WSU scientist seeks Christmas trees that can withstand climate change

Drier summers and warmer autumns spell trouble for that iconic winter evergreen, the Christmas tree.

Working to safeguard this important Pacific Northwest crop, Washington State University plant pathologist Gary Chastagner has traveled the globe on a hunt for hardy varieties. Dubbed “Dr. Christmas Tree” for his 44-year career studying the decorative conifers, Chastagner is now testing promising species that can stand up to an uncertain climate while looking and lasting their best in the home.

“I want to give growers and consumers more choices for high-quality trees,” he said.

Gary Chastagner, professor of plant pathology.
Gary Chastagner, professor of plant pathology.

Changing conditions

Through the Collaborative Fir Germplasm Evaluation Project, a 12-year partnership with scientists in Connecticut, Oregon, Pennsylvania, North Carolina, and Michigan, Chastagner and colleagues traveled to Turkey in 2020 to find mother trees of Turkish and Trojan firs, which are adaptable to the Pacific Northwest’s climate and resistant to disease.

Back home, in a research trial at the WSU Puyallup Research and Extension Center and a large planting site in the Nisqually Valley, he selects the best performers for hardiness, disease resistance, needle retention, structure, and other factors. Over the next two years, Chastagner will help establish orchards to produce seeds from the best mother trees. Those seeds will then be planted as future Christmas trees.

About 40% of the nation’s Christmas trees are grown in the Pacific Northwest. Oregon is number one in production and Washington is in the top five.

“Our rainfall, mild climate, good soils, and longer growing season are ideal for high quality trees,” Chastagner said. “Growers can produce trees in a shorter rotation, which helps cover the cost to ship them beyond the western U.S.”

However, the Northwest’s heat domes, dry summers, and warm falls of the past few years may be harbingers of seasons to come.

“Things are going to change—they’re already changing,” Chastagner said. “Christmas trees aren’t irrigated. Growers are losing young seedlings in the summer because of these hotter, drier conditions.”

Conifer tree cuttings.
Cuttings from more than 3,000 Turkish and Trojan fir trees are screened for their needle-retaining qualities at the WSU Puyallup Research and Extension Center. WSU scientists are working to identify improved Christmas tree varieties that keep their needles despite warmer autumns.

Most Christmas trees are harvested between late October and mid-November. Warmer autumns mean trees won’t get the cold days they need for maximum needle retention before harvest. While species can retain their needles after a warm fall if they’re properly watered at home, that responsibility falls on the consumer, causing uncertainty for growers and sellers.

“I want to find trees that don’t need the cold,” Chastagner said.

Research beyond climate adaptation

Elsewhere, a changing climate could bring more rain, worsening Phytophthora root rot, a devastating soilborne disease that kills trees.

“This becomes a challenge when the market wants highly susceptible species like noble fir,” Chastagner said. “It’s why we’re working to understand and identify resistant, high-quality alternative species.”

Currently, growers import seeds of new species of trees, such as Nordmann, Turkish and Trojan firs. The larvae of a small wasp called Megastigmus sometimes infests seeds, and if inspectors find any larvae, entire shipments must be destroyed.

Turkish fir cones.
Turkish fir cones collected from a forest tree during one of Chastagner’s trips to Turkey.

One of Chastagner’s latest breakthroughs helps reduce this loss of seed. He and postdoctoral researcher Thomas Whitney found that carefully heating seeds to 113 degrees for an extended period kills the wasp larvae without harming the seeds. It’s an inexpensive way to ensure the supply of new, top-quality varieties.

While time will tell if these new Turkish and Trojan fir tree species can benefit the Northwest tree industry, Chastagner sees promising signs from commercial plantings in the Sierra Nevada and elsewhere.

“Growers say these Eurasian species are more tolerant of warmer, drier conditions,” he said. “We think they will stand up to hotter summers, and they have good resistance to Phytophthora root rot and other common diseases and pests. Consumers already love them.”