CORVALLIS - Parts of the Pacific Northwest are in the grips of what may be its worst plant disease epidemic in a century, a destructive fungus of Douglas-fir that has expanded rapidly in the past decade and threatens hundreds of thousands of acres of commercial and public forest lands.
Called Swiss needle cast, the disease causes premature loss of needles and cripples the growth of this one tree species, which unfortunately is also the basis of the western Oregon forest products industry. While the exact cause of the crisis is unproven, Oregon State University experts say the intensive, even-aged cultivation of Douglas-fir may be one part of the problem, along with recent climate trends. A cooperative formed at OSU to address this problem has a new publication ready for forest landowners that will help them make decisions about how to manage their lands while research continues.
"Swiss needle cast is native to our forests, but it used to be considered a nonentity, not really that big a deal," said Greg Filip, an Extension forestry specialist in the Department of Forest Science. "To see it turn into an epidemic like this is hard to believe. It certainly reminds us we don't have all the answers."
But the slumbering threat posed by Swiss needle cast turned from a minor issue into a major one in just the past few years, Filip said, perhaps triggered by a 20-year cycle of cooler, wetter conditions that climatologists believe Oregon entered during the mid-1990s - conditions which favor the fungus.
Recent surveys show there is now a severe infestation of Swiss needle cast on 295,000 acres of forest land in western Oregon and 200,000 more acres in western Washington.
The epidemic has exploded just in the past few years, Filip said, and is also moving into parts of the Cascade Range as well as the Coast Range. There is no evidence the spread of the disease has peaked, he said. Barring changes in silvicultural practices or climate, the problems may last for some time.
"Some forest product industries are already doing premature clearcutting of Douglas-fir plantations because they have barely grown in the past 10 years," Filip said. "In the Coast Range, where the problems are most severe, private industry and small forest landowners are pretty concerned."
Swiss needle cast has always been in the Pacific Northwest, Filip said, and historically hadn't been much of an issue. The disease itself was first described in 1925 when Douglas-fir was exported from the Pacific Northwest to Switzerland and caused an infestation there.
In the old-growth forests of the Pacific Northwest with trees of many species, sizes and ages, the fungus caused no major outbreaks in recorded history.
"Within the species of Douglas-fir, there are some trees that are more resistant to this fungus and other that have less resistance," Filip said. "Those in the western portions of the Coast Range seem to have the most resistance.
But with the growth of plantation forestry, Filip said, there are more opportunities for this fungus to get a foothold. There is evidence the problems have been growing slowly for about the last 50 years, as forests were converted from perhaps 20 percent to 80 percent Douglas-fir, and from multi-aged to even-aged forest. Then, in the mid-1990s, the climate of Oregon and Washington became wetter due to what many experts believe is a natural 20-year cycle. Swiss needle cast problems skyrocketed.
"A criticism of planting one species of tree as a monoculture in our forests is that this can favor plant disease or insect epidemics," Filip said. "We don't yet know for sure, but this may be one example of that. At least 75 percent of the trees planted west of the Cascade Range are still Douglas-fir."
Complicating the problem, he said, is that Swiss needle cast can spread almost as quickly as an insect infestation because it has mobile spores that travel on the wind. Most fungal problems, he said, are not that aggressive.
More studies are being pursued on the possible causes and potential solutions to this epidemic of Swiss needle cast, including the development of genetically resistant Douglas-fir varieties. Until then, OSU researchers have outlined steps in an Extension publication that forest landowners can use to deal with the problem right now. They address several regeneration methods, vegetation management techniques, fertilization, thinning, pruning, and clearcutting.
Some of the developing trends towards uneven-aged silviculture and planting a variety of species, Filip said, may also be of value in addressing problems with Swiss needle cast. Those approaches, which were often originally begun with an eye to wildlife enhancement, long-term forest health or a more varied ecosystem, may find they have another role in addressing this epidemic, he said.
Copies of the new Extension publication, titled "Silviculture and Swiss needle cast: research and recommendations," can be obtained by calling (541) 737-4271; email at firstname.lastname@example.org; web site at www.cof.orst.edu/cof/pub/home; or writing the Forestry Publications Office, 256 Peavy Hall, OSU, Corvallis, Ore. 97331.
For stands with severe infestations, researchers are now recommending clearcutting as soon as possible and replanting with no more than 20 percent Douglas-fir seedlings. Other options include thinning of all the Douglas-fir trees and retention of other species, or more encouragement of alternative species in an uneven-aged silvicultural approach.