Heat without rain­fall won’t prod trees higher

Al­ti­tude not only an­swer for conifers in cli­mate change

The Denver Post - - NEWS - By Bruce Fin­ley

A $7 mil­lion gov­ern­ment­backed cli­mate change ex­per­i­ment over a decade in the Colorado high coun­try — us­ing scaf­fold­ing and heat lamps to sim­u­late global warm­ing — has found hot­ter air alone won’t be enough for stressed conifers to sur­vive by shift­ing to higher el­e­va­tions.

“By just heat­ing the air and land more, you might in­vite trees up higher, but they won’t be able to make it un­less you also cre­ate the rain­fall up there. … Rain­fall be­comes the lim­it­ing fac­tor,” said Univer­sity of Colorado evo­lu­tion­ary ge­neti­cist Jeff Mit­ton, a leader of the project done with Univer­sity of Cal­i­for­nia and U.S. Ge­o­log­i­cal Sur­vey sci­en­tists at el­e­va­tions around 11,400 feet.

“So are trees at lower el­e­va­tions go­ing to start dy­ing off as as­pen are start­ing to do? Will they grow up higher? Not nec­es­sar­ily. If we heat them at higher el­e­va­tions, but do not in­crease rain­fall, it does not look like trees will be able to move up.”

Funded by the U.S. Depart­ment of En­ergy, the project stands out as one of the larger ex­per­i­men­tal cli­mate change stud­ies in­volv­ing trees. The find­ings are ex­pected to help sci­en­tists and fed­eral agen­cies an­tic­i­pate what cli­mate change will mean in moun­tains around the world. Trees play key roles re­tain­ing snow, which sup­plies water for the western United States, and ab­sorb­ing car­bon emis­sions from hu­man in­dus­try and ve­hi­cles.

Sci­en­tists said they didn’t re­al­ize how im­por­tant water would be in tree adap­ta­tion. Many have un­der­stood that, as cli­mate change leads to higher tem­per­a­tures, trees gen­er­ally would “fol­low their cli­mate” and shift from high-stress lower-el­e­va­tion warmer zones to higher el­e­va­tions, where tem­per­a­tures cur­rently are too cool, caus­ing alpine tun­dra tree­lines to climb.

The peer-re­viewed re­sults were pub­lished in De­cem­ber in the jour­nal Global Change Bi­ol­ogy. A team from the DOE’s Univer­sity of Cal­i­for­nia lab, UC-Merced, the USGS and CU planted En­gel­mann spruce and lim­ber pine conifer seeds. The sci­en­tists in­stalled in­frared

heaters, sus­pended on the scaf­fold­ing, on plots above CU’s Moun­tain Re­search Sta­tion on Ni­wot Ridge west of Ward.

Few trees cur­rently grow around tree­line, around 11,200 feet el­e­va­tion here, be­cause of wind, cold tem­per­a­tures and in­suf­fi­cient soil.

The sci­en­tists used the heaters to raise tem­per­a­tures by 1.5 to 4 de­grees Cel­sius. They mon­i­tored ef­fects on trees planted in plots be­tween 11,200 feet and 11,400 feet, where they had hy­poth­e­sized conifers would mi­grate in re­sponse to global warm­ing.

In plots where tem­per­a­tures stayed the same, trees did not grow. In plots where tem­per­a­ture in­creased but water was not added, conifers be­gan to grow but died within two years. Where seeds were planted, tem­per­a­tures in­creased and water was ap­plied, trees grew for more than three years and sur­vived.

There’s no prac­ti­cal way to re­verse the im­pact of cli­mate change on trees be­cause global con­cen­tra­tions of car­bon diox­ide in the at­mos­phere have risen to around 400 parts per mil­lion, higher than in 400,000 years, Mit­ton said. A pre­pon­der­ance of sci­en­tists agree that hu­man ac­tiv­i­ties since in­dus­tri­al­iza­tion around 1850 have caused the in­creases in car­bon diox­ide and other heat-trap­ping gases. Many species, an estimated 3,000 a day in­clud­ing mi­crobes and in­sects, are dis­ap­pear­ing.

Even if Amer­i­cans con­tinue to re­duce green­house gas emis­sions, the in­creas­ingly af­flu­ent pop­u­la­tions ex­pand­ing in other coun­tries emit more gases — boost­ing over­all emis­sions, Mit­ton said.

“We talk a lot and we wring our hands, but we are not ac­com­plish­ing much yet. Car­bon emis­sions around the world are go­ing up,” he said. “And what we have found is that, as it gets warmer and seeds are re­leased in alpine ar­eas, trees might be able to go into higher el­e­va­tions. But that can only hap­pen if the amount of pre­cip­i­ta­tion is in­creas­ing. And, in Colorado, there is no con­sen­sus on whether pre­cip­i­ta­tion will in­crease or de­crease.”

At high el­e­va­tions, fierce winds trim lim­ber pine, En­gel­mann spruce and sub­alpine fir to ground-hug­ging shrubs called krummholz or elfin­wood.

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