Fifteen or so years ago, I worked in Big Bend National Park for a season. This large park, on the border of the United States and Mexico, is mostly desert, but with an old mountain range at its center. On the upper elevations of these mountains are the southernmost stands in the U.S. of quaking aspen and Ponderosa pine, a handful of acres of each.
How did they get there?
At the end of the last ice age, Big Bend was not desert, but forest. As the climate warmed, the pine forest moved up the mountains. Now, as we enter the Anthropogenic Age, and the planet warms up, these trees have run out of mountain.
They are not alone in their plight.
In response to warming, animals classically move to cooler ground, relocating either higher up in altitude or farther toward the poles. But in the tropics, animals have to move hundreds of miles north or south to find a different niche. Mountain species face even starker limitations: As they climb upward they find themselves competing for less and less space on the conical peaks, where they run into uninhabitable rocks or a lack of their usual foods — or have nowhere farther to go.
Update: or maybe not always.
In a paper published January 20 in the journal Science, a University of California, Davis, researcher and his co-authors challenge a widely held assumption that plants will move uphill in response to warmer temperatures. …
Between 1930 and 2000, instead of colonizing higher elevations to maintain a constant temperature, many California plant species instead moved downhill an average of 260 feet, …
“While the climate warmed significantly in this period, there was also more precipitation. These wetter conditions are allowing plants to exist in warmer locations than they were previously capable of,”
the new study reveals that other factors, such as precipitation, may be more important than temperature in defining the habitable range of these species.