‘Entering the town of Twin Peaks, five miles South of the Canadian border, twelve miles West of the state line. I've never seen so many trees in my life... I’ve got to find out what kind of trees these are. They’re really something,’ says FBI Special Agent Dale Cooper.
Later, Agent Cooper turns to his companion at the crime scene, ‘Sheriff, what kind of fantastic trees have you got growing around here? Big, majestic.’
‘Douglas firs,’ replies Sheriff Truman.
Cooper marvels as he repeats the words, ‘Douglas firs...’
These are the opening scenes from David Lynch’s cult 1990s mystery series Twin Peaks, set in the titular fictional town in the very real Washington state on the Pacific North West. The awe these trees inspire in Agent Cooper (Kyle MacLachlan), and one can only assume the director, makes it easy to understand how they became as emblematic of the show as they are of the region.
But now a fungal disease called ‘Swiss Needle Cast’ is threatening approximately four million acres along the western flank of the Oregon Coast Range, proving to be as much of a sinister menace as anything seen in the TV series.
‘The Douglas fir is incredibly important.,’ says David Shaw, associate professor at Oregon State University and Extension Forest Health specialist. ‘It is the number one timber species, the state tree of Oregon, an important old-growth forest giant (they can live a thousand years), and a very common tree.’
Also known as the Oregon pine or Pseudotsuga, it’s a genus of evergreen coniferous tree widespread in northwestern America. Douglas-firs are medium-size to extremely large, reaching 20 to 120 metres tall, with flat, soft, linear leaves, resembling those of the firs.
A new series of Twin Peaks was released in 2016, giving more screen time to the Douglas fir for a whole new generation to see. Yet in the time that’s passed since Agent Cooper first encountered them, a real-life creeping threat has spread its yellow shadow across the forests of the Pacific North West.
The story began ten years before Twin Peaks brought them to worldwide fame. In the early 1980s, foresters in Oregon noted that Douglas fir trees within several miles of the Pacific Coast were yellow, had thin crowns with minimal foliage, and didn’t appear to be growing well. As time went on, symptoms continued to become increasingly apparent throughout the coastal strip, from Coos Bay to Astoria, Oregon, and along the Washington Coast.
Mounting evidence suggested that the observed symptoms were attributable to a needle disease known as Swiss Needle Cast (SNC).
Although the name suggests the disease is from Europe, the fungus that causes the disease, Phaeocryptopus gaeumannii, is native to North America, and occurs wherever the Douglas fir is found.
A study by Ritóková et al, looking at two decades of aerial surveys, detected 53,050 hectares displaying visible symptoms of SNC in 1996, which increased until 2002, peaking at 156,630 hectares. According to the study, it appears the disease abated for the next two years, but from 2004 until 2015 it steadily increased once more, reaching a high of 238,705 hectares in 2015.
Although mortality from the disease is rare, it does cause premature loss of older foliage which reduces growth. This is a worry for more than just the image of the region, as Shaw points out the tree is not only a symbol: ‘The ecosystem contribution of Douglas fir to our region’s forests can’t be overstated. The biodiversity of our region is closely tied to its ecology.’
For this reason the consistent spread of the disease is causing increasing concern. ‘The impacts extend from the southern Oregon coast to the Northern Olympic Peninsula in Washington state, and we have reports of impacts in southwest British Columbia too,’ says Shaw. ‘Mortality caused by SNC is rare, but we are starting to observe it.’
More concerning for this pattern of spread is the indication that the gains made by SNC in recent years could be down to climate change.
‘There is definitely a threat, the epidemic that has developed along the coast is associated with a complex mixture of factors at play,’ explains Shaw. ‘Climate change is definitely an issue, warmer winter temperatures are thought to be very important in disease development, as well as conditions that wet the leaves during spore dispersal in May to August. Basically it appears a key factor will be whether late spring and early summer precipitation shifts with the changing climate.’
A 2017 Environmental Protection Agency study predicted that climate change will result in warmer winters and will likely continue to increase SNC severity, particularly at higher elevations where low winter temperatures currently limit growth of the pathogen.
‘There is mounting concern that SNC is increasing in severity, frequency, and range in association with rising winter temperatures and spring/summer precipitation,‘ says Edward Lee, author of the EPA study. Lee goes on to suggest that it will likely continue to intensify over the 21st century due to climate change.
According to Shaw, who is also director of the Swiss Needle Cast Cooperative, it is planning ‘a major aerial survey from northern California to southwest British Columbia in 2018’ in order to further track the progress of the disease. But should the trend of spread continue, in another 20 years the biggest mystery in the Pacific North West, will be how its ‘majestic’ evergreen symbol was a allowed to turn yellow.
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