The Canary on the Mountaintop

Something is going on in the high reaches of China’s Sichuan Province. The ancient evergreen forests of the Himalayas are being invaded by broadleaf trees, according to a study by SMC Biology Professor Carla Bossard and her research partner, Professor Tang Ya, the director of the Environmental Science Program at Sichuan University.

One tree, in particular, betula albosinensis, the Chinese red birch, usually found below 6,000 feet, is now proliferating at 8,000 to 9,000 feet, Bossard explained. This incursion has worried officials at Jiuzhaigou International Biosphere Preserve, the nature reserve and national park that is China’s Yosemite, so they asked Bossard and Tang Ya to investigate. Their research has found changes in forest composition similar to those also being observed in the Rockies and the Alps. “We’re seeing species moving in that didn’t used to be there,” Bossard said.

It’s at the extreme edges of nature—in arctic permafrost and high mountain elevations—where we first see big systemic changes, Bossard said. “With climate change, they are the canary in the coal mine or, in this case, the canary on the mountaintop.”

The conifer forests of Jiuzhaigou have prospered for thousands of years in their high dwellings, with saplings in early spring, unimpeded by the shade of broadleaf trees, able to photosynthesize food at top speed as soon as the temperature passes 5 degrees Celsius (41 degrees Fahrenheit).

“Evergreens are most competitive where it’s cold and wintry much of the time and the growing season is short. Broadleaf trees have a tougher time in those conditions,” Bossard said. But now, with more broadleaves moving in and extending their growing season, young evergreens have at least 20 fewer days of uninterrupted sunshine. “They can’t compete,” she said.

Why does this matter? “The problem with change in forest composition is that it changes other things,” Bossard said. “With less sun at ground level, herbaceous plants like wildflowers store less starch and set fewer seeds. Some will fade away.”

But there’s another complication, she added. “The Chinese red birch has very shallow roots, digging less than a meter into the mountains, which, unlike the granite bedrock of the Sierra Nevada, are made of 13,000 feet of unconsolidated, broken rock rubble.”

And what held it together all this time? The long, muscular taproots of those old evergreens.

“Keep in mind that all of Sichuan is also a giant earthquake zone,” Bossard added. “So they have a national park, getting 3 million visitors a year, in which trees that don’t hold anything are displacing trees that do.”

Upon hearing this, park officials quickly scrapped plans to build a visitor facilities site at the bottom of a potentially vulnerable slope.

This summer, Bossard has returned to Jiuzhaigou to study yet another piece of the puzzle. For millennia, the water runoff from the evergreen forest, which tends to be acidic, has dissolved out the calcium carbonate in the karst limestone of the mountains and deposited it at the bottoms of 22 lakes in the park, making them a striking turquoise blue. Bossard and Tang Ya want to know if that will change, too.

So, what is the takeaway from this story of Jiuzhaigou?

“You can’t change just one thing,” Bossard said.

— Jo Shroyer

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