Mysterious die-off threatens Seward Park

I was shocked when I first saw this die-off in 2015, and I contacted Paul Shannon of the Friends of Seward Park. He told me the forest stewards were aware of it and that they were alarmed. Since then, I have watched a section of once-lush understory turn into a dead zone, and it is spreading fast. The Magnificent Forest is at risk. Below is a guest post by Paul Shannon. Please read, and then please help. Links at the end will tell you how. -Denise Dahn


The Sword Fern Die-Off at Seward Park

by Paul Shannon, Friends of Seward Park

Ecologist Tim Billo, UW teacher and part-time stay-at-home dad, noticed something strange three years ago on one of his frequent visits to the Magnificent Forest at Seattle’s Seward Park.  This 100 acre forest, by a combination of good luck and good planning, has never been logged.  It is home to 500 year-old trees and nesting eagles, to Douglas squirrels and pileated woodpeckers, to ravens and the occasional coyote.

Native Douglas squirrel in Seward Park in 2012. (photo: Denise Dahn)

It is a tiny remnant of the million acres of ancient forest that covered the Puget Lowlands after the retreat of the glaciers 15,000 years ago. With his one-year-old daughter in a sturdy stroller, walking up the Hatchery Trail, Tim noticed that a hillside previously covered with waist-high sword ferns was now entirely bare.  All the ferns were dead.

Tim’s daughter is now four years old.  The sword fern die-off Tim first noticed three ago has spread rapidly, now covering ten acres.  By the time his daughter is in her teens, extrapolating from current rates of spread, very few ferns will be left in the 120 acres of rare and beautiful urban old growth forest.

Not only are the ferns dying: the new bare regions, emptied of ferns, are not regenerating. No new plants, neither weeds nor native species, have sprouted in the bare ground left by the dying ferns.  So as the ferns die, the understory structure of the forest disappears, and the overall structure of the forest – its interwoven ecology – is compromised.  Tim’s daughter, by the time she is a young woman, may find that the Magnificent Forest at Seward Park is but a weak and reduced version of what, for centuries, it has been.  We will lose an intricate and beautiful ancient plant and animal community, that rare wonderful thing, a wilderness in the city.

Before and after photos, taken in 2011 and in 2017 in Seward Park. Top photo: Jordan Jackson. Bottom photo: Paul Shannon.
Before and after photos, taken in 2011 and in 2017 in Seward Park. Top photo: Jordan Jackson. Bottom photo: Paul Shannon.


Tim joined with an ad hoc network of volunteers including amateur citizen naturalists, the Friends of Seward Park (including the author), UW ecologist Patrick Tobin, UW undergraduates, the staff of the WSU Puyallup Plant and Insect Diagnostic Laboratory, and plant ecologist Lisa Cieko from Seattle Parks.  We scoured the reference literature, consulted fern experts, cultured and sequenced DNA from plant tissue and soil samples, measured soil nitrogen, monitored mountain beavers and insect activity.  After three years and the death of hundreds of ferns, and in the presence of its continuing spread, no cause has been found, and no remedy is available.

In the last few months, we have learned of and followed up on reports of sword fern die-off from other parts of the Puget lowland.  There is an earlier and still continuing dramatic die-off on the Kitsap Peninsula which began in 2010.  There is a more recent and less extreme die-off on Mercer Island.  From these three sites, and from observations of healthy sword fern stands in regional forests, we have identified these (conservative) criteria by which to recognize a sword fern die-off site:

  • at least 400 square feet in extent
  • approximately symmetrical in shape (a circle or a square)
  • understory previously dominated by sword ferns (few or no Oregon grape, salal or shrubs)
  • has 25-40 dead crowns approximately evenly distributed across the 400 sq ft area
  • very few (<5) or no surviving ferns.
  • the affected area grows larger with each passing year

We initially hoped to discover that the die-off was part of the natural cycle of the forest.  Many ask, when encountering the barren ground at Seward Park, if Seattle’s recent dry weather, perhaps the drought of 2013, played a role.   Some shocked visitors ask “did someone spill toxic chemicals up there?”

None of the many hypotheses we have come up with, or that others have suggested, have withstood the scrutiny of our lab and field testing.  The die-off remains a mystery.  It appears to be spreading with increasing speed, both at Seward Park and now in a few isolated spots elsewhere in the region.   We have reports of die-off from other areas, in the city and further afield, which either do, or do not quite yet, meet the six criteria listed above.

We have received help in our work from some expert fern biologists.  Dr. Robbin Moran, Curator of Ferns & Lycophytes at the New York Botanical Garden, and Dr. David Barrington, Professor of Plant Biology, University of Vermont (and world expert on the genus Polystichum to which sword ferns belong) attest that this pattern of die-off is unique: they have never seen anything like this before.  This view is echoed by Dr. Alan Smith, research botanist emeritus at the UC Berkeley Herbarium, and Dr. David Wagner of the Northwest Botanical Institute.  (See discussion here)

These four scientists also cautiously concur on a most surprising feature of sword fern biology – the discovery which has been one delightful high spot in our work, which is that individual sword ferns in old-growth forests live a long time.  For centuries!  Sword ferns colonize bare ground left after fire, glaciation, or logging.  Once established, and once the forest canopy forms above them, they rarely (possibly never) reproduce by spore and gametophyte.  Vegetative reproduction by rhizome is very limited.  Thus there are almost no new young ferns sprouting up in the midst of an old forest.

So when you see ferns beneath big trees at Seward Park, in lush stands, in the die-off area, or in areas where the ferns are now dying, the odds are good that each individual plant you see has been rooted at the spot for hundreds of years.

It is possible that individual ferns may be hundreds of years old! (photo: Denise Dahn)


Urban forests are more fragile than those found in suburbs and rural areas, due to a combination of air pollution, relative isolation from seed and spore sources, overuse by people and dogs, and a higher risk of introduced pathogens.  It is plausible, therefore, that the sword fern die-off at Seward Park, which we now are starting to see elsewhere, may be an early sign of a larger Pacific Northwest regional phenomenon.

Tim and the ad hoc research group – our unfunded band of enthusiasts – have now established, by careful field observation and measurement, that the die-off is spreading rapidly throughout Seward’s Magnificent Forest.  We have documented its appearance in a few thus far isolated sites elsewhere in the region.

It is time now to develop and implement a research program to identify the causes of the die-off. The results of this research will shape our search for remedies, and guide replanting and restoration strategies.  The results of the research may offer broad, timely benefits to the region as a whole. Action is imperative: our centuries old understory is dying as we watch.

More about the research here. To follow the die-off blogsite, click here.

(photo: Denise Dahn)


You Can Help!

  • Contact your Council Member and the Mayor and tell them how important Seward Park’s forest is to you. Ask them to support preservation of natural areas in Seattle.
  • Help raise awareness about the fragility of Seward Park’s forest. Spread the word that the park is NOT an off-leash area for free-running dogs, which can damage this fragile forest habitat. Contact Citizens for Off Leash Areas and ask them to inform their members to leash their dogs, especially in Seward Park.
  • Let the Seattle Parks and Recreation Department know how important park natural areas are to you. Follow our blog to get updated information about how to provide your input.
  • Support Friends of Seward Park, and other park Friends Groups.
  • Vote for candidates that are committed to preserving urban forests and nature in Seattle.
  • Become a member of Seattle Nature Alliance!
It wouldn’t be spring without the unfurling of the ferns. (photo: Denise Dahn)

34 thoughts on “Mysterious die-off threatens Seward Park

  1. I wonder if harvesting of fern fiddle heads could impact the population? Is/was that happening? It’s such a trendy food phase.

    1. When I first saw the die-off, I thought maybe it was foraging, but Paul told me that was very unlikely, and they were looking at disease. In any case, foraging in urban forests is actually illegal in Seattle, and should not be encouraged. We have so little forest left, we need to treat it very carefully!

  2. I read recently that glyphosate is detected in rain samples now. Could that be causing the die off, can you test for it?

    1. That would be a question for the scientists, but it seems unlikely, just looking at the patterns of how it spreads. Wouldn’t rainfall have a more uniform effect over larger areas?

  3. I was told that there are women who routinely cut down that species of fern to make into soup. They go into the parks and cut every sword fern growth down to a short, bare stalk, stuffing them into plastic bags before moving on to the next park.

    1. The ecologists think foraging is unlikely to be the cause of this particular event. But, foraging in Seattle Parks is illegal, for good reason. No one should be foraging in Seward Park.

  4. I’d guess it has something to do with chem-trails and the chemicals they are pumping into the air by planes. I have heard of similar problems with forests dying in that area. Do a search for chem-trails for more information.

  5. The pattern of die-off described (expanding circle) suggests a pathogenic mycorrhizal culprit; perhaps a mutated fungal agent?

  6. Good suggestion, Robert.

    We work closely with Dr,. Marianne Elliott of the WSU Puyallup Plant and Insect Diagnostic Lab. Marianne identified Phytophthora ramorum as cause of the Sudden Oak Death ( a few years ago, and suspects some phytophthora species may be causal here. Repeated culturing, PCR and ITS sequencing has, alas, come up negative so far.

    The next step is to try to reproduce the die-off in a greenhouse experiment using soil taken from actively dying ferns at Seward Park. If that works, then environmental sequencing and some careful bioinformatics may identify the culprit/s – be they mycorhizal, oomycetes, viral, …

    The chemtrails hypothesis is new to me – though a few people have, tongue-in-cheek (mostly) suggested that the Blue Angels may have dumped fuel during their summer shows over Lake Washington. We have no evidence to support that, and (as Robert Fairfax points out) the subsequent radial spread after first appearance suggestions the involvement of some pathogen.

    For those interested, all lab reports, field studies (some very meticulous and fine-grained), soil tests, photos and videos, are avaialble at

    Thanks to everybody for their interest!

    – Paul

  7. I’ve seen people harvesting arm loads of the fiddleheads. Would overharvesting new growth cause a die off?

    1. They think this is due to disease. But, when you see people harvesting, it would be a good thing to alert the Parks Department. Or share it on our FB page, and we’ll contact the right people. Harvesting or removing any plant is illegal in Seattle parks.

    2. Mountain beavers who, like people, are known to overgraze on ferns, have also been evaluated. One of Tim’s undergraduate students is finishing up a meticulous study. Our tentative conclusion: that sword ferns are resilient against frond harvesting, but people of mountain beavers; the ferns bounce back the next year. Repeated grazing or harvesting from the same plant would perhaps eventually deplete food stored in the rhizome, but what we see is that new fiddleheads are NOT produced in affected plants. The infection (or whatever it turns out to be) so weakens the plant that existing fronds die, and no new ones are produced.

      I saw one exception to this a month ago, on the margins of the Upper Luther Burbank Park die-off site, in this year of ample rain. An affected fern, which had lost all of its fronds in the usual manner, DID produce some new fiddleheads this year.

      In summary, Joel, it appears that while harvesting fiddleheads does tax the plant, and it is a practice we wish to discourage in our forested parks, it does not seem to be causal here.

  8. Blaming the die-off on atmospheric chemical dumping is a silly premise if the newly-barren areas are indeed symmetrical. Likewise the foraging theory — I doubt foragers would bother tidying the shape of their vandalism.

  9. Has anyone experimented with replanting in a die-off area to see if the soil supports new plants? The article said that no other species are moving in on their own, but nothing about efforts to replant. I have grown very fond of sword ferns over the last few years, so I’m very sad about this.

    1. Hi Brenda, Yes, replanting has now begun. We put in a few dozen plants at ground zero (the southside of the Hatchery Trail) a bout a month ago; I will be watering them through the summer. We will do more experimental (treatment & control) planting in November.

      Less formally, in November of 2014, we planted two potted sword ferns at ground zero, watering them through the summer of 2015. One of these died (probably normal attrition) and the other – especially with this year’s bountiful rainfall – is doing well.

      One of our ecologists, from Earth Corps, collaborating with Seattle Parks, suggested that a full five years must pass before a potted fern full participates in the local environment – that, until then, they mostly partake of the potted soil environment. I have no experimental validation of that claim; pathogens, it seems to me, are more mobile than that theory suggests. In any case, we are monitoring our plants, doing regular rephotography to keep track.

  10. Have you tested for radiation? Fukushima has dumped three reactors worth of fuel into the air, sea and ground. The Pacific Ocean is dying. No humpback whale calf has survived more than a year post 3/11. The BC coastline is almost bare. The starfish population there is gone. There are multiple die-offs in the area – birds, fish and mammals.

    Please don’t ignore the Elephant in the room.

  11. Thanks for the suggestion, Kelly Ann. The geographic specificity and radial spread of the die-off argues, I think, for a more local cause than the Fukushima radiation release. However, we will keep that possibility in mind.

    1. Thanks for the suggestion. We, too, have wondered about the effects of drought. In our current thinking, rain patterns are a candidate contributing factor, but not the primary cause. This year’s abnormally high rainfall did not resucitate any of the recently moribund ferns. We are pretty sure they are past recovery.

  12. Possible acidification via S and N dry deposition onto vegetation during dry periods? Sulphur dioxide from automotive, industrial, and shipping transport just offshore, can combine with dimethyl sulphide from plankton breakdown processes in the surf, to deposit S onto needles and leaves. When the first Fall drizzles begin, this can turn the dry deposition into acid that can damage waxy coatings and drip to the understory vegetation. As the acidity needs buffering by calcium, the Ca turns to calcium bicarbonate which is not bioavailable to organisms. If the acidification is exacerbated by additionally being under red alder nitrification forestation, excess hydrogen ions and nitrates can produce more than the forest trees need for fertilizer, becoming excess pollution to the soils and streams. This depletes the water of more calcium by buffering, pushing some organisms out of their comfort zones for calcium utilization needs. We have increased toxic metal pollution in almost all surface waters, beyond what was present prehistorically (and in bones as well). Lead and cadmium are calcium utilization inhibitors. These toxic metals combine with low calcium availability to increase the hypocalcemia problems for sensitive organisms. Sword ferns may be another ‘canary in the coal mine’ just as the river mussels I am studying are for the low calcium aquatic salmon streams in mid coast Oregon watersheds. The mussels have shell degradation problems by dissolving to perforation stage and premature mortality…… due to the combined low calcium availability combined with toxic metal anthropogenic inputs to these streams. Perhaps the sword ferns are declining for similar reasons?

    1. Thank you, Ray – intriguing suggestions. I will forward them to Tim and Marianne (ecologist and plant pathologist, respectively). I don’t believe we yet have the chemistry know-how to pursue this. May we ask your advice on how, and from whom, we might get informed, and thus better able to pursue this kind of analysis?

      1. Paul, yes, during my attempts to understand possible explanations for freshwater mussel declines locally, I have read extensively in the literature about low pH waters have elevated risks from lead and cadmium toxic effects, since these metals are calcium utilization inhibitors that would exacerbate hypocalcemia. Locally we have substantial increased metals input to our salmon streams, that are very low calcium content waters. As the research that bears on this problem increase from hundreds of researchers working on related questions, I have come to see that it could be very possible that terrestrial organisms could also become adversely affected by acidification pressures in our forests. Our location in the coast range is generally more protected from the more complicated picture of pollution sources in most other regions. This allows for a somewhat simpler environment for teasing out potential causative factors for environmental degradations that could be influential in mussel decline… and salmon decline. Thousands of papers help clarify the possible degradative pathways, yet none really definitively characterize all of the overlapping risks I have come to see as being a ‘perfect storm’ of population decline causation potential locally. Very few waters elsewhere have as low calcium availability episodically as seen locally. Atmospheric dry deposition of S and N during drought summers may be a complicating pathway for additional acidification pressures to cause increased acidification in forest and streams, adding to the aquatic problems.

  13. I have read thru all the comments and have not seen anything about soil moisture, depth of moisture and most of all, fog.
    While growing up, I went camping with the Boys Scouts, yes an Eagle Scout, and always woke up with everything wet. Especially the ferns. Ferns of all types need a constant source of water and have a symbiotic relationship with other organisms. Multiple layers of ecological support maintains the top tier of plants. In this case, the sword fern.
    The current climate, has been lacking fog for the last few years.

    Studied and degreed in Ecology and Systematic Biology

    1. Thanks Allan. I’ll check and see if they’re aware of this. The last I heard, they had determined it was a pathogen. I’m no expert, but I think it had to do with the way it was spreading in a radial and outward pattern. If it was something climate-related, it would be more evenly distributed. But maybe the weather or climate is helping the pathogen get a foothold.

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