Climate Change: Forests, wildlife, fire danger all expected to be affected by warming Sierra
Many doomsday predictions of climate change focus on rising oceans, flooding coastlines and submerged cities, but some scientists are watching the Sierra to gauge other significant impacts.
Looking into the future it isn’t hard for researchers to picture the many different Sierra ecosystems ” wrapped like bands around different elevations ” retreating rapidly upward, squeezing each other and eventually running out of elevation to climb.
As future temperatures rise, predictions are for snow to melt faster and streams to swell earlier, out of sync with the breading cycles of aquatic species like fish and frogs.
Dry summers would leave entire forests more susceptible to fire and pests than ever before.
And, many experts agree, the changes become amplified as they move up the food chain, throwing the Sierra Nevada’s entire ecosystem, meticulously established over millennia, out of balance in a matter of decades.
The bottom line, some scientists conclude, is the extinction of vulnerable mountain species and increased fire risk for the Sierra’s human inhabitants.
“Our concern is with the rapidity of change ” most species can evolve over time and the planet has always been in flux ” but it’s the rate of change, which is really unlike anything we’ve been able to study,” said Josh Viers, assistant research ecologist at UC Davis.
The Sierra Nevada has been characterized as the “canary in the coal mine,” according to the U.S. Forest Service, an early alarm for the deleterious effects of rising temperatures.
But all parts of the Sierra won’t be treated equal. Despite Truckee-Tahoe’s more northern latitude, the area will likely be hit harder than the taller mountains to the south.
“The area around Tahoe and Donner Summit, for example, would be more affected then Kings Canyon,” Viers said.
And so Tahoe National Forest has been picked as an open-air laboratory for climate change ” a focal point in a global issue ” with researchers from academic bodies, conservation groups and the U.S. Forest Service gleaning whatever they can learn from the surrounding woods.
“When I started I was a naysayer, ready to poke holes in global warming,” said Carol Kennedy, the watershed project manager for Tahoe National Forest. “I don’t poke holes anymore.”
Perhaps easiest to predict and already in progress in some cases is the steady retreat of vegetation away from rising low-elevation temperatures and towards ever-shrinking snow melt, said UC Davis’ Viers.
However, not all species and ecosystems will move at the same rate, he said.
“What has been documented at higher elevation is the leading edge is moving up much slower than the trailing edge, and species are feeling the squeeze,” Viers said. “In practice the ponderosa pine is pretty hard hit.”
Kennedy said ponderosa pines have already moved up to 500 meters up-slope.
The different speed at which trees climb could also mean different mixes of species in future Sierra forests, she said.
Subalpine regions ” places where snow traditionally sticks for too long to for anything bigger then brush and grasses to survive ” are already seeing conifer growth, said Scott Conway, vegetation management officer for the Tahoe National Forest’s Truckee Ranger District.
“Places where 20 or 30 years ago trees couldn’t become established are now seeing baby fir trees,” Conway said.
Dr. Chad Hanson, director of the John Muir Project who is also doing post-doctoral research at UC Davis, agreed that subalpine species in the region are a concern.
“They may not be affected as early as species lower down, but subalpine species can’t go much higher,” Hanson said.
But his No. 1 concern is the sugar pine, Hanson said.
“What I’m really worried about are some of the conifer species associated with the mid-to-upper elevations. As the climate warms they may recede up the slope as the lower elevation becomes inhospitable, and wildlife species will have to go up with them,” Hanson said.
Another study tracking forest elevation gain is a collaboration between the Forest Service, the Nature Conservancy, UC Berkeley, Stanford University and others, said Patrick Gonzalez, climate change scientist with the Nature Conservancy.
Their work along the North Fork of the Yuba River focuses on three forest systems at different elevations, he said.
“In the Downieville the climate is warming at seven times the global rate,” Gonzalez said. “We’re seeing signs of many of the species shifting upward.”
But trees may not move simply up-slope and to the north seeking cooler clime, said Mark Nechadom, the climate science policy director for the U.S. Forest Service.
Cheryl Yeh, presidential management fellow with the Forest Service, said while some tree species climb higher, others could drop into cooler valleys with their own microclimates.
The complexity of change in the forest may mean trouble for the animals that depend on them, Nechadom said, where some species may be able to move with the change, but others may go extinct.
“One species we are paying close attention to is the Pika,” Nechadom said. “It’s a very high-elevation species related to the rabbit whose habitat is drying and warming up.”
The Forest Service’s Kennedy said generalist species, like deer, will likely come through climate change, whereas specialists may not.
“Some predictions show 15 to 35 percent of the species in our ecosystem effectively extinct in the next 100 years,” Kennedy said.
Other species dependent on streams or other watery environments don’t always have the ability to relocate, Nechadom said.
While rising temperatures will directly affect many species, indirect affects through changing water availability may be even more drastic.
“Between 7,000 and 9,000 feet the rain/snow mix line will be most severely affected,” Josh Viers said.
This means the timing and flow of streams and river could change, possibly three to seven weeks earlier, he said.
“Everything from what’s in the streams ” frogs breeding to vegetation along the side of the streams ” a whole series of affects, will come from just the timing,” Viers said.
The breeding cycles of both the mountain red- and yellow-legged frogs of the Sierra may no longer match with stream flows he said.
Trout require cold water, no more than 20 to 21 degrees Celsius, meaning many streams could become too warm, Viers said. Flowering plants may bloom with high flows before pollinators like bees and mosquitoes emerge.
Aspen trees, already diminishing in the West, are at risk because of drying stream habitat, Nechadom said.
And moisture could be dropping on the order of 40 to 60 percent by the year 2100, Kennedy said.
That kind of change doesn’t just affect the most water-dependent species, but almost all species across the board, scientists said.
Climate change could also make forests even more susceptible to problems currently plaguing the Sierra.
Federal forester Conway said warmer temperatures ” potentially an increase of 3 to 4 degrees Celsius in the winter, 4 to 7 degrees Celsius in the summer in the next 100 years ” will put significant strain on forests already struggling to survive fires, bark beetle infestations and other issues.
“One thing models are showing is we are likely to see more drought and therefore more fire,” said Mark Nechadom. “We’ll see more fire both in quantity and intensity.”
One or two extra months of summer means that Sierra species will not only go through a dormant period in the winter, but in the summer as well, leaving them open for bark beetle infestations, Carol Kennedy said.
And with 80 to 90 percent of trees in Truckee-Tahoe area forests susceptible to bark beetles, that could mean massive change, said Conway.
“That isn’t just out in the forest, but in peoples’ yards,” Conway said.
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