>> LONG BEFORE THE ADVENT OF CHRISTIANITY, EVERGREENS HELD
SPECIAL MEANING FOR PEOPLE DURING THE WINTER.
BRANCHES OF PINE AND SPRUCE AND FIR WERE HUNG IN HOUSES AS AN
OFFERING TO THE SUN GODS AND TO REMIND PEOPLE OF WARMER DAYS.
♪♪
AS CHRISTIANITY SPREAD THROUGHOUT EUROPE, THE PAGAN
TRADITION WAS ABSORBED INTO THE NEW RELIGION.
BY THE 16th CENTURY IN GERMANY, DECORATED TREES WERE FOUND IN
HOMES THROUGHOUT THE WINTER.
200 YEARS LATER, CHRISTMAS TREES WERE THE RAGE IN LONDON DURING
THE HOLIDAYS.
AND BY THE LATE 1800s, THE CHRISTMAS TREE TRADITION WAS
GROWING IN AMERICA.
>> I THINK -- YEAH.
READY, JESSICA?
>> YES.
>> 33.8.
>> AND, JESSICA, THE DENDROMETER BAND WAS 25 MILLIMETERS.
>> THESE RESEARCHERS FROM APPALACHIAN STATE UNIVERSITY
WANT TO MAKE SURE THERE ARE FRASER FIRS STILL GROWING IN
NORTH CAROLINA THAT CAN FILL THAT HOLIDAY TRADITION FOR YEARS
TO COME.
>> ALL RIGHT.
SO SOIL MOISTURE, 35.9.
>> THE AMOUNT OF MOISTURE IN THE SOIL DEPENDS PRIMARILY ON THE
TYPE OF SOIL.
SANDY SOIL HOLDS MORE WATER.
CLAY SOIL NOT AS MUCH.
THIS READING SHOWS SOIL THAT IS SOMEWHAT DRY.
SOIL MOISTURE IS CRUCIAL TO A TREE'S ABILITY FOR
TRANSPIRATION, OR TAKING IN WATER AND MOVING IT TO THE LIMBS
TO EVAPORATE.
SOIL MOISTURE ALSO IMPORTANT FOR TREES TO TAKE IN NUTRIENTS
FOR PHOTOSYNTHESIS, FOR MAKING FOOD, AND FOR GROWING.
SO WHY THE CONCERN?
WELL, BECAUSE THE PLANET IS WARMING, AND FRASER FIRS GROW
BETTER IN COOLER AND WETTER CLIMATES.
>> AND THEIR NATIVE HABITAT IS 5,000 FEET OR ABOVE.
AND, YET, ALL THE COMMERCIAL GROWERS ARE 4200 FEET AND BELOW,
FROM ABOUT 4200 TO 2200 FEET.
AND SO SINCE THEY'RE ALREADY GROWING OUT OF THEIR RANGE,
AND IF IT DOES GET WARMER, THEN MAYBE THE FARMERS AT THE
LOWER ELEVATION MAY START TO SUFFER.
THEIR TREES MAY NOT BE GROWING AS WELL.
AND THEN THE FARMERS UP HERE, THEY HAVE TO DEAL WITH WARMER
TEMPERATURES, AND THE CONSEQUENCES OF THAT ARE NOT
KNOWN.
>> LASTLY, 39.1.
>> SO RESEARCHERS ARE USING ELEVATION AS A SURROGATE FOR
WARMING.
IN OTHER WORDS, TREES GROWING AT LOWER ELEVATIONS, WHERE IT IS
WARMER, REPRESENT TREES GROWING IN A WARMER CLIMATE.
TREES AT MIDDLE ELEVATIONS REPRESENT TREES AT A SLIGHTLY
WARMER CLIMATE.
AND THOSE TREES AT THE HIGHEST ELEVATION REPRESENT TREES IN A
COOLER CLIMATE.
>> AS YOU GO UP IN ELEVATION, OF COURSE, IT GETS COOLER.
>> RIGHT.
>> WE CALL THAT THE ADIABATIC LAPSE RATE.
AND SO IF WE KNOW THE ELEVATION OF WHERE THE FARMS ARE, WE CAN
GET A ROUGH ESTIMATE ON AVERAGE OF HOW MUCH WARMER IT IS AT THE
LOW ELEVATION, THIS MID ELEVATION, AND THE HIGHER
ELEVATION.
BUT TO MAKE SURE, WE'VE ALSO INSTALLED WEATHER STATIONS AT
EACH OF OUR ELEVATIONS TO GET THE ACTUAL DATA.
AND SO FAR WE ARE SEEING THAT THERE ARE LARGE DIFFERENCES IN
TEMPERATURE.
>> THE EXPERIMENT MONITORS FRASER FIRS ON SIX WESTERN
CAROLINA TREE FARMS AT THREE DIFFERENT ELEVATIONS.
DAILY WEATHER DATA IS CONTINUOUSLY RECORDED.
THEN RESEARCHERS SPEND AN ENTIRE DAY AT EACH FARM CHECKING HOW
THE TREES ARE RESPONDING TO CURRENT CONDITIONS.
>> AND THIS HAS A NICE AIRTIGHT SEAL AROUND OUR BRANCH.
AND SO THAT ANY GAS THAT'S BEING EXCHANGED WE KNOW IS JUST COMING
FROM WHATEVER'S INSIDE OF OUR CUVETTE HERE.
>> SCOTT CORY IS USING A PORTABLE PHOTOSYNTHESIS SYSTEM
TO MEASURE HOW MUCH CARBON DIOXIDE THE TREE IS ABSORBING
AND HOW MUCH OXYGEN AND WATER VAPOR IT'S RELEASING AS IT
UTILIZES THE SUNLIGHT TO PRODUCE FOOD.
>> WE WANT TO KNOW HOW MUCH GAS IS BEING EXCHANGED BETWEEN THE
TREE AND THE ENVIRONMENT THAT'S JUST IN THIS CUVETTE HERE.
SO WHAT WE DO IS, WE SUPPLY A CERTAIN AMOUNT OF GAS INTO THIS
CUVETTE, AND THEN WE MEASURE THE GAS THAT'S COMING OUT OF THE
CUVETTE.
AND WE KNOW THE DIFFERENCE BETWEEN THE GAS THAT WE GAVE IT
AND THE GAS THAT'S COMING OUT OF THE CUVETTE.
THE DIFFERENCE WOULD BE THE RATES OF PHOTOSYNTHESIS AND
TRANSPIRATION.
>> SO INSIDE THIS BOX YOU'LL SEE WE HAVE A DEEP CYCLE MARINE
BATTERY, A WHOLE BUNCH OF WIRES, A CHARGE CONTROLLER, ETC.
AND FROM THIS BOX WE HAVE FIVE WIRES BURIED GOING TO FIVE
DIFFERENT TREES.
AND IN EACH TREE WE HAVE SAP FLOW PROBES, AND THEY'RE
GRANIER-TYPE SAP FLOW PROBES.
AND IT'S TWO PROBES AT 10 CENTIMETERS APART.
AND, ULTIMATELY, YOU CAN FIND OUT HOW FAST SAP IS FLOWING IN
EACH OF THE FIVE TREES.
>> MEASURING HOW FAST THE SAP IS FLOWING INSIDE A TREE GIVES AN
INDICATION OF HOW FAST THE TREE WILL GROW AS WELL AS HOW MUCH
WATER THE TREE IS USING.
BUT THERE'S STILL THE QUESTION OF JUST HOW STRESSED FOR WATER A
TREE CAN BE.
RESEARCHERS USE A SMALL TREE CLIPPING TO ANSWER THAT
QUESTION.
>> YOU PUT IT IN THE PRESSURE CHAMBER, PRESSURIZE, APPLY A
POSITIVE PRESSURE.
AND WHEN THE WATER COMES OUT OF THE CUT END, YOU KNOW THAT THAT
POSITIVE PRESSURE EQUALS THE NEGATIVE PRESSURE WITHIN THE
BRANCH.
>> THE HIGHER THE PRESSURE NEEDED TO SQUEEZE THE WATER OUT
OF THE CUTTING, THE MORE STRESSED THE TREE IS FOR WATER.
>> IT'S FESTIVE.
>> WHY DO YOU SAY THAT?
>> THE CHRISTMAS BUSINESS MAKES PEOPLE HAPPY.
AND SO CHRISTMAS TREES, YOU KNOW, IT'S A HAPPY THING TO
BE AROUND.
>> IF ALL THIS SCIENCE SEEMS A LITTLE OVERWHELMING IN TRYING TO
UNDERSTAND HOW WELL A CHRISTMAS TREE WILL GROW IN A WARMER
WORLD, CONSIDER THE TREE'S IMPORTANCE TO THE REGION.
WESTERN NORTH CAROLINA IS THE SECOND LARGEST TREE-GROWING AREA
IN THE COUNTRY.
THE INDUSTRY ADDS ABOUT $100 MILLION TO THE AREA'S
ECONOMY.
SO GROWERS NEED TO KNOW WHAT THEY MUST DO TO KEEP THE GREEN
IN EVERGREEN.
>> WHAT WE'RE -- WE'RE THINKING IS THAT THE TREES AT THE LOWER
ELEVATION, WHERE IT'S WARMER AND DRIER, IS THAT THEY THEN WILL
HAVE -- THERE'S A GREATER EVAPORATIVE DEMAND.
IN OTHER WORDS, THEY'RE GOING TO HAVE TO PUT MORE WATER THROUGH
THE TREE TO KEEP UP BECAUSE THE AIR IS DRIER.
AND SO WE'RE LOOKING TO SEE WHETHER THEY ARE MAKING ANY
ANATOMICAL CHANGES, FOR EXAMPLE, TO THE WOOD STRUCTURE WHERE THEY
CONDUCT THE WATER UP THE TRUNK.
WE'RE TRYING TO SEE WHETHER THEY ACCOMMODATE THE WARMER
TEMPERATURES BY MAKING THE WATER EASIER TO GO UP THE TRUNK TO GET
TO THE NEEDLES THAN, SAY, TREES AT HIGHER ELEVATION.
AND WE'RE LOOKING AT THE PHOTOSYNTHESIS RATES TO SEE
WHETHER THEY DO MORE PHOTOSYNTHESIS DOWN THERE
BECAUSE IT'S WARMER THAN THEY DO AT THE HIGHER ELEVATIONS.
AND WE'RE ALSO LOOKING AT CHANGES IN THE LENGTH OF THE
GROWING SEASON.
SO TREES AT THE LOWER ELEVATION MAY LEAF -- YOU KNOW, LEAF OUT
EARLIER AND KEEP PHOTOSYNTHESIZING FARTHER INTO
THE FALL THAN TREES AT THE HIGH ELEVATION.
SO EVEN IF, SAY, THE TREES WERE PHYSIOLOGICALLY DOING LESS WELL
AT THE LOW ELEVATIONS, IF THEY HAVE A LONGER TIME TO DO IT,
THEY MIGHT OVERCOME THAT.
THERE COULD BE COMPENSATION.
THAT'S A POSSIBILITY.
I MEAN, WE ALREADY KNOW, FOR EXAMPLE, FOR FRASER FIRS
THAT IT'S REALLY NOT POSSIBLE TO GROW THEM, SAY, DOWN IN THE
PIEDMONT AND RALEIGH OR WINSTON-SALEM, WHERE IT'S JUST
TOO HOT AND DRY.
IF IT GETS WARMER, THEN THE TREES AT THE LOWER ELEVATION MAY
EXCEED THEIR THERMAL LIMITS.
NOW, WE DON'T KNOW THAT BECAUSE NO ONE HAS TESTED THE THERMAL
LIMITS OF A FRASER FIR YET.
>> RIGHT.
>> BUT THAT'S WHAT WE'RE TRYING TO INVESTIGATE.