As the climate warms, the perfect Christmas tree may depend on the adaptability of growers

By | December 19, 2023

CHICAGO (AP) — Christmas tree grower Jim Rockis knows what it looks like when someone dies long before he can reach a buyer.

Rockis grows trees in West Virginia and Pennsylvania, where he and other producers often grow their iconic evergreens away from their preferred habitat higher in the mountains. But that may mean planting in soil that is warmer and wetter – places where a nasty fungal disease called Phytophthora root rot can develop, sucking moisture from the saplings and causing the needles to turn crispy to burnt orange.

“After a while it just gets to the point,” Rockis said. “They just wither away.”

Christmas tree growers and breeders have long prepared for a future with warmer weather that will also change soil conditions. People who buy trees may not have noticed a difference in availability this year and perhaps not even in the next few; it takes eight to ten years for the average Christmas tree to reach a salable size.

But that means the trees grown today will be tomorrow’s beloved holiday traditions for millions of families.

“You have to start thinking about how you’re going to adapt to this,” Rockis said.

That’s why researchers like Gary Chastagner, a professor at Washington State University, call “Dr. Christmas Tree” for his decades of work on spruce and other festive species, he has worked with breeders like Rockis to see whether species from other parts of the world – for example the Turkish fir – are better adapted to the conditions caused by climate change .

In the past two years, a surprising number of evergreens died due to fungal disease outbreaks in Washington and Oregon. Chastagner is concerned that changing soil temperature and moisture “could change the frequency with which we would see Phytophthora that are more adapted to warmer soil conditions.” Some may attack trees even more aggressively, he added.

Chastagner and his team are doing more sampling to understand the causes of these outbreaks and whether they represent a pattern that could continue in the future.

But some scientists say there isn’t enough research into soil warming, which could affect Christmas trees and many other crops, especially trees.

A European study this year in the journal Nature Climate Change found that ground heat extremes are increasing faster than atmospheric extremes, which could affect the health of grasslands, forests and some agricultural areas.

The same weather conditions that can stress trees promote many pests and diseases that can attack them, such as insects and fungi. The changes in forests and fields may not happen overnight, says Bert Cregg, professor of horticulture and forestry at Michigan State University. But the warming climate may make it harder for some trees to grow over time, he said.

Changes in the soil also affect soil carbon storage, a solution to climate change that the US has already invested a lot of money and effort into. Higher soil temperatures reduce the long-term ability to store carbon, in part because microscopic life underground is affected, researchers say.

“The activity of these microbes usually increases with temperature, so it is less stable to store carbon there,” says Almudena Garcia-Garcia, one of the authors of Nature Climate Change and a postdoctoral scientist at the Helmholtz Center for Environmental Research – UFZ in Leipzig. Germany.

While it’s critical to get more information about how changing soils will affect crops and carbon, scientists sometimes struggle to collect enough data, said Melissa Widhalm, associate director and regional climatologist at Purdue’s Midwestern Regional Climate Center University. Because soil temperature is measured differently than air temperature, the data doesn’t go back very far, making it difficult to understand long-term trends.

Widhalm, who was not involved in the Nature Climate Change study, said she wished more similar studies existed in other places like North America, and that the results are compelling because they combine physical observations in the ground with satellite data and computer simulations. “This paper did a good job of quantifying the relationships between soil temperature and moisture that scientists know exist but are difficult to measure,” she said.

Garcia-Garcia said her team plans to study soil temperature changes more often in the future, at more locations if they can. “All sources of information indicate this is happening,” she said. “We always study extreme events based on measurements in the air. But what is happening beneath our feet?”


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