A dramatic die-off of the long-lived, robust, drought-tolerant, dominant understory sword fern of PNW lowland douglas-fir forests was first reported in 2013 in an old-growth urban forest in Seattle, in Seward Park.
It has since been observed throughout the Puget Lowlands.
Sword ferns need bare mineralized soil and open sunlight to grow, so within mature forests with intact canopies, sword fern regeneration is rare.
Natural regeneration of other species is also very slow after the ferns die. Ten years have passed at the original Ground Zero die-off site, with nearly zero natural regeneration. We worry that long-term bare ground raises the dangers of cascading ecosystem decline in this already stressed, rare and beautiful old-growth urban forests.
Disease Progression on the Windfall Trail
This pure, lush stand lost a few ferns in 2020. And many more since.
We installed a photography station in September 2022 so we can track the changes, inviting all passers-by to contribute photos. You can see that time-lapse here, and in this video:
The die-off continues, moving up the slope at about 25 feet per year and, in recent months, spreading to the west, across the sqebeqsed trail.
Is Sword Fern mortality a natural phenomenon?
Wondering if die-off might be a natural phenomemon, and after looking far and wide throughout the Puget Lowlands, and finding signs of any dead ferns in any generally healthy sword fern sites, I turned to Polystichum genus expert, Dr. David Barrington of the University of Vermont, asking him how long sword ferns live. He offered us this perspective (email, October 2015):
“I very much like the idea that they are old individuals, established at a remote time when there was disturbance in the forest. Fire would create such a disturbance. As to age, 1000 years is not out of the question, possibly much longer but there are no data at all for deciding. There are very few sites for the establishment of new plants via gametophyte in the stable mature forests of the Northwest, though a single treefall would create such an opportunity. Polystichum munitum is essentially unbranched, which lends support to the idea that the populations are made up of independently originated individuals, not fragments of some giant clone.”
Where is it happening?
The die-off was first observed, and has been most studied, here at Seward Park.
But observations have come in from across the Puget Lowlands, as seen in the green and red markers in this iNaturalist map. The live map is seen here.
Research is Ramping Up
We work with Seattle Parks, WSU Plant Pathologists and UW ecologists. You can read about our 10 year effort to track and comprehend the problem on the Sword Fern Research Timeline website.
We have just begun a pilot study to identify microbes which may be responsible for mortality using DNA sequencing: fungi, bacteria or phytophthoras. Email us if you wish to know more.
We need your help.
In ten years working on this problem, there has been no academic or institutional funding awarded for its study. No academic or governmental research program has been conducted.
This is the case despite the gravity and regional reach of the die-off, and it long-term consequences. The loss of this foundational understory plant, and the low likelihood of subsequent forest floor regeneration, creates ecosystem fragility at Seward, and throughout Pacific Northwest lowland forests.
We welcome your donation! Of money, time, and expertise. Email for more information. Donate at the Seattle Parks Foundation.