introduction to the ecology of sky islands
A sky island is a mountain that is situated in isolation within an area of lowlands where the environment contrasts greatly to the environment of the uplands of the mountain. Instead of being surrounded by water they are surrounded by low lying land. In a location such as this the environment changes dramatically from the lowlands to the mountain summit. This results in significant differences evolving in the natural habitat of both lowlands and uplands regions of the mountain.
In such places it is not unusual to find species of fauna or flora that are limited to a certain altitudes. Such species of animals and birds may practice vertical migration up or down the mountain as the weather and seasons change in order to find food or shelter.
In such places it is not unusual to find species of fauna or flora that are limited to a certain altitudes. Such species of animals and birds may practice vertical migration up or down the mountain as the weather and seasons change in order to find food or shelter.
Distinctive features of sky islands
One of the most distinctive features of a sky island is its sheer isolation from other mountains. Sky islands rise dramatically out of the lowlands which may be an area such as a desert, or grassland. The environment of the mountain changes with altitude giving rise to varied living conditions for various types of flora and fauna.
A mountain may dramatically rise out of a sparse desert region yet have forest growing around its flanks and perhaps shrubs and grasses at higher altitudes. The animals and insects that live on the mountain will also vary with the different altitudes. The mountain ecosystem evolves into a richly diverse habitat surrounded by barren desert, or grassland.
A region that has a northern temperate climate experiencing warm summers and cold winters is termed boreal. In some cases, a sky island can be a refuge for some boreal species of organisms that became marooned by warming climates after the last ice age.
As well as this there is also a process known as ‘speciation’ at work. This is the same process that has taken place on marine islands such as the Galapagos Islands. This where a new biological species evolves, usually from one species, that divides into two or more species that are genetically unique.
One of the most distinctive features of a sky island is its sheer isolation from other mountains. Sky islands rise dramatically out of the lowlands which may be an area such as a desert, or grassland. The environment of the mountain changes with altitude giving rise to varied living conditions for various types of flora and fauna.
A mountain may dramatically rise out of a sparse desert region yet have forest growing around its flanks and perhaps shrubs and grasses at higher altitudes. The animals and insects that live on the mountain will also vary with the different altitudes. The mountain ecosystem evolves into a richly diverse habitat surrounded by barren desert, or grassland.
A region that has a northern temperate climate experiencing warm summers and cold winters is termed boreal. In some cases, a sky island can be a refuge for some boreal species of organisms that became marooned by warming climates after the last ice age.
As well as this there is also a process known as ‘speciation’ at work. This is the same process that has taken place on marine islands such as the Galapagos Islands. This where a new biological species evolves, usually from one species, that divides into two or more species that are genetically unique.
Origin of the term, ‘sky island.’
In 1943, Natt N. Dodge writing in the magazine, Arizona Highways used the term ‘sky island’ when referring to the Chiricahua Mountains. Later in 1967, Wealdon Heald a writer from south eastern Arizona wrote a book describing a drive from Rodeo in New Mexico, to a mountain peak in the Chiricahua Mountains dome 35 miles (56 km) distant and rising to a higher altitude of 5,600 feet (1,707 metres).
He observed how the environment, wildlife and living conditions changed on his journey. He described how he drove through scorching hot, barren desert, rising through grasslands and ascending through forests of oak and pine before ascending into woodlands of aspen, spruce and fir trees. In the book he makes reference to the theories of Clinton Hart Merriam who developed the idea of life zones to categorize biomes. Other writers around this time including John McPhee and David Quammen also used the term and it began to be used by scientists.
The term, ‘sky island’ is not restricted to mountains in the south west parts of North America. It is a concept that and can be practically used in relation to mountains and high places around the planet.
In 1943, Natt N. Dodge writing in the magazine, Arizona Highways used the term ‘sky island’ when referring to the Chiricahua Mountains. Later in 1967, Wealdon Heald a writer from south eastern Arizona wrote a book describing a drive from Rodeo in New Mexico, to a mountain peak in the Chiricahua Mountains dome 35 miles (56 km) distant and rising to a higher altitude of 5,600 feet (1,707 metres).
He observed how the environment, wildlife and living conditions changed on his journey. He described how he drove through scorching hot, barren desert, rising through grasslands and ascending through forests of oak and pine before ascending into woodlands of aspen, spruce and fir trees. In the book he makes reference to the theories of Clinton Hart Merriam who developed the idea of life zones to categorize biomes. Other writers around this time including John McPhee and David Quammen also used the term and it began to be used by scientists.
The term, ‘sky island’ is not restricted to mountains in the south west parts of North America. It is a concept that and can be practically used in relation to mountains and high places around the planet.
Characteristics of sky islands
In North America the Madrean sky islands of Arizona, New Mexico in the U.S.A., and the states of Chihuahua and Sonora in Mexico are numerous links that connect the northern parts of the Sierra Madre Occidental to southern part of the Colorado Plateau. In some parts of the U.S. these links are known as island ranges, especially by local people.
Many species of flora in the higher reaches of the sky islands of the southern United State and Mexican border regions have many plants that have similar features of those found at more northerly latitudes. Flora in the lower reaches has similarities to flora of the desert regions and more southerly mountains.
Animals and plants
Sky islands can be home to many unique plants and animals. Examples of this are the mountain yucca, the Mount Graham Red Squirrel, the Huachuca spring snail and the Jeme Mountains Salamander. Some species such as the Mount Lyell Shrew appear to have evolved on their sky island home.
In the past it is known that some sky island species have become extinct. This is possibly due to the isolated nature of sky islands which also makes it difficult for new species to arrive from elsewhere.
Vertical migration with the seasons
Some species move vertically between the lowlands of the mountain to the uplands with the changing seasons. On the sky islands of the Great Basin Mountains the Mountain Quail lives in the higher reaches until the snow season arrives when it migrates to the lower elevations of the mountain.
In some cases in an archipelago of sky islands the valleys in between can act as barrier to the movement of some species while also be a convenient migration route for others.
Sky islands around the world
There are many sky islands situated all around the world. In the U.S.A as well as those already mentioned there are numerous others such as the White Mountains, Mt. San Jacinto, the Spring Mountains, and many others. The best studied are probably those of the Madrean Archipelago of the U.S.A and Mexican border regions.
In the state of Montana the Highwood Mountains and the Little Rocky Mountains are forested with snow pack and tundra beyond the tree line. These ranges are not linked to other ranges and are encircled by prairie, grassland or scrubland with few if any trees.
Lost worlds
In South America the Tepuis of Guyana, Venezuela and Brazil are good examples of sky islands. In many cases they are flat topped and have developed unique species of fauna and flora and often called ‘lost worlds’ in cinema and literature. Sky islands can also be found in Taiwan, Vietnam, Africa New guinea and many other regions around the globe.
© zteve t evans October 6, 2013
In North America the Madrean sky islands of Arizona, New Mexico in the U.S.A., and the states of Chihuahua and Sonora in Mexico are numerous links that connect the northern parts of the Sierra Madre Occidental to southern part of the Colorado Plateau. In some parts of the U.S. these links are known as island ranges, especially by local people.
Many species of flora in the higher reaches of the sky islands of the southern United State and Mexican border regions have many plants that have similar features of those found at more northerly latitudes. Flora in the lower reaches has similarities to flora of the desert regions and more southerly mountains.
Animals and plants
Sky islands can be home to many unique plants and animals. Examples of this are the mountain yucca, the Mount Graham Red Squirrel, the Huachuca spring snail and the Jeme Mountains Salamander. Some species such as the Mount Lyell Shrew appear to have evolved on their sky island home.
In the past it is known that some sky island species have become extinct. This is possibly due to the isolated nature of sky islands which also makes it difficult for new species to arrive from elsewhere.
Vertical migration with the seasons
Some species move vertically between the lowlands of the mountain to the uplands with the changing seasons. On the sky islands of the Great Basin Mountains the Mountain Quail lives in the higher reaches until the snow season arrives when it migrates to the lower elevations of the mountain.
In some cases in an archipelago of sky islands the valleys in between can act as barrier to the movement of some species while also be a convenient migration route for others.
Sky islands around the world
There are many sky islands situated all around the world. In the U.S.A as well as those already mentioned there are numerous others such as the White Mountains, Mt. San Jacinto, the Spring Mountains, and many others. The best studied are probably those of the Madrean Archipelago of the U.S.A and Mexican border regions.
In the state of Montana the Highwood Mountains and the Little Rocky Mountains are forested with snow pack and tundra beyond the tree line. These ranges are not linked to other ranges and are encircled by prairie, grassland or scrubland with few if any trees.
Lost worlds
In South America the Tepuis of Guyana, Venezuela and Brazil are good examples of sky islands. In many cases they are flat topped and have developed unique species of fauna and flora and often called ‘lost worlds’ in cinema and literature. Sky islands can also be found in Taiwan, Vietnam, Africa New guinea and many other regions around the globe.
© zteve t evans October 6, 2013
References and Attributions
Copyright zteve t evans 6th October 2013
Copyright zteve t evans 6th October 2013
- File:SkyIslands from SantaCatalinaMtns.JPG -View of "sky islands" from the w:Santa Catalina Mountains, Arizona,
- USA. - Author: Unknown - Public Domain
- File:Baboquovari, Sonoran Desert.jpg From Wikimedia Commons -Sonoran Desert, Arizona, USA. Picture 1990.- Author Phillip Capper from Wellington, New Zealand - Creative Commons Attribution 2.0 Generic licence -
- File:Chiricahua nima3.JPG From Wikimedia Commons - en:Chiricahua National Monument, with w:hoodoo (geology) rock formations, and pine forests.- Author Zereshk - Creative Commons Attribution-Share Alike 3.0 Unported licence
- From Desert to "Sky Island" Vegetation
- The Sky Island Alliance - Explore Our Sky Islands
- The Madrean Sky Island Archipelago:A Planetary Overview - Peter Warshall