Brief reflection on the mountain beaver hypothesis

The mountain beaver hypothesis - that the sword fern die-off is substantially, and maybe primarily the result of mountain beaver predation - is persuasively presented by Tristan, Kramer and Tim.

I wonder what they make of the absence of mountain beaver evidence in the original ground zero, and the radial spread outwards from ground zero around the Hatchery Trail?  

Perhaps there are two primary causes (mountain beaver and a cryptic infection), and that sometimes the effects are mingled?

It would be helpful if we knew the dynamics of the mountain beaver population, which may well be at a peak now, rising perhaps from a minimum in 2008 when coyotes were resident in the park.

 - Paul

Kramer adds details & proposals regarding the mountain beaver hypothesis

I just sent out a link to the shared drive spreadsheet containing the fern data. If you wish to play around with this data, copy and paste it onto another spreadsheet so that none of the numbers get out of place. I do have a backup document but wish for the one posted to stay nice and organized. 

I agree with Tristan that the mountain beavers appear to be having more and more of an impact on the fern population as we continue to further explore around the forests at Seward Park. We came across one section today that looked as if it had been mauled by a pack of mountains beavers. Numerous ferns were completely smashed and flattened as if they had been trampled by a large animal, but the only sign of disturbance appeared to be from mountain beavers. As the surrounding vegetation was not disturbed and countless fronds had been snipped from the smashed ferns. 

Today it seemed that nearly everywhere we walked, we were coming across active mountain beaver dens. We were also thinking that if the system of dens is extensive enough and shallow enough beneath the surface, that this could possible pose problems for increased drought stress on the plants present through disturbing the soil layers and reducing the soils ability to retain moisture throughout the summer. 

As posed numerous times by Tim, I also believe that 5 to 10 exclosure plots in areas where we know mountain beavers are present would be the most effective way to collect quantitative data on the mountain beavers interaction with the sword ferns. Possibly, using the same protocols we have been using for the current 20 plots, we could set up 3x3 exclosure plots inside of larger 5x5 vegetative plots. 

This way we could have an initial data collection on the health of all ferns within the 5x5 plot and then leave the 3x3 exclosure in place for multiple months and come back and re survey the plot and quantify the impact of the mountain beavers on the sword fern population by comparing the amount of fronds removed from the ferns within the 3x3 exclosure and outside of the 3x3 exclosure. 

Many things to ponder here, but seeing that nothing significant is coming from the soil and root samples, testing other hypothesis now may be very worthy. 

Thank you, 

     Kramer

Tristan reports that plots are now complete, that mountain beaver activity is extreme

Kramer and I finished setting up all the plots today! Kramer will send out the coordinates and data this weekend. While we were surveyed we noticed an extreme amount of mountain beaver dens and activity near the plots we were installing. We are starting to further suspect that the beavers may be a high contributor or the sole reason for the die off. I've attached some photos that I took today near plots 18-20 that have lots of beaver dens and activity. 

Best,

Tristan

Tristan O'Mara

Merrell College Ambassador, Outdoor Nation

Program Coordinator, Northwest Women Exec Board

College of the Environment & Department of Biology

University of Washington, Class of 2017

Overview

A mixed lay/scientific group here in Seattle (Seattle Parks ecologists, UW researchers, the Friends of Seward Park) is trying to figure out an unprecedented and alarming sword fern die-off in one hundred acres of old-growth forest in Seward Park.  The affected area is spreading radially; lush understory of two years ago is now bare ground.  Drought, pollution and mountain beaver activity may be contributing factors, but deeper and as yet unknown causes appear to be at play.

Survey: October  2014

Fronds in Detail: October 2015

This blog serves to document and  present our work.  Please contact paul.thurmond.shannon@gmail.com for further information.

Candidate Sword Fern Pests 

Provided by Jenny Glass, from the USDA-APHIS Fungal-Host Database

I am not sure that I ever sent you the list of possibilities that I went through during your DEC 2014 submission:

The literature generally suggests the species Polystichum munitum is relatively disease and pest free and an investigation of other Polystichum species revealed more or less the same information.  As discussed, the laboratory investigated a similar concern about dying sword fern in the Jefferson County area in 2013.  We were also unable to pinpoint the origin of that damage beyond the impression that the sample contained no apparent disease or pest origins of damage.  

The USDA-APHIS Fungal-Host Database had these fungi listed as being observed on sword fern but none of the described fungi are likely to be associated as the cause of this patch of dying plants.

Chaetasbolisia falcata:  Polystichum munitum: California 

Helotium polystichi:  (Basidiomycete):

     Polystichum munitum (On stems.): California 

Herpobasidium abnorme:  (reported to cause distortion):

     Polystichum munitum: Idaho - 

Milesia polystichi - (Milesina winelandi):   (rust- obligate parasite unlikely to kill host)

     Polystichum munitum: California, Canada, Idaho, Montana, Oregon, Washington 

Milesia vogesiaca - (Milesina vogesiaca): (rust- obligate parasite unlikely to kill host)

    Polystichum munitum Canada, Oregon  

Milesina vogesiaca:  (rust- obligate parasite unlikely to kill host): 

    Polystichum munitum California

Milesina winelandi:  (rust- obligate parasite unlikely to kill host):

    Polystichum munitum: California, Idaho, Montana, Oregon, Washington  

Mycena fragillima:  (small saprophytic mushrooms): 

    Polystichum munitum: California, Oregon, Washington  

Phoma adianticola - (Didymella adianticola):  Phomopsis sp.: 

    Polystichum munitum (On fronds.): Oregon 

Phyllosticta sp.: Polystichum munitum (On fronds.): Oregon 

Phytophthora cinnamomi:  (thrives in saturated soils/poor drainage):

     Polystichum munitum (Root rot.): California 

Pythium sp.:  (thrives in saturated soils/poor drainage):

    Polystichum munitum California  

Rhizoctonia solani: (frond blight is a common symptom): 

    Polystichum sp.: California 

Taphrina faulliana: (leaf blister): 

    Polystichum munitum: Canada, Idaho, Oregon, Washington  

Valdensia heterodoxa: (apparent leaf spot/leaf blight pathogen):

    Polystichum munitum: Canada 

Xenasma filicinum - (Phlebiella filicina): 

     Polystichum munitum: Canada

Lab Report from Jenny Glass (12/04/15)

Dr. Marianne Elliott's Report (12/3/2015)

I have attached the sampling procedure and list of samples we collected. We did not find any Phytophthora, but I am not ready to rule it out as the cause of the die-off. It could be a species that is slow growing and difficult to culture, so we missed it. Or it was replaced by something else in dead material. Or this was the wrong time of the year to sample. I think the students who are working on this should keep an eye out for it.

There were a few Pythiums and other similar organisms that we see commonly in soil and roots. We didn't find anything associated with the dying sites vs the healthy sites, or with the dead cedar transplants. I have been asking various people I know and nobody has seen it in their travels, but now they are aware of the situation. I will let you know if anything turns up.

--Marianne

Sample Processing Protocol (Sword fern dieoff samples collected at Seward Park 11/10/15)

Sample #	Description	Treatment
1	5 x 5 plot, healthy, symptomatic fern foliage	Surface sterilize, plate 5 segments on PARPHV8 (3 plates)
2	5 x 5 plot, healthy, crown from healthy fern plant	Surface sterilize 10 necrotic root segments per plate (PARPHV8), dissect crown and look for brown staining symptoms (3 plates). If present, surface sterilize and plate 5 segments on PARPHV8 (1 plate).
3	5 x 5 plot, healthy, soil from base of 3 healthy ferns, upper 5 cm depth + litter & roots	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
4	Ground zero, foliage and fronds from dying ferns	Surface sterilize, plate 5 segments on PARPHV8 (3 plates)
5	Ground zero, crown and roots from dead ferns	Surface sterilize 10 necrotic root segments per plate (PARPHV8), dissect crown and look for brown staining symptoms (3 plates). If present, surface sterilize and plate 5 segments on PARPHV8 (1 plate).
6	Ground zero, soil from base of 3 dead ferns, upper 5 cm depth + litter & roots	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
7	Ground zero, soil from base of 3 dead, planted cedars	Bait in 1 L bottles. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water.
8	Symptomatic foliage from other hosts along trail by Ground zero and road	Surface sterilize, plate 5 segments on PARPHV8 (3 plates).

Baiting protocol for soils

Label 1L bottles with sample and rep numbers. Use rhododendron leaves and healthy sword fern leaves. Place one intact rhody leaf and one sword fern frond in each of 3 bottles containing 100 g soil and 500 ml water. Cap tightly and incubate bottles on their sides for 48-72h.

After incubation, remove baits from bottles and rinse with water, then blot dry. If asymptomatic incubate an additional 3-7 days in ziplock bags containing moist paper towels. Plate symptomatic areas of foliage (5 per plate) on PARPHV8. Use two plates for each bait type per bottle.

All samples

Check for Phytophthora colonies on all plates after 2-5 days and isolate onto small PARP plates for identification.