Tuesday, May 1, 2018


Since 2014 we have been observing and attempting to understand a dramatic die-off of the dominant understory sword fern species, Polystichum munitum, in the 120-acre old growth "Magnificent Forest" in Seattle's Seward Park Extensive lab and field work, consultations with fern experts throughout the US, and recent reports of die-off from elsewhere in the Puget Lowlands of Washington state, lead us to conclude with considerable confidence: 

  • The die-off is caused by an (as yet unidentified) pathogen 
  • Climate change may be a contributing factor, but until the proximal cause of the die-off is determined, the role of climate change can not be known.  
  • Drought is probably not a cause (see rainfall records below).
  • Is unprecedented, not part of the P.munitum life cycle, in which ferns colonize open ground, do not reproduce under a closed canopy, with individual plants living for hundreds of years.
  • Holds implications for the forest at Seward Park, and for other forests in the region.

Some selected blog entries

  • A Lazarus Fern? (March 2018)
  • Experimental Plantings at and near Ground Zero (March 2018)

Contact: Paul Shannon, Forest Steward

Thursday, March 15, 2018

A Lazarus Fern?

When I returned to Ground Zero a week after the two lines of twelve ferns were planted, in order to take the first set of time-lapse photos, I was shocked and delighted to discover a healthy fern which had not been planted by us.    Since sword ferns, we are told, will not reproduce under a closed forest canopy, I assume that this fern has come back from the dead:  enough life lingered in the rhizome for it to regrow after three years of inactivity.   Hence: the Lazarus Fern.   Definitive evidence for this claim - of regrowth rather than new growth - could come from removing soil and locating (or not locating) a large rhizome; young ferns do not acquire a rhizome for at least five years.    I do not want to disturb this rare, resuscitated, old survivor - or is it a new young plant? - not yet.

Based upon the size of the seven fronds, and the time of year, these fronds must have been 2017 growth.   I did not notice this frond last year.  This is puzzling, but not completely unlikely:  inasmuch as  I did not expect to see any fern regrowth,  I may well have overlooked this one instance.

There are a few other rather straggly ferns surviving at ground zero.  They are all - except for this fern, and one other I will describe in a moment - found very close to the trail or to large trees.   All of these survivors are failing, and fewer of them are found with each passing year.   Perhaps some sort of micro-site effects, or interspecies cooperativity, is responsible for their imperfect survival. 

The other healthy fern found at ground zero is one of the two nursery ferns we planted in November 2014, at the suggestion of Jillian Weed, parks plant ecologist.   I watered both ferns through the first two summers; one has survived:

This survivor, and the surprising regrowth of the Lazarus Fern suggests a possibility: that the putative pathogen killing the ferns,  which spreads at the rate of about 30 meters a year, may now be absent from ground zero.    Perhaps something in the genetic makeup of the Lazarus Fern, or its micro-site, of some unknown factor - some apparently unique factor/s allowed it to regrow.   The survival of one of the two 2014 plantings is consistent with this hypothesis:  whatever kills the ferns now appears to be gone.    This may be a cause for optimism - or it may be that the killing agent will return and once again attack ferns at ground zero if the ferns are re-established.  

For now, I will take comfort in the possibility that the scourge has moved on, and that at least one native plant is resistant.   We will collect spores from the Lazarus Fern in July and raise up a bunch of baby ferns,  which will also possibly be resistant, for further experimental planting.   If this is a genetic trait, and if it has high penetrance, we may have stumbled upon a partial remedy for the sword fern die-off.

Experimental planting at Seward Park

In February we planted three lines of young sword ferns, twelve ferns in each line.  These ferns were part of our annual generous allotment of three hundred restoration plants from Seattle Parks and the Green Seattle Partnership.  They come from regional native plant nurseries; the plants are about two years old. 

Two of these lines are in the original ground zero at Seward Park, an area that has been barren now for three years, with no natural regeneration of any species.    The third line is about fifty yards north and just outside of the current boundaries of active die-off.   Every fern was "watered-in".  Half of them - every other fern in each line - were infused with mycorrhizal spores.

I hypothesize (based on evidence presented in the next blog post "A Lazarus Fern?") that the likely pathogen responsible for die-off has swept through ground zero and is no longer present.  Thus I predict that the two lines of twelve ferns in ground zero, if we water them through the first summer or two, will mostly survive.  As the die-off zone spreads it will soon encompass the northern line of twelve ferns.  I predict that most of these twelve ferns will die.    More specifically, and as a nod to statistical rigor, I predict a p-value < 0.05 when, after five years, we compare the survival rates at the two contrasting sizes, ground zero (24 ferns) and the northern line (12 ferns, aka AD for "active die-off).  Here this is mocked up in a little R code:

GZ <- as.integer(runif(24) + 0.7)       #   75% survival: 0 1 1 1 1 1 0 0 1 0 1 0 1 1  
                                                           #                           1 1 1 0 1 1 1 1 1 1 
AD <- as.integer(runif(12) + 0.25)    #   25% survival: 1 0 0 0 1 0 0 0 1 0 0 0
t.test(GZ, AD)$p.value                      #   0.0047

I photograph all thirty-six ferns every week and will create a time-lapse video for each fern as these weekly photos accumulate.  The two GZ lines are shown in the picture above.

Thursday, January 11, 2018

Report of Die-off in Snohomish County: Lord Hill Regional Park

Amy Lucas, Senior Park Planner with Snohomish County Parks, reports:

We recently received a citizen report of a similar die-off at our Lord Hill Regional Park. I went in the field yesterday with one of our Senior Rangers and found 3 suspect sites. Two sites were small, and surrounding salal had spots, much like black spot on a rose plant.

We hiked to a much larger site that showed signs of complete sword fern mortality that looked like it was spreading radially. The ground at that site was barren, and the brown fronds were spreading to surrounding plants. 

These photos seem convincing to me, though I have not yet visited the site for a close inspection, and we as yet do not have measurements of extent or rate of spread.  Leaves in the bottom-most photo perhaps obscure dead fern crowns?  It usually takes two years to progress from first symptoms to crown stubble.  

This report, if confirmed, indicates a new direction of spread, to the north and east of Seattle, about 30 miles from Seward Park, and 30 miles west of Baring, a small and apparently isolated residential die-off   - Paul

Thursday, December 14, 2017

Bainbridge Island Blakely Harbor Die-Off Markedly Worse

In September, Darrell Howe reported some isolated sword fern die-off at one spot on Bainbridge Island, on the trail between Fort Ward and Blakely Harbor Parks - see map below.

This week Darrell reports:

I had a chance to return to Bainbridge and walk back into the sickly fern site I noticed in September.   I will attach a few new photos.   I was way too conservative in my estimate of impacted area earlier in the fall.   I would now guess the total site may be more like 7,500 sf.    I did not see any other signs anywhere else on the Island for now.

Photos below the map.    

Fort Warden Die-Off Update

Erik Kingfisher, Director of the Jefferson Land Trust, along with his daughter Samara, paid a citizen science visit a few weeks ago to Fort Warden State Park, at the northeast tip of the Olympic Peninsula.  They verified observations made by Kitsap resident Heidi Danlicheck in October. 

Follow this link to see the Kingfishers' video and commentary:


Monday, November 20, 2017

Possibly related, at least of interest: diseased and dying western hemlocks at Seward Park

Seven years ago, in 2010, I noticed a cluster of four mature dying hemlocks at the dog-leg bend in the sqebeqsed trail.   I had witnessed the death and disappearance of eastern hemlocks in Shenandoah National Park in the 1990s due to the wooly adelgid.   Concerned that something similar was taking place in this related species, I began an informal survey.   Which I happily abandoned after a few months, discovering that all the hemlocks in other regions of the forest were apparently in good health.

Unfortunately this no longer seems to be true.  Many mature hemlocks have recently been affected by factors unknown, many of them dying.   Perhaps the annosus fungus is responsible, as was suggested to me by UW's Bob Edmonds in 2010.  There is now a loose cluster of tall dead hemlocks on the Huckleberry Trail, and Kramer pointed out many dead or dying hemlocks just south of sword fern ground zero.

Here are my unedited notes from 2010, the result of informal research and email exchanges:

   Notes from 2010