SKY ISLANDS, DESERT SEA-Part 1
By Arthur V. Evans
“…some of the earth’s most interesting “islands” are nowhere near oceans or lakes. They are strictly land islands but with a climate, vegetation, and animal life as different from their surroundings as if they rose from some remote sea.”
Weldon Heald in Sky Islands
A conservationist and journalist, Weldon Heald coined the term “Sky Islands” nearly 60 years ago to describe the archipelago of mountain ranges spanning the gap between the Rocky Mountains and the Sierra Madre Occidental of central Mexico. Made up of more than 40 isolated mountain ranges, the Sky Islands cover two countries in the states of Arizona, New Mexico, Sonora and Chihuahua. The diversity of flora and fauna inhabiting this region is unmatched in temperate North America. Warmer than the Rocky Mountains and drier than the Sierra Madre Occidentale, these unique and isolated mountain ranges support a wealth of temperate and tropical arthropod species.
The Arizona Sky Islands consist of the Santa Rita, Rincon, Huachuca, Santa Catalina, Whetstone, Bobaquivari, Pinaleño, and Chiricahua Mountains. Climbing thousands of feet into the sky, these lush mountains and their canyons stand in stark contrast to the surrounding lowlands. It is the sheer mass and altitude of these ranges that keeps their peaks and canyons much cooler and wetter than the surrounding desert scrub and grasslands. On average, mountain temperatures drop 4 º Fahrenheit for every 1,000 feet of elevation, while at the same time, annual precipitation increases by four inches. These moisture and temperature gradients create life zones that support populations of arthropods poorly adapted for survival in the relatively harsh, dry environs below. Unable to migrate across this “desert sea,” many of the arthropods inhabiting Arizona’s Sky Islands have been marooned for hundreds of centuries.
© 2010, A.V. Evans