Costly fir disease threatens our coastal economy

A series of maps shows the spread of Swiss needle cast disease (in yellow and red) on the North Coast between 1996 and last year.

New forestry research is an invaluable reminder that our changing climate has local consequences that demand action, even if everyone isn’t yet convinced human action is to blame.

A time-progression map of the Oregon Coast Range is the most immediately eye-catching aspect of a study by Oregon State University, the Oregon Department of Forestry and Weyerhaeuser Corp. It shows an explosion in Swiss needle cast, a disease in Douglas fir, between 2015 and the start of aerial surveys in 1996. Swiss needle cast is believed to have first gained a foothold in our region in the 1970s in Christmas tree farms, from which it spread to major commercial tree plantations and state forests.

The map shows a troubling expansion throughout the Coast Range, with a moderate infection level now widespread in Clatsop County and severe outbreaks here and there, especially in Tillamook County. Overall, the amount of acreage impacted grew by 4 1/2 times between 1996 and last year. In far-western Oregon’s 5,800 square miles of coastal forest, 922 square miles were infected by last year — getting close to the size of the entirety of Clatsop County. (Swiss needle cast also is a significant issue in the Willapa Hills of southwest Washington, though it hasn’t been so thoroughly studied there.)

Here in Clatsop County, the important Hampton Mill in Warrenton relies on a mix of 60 percent Douglas fir and 40 percent hemlock. Anything that harms the viability of Douglas fir is going to impact local forestry, which remains a vital part of our economic mix.

Swiss needle cast doesn’t kill Douglas fir but saps their productivity, reducing it by 23 percent in the epidemic area at a yearly economic cost currently estimated at $128 million.

The scientists cautiously say a complex combination of factors related to local climate change — such as spring moisture and warm winter temperatures — may be creating conditions favorable for Swiss needle cast. Another significant factor, they say, is the extent to which forest managers have deliberately increased the prevalence and density of valuable Douglas fir, providing large swathes of genetically similar forest. Starting in the 1960s, forests that were once comprised of mixed western hemlock, Douglas fir, Sitka spruce, red alder and western red cedar were converted to monocultures of young Douglas fir.

The researchers conclude that fungicides and other chemical treatments are either ineffective or impractical, and urge an integrated pest management approach. These options include restoring greater diversity to forests by planting more cedar, hemlock, spruce and alder. Unfortunately, depending on market conditions, switching to less Douglas fir can have big economic downsides. Thinning trees before they reach full commercial-harvest maturity is another option, also with financial costs.

Guided by this latest study, it’s vital we work out optimal ways to adjust to changing conditions in order to preserve forests and the coastal economy that depends on them. Agencies can help by continuing to fund aerial surveys and science devoted to helping forest adapt to changing conditions.

The SNC study can be downloaded at http://bit.ly/2bqr495.