Real islands are framed by an imposing barrier of water, hemming in various species in a natural menagerie. Sky islands of the world – isolated mountains with forests separated from each other by bordering, non-wooded habitats – are virtual islands. Both real and sky islands share much in common, including their vulnerability to ecological damage.
Such, unfortunately, is the case with our own Madrean Archipelago. Here approximately 43 mountain islands dot the landscape of southeast Arizona, the boot heel of New Mexico, and northern Sonora.
Islands are evocative, exotic, even mystical. They conjure images of distant, strange lands where mere mortals might temporarily banish themselves in blissful, verdant obscurity. Islands, it turns out, are also surprisingly fragile. Scientists – long fascinated with real islands – have learned much from the world’s isolated lands, eventually coming up with the science of island biogeography.
What do real islands teach us about isolated habitats, such as those perched on our own Sky Islands?
The Hawaiian Archipelago, the Caribbean Islands, New Zealand and many other islands large and small have suffered more known species extinctions at the hands of humans than all other land masses on earth combined! The Hawaiian Islands rank first in bird extinctions versus the rest of the planet over the last thousand years. Why? They are small and highly isolated from other land masses.
Big lessons lurk here, as our Sky Islands are also tiny and sequestered from the next-nearest like habitats.
Think of an Engelmann spruce population atop the highest portions of the Chiricahua Mountains. The next nearest stand of the species grows in the Pinaleno Mountains, just to the north. Now torch the Chiricahuas with the 1994 Rattlesnake Fire and the much larger 2011 Horseshoe II Fire. Smokey the Bear Forest Service policies and climate change make a deadly combination, where undue levels of wild fuels and a warming, drying planet meet.
The spruce population in the Chiricahuas is now severely depleted, perhaps on the ropes. That of the Pinalenos is faring much better. Now, let’s imagine that the last spruces are ultimately extinguished from the Chiricahuas within the next 50 years. More fires, stress from insects, and other factors spell their demise. What, then, would be the chances that a bird might fortuitously carry a spruce seed from the Pinalenos to the Chiricahuas over the expanse of 40-plus miles of intervening and foreboding desert and grasslands? Slim to none. Repopulation after extinction on islands is often tenuous-to-impossible.
Small populations are susceptible to extinctions as are isolated ones. Add the two factors together and you get small, isolated populations that are hypersensitive to local or – if they are endemic – total extinction. Habitat destruction, nonnative species, climate change, and a host of other factors are all now impinging upon the wide array of species that collectively make our Sky Islands one of the most biologically diverse temperate areas on Earth.
Thick-billed parrots, Mexican grizzly bears, Mexican wolves, and likely other species have already locally vanished from all or part of the Madrean Sky Islands within the last 100 years. Who will follow? The immediate candidates include jaguars, ocelots, and species already at the margins of their ecological tolerance, including spruces. Once such species are lost, a sort of ecological decay ensues. Species that depend upon wolf kills or seed dispersal by parrots, for example, also wane or fade completely. Soon, local environments look much less like they did mere decades ago.
I recall, with no small degree of horror, seeing non-native tumbleweeds thriving amidst the hoodoos of Chiricahua National Monument after the 2011 fire. Each such natural and human-incited catastrophe will push our Sky Islands species more and more towards the ecological precipice.
Fragile species with narrow habitat needs go first, as do top predators. Following them will be a slew of other species as assault after assault collectively overwhelms them. Mining here, water-table draw-down there, more roads, more houses. Finally, only the most adaptable species will persist here and elsewhere, hearkening to writer David Quammen’s essay, “Planet of Weeds.” Yes, there will be feral cats, tree of heaven, coyotes, and other “bomb-proof” weedy species. Alas, however, our Sky Islands would have suffered the same fate as oceanic ones that undergo mass extinctions. Skeptical? Go ask the moas of New Zealand or the dodo of Mauritius – see what they have to say.
Vincent Pinto and his wife, Claudia, run RAVENS-WAY WILD JOURNEYS, their Nature Adventure & Conservation organization devoted to protecting the unique biodiversity of the Sky Islands region. Visit: www.ravensnatureschool.org