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UC Santa Cruz researcher Sharon Martinson studies galls such as this one near Mammoth, California. In her eyes, the most striking effects of climate change may come from the least conspicuous places. photo by Terray Sylvester |
Comments (3)Tufa, Sagebrush, Fire and Flood
Regional conference shines light on varied effects of Sierra climate change
Published: January 14, 2009by Terray Sylvester
CSU Hayward scientist Scott Stine strides along the muddy shore of Mono Lake. The climatological record he has constructed from evidence in and around the lake, and from sites scattered across the Sierra Nevada, indicates that human-induced climate change could bring extraordinarily dry times to California.
photo by Terray Sylvester
Tufa forms where calcium-laden groundwater mixes with the carbonate-rich water of Mono Lake. When the towers formed, they were underwater. Today, many tufa formations stand above springs, or in boggy places where freshwater percolates from the ground.
photo by Alyson Stetz
Over 200 land managers, scientists, and conservationists gathered for the symposium Climate, Ecosystems and Resources in Eastern California.
photo by Terray Sylvester
Snow fences north of Mammoth provide a laboratory for studying the less-than-obvious effects of climate change.
photo by Terray Sylvester Moonshineink.com to listen to an excerpt of his speech.
photo by Terray Sylvester ">
H. David Nahai, CEO and general manager of the Los Angeles Department of Water and Power spoke during the climate change symposium. Visit Moonshineink.com to listen to an excerpt of his speech.
photo by Terray Sylvester
Click on images for slideshow
The event itself was a sign that climate change in the Sierra is being taken seriously.
In early November, more than 200 researchers, land managers, and conservationists gathered in Bishop, California, for a symposium titled, “Climate, Ecosystems, and Resources in Eastern California.” It was the first conference to focus on the impacts of climate change across the basin and range of the eastern portion of the state.
Over the course of four days, attendees discussed topics ranging from the temperature requirements of California’s state fish, the Golden Trout, to the foraging patterns of Bighorn Sheep; from the behavior of glaciers in Yosemite to the growth patterns of Bristlecone Pines; and from the water rights agreements of Mono Lake to the shifting business strategies of Sierra ski resorts.
One participant called it “a step in the right direction.” It drew scientists from a wide array of disciplines, as well as stakeholders such as the Forest Service, Park Service, BLM and the Los Angeles Department of Water and Power, which relies heavily upon the water resources of the eastern Sierra.
The content of the event was somewhat less hopeful. Nearly every speaker offered dire predictions for the mountain range we call home.
Daniel Cayan of the Scripps Institute of Oceanography described the climbing temperatures the Sierra has already seen. He predicted further increases accompanied by a drying trend and a tendency for snow to become rain in mid-elevations.
“A lot of our heavier precipitation falls in the not-too-much-cooler-than-zero degrees Celsius range,” Cayan said. “So that implies that ironically while we get drier we’re also going to get floodier.”
A number of presenters predicted Sierra snowpack could dwindle by as much as 80 percent over the next 90 years, depending on how successfully we curb our emissions.
Others spoke of declines in species diversity.
“These species around here evolved 60 million years ago. They’re very hardy,” said Connie Millar, a research paleoecologist at the Forest Service’s Sierra Nevada Research Center, while discussing natural climate changes of the past. “But I think we get blinders in forgetting that the environment is not conducive for species to do what they need to do to adapt. We’ve locked everything in place with buildings and pavement.”
But perhaps the most striking comments came from Scott Stine, a geomorphologist and paleoclimatologist at California State University, Hayward, who delivered the keynote address of the event.
After the dishes of the symposium’s dinner banquet had been cleared, Stine took the podium to talk about the weather – the previous 2,000 years of weather. For more than three decades, he has been collecting climate clues across the Sierra.
Submerged trees standing deep within Tuolumne’s Tenaya Lake, indigenous artifacts on the dusty bed of the now-depleted Owens Lake, stumps in the Walker River – these and other hints have led Stine to the conclusion that the weather of the last two millennia has been strikingly varied, and that not many years of those millennia have been nearly as moist as what we call “average.”
“What we consider to be normal wetness today is a chimera. We are kidding ourselves,” Stine intoned into the low light of the banquet room. “We have built the most phenomenal urban and agricultural system in the world, all of it based on storage and transport of water, all the while thinking we’re living in what is normal precipitation and we’re living in an abnormally wet time.”
According to Stine, only three periods in the last 2,000 years have rivaled the 20th century’s abundant moisture.
“The 20th century was probably the fourth-wettest, century-scale period in the last 4,000 years,” Stine said. “Our problem is that we tend to think of today’s climate as being normal, that’s a big mistake as it turns out.”
Over the last 2,000 years, exceptional precipitation has been offset by extraordinary drought.
According to Stine, the bulk of the last two millennia has been “moderately dry by today’s standards.” But sometimes, “moderate” has veered into “severe.” Before an exceptionally wet half-decade of the 12th century, precipitation in the Sierra had been hovering at roughly two-thirds of what we call normal today, and had been doing so for at least 140 years. When a second wet period arrived in the 14th century, it came on the heels of a slightly milder drought that had lasted at least 100 years.
“These are the things we, for very good reason, dread,” Stine said. “This is hopefully not where we’re headed, but it has happened before under natural conditions – century-plus long droughts.”
Stine’s findings aren’t exactly new news. He published them in the journal, Nature, in 1994, and the mainstream press caught wind of it soon after. The Los Angeles Times picked up the story in June of that year, and a few weeks later the New York Times cried, “Severe Ancient Droughts: A Warning to California.”
But during the conference, Stine approached the issue from a new angle. He cast his findings in the context of the tufa of Mono Lake, whose iconic towers are a product of the last 2,000 years of Sierra weather. Against the backdrop of Stine’s research, the tufa towers become signposts. They inform us that as the globe warms, the Sierra Nevada could become much drier than any of us would like to imagine.
All Along the Shoreline: Past droughts, the coming climate, and the tufa of Mono Lake
Scott Stine, muck boots crunching in pale rubble, stoops near the base of a particularly large tufa tower and begins to search. At such close range the huge limestone deposit obscures our view of nearby Mono Lake. It rises above us, alabaster and grotesque, like a cross between a child’s sand-drip castle and a handful of thunderheads.
Without much trouble Stine finds what he was looking for. He points to an oblong, knotty bulge in the tufa, follows it a short distance, and then picks up a crumbly block that was, until recently, attached to it. There, set within the tufa, lies a branch of Artemisia tridentata, the most common sagebrush of the Sierra. The outer edges of the woody matter have long since petrified, but in the center of the stone lies a rich, brown twist of the ancient vegetation itself.
“See that piece right there? That’s going to be 600-year old wood,” says Stine.
He can be so certain because he has collected many similar chunks of vegetation, packaged them up and sent them off to be radiocarbon dated at Lawrence Livermore National Laboratory. The data he’s received from the lab, along with his background knowledge of the historic and prehistoric climate of the Sierra Nevada, have allowed him to draw the link between the growth patterns of the tufa, the weather patterns of the past, and precipitation shifts that could accompany the warmer climate of the future.
Tufa can form through an inorganic reaction between the area’s calcium-rich groundwater and the carbonate-laden water of Mono Lake. Carbonate is essentially the same substance as baking soda, and when dissolved in water and combined with significant concentrations of calcium, calcium carbonate results. This is the white, crumbly stuff of tufa, though we may know it better as limestone.
With turbulence to stir together its constituent compounds, and something to adhere to, tufa can form very quickly. In Stine’s words, it can “flash” into existence, and that’s just what it did during the pronounced climate shifts of the past 2,000 years.
Before the wet period of the 12th century, Mono Lake’s surface lay as low as 6,368 feet of elevation. (That’s 50 feet lower than the lake stood in 1919, before Los Angeles began diverting water from its tributaries.) Then, over a period of less than 50 years, the lake climbed 60 feet. As the carbonate-laden water rose, it mixed with groundwater deposits and tufa began to accumulate.
From a geologic perspective, the wet period of the 12th century ended almost as soon as it began, but its receding waters left behind the bulky cores of the tufa towers. The ensuing wet eras drew Mono Lake up again, and each time additional layers of tufa coalesced on the previously established cores.
Stine compares the layers of the tufa towers to the leaves of an onion, and can trace each to particular weather pattern of the past. In this way, the towers record the climate of the last two millennia, and point to the sort of changes the Sierra Nevada could experience as a result of the enormous amount of carbon dioxide humans have released into the atmosphere.
“Looking at the past shows us what the atmospheric and oceanic system of the planet is capable of bringing California,” Stine said. “We tend to think that it’s capable of bringing us essentially the droughts we’ve seen in our lifetimes, and the wet periods we’ve seen in our own lifetimes. We don’t think of climate as conceivably being much different than that. In fact, it is much different than that. All we have to do is go back a few grandmothers and there it is.”
So far, scientists in the Sierra are finding it harder to predict future precipitation than to predict temperature. But against the backdrop of the climate record he knows so well, Stine sees little reason to expect precipitation changes will be benign.
“We’re coming out of what may be the coolest period in the last 8,000 years into what we ourselves are making the warmest period in the last 10,000 years,” Stine said.
“Precipitation will be a function of temperature changes, and there’s no way we can expect it won’t change. There are good theoretical reasons why we would expect it to get dryer as it gets warmer.”
After Stine’s speech at the conference, Millar, the Forest Service researcher, took the microphone to offer a few closing remarks. She emphasized that the work of scientists is to collect information before necessarily knowing what it will add up to; that often, gathering data amounts to answering questions that haven’t yet been asked. But occasionally, she added, questions crop up in need of answers.
“Science is the watchman of the detail,” she said, speaking to Stine. “You have provided the details we will watch in the next decades. We didn’t realize tufa mattered so much, but now we know.”
The myriad threats of global warming have provided just the sort of context that imbues raw data with meaning. According to Millar, who helped organize the symposium, scientists have only recently begun seriously delving into the impacts of climate change upon the living systems of eastern California.
“The climatologists have been doing this for 20 years or so. But much more recently the ecologists have been cranking out important studies, and that’s been the richness in the last five years,” she said.
One such researcher is Sharon Martinson, a population ecologist studying Artemisia tridentata, the great basin sagebrush.
Taking the sagebrush as a lens, Martinson is peering into the indirect effects of climate change. Not satisfied with understanding only how the plants themselves will react to shifts in weather patterns, she is wondering what will happen when the changes in the plants become causes in their own right, and their effects ripple out through the greater ecosystem.
As she explained during the conference, “You start with understanding direct effects, but we also know that everything is connected. There’s a compelling case that the indirect effects of climate changewill prove more powerful.”
If Martinson is correct, subtle responses in the sagebrush could cause big shifts in the biodiversity of the ecosystem it supports, and bring hotter, more frequent fires in the process.
The Devil in the Details: Insects and the subtle effects of climate change
Sharon Martinson stoops by a clump of sagebrush, picks through its foliage and then, with a grin, stands up holding a sprig of vegetation. Tucked amongst the fragrant, three-lobed leaves there’s a fibrous growth about the size of a hazelnut – just what she was searching for.
“A ‘furball’ gall,” jokes the scientist, obviously pleased.
I pry open the gall to reveal a pocket of downy material, and within that, a minute nub of insect life. Such galls form on artemisia when an insect lays its eggs on the sagebrush, and according to Martinson, they come in at least 24 varieties. She should know, over the past few months she has counted tens of thousands of them, sometimes discovering more than 100 on a single sagebrush shrub. But the profusion doesn’t stop there.
“A single gall represents a huge wedge of insect diversity,” explains Martinson. “It’s one gall but it might nourish 20 parasitoids” – spiders and other insects who prey on the galls and their occupants.
And in their turn, all these bugs nourish larger animals such as lizards, rodents, and birds.
“Almost all the birds out here are insectivorous. There are not that many fruits and berries in the high Sierra for them to eat,” Martinson said.
We’re standing a few dozen miles north of Mammoth. Approaching snow has veiled the Sierra crest, and in the chill, pre-storm light the sagebrush glows a richer green. Martinson and her colleagues at the University of California, Santa Cruz, didn’t choose this site for its scenery, though. They were wondering what will happen to the sagebrush when climate change alters the snowfall patterns of the Sierra, and they found an answer in Caltrans infrastructure from the first half of the century.
Between Mammoth and Lee Vining, lines of 20-foot fences reduce snow loads on the highway by interrupting the prevailing westerly winds. As storms blow in from the Pacific Ocean, drifts form near the lee of the fences while the road and the shrub lands slightly farther east receive roughly half as much snow as they otherwise would. After more than 50 years, the sagebrush shrubs in the drift zones and the dry zones have adapted to their modified circumstances. It’s an ideal situation for Martinson since the climate models she works with are, to borrow her term, “agnostic.” They indicate precipitation levels near Mammoth will change, but struggle to predict just how.
Martinson has learned that fewer galls grow on the sagebrush in the lee of the Caltrans fences, where drifts accumulate. She reasons that if snow loads do increase – and right now, her models indicate that at least in the Mammoth area they might – a decrease in galls could cause the area’s biodiversity to suffer.
But there’s a more ominous message in the insect life near the snow fences.
In addition to galling insects, Martinson has been keeping an eye on leaf-eating creatures about two millimeters long. They have six legs and zebra-stripes, and are active on the sagebrush throughout the summer. They might not seem much more than whimsical, but they could bring more severe fires to the sagebrush.
Whether snowfall increases or declines, the tiny herbivores tend to eat more. As yet, Martinson isn’t quite sure why that is, but she hypothesizes that shifts in snow levels weaken the sagebrush and leave it vulnerable to predation.
Typically, sagebrush sheds its leaves as the winter snows are melting. The moist soil of spring causes the leaves to decay relatively quickly, leaving the soil between individual sagebrush plants largely bare by the time summer arrives. But as the minute herbivores amp up their feeding habits, the sagebrush sheds its damaged foliage when it otherwise wouldn’t. In both of the experimental plots near the Caltrans fences, Martinson has found yellowish piles of leaf litter persisting through the dry months of summer.
The change may seem slight – artemisia leaves just aren’t that large – but multiplied across the vast acreage of sagebrush ecosystems it could result in a landscape-scale increase in fuel loads. Under one scenario, larger fires could clear areas of sagebrush, leaving habitat available for invasive grass species such as cheatgrass, which has already colonized large swaths of the great basin.
Sagebrush establishes itself slowly and thrives where fires are relatively infrequent. Researchers think that under natural conditions, sagebrush ecosystems burn once every 40 to 100 years. Not so with cheatgrass, which grows quickly, burns readily, and then sprouts again in the charred landscape. Cheatgrass ecosystems tend to burn every three to five years, creating a fire regime with which the relatively slow-growing artemisia would not be able to compete.
The cheatgrass scenario is just the sort of situation that stirs Martinson’s interest in the subtle effects of climate change. Shifts in the weather weaken the sagebrush, and at first glance the sagebrush’s response may seem innocuous. But just a few links farther along the chain of cause and effect, the actions of a tiny insect could stir up big trouble. Martinson’s research implies that we’ve only dipped our toes into the implications of climate change.
“There’s no doubt that there’s going to be something here in 50 or 100 years. But will it be an ecosystem bearing any resemblance to what’s here today? It’s questionable,” Martinson said. “Through geologic time ecosystems change a lot. The problem is that now the change is happening so rapidly that it’s hard to predict where things are going.”
Information:
Climate, Ecosystems, and Resources in Eastern California
White Mountain Research Station: 760-873-4344
Conference program, presentations, photos: wmrs.edu/projects/CEREC/
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