New Documentary Film Released 

Support Research into Species Decline in Seward Park’s Old-Growth Forest

Tim Billo on the current status of the sword fern die-off: full video of the WNPS event

 Tim gave a detailed and compelling report on the regional sword-fern die-off, and all of the research and findings from the last several years, sponsored by the Washington Native Plant Society.

The full video may be viewed here.

Fourth year of 5-year 36 fern experimental planting: "Ground Zero" ferns still thriving

In February 2018, we planted 3 lines of nursery sword ferns, 12 plants per line,  hypothesizing that those planted into Ground Zero (GZN, GZS) would survive, but that those planted into (actually just ahead of) the active die-off zone (ADZ) zone would not do well.  All 36 plants have been watered through three summers.  The prediction continues to hold: 

ADZ: 4/12 ferns dead, 1 marginal, 1 with very slight recover: a few diminutive new fronds
GZS: 0/12 ferns dead, 11 healthy, 1 with 0 fronds last year now has 6
GZN: all 12 ferns are healthy
t.test pvalue, likelihood of this difference occurring by chance: 8.7e-4

We surmise that the presumed pathogen no longer resides at Ground Zero - but could possibly return.  A continuous dense population of affected sword ferns may be needed for reinfection: the GZ sword ferns may be "socially distant" from current areas of active die-off.

Third year of 5-year 36 experimental fern planting: "Ground Zero" ferns still thriving

In February 2018, we planted 3 lines of nursery sword ferns, 12 plants per line,  hypothesizing that those planted into Ground Zero (GZN, GZS) would survive, but that those planted into (actually just ahead of) the active die-off zone (ADZ) zone would not do well.  All 36 plants have been watered through three summers.  The prediction continues to hold: 

ADZ: 5/12 ferns dead, 2 are marginal, 5 healthy
GZS: 1/12 ferns dead, 11 healthy
GZN: all 12 ferns are healthy
t.test pvalue, likelihood of this difference occurring by chance: 8.7e-4

We surmise that the presumed pathogen no longer resides at Ground Zero - but could possibly return.  A continuous dense population of affected sword ferns may be needed for reinfection: the GZ sword ferns may be "socially distant" from current areas of active die-off.

Die-off hits an old pure stand of ferns, one of the last unaffected

 The “high ground” is about five acres in the forest at Seward Park,  bordered by the sqebeqsed and Windfall Trails. It occupies the highest elevation area in the forest. The southern quarter of the high ground is dominated by large sword ferns, with few other understory plants.  

In January I found that about 3% of the ferns in these five acres were dead, all of them intermittently distributed, no regions of contiguous death.

Now, October 2nd 2020, contiguous die-off has appeared, showing the classic signs of the die-off.
The sword fern die-off can now be found throughout the entire 100 acres of the Magnificent Forest AND it spreads in concentrated, presumably more virulent form northward from the original ground zero.  Now, after six years of northward spread, this beautiful area - one of the last, large, old and intact sword fern communities at Seward - appears to have been hit.  There is no "social distancing" among these ferns.  A rapid (one or two year) demise is likely. 

It is always possible that this is a transient phenomenon, strictly limited to the small area pictured below - and thus not the first appearance of concentrated die-off.  Unlikely but possible.   Time will tell.

  A 15 second video that captures this beautiful, now threatened area: 

  Location in context (note the black dot):

Is the die-off (principally) caused by drought or climate change?

 When novel & dramatic events  happen at roughly the same time,  we humans tend to think they are causally related - that one event caused the other, or that they both had a shared cause.

For these reasons, we are often asked whether, and it is often suggested, that the PNW lowland sword fern die-off is caused by drought or climate change.

We suggest that the following multiple lines of evidence, in aggregate, conclusively establish that this is NOT the case.

The single strongest argument against the hypothesis that PNW drought causes sword fern mortality is this 2016 New Phytologist research paper by Jarmilla Pittermann and colleagues:  

Not dead yet: the seasonal water relations of two perennial ferns during California's exceptional drought

Peer reviewed, published in a high impact journal, this paper presents lab and field evidence that sword ferns routinely survive extended severe drought.  If these findings hold up, and if they are as applicable to PNW forests as to California redwood forests, then drought (alone) cannot explain the sword fern die-off.  

The first reports in the region of dramatic die-off are from 2010.  UW PhD atmospheric scientist Joe Zagrodnik looked for drought/die-off correlations and reported:

The period from 2007-2012 was generally characterized by near-normal temperatures and precipitation (2011 was a cool year). By all measures the current period anomalous weather started in 2013 and I can say confidently that anything happening prior to 2013 is not caused by unusually warm or dry weather patterns. 

Reed College ecologist Dr. Aaron Ramirez and his undergraduate student Caleb Goldstein-Miller report 

the ecophysiology analysis of ferns from healthy, intermediate and die-off areas in Seward park [show] that moisture stress is not a driver of physiological stress for Seward ferns.

More detail from Caleb's final report.  The full text from 29 nov 2019 is here.

For the ecophysiology analysis portion, our hypothesis was that plants in non-die off areas would have higher values for stomatal conductance, Fv/Fm, and possess a ​Ψ​ closer to the optimum for the species in question (or further from the turgor loss point for the local population) in comparison to plants in active die off areas. Three distinct areas of decline were established at Seward Park, die off, intermediate, and healthy. These areas were characterized with the help of Paul Shannon (Seward Park Steward) and Olga Kildisheva (Verdant Counseling, LLC) and sampled on August 19th, at the peak of the dry season. We used the following metrics to compare physiological stress of ferns in the die off, intermediate, and healthy treatment areas: dark-adapted fluorescence (Fv/Fm) to determine the efficiency of photosystem II, stomatal conductance (Gs) to ascertain whether or not ferns are closing their stomata during photosynthetically active periods, and xylem water potential (​Ψ)​ to determine water status (Toivonen and Vidaver, 1988; Schreiber and Bilger, 1987; Corcuera and Notivol, 2015; Angelopoulos et al., 1996; Jordan and Ritchie, 1971). Healthy tissue from ten ferns within each treatment group was analyzed for predawn and midday water potential and dark-adapted fluorescence. Stomatal conductance measurements were taken in between predawn and midday sampling. We found no significant differences between treatment groups in any of the metrics except midday water potential. The ferns from the die off treatment area had an average midday xylem water potential of -1.7574 MPa, versus -0.9074 MPa and -0.9474 MPa for the intermediate and healthy treatment groups respectively. This result is complicated by the fact that we ran out of compressed nitrogen during the midday water potential readings from the die off treatment area. Samples were immediately transported from Seward Park to Reed college in a cooler so that water potential measurements could still be taken. Due to the unstandardized approach in xylem water potential analysis between the die off and the other treatment groups, we cannot be confident of the accuracy of this result. However, a pressure-volume curve was created from samples taken across the three treatment groups, which gave us a turgor loss point of -2.3 MPa for ​P. munitum​ at Seward Park. Since the significant water potential result was well above this moisture stress-indicating threshold, we are confident in our conclusion that moisture stress is not driving the die off at Seward Park. This increases our confidence that the regional decline is caused by some still unknown biotic vector.

Dylan Mendenhall conducted transmission experiments at the UW greenhouse in the Fall of 2019, establishing that die-off like symptoms are reproducibly transmitted from affected fronds to unaffected fronds via shared sterile water.  Full details here (todo).

We received in 2017 reports, photos and videos of die-off on Artillery Hill at Fort Warden, outside of Port Townsend, average rainfall about 25 inches.    By 2019, all ferns had recovered.  This, we suggest, is the normal response and recovery of sword ferns to drought stress.   As an ancient and widespread PNW understory plant, it seems likely that it has well-established mechanisms with which to survive drought.

We are half-way through a five-year restoration planting experiment at Seward Park, described here.  36 ferns, in three groups, all ferns watered through drought months, show statistically significant survival - correlated with location - in an active die-off zone (low survival), and in area hypothesized to be free of any die-off activity (> 95% survival).  

At Seward Park, and in the other regional die-off sites we monitor (ranging from near Quilcene on the Olympic Peninsula, to the Goldmeyer Hot Springs Road  in the foothills of the Cascades) no other understory plants exhibit the die-off or decline symptoms we see in sword ferns.  The die-off thus appears to be specific to P. munitum:  no other fern species are affected, no other shrub or herbaceous species.  It seems unlikely that the sword fern - famously robust and very long-lived ("1000 years is not out of the question" - David Barrington, University of Vermont, Polystichum genus expert)  - that the sword fern alone would be affected by drought and temperature.  

The die-off at Seward Park spreads in two ways:  radially from heavily affected areas, and by leaps into distant previously unaffected areas.  The radial spread includes movement uphill, jumping across trails after some delay, and downhill into presumably wetter soil.  Large regions of low- and high-density fern populations are unaffected - within a short distance of affected areas.  This distribution is hard to explain by drought effects.    Pathogenicity, perhaps abetted by weather and climate,  makes much more sense.

 

 

Restoration Experiment at Seward Park

Two years ago, with some guidance from Verdant LLC, and generous support from Seattle Parks, Suzanne Bouchard and I planted young nursery sword ferns at and near Ground Zero in Seward Park.  This is an ongoing experiment, to last at least three more years.  You can read an earlier report here.

The die-off at Ground Zero had reached steady state by 2014, leaving almost entirely bare ground.   10% of the original ferns, as we assessed in a June 2019 study.  This quarter acre was subject to erosion and likely undergoing further ecological degradation:  underground mycorrhizal networks need photosynthesizing plants, of which there were very few.   No natural restoration had taken place until a few fringecups - most happily - appeared in 2019.

Suzanne and  planted three lines of 12 ferns, two lines at Ground Zero, 1 line just north of what was then the boundary of the expanding die-off region.   I hypothesized that the agent of the die-off, whatever it turns out to be, was no longer active at Ground Zero, but that it was likely to be active and virulent at the die-off's leading edge.

This hypothesis was a generalization from a single fern planted at Ground Zero in 2014.  Inspecting the die-off with Seattle Parks plant ecologist Jillian Weed, I asked, "What should we do?".   "Monitor closely", she said, "and why don't you plant a couple of nursery ferns?".  We did, I watered the pair through a couple of summers, and one (dubbed "Jillian Weed #1") is thriving now six years later.   A 50% survival rate for restoration planting is better than I usually achieve.  So I surmised that the die-off agent/s were gone - at least temporarily.

I water all 36 plants weekly during summer drought, two liters per palnt.  The Ground Zero ferns (with one exception) are thriving.  The northern line ("ADZ" for active die-off zone) is about 50% dead or dying.   I have made every attempt to treat all three lines identically.

In April, Bonnie Drew, Jeff Kelley and I twice independently surveyed all three lines.  We counted fiddleheads, interpreting them as simple markers of overall plant health.   Here are the results, summarized for each of the three 12-fern lines, in box plot form.   The full dataset is available on request.

I provisionally conclude that there is currently no active agent affecting ferns at Ground Zero.  The degraded site is now recovering, which is very fine to see.   The agent may return.

(Seattle Parks contracted out some additional restoration planting at Ground Zero, installing more than 100 plants of mixed native species in the winter of 2018-2019.  I water these plants in the summer as well, and part of the returning health of Ground Zero comes from this generous action by Seattle Parks.)

Dead Fern Mapping at Seward Park

I have mapped dead sword ferns on three successive Sunday afternoons.  I include and collect lat/long for unambiguously dead ferns, in which all (or almost all) fronds are brown.  Usually all that remains is a brown stubbly crown.  The die-off is much broader than the map suggests.  I will fill in the as-yet-unmapped regions in time.

On January 12th, I counted and geo-located dead ferns in the trail-encircled area shownabove. This area has the healthiest population of sword ferns remaining in Seward's forest. Despite the dominance of healthy ferns, the die-off has reached into this area as well.

One surprise emerge.  Last summer David Perasso established that even an apparently dead fern can sprout small fronds in the spring, apparently supported by a small amount of remnant healthy tissue in the rhizome. In the area I surveyed today, I found about a dozen classically dead crowns which had nonetheless a few full-size fronds coming out of them.  This may be due to the cooler, wetter summer of 2019, which perhaps allowed these resprouted-from-remnant-rhizome fronds to live and grow through the summer. More observation may help to clear that up.

In the marked survey area above, I estimate that dead ferns are less than 3% of the total fern population.

Sunday, January 19th 2020: 251 additional dead fern geo-locations, from the northwest corner of the forest:

Latest Map - with detailed summer assays of 14 sites

Click on map to visit interactive version.

Detailed tabular assay data included for 14 sites:

click on site to see popup.

(January 10th, 2020)

Note two Oregon sites, east-west extent in lowlands from Olympic

to Snoqualmie National Forests

KUOW's brief report and subsequent retraction

Last Thursday, December 5th, I heard from a couple of friends that KUOW had a 20-second afternoon (maybe drive-time) news spot reporting that the ferns at Seward were recovering.

Alas, not so.

It is easy to understand KUOW's misinterpretation of the  South Seattle Emerald article.   KUOW followed up with a correction the next day.

The on-air retraction, just like the original report, was only 20 seconds long.   Here's what they might have aired if they had more time:

Now, a clarification on a story we ran Thursday about sword ferns dying in Seward Park.  At Seward, at other sites in the Puget lowlands - from the Kitsap Peninsula to the Snoqualmie National Forest, and now also in a few sites just reported from Oregon -  sword ferns are experiencing an unprecedented and mysterious die-off, with no recovery in sight.  

Sword ferns are common, hardy and long-lived.  Just like their larger ecosystem companion, the Douglas Fir, they colonize open ground, then live for centuries without reproducing.  This unusual life cycle means that, once lost to an intact forest, they do not return.  Nor do other native plants - at least not quickly.  This loss of understory and ground cover creates a serious "ecosystem hole”.  This is a situation unlike what PNW forests normally experience, where an ecosystem disturbance also takes out the forest canopy, the overstory, and ample sunlight hits the ground to drive new growth. At Seward, the normal recovery of a disturbed forest - after fire, flood, insects, windstorms - is simply not happening.

In response to this, volunteers and Seattle Parks are engaged in labor-intensive restoration at Seward Park, filling in where the ground has been bare for five years.  They have planted nursery-grown native plants - including ferns - and hand-watering them through the summer drought. The natural regeneration we mentioned in our reporting on Thursday story is very limited:  after five years,  only ten small, seasonal plants of just one species (the Fragrant Fringecup) has sprung up in the acres of forest which used to be filled with sword ferns.

The cause of the die-off is still a mystery - but recent lab work strongly suggests that a pathogen is involved. Citizens, students and a few university scientists are working together, without pay, on this ongoing problem.  They track the die-off throughout the region, run experiments to figure out the cause, and hope eventually to find an effective response. 

Here's the actual story as it aired on Thursday 12/5  (my emphasis):

Some good news from Seattle's Seward Park.

In 2017, sword ferns there were mysteriously dying ... about a third of them were lost.  But the South Seattle Emerald reports that re-planting has been successful ... and there are signs of natural regeneration.  The Emerald says a women's group raised thousands of dollars to study the die-off.  And early research suggests that it's not drought that was responsible ... but some kind of pathogen.

Recent Findings and Community Support

We received a very generous donation last summer.   Laboratory & greenhouse research, and extensive regional die-off site surveys provide new insight into the nature and extent of the ongoing sword fern die-off.   Herewith an update.

• The Seattle branch of 100 Women Who Care raised almost $8000 to support research into the cause and nature of the sword fern die-off.  We were delighted.  We are grateful!
• Forest ecologist Dylan Mendenhall (trained at UW and UBC, himself once a Seattle Parks GSP forest steward at Schmitz Preserve) has conducted pro bono research at the UW CUH greenhouse over the last two months.    Greenhouse rental fees and material costs were paid for out of the 100 WWC donation.   Dylan tested the hypothesis first raised in the ad hoc beer-bottle experiment: that the die-off effect can be transmitted in water from an affected frond to a healthy frond.   Dylan's experiments proved this hypothesis, at scale, and with rigor - a huge breakthrough in our ongoing effort to determine the cause of the regional PNW lowland sword-fern die-off.  High resolution microscopy and metagenomic sequencing are likely next steps.
• Reed College undergraduate researcher Caleb Goldstein-Miller, working under the guidance of Professor Aaron Ramirez, spent many weeks over the summer, and some subsequent time in the lab, on two topics: a regional die-off site survey, and ecophysiological water relations.   The results of the regional survey may be seen in this map.  (UW students and Dr. Tim Billo assisted in the survey.)  Caleb summarized the ecophys lab work: "[W]e are confident in our conclusion that moisture stress is not driving the die off at Seward Park. This increases our confidence that the regional decline is caused by some still unknown biotic vector".
• Seattle Parks ecologist Lisa Cieko led (and continues to guide) a crucial response to the die-off at Seward Park: the ecological restoration of the original die-off site, "Ground Zero".  About 100 native plants of mixed species were installed, mulched, then watered over the summer, with thus far good survival rates.  In combination with the 24 sword ferns we planted in February of 2018 - which have a nearly 100% survival rate - Ground Zero is no longer the barren, non-regenerating  slope it was for several years.  In addition, a few fringecups have sprung up in the first instance of natural regeneration. 

Visit to NatureBridge School in Olympic National Park

With an invitation from education manager Chris Morgan, I paid a visit and gave a talk to the educational staff at NatureBridge, on the shore of Lake Crescent.   I had an engaging exchange with about twenty staff members, all of them environmental educators whose mission

"is to connect young people to the wonder and science of the natural world, igniting self-discovery and inspiring stewardship of our planet. Through our overnight, hands-on environmental science programs, we take more than 35,000 children and teens each year into our national parks to explore the outdoors, connect with their peers, discover themselves and develop a lasting relationship with the environment." 

The low elevation mature and old-growth forests surrounding Lake Crescent are healthy.  Sword ferns dominate large areas of undergrowth - with no sign of any die-off.

We emerged from this meeting, which concluded with a walk in the woods, with a tentative plan: that NatureBridge staff and their students may contribute to understanding the die-off, and more fundamentally to the understanding the ecology and biology of sword ferns, through careful  observations over the coming years. 

Some of the topics we discussed:

1.  Sword ferns rarely reproduce under a closed forest canopy.  See Robbin Moran's  Natural History of Ferns report that the prothallus (the gametophyte) needs recently exposed bare soil (and presumably ample sunlight) for propagation.  
2. Individual plants (the familiar sporophyte generation) are very long-lived ("a thousand years is not out of the question" - David Barrington, University of Vermont polystichum expert)
3.  Are there any signs of fern mortality, or propagation, in the healthy fern communities in Olympic National Park?  To suppport or contradict topics 1 and 2?

 We know little about the variability of the annual life cycle of healthy ferns and their fronds.   Perhaps a multi-year phenology project would be a good match for NatureBridge students?   A combination of careful observation in the forest, data collection, hypothesis generation and testing?

In this scenario, student scientists, backed up by trained academics (we have contacts with some helpful ones) could contribute new understanding of this signature PNW species, and provide baseline and background information we need to explore the die-off

Is there a pattern to the 10% sword fern survival at Ground Zero?

In 2013, 215 large healthy sword ferns occupied the understory of the quarter-acre of Seward Park's Ground Zero.  Twenty of those ferns survive six years later. Is there a pattern to that survival, perhaps some clue to the cause of the die-off?  It appears that proximity to trees or logs correlates with survival - but does that stand up to close inspection?  We found that there is a small but statistically significant association.

In this map dead ferns are black circles, survivors are in light green, trees are larger solid circles, and logs are thick black lines.

Leo Shannon and I collected the location and status of all ferns, trees and logs in this quarter acre on May 18th and 19th, 2019.   Dylan Mendenhall did the analysis.   Results are summarized below the map.

Dylan's summary and suggestions:

The survival rate was 10.2% for sword ferns within 15 ft of a tree or log. In contrast, the survival rate was 2.3% for sword ferns further than 15 ft from a tree or log... the odds of a fern surviving are 4.8 times greater if it is located within 15 ft of a tree or log. 

Based on these findings, management recommendations are to:

• Maintain or increase coarse woody debris and mature trees in natural areas
  susceptible to sword fern die-offs
• Prioritize restoration planting within 10 ft of CWD or mature trees

All preliminary data, subsequent revisions, R scripts and figures are available on github . 

First sign of natural regeneration at Seward Park's Ground Zero

Three fringecup plants (Tellima grandiflora if I am not mistaken) have popped up close to each other near the western edge of Seward Park's ground zero.   This is the first regeneration I have seen in the five years since the dominant sword fern community died in this quarter acre.   Here is one of the three. 

Seattle Times Pacific NW article on the Die-off

Seattle Times journalist Sandi Doughton and photographer Erika Schultz have published a magnificent article on the regional sword fern die-off.  Their grasp of the science, the historical context, the social interactions, the politics and complexity of grassroots activism - is, in so many ways, skillful, on point, and insightful.    They tell our story better than we ever could.

Regional Die-off Map (updated March 31 2019 and December 1st 2019)

(click on map to view the interactive version)

Includes 14 sites carefully assayed in the summer of 2019
(1 December 2019)

Better use of color, older data (31 March 2019)

Tim Billo's Presentation to the Washington Native Plant Society, January 3rd 2019

Tim, assisted by Kramer Canup, gave a masterful and comprehensive report on the regional die-off last Thursday.   Here are his slides - accompanied by extensive notes. 

Get the pdf.

Overview

New Posts (please scroll down):

December 2018: request for research proposals, site visit by LSU plant pathologist

October 2018: two experiments, possible insight into mechanisms of spread

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. 

Please add your own observations at our iNaturalist project.

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 (see annotated regional map), 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)
• Port Ludlow die-off, some recovery: 2010 - present
• Experimental Plantings at and near Ground Zero (March 2018)
• Hypotheses

• Die-off reported from Snohomish County, Lord Hill Park (January 2018)
• Extensive die-off confirmed on Bainbridge Island and the NE tip of the Olympic Peninsula (December 2017)
• Narrative Essay - an overview
• Soil Analysis (June 2017)
• King 5 video (2 minutes, May 5th 2017)
• KUOW (27 july 2017)
• Sierra Magazine (August 2017) by Sarah DeWeerdt
• Seattle Precipitation Records (2012-2016, evidence against drought/die-off causality)

Contact: Paul Shannon, Forest Steward

RFP: time to issue requests for research proposals?

Research and experimentation on the sword fern die-off has, over the last four years, been  rather unsystematic.  It has taken us a while to realize the nature and extent of the problem.  Seattle Parks, WSU, UW and citizen scientists have cobbled together some low levels of funding and lots of volunteer effort to run studies as they occur to us.  Seattle Parks ecologist Lisa Cieko has consistently supported the work, finding some funding for consultants and experimental restoration.  

A more systematic approach to research and remediation may now be worth a try.  
In the research circles in which I work - my day job is in computational biology at the Institute for Systems Biology - research strategies and priorities are typically set by a central funding agency.  For us, this is usually the NIH, which identifies topics of interest, circulates requests for proposals, then convenes study sections to review, critique and prioritize the submissions.

The central agency’s budget is usually not known in advance. Once the the annual budget is decided, the top-ranked proposals are funded, and the research begins.  In addition, if especially compelling proposals are received, addressing urgent problems,  these can motivate the search for increased funding.

For the sword fern decline, I propose a similar approach:

• The sword fern working group (or a subcommittee) identifies  broad research topics.
• RFPs are drafted and circulated, with full candor about the uncertainty of funding.  
• Research proposals (with budget options) are submitted by prospective researchers.
• The working group then sketches out various budget scenarios, on the assumption of finding zero, moderate or generous funding.  Funding sources are identified and approached.  
• Proposals are scored and ranked and then awarded funding depending on merit and the actual funding available.

Here are some research topics and projects for which RFPs could be issued:

1. What are the causes of the die-off?
2. How best to monitor die-off, at regional scale, and at the scale of selected small sites?
3. Ongoing actual monitoring projects (based on 2)
4. Determine the population structure (age distribution, mortality, natural replacement)  of healthy fern communities in order to establish a baseline against which to assess and understand the die-off.
5. What happens after die-off?  In what circumstances does unassisted regeneration occur?  In what circumstances does it not?   This topic could include strictly observational studies and/or restoration experiments.