Wednesday, February 26, 2020

The Islands of Interior California: The Pygmy Mammoths and the Doomed Sky Islands

An 80,000-year-old pygmy mammoth tusk discovered on Santa Rosa Island. (Image credit: Daniel Muhs, USGS.)

The waves crash against the cliff, tearing at the rock on Santa Rosa Island off of Southern California. The face of the cliff is in constant retreat, changing yearly, and sometimes daily as more of the rock disappears into the surf. In one brief moment, a visitor notices a strange object exposed in the cliff. Is it a tree trunk? No, that white stuff is's a tusk! There were elephants on the island! How in the world did that happen?

The presence of fossils of elephantine species on the island has been known since the late 1800s, and a survey in the late 1990s discovered at least 150 sites with remains of the creatures, now called the Pygmy Mammoth (Mammuthus exilis). There is little doubt that these creatures were descended from the mainland's Columbian Mammoth, but as their name suggests, they were small. A full-sized Columbian Mammoth stood 14 feet high, but the Pygmy Mammoth was only half as high at most, and perhaps a quarter the weight. A nearly complete skeleton discovered and excavated in 1994, and the adult was only 5.5 feet tall (below).
Pygmy mammoth skeleton found on Santa Rosa Island in 1994. It was 5.5 feet tall (Image: © Bill Faulkner, NPS)
It seems impossible that mammoths could have made it out to the islands, and under current conditions it probably would be. The nearest island is more than 20 miles away from the mainland. But things were much different 150,000 years ago. A phase of the ice ages was ongoing, and when a vast ice sheet covered Canada and 30% of the United States, sea level was around 300-400 feet lower than today. The four main Channel Islands (San Miguel, Santa Rosa, Santa Cruz, and Anacapa) would have been a single large island, which has been given the name Santarosae. The open water gap between the island and the mainland was only about 4.5 miles.

Elephants actually are excellent swimmers, what with having a natural snorkel and all. Present-day elephants have been documented as have swam more than 20 miles. So it is not hard to imagine mammoths on the mainland, perhaps suffering food shortages because of drought or wildfires, catching the scent of fresh vegetation on the islands and swimming out to investigate. A population was established, but then things began to change. The ice age was ending and the globe was warming up. The ice melted and sea rose to near today's level. The single large island was inundated, forming the four islands of today, and the total area was reduced by 76%. For the mammoths, this was a crisis. The islands were no longer big enough to support the mammoth population.
Outline of Santarosae and the present-day Channel Islands (Image credit: U. S. Geological Survey)
The outcome might come as a surprise because the cliché about evolution is sometimes misstated as "survival of the strongest". It is actually the survival of the best adapted. Although the biggest mammoths may have been able to consume much of the decreasing food supply, their dietary needs were also much higher. The evolutionary lottery favors those individuals who have the best adaptations for the specific environment, and it was the runts of the litter who could survive on less food. Over time the size of the adults decreased until they constituted a new species, the Mammuthus exilis. They survived on the islands for tens of thousands of years (from at least 80,000 years before present).

In the end, the Pygmy Mammoths also succumbed to extinction sometime around 12,000 years ago. Their disappearance coincided with the extinction of numerous other large mammals in North America, the "megafauna". Many reasons have been offered as hypotheses, but the cause (or causes) remain elusive. It needs to be noted that humans arrived on the islands around 11,000 years ago, and the small mammoths would have had few defenses against armed human beings.

As we can see, islands are places of refuge, but they can also be a prison of no escape. Which brings us to the doomed sky islands of the Mojave Desert.
The New York Mountains in the Mojave National Preserve (image credit: Garry Hayes)
People may envision a number of stereotypes of what constitutes a desert. Many people see vast seas of sand dunes, while others may see mesas and spires inspired by childhood memories of Roadrunner and Coyote cartoons. Others might see a landscape of huge saguaro cacti. These kinds of deserts exist of course, but except for several dune fields here and there, they don't exist in California. The deserts of eastern California (along with parts of Arizona and Utah, and all of Nevada) are within the Basin and Range Province, a region of the Earth's crust that has been stretched and broken into hundreds of high mountain ranges and deep faulted basins.
The Clark Mountains as seen from Kokoweef (image credit Garry Hayes)

Because the relief (the difference between the highest and lowest points) can range up to two miles, these mountain ranges encompass numerous life zones or ecosystems, from the hottest barren salt flat to alpine peaks. These mountains constitute rich biologic islands that are analogous to the Channel Islands off the coast of California. And like the Channel Islands, some of the inhabitants are ultimately doomed.

Because the mountain peaks are so isolated, one might not expect much diversity, but these environments are not static nor were they always isolated. They were influenced by the ice ages, even though the ice fields never reached the arid region. The climate was cooler and wetter so trees more characteristic of the Rocky Mountains or the Sierra Nevada were able to migrate into the region, including the Rocky Mountain White Fir. But as the ice age waned, the rising temperatures and growing aridity caused the trees to retreat higher and higher into the mountains. If the mountains weren't high enough, the trees were extinguished. In the present day, only three islands remain that possess the Rocky Mountain White Fir: the New York Mountains, Clark Mountain, and Kingston Peak.
Scene from the Kingston Peak area (Image credit: Bureau of Land Management)
None of these relict forests are easy to get to, and I have never had the privilege. And unfortunately I may never have the chance because these trees are ultimately doomed. They are at the very edge of survival, clinging to the cooler north-facing slopes in a micro-climate that is just wet enough to allow the trees to cling to life. As the world continues to warm up, the dry desert will continue creep up the mountain slopes, ultimately "flooding" the last trees in hot dry air.
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We will never fully comprehend the full effects the changes on our planet brought about by global warming and climate change. In the mountains of the Mojave Desert, the "islands" are not occupied just by fir trees. There are dozens of species that shelter within these small forests and they will disappear too. It's a small corner of the world rarely visited by humans, but climate change is global, and there are literally millions of micro-environments like these that will disappear without ever being studied or appreciated. It's a crying shame and all the more tragic considering we've lost three decades of time that we could have acted on behalf of our planet.
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1 comment:

Anonymous said...

Stunning pic of the New York Mtns.