Climate change may be factor in spread of tree fungus

Signs of hope? A single Douglas-fir grows at the base of the clearcut area along Swan Mountain Road. It'll be interesting to watch the area during the next few years to see how it regenerates.
Global warming may be promoting growth of a tree-damaging fungus in the Pacific Northwest. @bberwyn photo.

Commercially valuable tree stands take hit in Pacific Northwest

Staff Report

Global warming may be a factor in the spread of a fungus affecting valuable Douglas fir forests in the Pacific Northwest. Needle cast disease has recently spread across 590,000 acres in Oregon,  quadrupling since the start of surveys in 1996. The annual economic loss has been estimated at $128 million.

“The correlation between disease severity and climate factors, such as spring moisture and warm winter temperatures, raises the question of a link between disease expansion and climate change,” said  researcher Gabriela Ritokova. “Those factors, in combination with lots of Douglas fir and with large springtime fungal spore production, have us where we are now.”

The fungus, Phaeocryptopus gaeumannii, doesn’t kill trees, but can slow growth but up to 50 percent. In some cases, forestry experts recommend replacing Douglas fir with other species that are more resistant to the fungus and more adapted to a wamer and wetter climate.

The pathogen spreads via tiny spores that land on Douglas fir needles and block them from breathing normally. The trees often lose their needles about two years after being infected.

The losses have mounted in the past 20 years as the disease continues to spread. In previous decades, the outbreaks were kept in check by cyclical changes in the regional, as spells of colder and drier weather interrupted fungal growth. But those hoped-for respites haven’t come recently, according to forest managers in the region.

Ritokova, a faculty research assistant at Oregon State, said the epidemic may have started at least partly because of using seeds from outside the area. Swiss needle cast was first discovered among Douglas-fir trees planted in Switzerland in the early 20th century.

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