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The 70,000-square-mile Sky Islands region of southeastern Arizona, southwestern New Mexico, and northwestern Mexico is globally important because of its rich diversity of species and habitats, its history as the birthplace of Aldo Leopold's great American conservation ethic, and as the last North American stronghold of such magnificent predators as the Mexican wolf and jaguar.

These mountain "islands," forested ranges separated by vast expanses of desert and grassland plains, are among the most diverse ecosystems in the world because of their great topographic complexity and unique location at the meeting point of several major desert and forest biological provinces. The region is a blend of tropical and temperate, harboring well over half the bird species of North America 29 bat species, over 3,000 species of plants, and 104 species of mammals--a diversity exceeding anywhere else in the U.S.

This diversity is among the most threatened in North America by land development, climate change, poor livestock grazing practices, fire suppression, off-road vehicles, and resource extraction.

"To my mind these live oak-dotted hills fat with side oats grama, these pine-clad mesas spangled with flowers, these lazy trout streams burbling along under great sycamores and cottonwoods, come near to being the cream of creation." - Aldo Leopold 1937.

image of gila valley

Tumacacori Highlands, looking towards Baboquivari Peak

Weldon Heald coined the term "sky islands" in 1967 to denote mountain ranges that are isolated from each other by intervening valleys of grassland or desert. The valleys of this basin and range country act as barriers to the movement of certain woodland and forest species, somewhat like saltwater seas isolate plants and animals on oceanic islands - hence the common association with the archipelago phenomenon. Other species, such as mountain lions and black bears, depend on movement corridors between mountain islands to maintain genetic diversity and population size.

The greater Sky Islands region is globally important for the lessons it taught Leopold, for its role in launching the wilderness preservation movement, and for its wild and enchanting landscape. We now understand, as he did many decades ago, that the region is also of international importance because of its outstanding biological diversity.