Friday, July 14, 2017

Sword Fern Die-Off Overview: short video, narrative essay

The Sword Fern Die-Off at Seward Park 
 (and a few other Puget Sound locations)
Paul Shannon, Friends of Seward Park
May 5th, 2017

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. 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.

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:

  1.  at least 400 square feet in extent
  2.  approximately symmetrical in shape (a circle or a square)
  3.  understory previously dominated by sword ferns (few or no Oregon grape, salal or shrubs) 4) has 25-40 dead crowns approximately evenly distributed across the 400 sq ft area
  4.  very few (<5) or no surviving ferns.
  5.  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 elsewhere on this blog.)

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.

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. 

Regional Map of Confirmed and Candidate Sword Fern Die-off Sites

  1. Seward Park, 15 acres, first observed 2014, severity 10
  2. Suquamish (private property), 2 acres, 2010, severity 10
  3. Indianola > 1 acre, 2017, severity 8
  4. Port Ludlow, private forest, 0.5 intermittent acres along a trail, 2017, severity 8
  5. Cheasty Mt. View, a Seattle Park, ~0.5 acre, 2016, severity 6
  6. Upper Luther Burbank Park, Mercer Island, 0.1 acre, 2016, severity 6
  7. Baring, private property, 0.1 acres, 2016, severity 5
  8. (Rochester, unconfirmed, > 1 acre, 2016)

Confirmation of Two New Die-off Sites: Baring and Port Ludlow

Tuesday (July 11th) of this week I visited two new candidate die-off sites:

  • A vacation home's yard outside of Baring, Washington,  about 25 miles west of Stevens Pass.  This is at present a minor site, but interesting due to its location: far from any previously previously reported sites, disconcertingly close to the Cascades.   There are bout 30 dead ferns in a few clusters.  All ferns observed on neighboring properties are healthy.  First observed in 2016.  
  •  A private second growth forest near Port Ludlow, Washingtion, 80 miles west of Baring, 20 miles north of the Kitsap sites documented below.  Extensive die-off along 200 yards of trail.
Though neither of these sites meet the stringent criteria I have previously proposed(400 sq. ft., symmetrical,  high density, formerly uniformly sword fern understory), I judge both to be convincing instances of the die-off we see elsewhere.    

Two Short Videos from Baring

One Longer Video from Port Ludlow

Monday, July 3, 2017

Dan Hinkley's Interesting Conjecture

At risk of offering a suggestion that has more than likely already been examined as obvious, the photos in your blog appear as if we might be dealing with a mycelium complex in the soil that has made the edaphic environment hydrophobic.

It appears as if nothing is regenerating, making it seem evident that the pathogen is not conspecific to Polystichum but simply establishing in Polystichum-friendly habitat. 

Have any observations been made of fungal fruiting bodies on the outer edge of the infection sites or have soil samples been examined for the presence of mycelia?  This has the gestalt of a ‘fairy ring’ in a lawn.  Has anyone attempted to mechanically aereate the Hatchery Creek site to see if something will again begin to grow?  The dead zone can seemingly only point to a hydrophobic condition, or to an unlikely pathogen that kills everything in its wake and disallows anything to reestablish.

Port Ludlow report by Jim Gormly

Beyond Kitsap Peninsula, across the Hood Canal, there is a greenbelt in Port Ludlow, ca. 2000x400 feet. It is a second-growth forest primarily with western red cedar, douglas fir and large-leaf maple trees. It is mostly shaded, but there is the occasional small open area free of trees. The understory is mainly sword fern, salmon berry, blackberry and other nasty vines. Apparently, a few years ago a beetle infestation caused the death of a large number of alders.

Yesterday I became aware of an area, perhaps 75x25 feet rectangle of dead ferns. I estimate that more than 50 plants were obvious. Since I don't know how the problem is transmitted, I chose not to be a vector, just in case it might be a spore transfer, so I didn't climb in to get a more accurate number of dead ferns. Throughout the greenbelt, there is the occasional dead or dying fern, but this is clearly the largest concentration I observed. There was also a dying salal plant among the cluster of dead ferns (see photo). I'm sorry the exposure is not the best.

When I saw the dead ferns, my first reaction was that someone dumped a herbicide, but that made no sense, so I did a Google search and found your blog. I must say that this is very disconcerting. I hope you find a solution. I will continue to monitor here, and will update you as time passes. . We have extensive greenbelts here with trails through them, and many residents enjoy walking the trails. It would be a sad loss if the apparent trend continues. 

Jim Gormly

Regional Map (Verified and Candidate Sites)

An informal regional Puget Sound map, with dots showing verified and candidates die-off sites, size and color a very rough indicator of status and severity.  Small, unverified sites may not stand up to scrutiny.
  • Seward Park (first reported 2014, 15 acres, verified, spreading)
  • Suquamish (2010,  2 acres, verified, spreading)
  • Indianola (2017, < 0.1 acres, not yet visited)
  • Cheasty Mountain View (2017, 0.5 acres, verified, spread status unknown)
  • Mercer Island Upper Luther Burbank Park (2016, < 0.1 acres, verified, spread status unknown)
  • Port Ludlow ( 2017,  < 0.1 acres, not yet visited)
  • Baring (2017, < 0.1 acres, not yet visited)

Thursday, June 22, 2017

Field Reports Welcome!

We welcome reports of sword fern die-off from anywhere in the Pacific Northwest.   No governmental organization or NGO is collecting reports, so I figure that an informal and ad hoc log kept here may prove useful.

I will catalog and map them as (and if) they come in.   Most helpful will be reports which include a photo, a location, and an estimate of dead fern count and density.    For example:  "12 dead ferns within a 20 x 20 foot area,  in  a second growth forest dominated by maple and cedar, near Suquamish Washington."  

Please add your report as a comment to this blog post, or send mail to me.   Thanks.