"I found far more answers in the woods than I ever did in the city." — Mary Davis

Being a naturalist is at its core a sense of place. It is a walk in a forest, across a desert dune, or exploring a tide pool, acquainting yourself or reacquainting yourself with new and old friends by identifying them by name, those plants, lizards, and starfish. In that you see yourself as part of, not apart from, the natural world around you. It is not just taking a class; it is a lifelong passion. When you visit someplace new, as a naturalist, your curiosity is piqued; who are these new trees, grasses, birds, and beetles? Your sense of place broadens, and you become part of that larger world.

The arid southwest of North America is noted for its deserts. However, conifer forests are found there as well, having found refuge in sky islands, isolated mountains that reach 6,000 feet or more above the desert floor. These sky island forests owe much of their biodiversity to the multiple ice ages of the Pleistocene, ice sheets pushing plants and animals south, then as the ice sheets retreated, stranding some of those plants and animals along the elevation gradients of the desert mountains. Sky islands occur in the deserts of southern California, the San Bernardino, and San Gabriel Mountains, the San Jacinto and Santa Rosa Mountains, and extending south along the Peninsular Mountain Range into Baja California. Sky islands also occur in Arizona; there are at least a dozen isolated mountains in the southeast corner of the state, along with the White Mountains along the eastern edge, and the San Francisco Peaks – Mogollon Rim region of the north central portions of the state. All include conifer forests; all of those forests exist due to the ebb and flow of ice sheets during the Pleistocene. With the same repeated climate shifts and roughly similar elevations, one might expect there to be the same assortment of conifers and associated species on each sky island, but one would be mistaken.

Walking through the conifer forests of the San Jacinto and Santa Rosa Mountains, the higher elevations of the Chiricahua Mountains in southeast Arizona, or the San Francisco Peaks just south of the Grand Canyon, there is a sameness. The pines look the same; white fir is a co-dominant at each site. However, take a closer look. Along with white fir, Ponderosa pines and Douglas fir dominate the Arizona sky islands. On the southern California sky islands Ponderosa pine is present but relatively uncommon and Douglas fir is absent. To find Douglas fir in California you need to travel to the Sierra Nevada mountains or the redwood belt along the northern coast. Jeffery pine dominates the southern California sky islands, but it is absent from Arizona. Limber pine can be found above about 9,000 feet on the southern California sky islands and is also be found at about the same elevations on the San Francisco Peaks, but these pines are absent elsewhere in Arizona, even though the highest elevation in the Chiricahua mountains is 9,759 feet. Lodgepole pines occur in the northern portion of the southern California sky island chain, but not in Arizona.

There are common denominators, white fir and Ponderosa pines, mountain mahogany and skunk bush sumac, but the differences are intriguing. Why is Douglas fir absent in southern California? At least part of the answer is that Douglas firs had entered southern California during one or more of those ice ages, but then became stranded when warmer-drier conditions returned. Rather than shift upslope, they evolved into a different species. The scientific name for a Douglas fir is Pseudotsuga menziesii, literally translated to Menzie’s false hemlock. Today there is a close relative only found in the southern California sky islands, Pseudotsuga macrocarpa, literally translated to the big-coned false hemlock, but colloquially called “big-cone spruce” (who knows why). Its cones are at least twice the size of a Douglas fir. Apparently, during the interglacial warming periods a small population of Douglas fir evolved into a new species, leaving no place for the original Douglas fir to occupy. Other between sky island differences are more difficult to explain. Perhaps differences can be found in the amount of rain each mountain receives. Many of the differences in plant species between the San Jacinto and Santa Rosa Mountains can be explained because the Santa Rosa Mountains are much drier. Or perhaps it is just by chance. The diaspora of trees escaped the growing ice sheets by heading south, but the sky islands were isolated targets, targets that may have been simply missed by some species.

There is a sameness in the bird species encountered among the southwestern sky islands. Mountain chickadees, Steller’s jays, yellow-rumped warblers, black-throated gray warblers, ravens, white-breasted, red-breasted, and pygmy nuthatches, lesser goldfinches, hairy woodpeckers, northern flickers, western tanagers, western bluebirds, and violet-green swallows will serenade you no matter which sky island forest you choose to walk into. There used to be more, but recent genetic analyses uncovered differences that were hidden under their feathers. Western flycatchers are now Pacific slope (California and the Pacific northwest) and cordilleran flycatchers (Arizona and the Rocky Mountain states). With those same geographic separations, plain titmice are now oak and juniper titmice; solitary vireos are now Cassin’s and plumbeous vireos; scrub jays are now California and Woodhouse’s scrub jays. However, with those as exceptions, for most birds the isolated sky islands were not so isolated at all. Arizona sky islands, especially those in the southeastern corner of the state, do have a handful of bird species of mostly tropical origin that rarely if ever make it to California. Red-faced warblers, painted redstarts, olive warblers, and hepatic tanagers are examples of otherwise Mexican species that entice California birders into Arizona’s sky islands.

That sameness disappears when it comes to reptiles, annual plants, and insects. For these groups nearly everything seems new between each sky island. Certainly, between southern California and Arizona sky islands, but even the differences between the San Jacinto and San Bernardino mountains are large in what annual plants you will encounter on your walk through the forest. Why these groups? In part the answer is that for reptiles, annual plants, and many insects, the isolation between sky islands is real. Even the small gap between the San Jacinto and San Bernardino mountains is significant due to the dramatic elevation gap between these two mountain ranges. The other factor is generation time. Conifer trees can live for centuries, so evolutionary change takes more time than the 10-20 thousand years since the last ice age. Generation times for annual plants, and insects is typically one year or for reptiles less than 10 years. These groups have the potential to adapt to change comparatively rapidly, and so with enough isolation, and enough differences in habitat character between sky islands, new species can evolve.

Get out and broaden your sense of place.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe