Oh Christmas Tree

Scientists are studying what effect a warming climate will have on NC's $75M Christmas tree industry, which ranks second in the country in Christmas tree sales.

WESTERN NORTH CAROLINA — The Christmas tree has become one of the traditional symbols of the holiday season. Adorned with lights and ornaments, Christmas trees are found in homes, stores and businesses, but it turns out there weren’t always “Christmas” trees. Nevertheless, long before the advent of Christianity, evergreens held special meaning for people during the winter. Branches of pine, 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. Two hundred years later, Christmas trees were all the rage in London during the holidays. By the late 1800s, the Christmas tree tradition was growing in America.

And it’s a tradition that has become very lucrative in North Carolina. The state ranks number two in the nation in Christmas tree production. Oregon is number one. There are roughly 1600 growers throughout the state, producing about 50 million Fraser fir Christmas trees, the most popular type. The industry generates approximately $100 million dollars in sales per year.

And that’s why researchers at Appalachian State University are launching a multi-year project to study the state’s Christmas tree industry in a future in which the planet is warming. The concern is that Fraser firs grow better in a cooler climate. What happens as the weather warms?

“The traditional growing area for Fraser firs is 5000 feet and above, yet all of the growers are at 4200 feet and below,” explains Dr. Howard Neufeld, Professor of Physiological Plant Ecology, Plant Water Relations Ecosystem Ecology and Air Pollution Effects at Appalachian State University. “Since the trees are already growing out of their range, farmers at lower elevations could have some difficulty and at the same time farmers at higher elevations may have some issues. We just don’t know.”

So researchers are studying how Christmas trees grow in different climates, 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 higher elevations, and cooler temperatures, represent trees in a cooler climate.

To help answer those questions, researchers have installed weather stations on six western North Carolina tree farms at three different elevations. While daily weather data is continuously recorded, researchers also spend an entire day at each farm, checking how the trees are responding to current conditions.

Graduate student Scott Cory is enclosing a portion of a tree branch inside a clear plastic cylinder. There are sensors inside the cylinder connected to wires that run down to a computer on the ground. The device is called a portable photosynthesis system. It measures how much carbon dioxide the tree is absorbing and how much oxygen and water vapor it is releasing as it utilizes the sunlight to produce food. The hypothesis is that trees in lower elevations, or warmer climates, will have a lower rate of photosynthesis and won’t grow as well.

“The goal of this experiment is to find out how much gas is being exchanged," explains Cory, who is studying ecology and plant physiology. “So we pump gas into this cube, and then we measure what is coming out, and the difference is the amount of transpiration, or how much oxygen the tree 'breathes' out.”

Another experiment measures how much sap is flowing inside the trees. To do that, two probes are inserted into the trunks of five trees about 10 centimeters apart. The wires are connected to a data collector that is housed in a plastic tub in the middle of the stand of trees. The collector records the speed at which the sap is flowing between the sensors. The information will reveal how fast the tree will grow and how much water the tree is taking from the ground.

But that still leaves the question of just how stressed for water the trees may be. There is one additional experiment the researchers will perform during their day spent at the farm. The test uses a small clipping from a tree to answer that question. The clipping is placed in a pressure chamber.

“You put a clipping in this tube, close it up and then insert it into this machine,” says Jessica Stevens, an undergraduate student in soil ecology, as she flips a switch and turns on what sounds like a pump. Stevens then bends over to examine the end of the clipping with a magnifying glass. “The machine applies a positive pressure, and when the water comes out the cut end, you know that positive pressure equals the negative pressure in the branch.” 

The higher the pressure needed to squeeze the water out of the cutting, the more stressed the tree is for water.

The study is just getting started so there are no findings to report and there are no conclusions that have been reached. But Dr. Neufeld admits that if the theories that prompted the study prove true, it could mean some profound changes will be required for Christmas tree growers across the western mountains.
 
“What we’re thinking is the trees at the lower elevation, where it is warmer and drier, will have a greater evaporative demand,” explains Dr. Neufeld. “That means trees are going to have to bring in more water to keep up with demand because the air is drier.”

That may require growers to irrigate their farms, unless researchers find that the trees themselves are making anatomical changes to better conduct water up the tree. In other words, if the trees are able to change their wood structure to better draw in water, then it may not be necessary for growers to add more water.

Finally, scientists are also looking at the effects of a longer growing season in conjunction with photosynthesis rates. The question is whether trees are able to do more photosynthesis at the lower elevations because there is a longer growing season. That would be a way to compensate for the heat. So, even if the trees at lower levels are struggling because of the increased water demand, if they have a longer time to grow, they could make up for the more challenging growing conditions.

“The biggest question to answer, or course, is just what are the thermal limits for Fraser firs,” says Neufeld. In essence, at what temperature is it simply impossible for a Fraser fir to grow because the conditions are too warm, too dry and simply too extreme. “Nobody knows the answer to that because no one has tested the limits. We want to find that out so North Carolina’s Christmas tree growers can be prepared.”


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