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Washington State University
WSU Puyallup Ornamental Plant Pathology

Sword Fern Die-off


Sword fern is an important species in the forests of the Pacific Northwest. However, many acres of sword fern plants have ‘mysetriously’—as many news articles suggest—died off throughout the Puget Sound.

Researchers and citizen scientists continue to investigate the die-off. See below for updates, more information and resources about the sword fern die-off.

Sword Fern

Vital to the Vibrant Understory

Sword fern (Polytichum munitum) is a major component of the understory of the coastal forests of the Pacific Northwest. It provides many social and ecological services.

Ecologically, sword fern provides nutritional value to mountain beaver, deer and elk. It is also provides critical habitat for many species and serves as important source of cover during breeding ceremonies of Pacific ruffed grouse. Sword fern also has the ability to resprout after disturbance and is important for nutrient cycling, erosion prevention and soil health.

Economically, sword fern is commonly used in floral arrangements and produced for restoration activities.

Culturally, sword fern has served many purposes for indigenous communities in the region. It has a rich cultural heritage because it has been used in games, ceremonies, as medicines, as fibers for mats, rugs and beds, and it can provide nutritional value during critical times of need such as during famines or seasons with limited food availability.


See the SFDWG Strategic Plan for a summary of insights from research before Dec. 2018.


Observations of the loss of sword ferns from the understory of forests in the Kitsap Peninsula date back to 2010. Additional reports of die-off in sites at Seward Park in 2013 raised substantial alarm. These sites are generally characterized by large circular areas (at least 400sq ft) with uniform patches of die-off and very few surviving ferns.


Sword fern die-off is generally represented by the complete collapse of plants and the absence of regeneration within a close proximity. Symptoms begin with foliar discoloration, browning, wilting and collapse of individual fronds, eventually leading to the death of the entire plant. The absence of the growth of new fronds (no fiddle heads) in a given area in contrast to other parts of the forest may be cause for concern.

The Cause

No single cause has been discovered and additional research is needed. Many hypotheses have been proposed (see presentations below), but more evidence is needed.  Given the die-off is localized and limited to a few areas, researchers suspect the cause is biotic (rather than attributed to drought or other abiotic factors). However, investigations have not revealed an association of the symptoms with suspected soilborne fungi such as Phytophthora or Rhizoctonia.

Healthy Sword Fern

Sword Fern Die-off

Report New Sightings

Share Your Observations on iNaturalist

Join the project on to share observations of western sword fern die-off. Observations can be uploaded from a computer or with the iNaturalist smart-phone application.

Die-off Resources

More Information and Resources

Strategic Plan


News Articles

Blog Posts



Join the Discussion

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Subscribe and post to the Sword Fern Die-off community by visiting this webpage or sending an email to the subscribe email listed to the right.

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Community Research

Many concerned citizens and partners have conducted research to advance knowledge about the cause of the sword fern die-off. Summaries and findings of the research efforts prior to the end of 2018 are available in the Seward Park Sword Fern Decline Strategic Plan produced by Seattle Parks and Recreation and the Green Cities Partnership.

Research projects have included:

  • Mapping and monitoring sword fern die-off throughout the region
  • Investigating soil and microbial factors
  • Confirming that rodent and mammal browse are not primary factors
  • Testing for physiological metrics associated with decline

Additional Research is Needed

Research to determine the primary factor driving the die-off of sword ferns is critically needed. Identifying the primary cause will provide vital information for mitigating and restoring the die-off sites and preventing new ecosystems from becoming impacted.

Join the conversation by subscribing to the mailinglist or contact us if you’re interested in contributing time or support for more research about the sword fern die-off.