/s+t/noframe/r119.htm>