A far-off food source for Sierra for­est

The global jet stream de­posits nu­tri­ent-rich dust from Asia in Yosemite, study says.

Los Angeles Times - - CALIFORNIA - JOSEPH SERNA joseph.serna@la­times.com Twit­ter: @JosephSerna

What does the Yosemite Na­tional Park for­est have in com­mon with the Ama­zon rain­for­est? A food sup­ply from a far-off place.

Dur­ing Cal­i­for­nia’s rainy sea­son, cli­mate sci­en­tists say, dust from as far away as the Gobi Desert in Asia is car­ried by the global jet stream and de­posited on top of Yosemite’s gran­ite bedrock, where mi­cro­scopic ma­te­rial within the dust feeds the vast forests of the Sierra Ne­vada.

The process has been go­ing on for hun­dreds of thou­sands of years, but not un­til re­cently did sci­en­tists aim to un­der­stand the im­pact of that re­la­tion­ship in the Sierra.

In gen­eral, plants are sup­plied nu­tri­ents as bedrock is con­verted into soil, a process that helps reg­u­late life across much of the Earth’s sur­face. But where that process is lack­ing — such as in the gran­ite moun­tains of Yosemite Na­tional Park, or the Ama­zon, where con­stant rain and flood­ing wash away nu­tri­ents — desert dust can make all the dif­fer­ence.

The Ama­zon re­lies on the Sa­hara Desert in Africa for much of its nu­tri­ent sup­ply, and sci­en­tists sus­pected that the Sierra Ne­vada conifers re­lied on a sim­i­lar re­la­tion­ship.

So last year, sci­en­tists from UC Merced, sup­ported by the Na­tional Sci­ence Foun­da­tion, ex­am­ined Yosemite’s dust and con­firmed their the­ory in a study pub­lished in March. They found that some of it was com­posed of ma­te­rial from the Gobi Desert in China and Outer Mon­go­lia mixed in with dust from Cal­i­for­nia’s own Cen­tral Val­ley.

But af­ter Cal­i­for­nia’s five-year drought was washed away by the wettest win­ter in a decade, re­searchers want to see how the weather has changed the trees’ menu and said they plan to re­visit the same test sites in Yosemite next spring.

The re­search will not only help an­swer ex­perts’ ques­tions on how bands of conifer forests filled with se­quoias and pines in the Sierra man­aged to grow for hun­dreds or thou­sands of years on nu­tri­ent-poor gran­ite, but how they may re­spond to cli­mate change.

“As you get more warm storms and fewer colder storms, you will see changes just like this hot, drought­caused tree mor­tal­ity,” said Roger Bales, a UC Merced en­gi­neer­ing pro­fes­sor and direc­tor of the Sierra Ne­vada Re­search In­sti­tute.

As it turns out, the last few years were a good time frame in which to ex­am­ine how cli­mate ex­tremes can af­fect Cal­i­for­nia’s moun­tain­ous ecosys­tems. UC Merced ecol­ogy pro­fes­sor Stephen Hart said that was be­cause it in­cluded an av­er­age year for pre­cip­i­ta­tion tucked between his­tor­i­cally dry and wet years.

The team’s re­search, pub­lished in Na­ture Com­mu­ni­ca­tions, showed that dur­ing the peak of the drought, the forests in the Sierra Ne­vada foothills and low el­e­va­tions were fed by dust from the San Joaquin Val­ley, where with­er­ing fields turned brown, lakes eva­po­rated and the earth lit­er­ally sank due to ground­wa­ter pumping.

That dust was chock-full of nu­tri­ents like phos­pho­rous, cal­cium, mag­ne­sium and potas­sium and stood in stark con­trast to the ma­te­rial stored in the gran­ite that char­ac­ter­izes Yosemite, which is rel­a­tively young and helps shape the older val­ley floor, Hart said.

The earth that once cov­ered Yosemite’s gran­ite peaks was worn away long ago dur­ing moun­tain for­ma­tion. Much of that mat­ter was washed down­hill dur­ing storms — which is why the Cen­tral Val­ley is such a fer­tile bread­bas­ket, Hart said.

So re­searchers were not only sur­prised to find nu­tri­ent-rich dust at the moun­tain’s higher el­e­va­tions, they were also sur­prised to find that it came from an­other con­ti­nent.

The team col­lected the dust from mar­bles that were left on an el­e­vated bundt pan. Af­ter the mar­bles had col­lected a layer of dust, they were rinsed with dis­tilled wa­ter and that wa­ter was then an­a­lyzed.

Up to 45% of the dust at the high­est el­e­va­tions in Yosemite was from Asian sources, said UC Merced grad­u­ate stu­dent Ni­cholas Dove, who worked on the study. Study au­thors said they were able to iden­tify the dust’s re­gion of ori­gin by an­a­lyz­ing its chem­istry, ge­o­logic age and iso­topic con­tent.

Sand storms in the Gobi Desert lift the dust into the sky, where it is car­ried thou­sands of miles over the Pa­cific Ocean for sev­eral days, ac­cord­ing to Dove. When it reaches the United States, the air car­ry­ing it is squeezed like a dirty sponge against Cal­i­for­nia’s moun­tains, and the dust is de­posited along with rain or snow.

“Peo­ple have known that’s oc­cur­ring for quite a while, they just didn’t know how im­por­tant it was to the ecosys­tem,” Bales said.

Brian van der Brug Los An­ge­les Times

HALF DOME as seen from Glacier Point in 2015. Re­searchers say dust from the Gobi Desert is de­posited atop Yosemite’s gran­ite bedrock.

NASA

PLUMES of dust are blown out of the Gobi Desert in 2012. The dust is car­ried over the Pa­cific for sev­eral days, ac­cord­ing to a stu­dent who worked on the study.

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