Are Earth's oldest trees losing the race in a warming climate?

Bristlecone
CC BY 2.0 Rick Goldwaser/Flickr

As treelines move up the mountains in the western US, the famed and ancient bristlecone pines are losing ground to competitors.

Until 2013, the oldest known individual tree in the world was Methuselah, a 4,845-year-old bristlecone pine (Pinus longaeva) in California's White Mountains in the Great Basin. Researchers then found an even older one in the area, ringing in at a mind-boggling 5,062 years old.

For millennia the bristlecone pine has dominated the Great Basin, a region stretching from California's Sierra Nevada, across Nevada to Utah's Uinta Mountains, and bordered on the north and south by the Columbia and Colorado rivers' watersheds. These grarled beauties have reacted to a gradually changing climate by slowly advancing across the landscape, moving from the lowlands of the Great Basin up to the current tree line where they are now.

As has been predicted for all kinds of species, as the planet warms, migrations will occur northward and/or to higher elevations – it's no different with the trees. The treeline in the Great Basin has been inching up over the last 50 years, the problem for the bristlecone pine is that the new kid on the block, the limber pine, is getting to the top more quickly.

In a new study out from UC Davis and the USDA Forest Service, the authors report of the limber pine "leapfrogging" the bristlecone. Taking over soil once almost completely inhabited by bristlecones, the limber pines appear to be winning the race.

"We are seeing very little regeneration anywhere in bristlecone ranges except in the tree line and, there, limber pine is taking all the good spots," says one of the study's author Brian Smithers, from UC Davis. "It's jarring because limber pine is a species you normally see further downslope, not at tree line. So it's very odd to see it charging upslope and not see bristlecone charging upslope ahead of limber pine, or at least with it."

Bristlecone © (Brian Smithers/UC Davis) Dead bristlecones and young limber pine growing around them. Limber pine is beginning to colonize areas of the Great Basin once dominated by bristlecones.

The researchers explain that neither species of pine have ever experienced "climate change and temperature increases as rapidly as what has been occurring in recent decades."

The ancient adult trees will likely prove resilient to current climatic shifts, expects Smithers, thanks to their being so well established. (Like, 5,000-years established!) But how new bristlecone pine trees will come to life is unclear, especially if competitors like limber pine start taking up the valuable space required for germination. If bristlecone pines are unable to find their way up the mountain because other trees have beat them to it, concludes the study, bristlecone populations could face a reduction of their range ... and possibly become extinct in some areas.

bristlecone pine© (Brian Smithers/UC Davis) Stand of adult bristlecones; the small dots of green above the treeline are limber pine, now growing where only bristlecone grew before.

"The things we're doing today have legacy effects for thousands of years in the Great Basin," Smithers says. "When those trees do start to die, they won't likely be replaced because it's just too hot and dry."

The study was published in Global Change Biology.

Are Earth's oldest trees losing the race in a warming climate?
As treelines move up the mountains in the western US, the famed and ancient bristlecone pines are losing ground to competitors.

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