In another sign of the warming climate, key species of trees in California’s Sierra Nevada mountain range — including lodge pole pine, red fir and western white pine — are shifting to higher elevations in search of cooler temperatures, a broad new study by state biologists has found.
From south of Lake Tahoe to the northern Sierra, the areas where the trees are growing has moved on average almost 500 feet higher during the past 80 years, as new saplings are taking root farther up mountainsides, according to researchers from the California Department of Fish and Wildlife.
“The good news is that trees are adjusting. They aren’t just all dying in place as conditions become unsuitable,” said David Wright, a senior environmental scientist with the department who helped lead the study. “The bad news is that if they have to move up at all, it shows our impacts are happening and are continuing, and that some of these trees might end up with no place to move up to.”
In the Sierra Nevada, overnight low temperatures in June, July and August have risen by 2.34 degrees during the past 100 years.
From 2009-15, the scientists compared detailed forest surveys taken by researchers in the 1930s with hundreds of the same locations today. The study, published in the journal California Fish and Game, is the latest to document how climate change already is affecting California’s landscape, from rising sea levels to migrating species.
In the Sierra Nevada, overnight low temperatures in June, July and August have risen by 2.34 degrees during the past 100 years. The warming of the planet is driven by emissions from the burning of oil, gas and other fossil fuels, which trap heat in the atmosphere.
Last year was the hottest year on Earth since modern record-keeping began in 1880, breaking the record set in 2014, according to NASA and the National Oceanic and Atmospheric Administration. All 10 of the hottest years since 1880 have occurred since 1998.
“Nature’s many thermometers — from shifted ranges of plants and animals to earlier snow melt — confirm the pattern in weather-station thermometers,” said Chris Field, a professor of Earth system science at Stanford University who was not involved in the study.
“Climate change is real and local,” he said. “When forests operate like rapidly shifting pieces on a chess board, we face a growing risk of losing pieces or even an eventual checkmate.”
When forests operate like rapidly shifting pieces on a chess board, we face a growing risk of losing pieces or even an eventual checkmate.
Chris Field, professor of Earth system science at Stanford University who was not involved in the study
Scientists around the world have documented that some species of plants and animals that rely on cooler temperatures already have been gradually moving their ranges higher, like castaways on islands in a rising ocean. That’s because the air is cooler at higher elevations.
But mountains are cone-shaped, so the higher that plants, animals and trees move, the less habitat is available. And that means wildlife that depend on the affected forests for food and shelter are likely to be squeezed in the coming decades as warming continues.
“Eventually, you run out of ground,” Wright said.
One bright spot: Eight other species of conifer trees in the Sierra Nevada that can better tolerate warmer weather, including ponderosa pine and Douglas fir, did not show shifts to higher elevations. The researchers worry, however, that as the climate continues to warm, they too could reach a tipping point, along with the animals that rely on them.
“It’s like the frog sitting in the pot. He says ‘so far everything is fine,’ ” Wright said.
The warming of the planet is driven by emissions from the burning of oil, gas and other fossil fuels, which trap heat in the atmosphere.
Other studies in California have shown similar trends. Almost 20 years ago, Rafe Sagarin, a researcher at Stanford, found an old thesis from a Stanford student in the 1930s in the library at Hopkins Marine Station in Pacific Grove. The study, done by Willis Hewatt, documented the number and types of sea urchins, anemones and other creatures living in the tide pools along Monterey Bay in the 1930s. Sagarin painstakingly located the same tide pools 70 years later, including the metal markers that Hewatt had pounded into the rocks. When he resurveyed them, he discovered far more warm-water species, historically found in Southern California, and far fewer cold-water species, than had been in the tide pools in the 1930s.
In the most recent Sierra Nevada study, Wright, along with state biologists Canh Nguyen and Stacy Anderson, pored over surveys done in 1934 and 1935 by researcher Albert Wieslander for the U.S. Forest Service. They compared 2,160 plots — each one-fifth of an acre — that he surveyed between Alpine County, south of Lake Tahoe, and Plumas County, near Lassen Volcanic National Park, with 381 plots of the same size that they selected randomly by computer. Over six years, they visited each of the 381 plots, and counted and documented every tree in each plot and compared the changes over the 80 years.
Almost 500 feetThe average amount that the trees have moved during the past 80 years.
They found that young lodge pole pine trees on average shifted upward in elevation by 246 feet, western white pines by 367 feet, mountain hemlock by 390 feet and red fir trees by 482 feet. All four species lived mostly between 7,500 feet and 8,500 feet.
“There’s definitely the temptation to say, ‘the Sierra Nevada is far away, this isn’t affecting my life,’ ” Wright said. “But it’s another one in yet another line of evidence that changes are happening.”