Refugium, plural Refugia: def. "An area in which a population of organisms can survive through a periof of unfavorable conditions."

By DR. CAMERON BARROWS

Our earth’s long history has been punctuated with climate shifts, many of which have resulted in massive extinction events. Sometimes those climate shifts were the result of orbital changes, tilting us closer to or farther from our sun. Sometimes a climate shift was due to massive volcanic activity or an asteroid impact that spewed debris into our atmosphere, blocking the warming energy of our sun. Sometimes when continents slammed into one another they blocked ocean currents and the climate-moderating effects those ocean currents have. Each time this happened, there was a “re-shuffling” of life on earth, with some losers (extinctions) and winners (survivors). Never was life totally extinguished.

This dichotomy of winners and losers begs the question of what determines who wins and who loses. Is it a random rolling of the dice? Is there something about a species’ adaptability? Do generalists prevail while specialists, those species which have carved out a narrow niche to reduce competition with other species, lose? Or is it geography, places where the impacts of a changing climate are buffered due to elevation, slope, or the availability of surface water due to earthquake faults? The answer is yes to all the above. Sixty-five million years ago, after a huge asteroid struck the western hemisphere near Mexico’s Yucatan peninsula, all the large dinosaurs were suddenly extinct. Yet, some small, feathered dinosaurs (birds) survived, as did some crocodiles (genetically the closest relatives to today’s birds), lizards, snakes, mammals, fish, arthropods, and some plants. Survivors were those farther away from the impact zone, and those that could survive months, probably years, underground, in torpor or hibernating, as seeds, or by consuming the carcasses of those that did not survive.

More recently, a mere 20,000-60,000 years ago, our earth, or more precisely our earth’s northern hemisphere, was enduring the most recent of what had been a series of ice ages expanding and ebbing over the past two million years, This ice age was catalyzed by a convergence of orbital anomalies that put our northern hemisphere farther from the sun. Ice sheets covered the most northern latitudes dipping down into the northern tier states of what is now the continental United States. South of the glaciers, our earth was dominated by giant mammals, mammoths, mastodons, ground sloths, camels, horses, and wolves, bears, and cats, each bigger than any similar species alive today. Then, around 10,000 years ago, the earth’s orbit and tilt put the northern hemisphere closer to the sun and the ice sheets retreated to the polar regions. All those giant mammals went extinct.

Still, every species alive today survived. The patterns of high biodiversity across the United States today reflects which areas were both ice free throughout the ice ages, and have a varied topography providing multiple habitats, providing homes for a multitude of species. During those ices ages species were shifted south into  ice-free areas with a complex topography that included high peaks and low valleys, some even lower than sea level. When the ice retreated many species shifted back north, but many species also stayed in their southern ice age refugia. Today, lodgepole and limber pines still thriving atop mount San Jacinto are evidence of how our desert sky island mountains served as refugia during those ice ages. These species were able to escape the ice sheets, and then find a home in our mountains.

High mountain peaks serve as habitat refugia for cold adapted species during warming cycles. Lower down the mountain, north facing exposures receive less solar radiation and so are cooler and retain higher soil water (by not losing precious rainwater to evaporation nearly to the degree that south facing slopes do). Those north facing slopes can extend species’ ranges into lower elevations serving as refugia for both cold adapted and intermediate, cool-loving species. At still lower elevations, where water is at or near the surface year-round, cool temperature habitat refugia exist. In our deserts such areas are associated with earthquake faults.

Lizards can serve as indicators of the existence of habitat refugia for cool-adapted species. Western fence lizards and granite spiny lizards occupy low elevation habitats in coastal, cooler Southern California. However, in our warm deserts, on the desert slopes of our local mountains, both species are rarely found much below about 4,000 feet. They can, however, be found up to 7,000 feet (fence lizards) to 8,600 feet (granite spiny lizards). Lower desert elevations are just too hot for these species. Except in habitat refugia. At 49 Palms Oasis, in Joshua Tree National Park, the fence lizards can be found at 2,800 feet. I can imagine, more than 12,000 years ago when our deserts were much cooler than they are today, that fence lizards were widespread, much like they are today on the coastal side of our mountains. Then as it got increasingly hotter these lizards retreated to higher, cooler elevations. Except at 49 Palms oasis where the year-round water and palm trees kept it cool, allowing these lizards to continue to live there today.

Fence lizards also occur at the Big Morongo Canyon Preserve. Again, year-round water and dense shade from cottonwood trees keeps it cool enough for these lizards at 2,500 feet. On our recent community science hike in Murray Canyon, one of the palm oases found within the Agua Caliente Band of Cahuilla Indians’ lands, we found an abundant population of granite spiny lizards at elevations as low as 850 feet. What was astonishing was that we also found a single, healthy western fence lizard at that same elevation. Although not on our most recent visit, we have also found another otherwise high elevation lizard species here, the western skink. As these lizards have demonstrated, these sites are functioning as effective climate refugia, allowing species to still occupy a small portion of the same range they called habitat during the past ice age.

As we are all aware, our climate is currently warming. This time there are no orbital anomalies to explain this change. We have only ourselves to blame. As it continues to warm, inevitably, just as with past climate changes, there will be losers and winners, some species will go extinct, and others will survive. For those that survive, climate refugia, like Big Morongo Canyon, the 49 Palms oasis, and the oases protected by the Agua Caliente Band of Cahuilla Indians will play a critical role.

Nullius in verba – Go outside, tip your hat to a chuckwalla (and a cactus), and think like a mountain.