Arizona Sky Islands–Another Ecological Analogue for Pleistocene Georgia

Rapid climate oscillations, megafauna foraging, fire, and wind throws shaped the landscapes of southeastern North America during the Pleistocene.  The resulting environment in the piedmont region consisted of open oak and pine woodlands but with significant patches of closed canopy forests, savannah, prairie, scrub, and wetland.  This variety of habitats in close proximity supported a great diversity of wildlife.  The Pleistocene ecosystem in this region was unlike any extant environment.  Nevertheless, I’ve previously considered some regions as relatively close ecological analogues, resembling the Pleistocene piedmont.  Russian’s Far East was until recently a vast untracked wilderness of mixed forests with abundant game and apex predators.  (See: https://markgelbart.wordpress.com/2011/06/06/russias-far-east-the-modern-worlds-closest-ecological-match-to-pleistocene-georgia/ )  The Cross Timbers region of Texas and Oklahoma where the eastern deciduous forest gradually gives way to prairie may also be a vaguely similar analogue.  (See: https://markgelbart.wordpress.com/2012/06/13/the-cross-timbers-ecoregion-an-analogue-for-georgia-environments-during-some-stages-of-the-pleistocene/ ) I’ve come across a 3rd region that in some ways may resemble Pleistocene piedmont Georgia–the Sky Islands of Arizona, New Mexico, and northern Mexico.

Sky Islands are mountains that stand in the middle of the desert.  They host a variety of environments that change according to elevation.  A change of a few thousand feet in elevation equals the climatic difference of hundreds of miles in latitude.  In a day a man can ascend from an hot desert to temperate oak/pine woodland to boreal spruce/fir forests.  During Ice Ages the lowlands surrounding Sky Islands hosted continuous temperate forests, but now these forested environments are isolated on the mountains, surrounded by desert, hence the name Sky Island.

Mountains rise from the desert floor in Arizona, New Mexico, and northern Mexico.  They host diverse flora and fauna because the change in elevation supports a variety of environments adjacent to each other.

Sky Islands are rich in floral and faunal diversity because so many different natural communities are in such close proximity.  Sky Islands are home to 500 species of birds (over half of the species found in North America), 104 species of mammals, and 120 species of reptiles and amphibians.  Tree squirrels including Mexican fox squirrels, Arizona gray squirrels, and Mt. Graham red squirrels co-exist with rock squirrels (Spermophilus variegatus).  Rock squirrels live and nest in the ground, not trees.  13-lined ground squirrels, another species in the Spermophilus genus, also co-existed with tree squirrels in southeastern North America during the Pleistocene.  13-lined ground squirrels no longer occur in the region because they prefer open environments.  Their presence along with tree squirrels at some fossil sites suggest a more varied environment existed here during the Pleistocene.

Image result for Spermophilus variegatus

Rock squirrel (Spermophilus variegatus).  Sky islands are home to 7 species of squirrels.  During the Pleistocene a squirrel in the spermophilus genus also co-existed with tree squirrels in southeastern North America, suggesting a more diverse variety of habitats within the region.

Arizona Sky Islands are also famous for a small subspecies of white tailed deer known as the Coues.  For some reason the Coues deer is a popular trophy among deer hunters.  Jaguars and coati-mundi roam the Sky Islands as well.

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Coues deer–A small subspecies of white tail that lives on the Sky Islands of Arizona.

The oak savannahs and oak/pine woodlands of Sky Islands likely resemble natural communities that occurred in the piedmont region of Georgia during the Pleistocene, though they are composed of different species of trees.  Emory oak, Arizona white oak, Gambel’s oak, Canyon live oak, and blue oak grow with Arizona juniper, pinyon pine, yucca, bull grass, and bear grass.  Higher in elevation, silverleaf oak grows with ponderosa pine and Arizona pine.  Higher still, the forest may consist of ponderosa pine, Englemann Spruce, and Douglas Fir–trees of the northern Rocky Mountains.

Acorn Woodpecker Photo

Acorn woodpeckers are a communal species that hoards acorns.  They are a common species on Sky Islands.

The different types of forest attract many different species of birds.  Birds that prefer coniferous forests can be found with those that like oak forests. Tropical species including trogons, thick-billed parrots, buff-colored nightjars, and Arizona woodpeckers inhabit Sky Islands.  These species are found at few other sites north of the Rio Grande River.

 

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3 Responses to “Arizona Sky Islands–Another Ecological Analogue for Pleistocene Georgia”

  1. m Says:

    Coues (cows not coos) deer are elusive and are like hunting sheep, lots of glassing and stalking. The experience exceeds ‘trophy’ size.

    https://en.wikipedia.org/wiki/Elliott_Coues

  2. Jess T. Says:

    Interesting article. Does anyone live or travel to these Sky Islands? Or are they protected and only researchers are allowed to travel there?

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