Monday, May 1, 2017

The (Highly Speculative, as yet unsubstantiated) Nitrogen Deficiency Hypothesis, Yet Again

The sword fern die-off at Seward Park comes with a complicating factor:  in three years since our first observations, there have been no new colonization of the ground by native or invasive species.

The only exception to this is the large number of big-leaf maple seedlings which appear briefly each spring, and which are all dead within a matter of weeks.   This year, due to unprecedented amounts of spring time rain, these seedlings are still doing well.  I will report on their survival at ground zero over the summer months.

In addition to the ad hoc nitrogen sampling reported earlier on this blog, and the tree canopy Lobaria oregana nitrogen sources reported by Bill Dennison from the Andrews Experimental Forest, there has been related research by the Reimchen lab at the University of Victoria,  suggesting - in some circumstances - that salmon can be a nitrogen source.




Sunday, April 23, 2017

Die-off at Seattle Park Cheasty Mountain View

Tim, Al and I followed up on Al's initial report of sword fern die-off at Cheasty Mt.View, a few dozen yards west of the intersection of Columbian Way and Mountain View Drive.

The area is second growth forest, mostly big leaf maple, with a mixed sword fern, Indian Plum, salal and invasive understory.

We did an informal survey of a mixed flat and steeply sloping area, about 135 feet east-west by 100 feet north-south.  We placed 110 orange marker flags at each unambiguously dead fern; closely clumped dead crowns were treated as a single fern.  We excluded any fern showing any trace of green. This yields a concentration of  ~120 sq.ft per fern - which is consistent with a second growth, mixed understory rich in ferns.  The understory of this site is decidedly not dominated by ferns in the manner that the Seward, Suquamish and Upper Luther Burbank sites are.

Tim, Al and I then each separately estimated the ratio of dead/live ferns across the  135 x 100 foot region.  This was exceedingly informal.  Our average estimate was about 50%.  We did not distinguish a third group:  affected ferns still showing some green.  That group was lumped in with the healthy ferns.

This site does not meet the six criteria - which were inferred from die-off sites in which the sword ferns been the dominant - indeed, nearly exclusive - understory plant.

We left ten short orange marker flags in ferns with medium-to-good health.  One of Tim's natural history students will do repeat photography of these ten ferns over the next two months.



Sunday, April 9, 2017

Suquamish (Kitsap) Die-Off: stats and video

Site walk-through

Yesterday (Saturday, April 8th) I returned to private property, on the Kitsap Peninsula, near the Suquamish Reservation.   The owner first noticed extensive die-off in 2010, making this the first report of the phenomenon.

Some details:

  1. west-facing slope, dominated by large red cedars, from 2'-4' dbh.  Some big leaf maple.
  2. 140 dead crowns in 2300 sq ft: crown density about 16 sq ft.
  3. two surviving ferns for density comparison: large at 36 sq ft, small at 9 sq ft
  4. no doug firs in the 2300 sq ft
  5. good regeneration of other species, mostly Indian Plum, some bracken fern
  6. crowns are marked with orange flags (otherwise hard to see in the video among small new Indian plum)


Friday, April 7, 2017

Table of Contents

Two Informally-Validated Die-Off Sites Beyond Seward Park

On private property on the Kitsap Peninsula, near Sandy Hook, the owner has watched their several acres of sword-fern dominated second growth forest die off.  This beganin 2010, and is thus our earliest report so far.  Sword fern root and soil samples are under analysis at WSU Puyallup.   This site meets the proposed six criteria by which a die-off site is identified.

The die-off occupies a gentle west-facting slope with a marked (possibly relevant) absence of doug firs.  Cedars and maples dominate.  The area is largely open beneath these moderately spaced second-growth trees.  Regeneration is taking place, including (at least) the native Indian Plum.

The Upper Luther Burbank Park site is smaller.  Its status as a die-off site is, I believe, contested by Mercer Island Parks staff.    This legitimate, and currently unresolved difference of opinion partly inspired my six proposed die-off criteria.  This site meets all criteria except number six: that the die-off area has been assayed in successive years, and is growing radially.     Annual monitoring of the Mercer Island site will resolve this.


The Die-off Jumps the sqebeqsed trail

Over the last three years our attention, and our monitoring efforts, have been mainly upon the southeast sector of the Magnificent Forest, south of the Hatchery Trail, east of the sqebeqsed trail.

On an evening walk in the woods on Wednesday (5 April 2017) I was surprised and alarmed to see many instances of new brown sword fern crown stumps within a few hundred feet of ground zero, on the west side of the sqebeqsed, on the Andrews Bay Trail.  See map below.

This new discovery, along with our current pessimism about identifying the cause of the die-off, and the two informally validated new sites (Suquamish Sandy Point on the Kitsap Peninsula, Upper Luther Burbank Park on Mercer Island), triggered a state change in my assessment.

Which is that the die-off will likely continue to propagate through the Magnificent Forest in semi-exponential growth - that is, faster than linear, but not so fast as annual doubling.  It is likely therefore, that within ten years all of the sword ferns will be dead or dying.  Furthermore, and for reasons unknown, regeneration is non-existent in all of our die-off areas.  Ground zero has been open for colonization for three years; not one new plant has appeared. (See reference below for possible insight into this "regen problem" based upon 2012-13 research at Lincoln Park.)

There exists, therefore, a grim possibliity:  that a full half of the understory will be destroyed without replacement, disrupting the structure and likely the function of the old-growth forest with unknown but worrisome consequences.

Note that the two other informally validated die-off sites, on Mercer and the Kitsap, ARE regenerating.   Seward is an anomaly in this regard, perhaps due to coarse woody debris removal in the 1960s, and the absence of any of the well-known old forest nitrogen sources.

Seed limitation and lack of downed wood, not invasive species, threaten conifer regeneration in an urban forest  Ailene K. Ettinger,  Benjamin R. Lee, Sarah Montgomery