PART THREE: Tree mortality in the Sierra continues to rise

 

This is the third and final installment in a multi-part feature on tree health in the Sierra and throughout California. Previous installments may be read online at www.kaweahcommonwealth.com/news/tree-mortality-sierra-continues-rise

Read Part One here.

Read Part Two here.

California is currently in its fifth year of severe drought. Locally, the lack of rain and snow is taking a noticeable toll.

The warmest year on record for California was 2015. And, according to a NASA report released this week, the six-month period from January to June was Earth’s warmest half-year in the annals of modern temperature, which dates to 1880.

Add to this, the National Oceanic and Atmospheric Administration announced that the El Nino event of 2015-2016 has dissipated. Californians can expect the opposite for the upcoming fall and winter seasons: La Nina. La Nina is known around these parts to be accompanied by low precipitation levels.

Things were looking up when, on March 30, 2016, the California Department of Water Resources measured the statewide snowpack to be at 87 percent of normal. The water year was shaping up nicely until June 13, when the statewide snow-water equivalent was measured at a paltry 6 percent of average for this date.

The U.S. Forest Service released figures last month that 66 million trees are dead throughout the state. In Kaweah Country, from the foothills to the conifer belt, there are huge swaths of manzanitas, oaks, pines, cedars, and firs that are all casualties of a drought of epic proportions, which began in 2012 and is persisting despite the near-normal winter of 2015-2016.

 

Drought and giant sequoias

 

It is arguably the most famous forest on the planet. Giant Forest is the principle visitor attraction in Sequoia National Park and the reason the park was established in 1890 as the nation’s second national park.

John Muir wandered about this forest in 1875 and was so taken by it that he is credited for naming it “Giant Forest.” The namesake giant sequoias are the largest, most famous, most beloved trees in the world. 

Half of the 10 largest giant sequoias are located in the Giant Forest Grove, including the planet’s most colossal tree of all, the General Sherman. The other five on this top-10 list are more dispersed, located in five separate groves.

Sequoias definitely have super-powers. How else could they live to a ripe, old age of 3,000 years, grow to 300 feet in height, and have a waist-size of 150 feet?

The high tannin content of the Big Trees provides a defense against most, not all, insects and fungi. Perhaps sequoias would live to infinity and beyond if they weren’t eventually toppled by the relentless forces of nature: wind or fire, storms or erosion, or all of the above.

Although this is far from the first drought the sequoias have ever experienced, all bets are off on how this current dry cycle will affect these resilient trees. Or, in the bigger picture, human-caused climate change, which is unprecedented in the trees’ lifetimes.

The National Park Service isn’t sitting idly by. They have scientists on staff, at the Sequoia-Kings Canyon Field Station of the U.S. Geological Survey, and from nonprofit research centers and academia, all studying the effects of a half-decade of drought as well as warming temperatures on giant sequoias.

In fall 2014, Nate Stephenson, Ph.D., a research ecologist with the local USGS field station since 1997, sounded the alarm that the foliage way up in the tops of some mature giant sequoias were showing signs of stress. The following summer, scientists converged among the Big Trees, and the Leaf to Landscape Project was founded.

The NPS and USGS — with the assistance of UC Berkeley researchers, a Stanford grad student, and the Carnegie Institute for Science’s Airborne Observatory — took measurements of, and samples from, the massive trees. This was accomplished with some technical climbing into the crowns of the trees and through remote sensing from the flying laboratory known as the Carnegie Airborne Observatory.

Although research is ongoing, there have been some conclusions. In Giant Forest, the most stressed trees are on the southwest and southeast perimeters, from Giant Forest Museum to Moro Rock and in the vicinity of Crescent and Log meadows.

“Of all the species on the landscape in these lower elevation forests, sequoias did the best,” said Stephenson in a YouTube video that highlights the Leaf to Landscape Project. “The firs did a lot worse, the pines did a lot worse, the cedars did a lot worse, the oaks are doing a lot worse.”

Giant sequoias are selective about where they grow. Their native range is a narrow band, about 250 miles in length, along the western slope of the Sierra Nevada.

They grow where there are water sources that are deep, reliable, and year-round, the researchers determined. This innate ability to tap into the underground aquifers could help them weather this most recent threat that they and most other Sierra tree species face. 

But these deep subterranean water supplies could be changing too, as the snowpack that replenishes them moves ever higher in elevation. So although the giant sequoias have fought off two and three millennia of climate threats, the temperature of the Earth is warmer than it has been in nearly 12,000 years, according to a study published in the journal Nature Climate Change. And with temperatures forecast to continue to rise throughout the 21st century, these ancient trees will face challenges they have never yet endured.

Will giant sequoias persevere in spite of drought and heat-induced threats? Time will tell.

For more information on the Leaf to Landscape Project, go to: www.youtube.com/watch?v=PYcsL29XNGw&feature=youtu.be

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