Rising temperatures could be spurring the growth of mountaintop Great Basin bristlecone pines

EXPANDING TREE RING: As climate change warms mountaintops, Great Basin bristlecone pine trees undergo a growth spurt.
ISTOCK/SIERRARAT

Bristlecone pine trees dot the White Mountains in eastern California, giving the stark and rocky landscape one of its few highly visible signs of life. These gnarly-barked trees can survive at altitudes of up to 3,470 meters, although their growth rate at these heights is limited because of cold temperatures. But those limits have been loosening lately. In the past 50 years, as regional temperatures have warmed, the growth of bristlecone pine trees at high altitudes has been accelerating, whereas that of trees lower down the slopes has not, according to the results of a study published November 16 in the Proceedings of the National Academy of Sciences.

The research focused on Great Basin bristlecone pines (Pinus longaeva), which grow in six western U.S. states and are among the longest-lived organisms on Earth. Some pines reach ages of up to 5,000 years, which gave the study authors an opportunity to put together a record going back nearly as far that compares bristlecone growth rates at various altitudes.

To arrive at their findings, study lead author Matthew Salzer, a research associate in the Laboratory of Tree-Ring Research at the University of Arizona in Tucson, and his colleagues studied 678 tree ring radii of bristlecone pines, both living and dead, from a site on the White Mountains and two sites in Nevada—on Mount Washington and Pearl Peak. In the White Mountains the team sampled trees living at the maximum altitude, or tree line, which can be as high as 3,470 meters or as low as 2,805 meters. To measure annual tree-ring width, the scientists drilled out pencil-size sections from one side of living trees, or sawed-off cross-sections of dead ones.

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