The Southwest is well known for its deserts, but coniferous forests exist, especially in rare regions known as “sky islands.” These are isolated mountain ecosystems that reach 6,000 feet in elevation or more, surrounded by a sea of desert. The island analogy refers to a key feature of these areas, which is their distance from one another.
Much of their biodiversity has been influenced by past climate cycles, with multiple ice ages followed by warming periods. Pack rat middens that contain fossilized plant material act as a time capsule that can shed light on these past climates and their associated plant communities. One study showed that 18,000 years ago during the last ice age the sky islands were connected by continuous woodlands. As temperatures warmed the woodlands receded to higher elevations, leaving grassland and desert behind.
In Arizona there are a dozen of these special sky islands, mostly in the southeastern part of the state where they extend into Mexico. They also occur in the White Mountains, San Fransisco Peaks, Hualapai Mountains, and parts of the Mogollon Rim. They can contain Engelmann’s spruce and alpine fir at the highest reaches, as well as bristlecone and limber pine, Douglas fir, and oak.
At sky islands, one can witness incredible botanical diversity in a short distance; places where the warm desert breeze meets the cool fresh mountain air.
