Mountain Beaver hole close-up
In context (ground zero?
Saturday, February 20, 2016
Paul Talbert's Skepticism regarding the Mountain Beaver Hypothesis
It seems likely that several interacting factors cause the sword fern die-off. Phythophthora and mountain beavers have been proposed. To promote discussion, and in hopes of eventually identifying causes and remedies through open debate, I am posting Paul Talbert's reply to an earlier mountain beaver post here, as a proper blog entry. - Paul Shannon
I remain deeply skeptical of the mountain beaver hypothesis.
1) The area where the fern die-off is currently being documented has been riddled with mountain beaver burrows for years, as I discovered wandering through this area in 2008 when surveying social trails and possible alternative routes during our Comprehensive Trail Plan. However, the ferns were flourishing then.
2) Mountain beavers do eat sword ferns, but when I've seen them, they neatly clip off fronds and drag them into their burrows or eat them in the open. Instead we see fronds that look weak, then turn brown, then die, and eventually drop off. Once they have fallen off, they may resemble clipped fronds (and there also may be clipped fronds), but mountain beavers cannot cause drooping and browning on the plant unless possibly through underground activity that affects the roots. That doesn't seem plausible at ground zero, where there are no burrows.
3) Mountain beavers are found in many other locations, and have been throughout the Holocene at least, but we have not so far received any reports, current or historical, of ferns being laid to waste by mountain beavers.
4) It is possible that if Phytophthora or some other scourge is attacking the roots, mountain beavers may play a role in spreading the oospores, chlamydiospores, and sporangia from place to place. This might help explain the rapid spread, though the various spores can probably get around without assistance.
From the look of the photo, it seems that Oregon grape is still unaffected. While it is plausible that sword fern might be more susceptible to drought, enhanced by mountain beaver activity or not, if it is true that sword fern is being decimated while oregon grape is remaining untouched, that seems more like a species-specific pathogen than a drought, which I would expect to affect everything to some degree or other.
It is great that you are gathering data that can help address these questions.
1) The area where the fern die-off is currently being documented has been riddled with mountain beaver burrows for years, as I discovered wandering through this area in 2008 when surveying social trails and possible alternative routes during our Comprehensive Trail Plan. However, the ferns were flourishing then.
2) Mountain beavers do eat sword ferns, but when I've seen them, they neatly clip off fronds and drag them into their burrows or eat them in the open. Instead we see fronds that look weak, then turn brown, then die, and eventually drop off. Once they have fallen off, they may resemble clipped fronds (and there also may be clipped fronds), but mountain beavers cannot cause drooping and browning on the plant unless possibly through underground activity that affects the roots. That doesn't seem plausible at ground zero, where there are no burrows.
3) Mountain beavers are found in many other locations, and have been throughout the Holocene at least, but we have not so far received any reports, current or historical, of ferns being laid to waste by mountain beavers.
4) It is possible that if Phytophthora or some other scourge is attacking the roots, mountain beavers may play a role in spreading the oospores, chlamydiospores, and sporangia from place to place. This might help explain the rapid spread, though the various spores can probably get around without assistance.
From the look of the photo, it seems that Oregon grape is still unaffected. While it is plausible that sword fern might be more susceptible to drought, enhanced by mountain beaver activity or not, if it is true that sword fern is being decimated while oregon grape is remaining untouched, that seems more like a species-specific pathogen than a drought, which I would expect to affect everything to some degree or other.
It is great that you are gathering data that can help address these questions.
Saturday, January 9, 2016
Phytophthora: oft-proposed candidate pathogen
There are more than 100 species in this genus, whose name translates as "plant destroyer".
P. ramorum is responsible for sudden oak death; P. infestus caused the Irish Potato Famine. Lisa Cieko discovered a 1984 report:
Root Rot of Western Swordfern Caused by Phytophthora cinnamomi in California
The California conservation community is actively monitoring and attempting to remedy extensive outbreaks of Phytophthora species which primarily come from nursery stock, described here:
Bay Nature: New Strains Breaking the Mold
From the California Forest Pest Council:
We have not been able to verify the presence of Phytophthora at Seward Park.
Seward Park Audubon's Kathryn Sechrist asked a San Francisco State botanist colleague to comment on our videos, and received this response:
As to the fern die-off ... I looked over the blog. Although not confirmed, it sure sounds like Phytophthora. It has become a huge problem here in CA, particularly with native plant propagation. I was just at a CNPS board meeting where a policy was passed to try to deal with protocols for raising natives. Huge burden on propagators! Really too bad. But, serious implications for natural systems as well."
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Sharon Baker (Lincoln Park steward) reports possibly related observations from the north coast
With thanks to David Perasso (Martha Washington Park steward) we are able to include this report from Lincoln Park steward Sharon Baker. Our thanks to you both.
Hi David, We hiked there [Sharpe Park on Fidalgo Island, just north of Deception Pass] about a month ago. We hiked the outer loop. There are very few sword ferns on much of the loop, but we did notice a few looking dead on the part of the loop where ferns are scarce. The trail to Sares Head has recently been rebuilt. It is in an area with maybe a 75% cover of sword ferns. There were a lot of dead looking ferns in that area. I couldn't feel any fiddlehead down at the base of the ferns. That may not be a good test, I've now been checking and noticing that on healthy looking ferns too.
We hiked Washington Park, in Anacortes about 3 weeks ago. Again, an area that generally doesn't have a lot of sword ferns. We did come into one area with maybe 30-50% sword fern coverage and there were dead ferns there. No other disturbance apparent (in contrast to trail rebuild near Sares Head).
Nelson Salisbury's Map of the Affected Area, September 2015
Nelson and I walked the boundary, GPS in hand, in late August. Though the boundaries of necessity are rendered as hard well-defined edges, the phenomena themselves were not always clear cut. We informally applied Tim Billo's criteria: include any area in which 30% of the ferns are more then 50% affected.
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
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
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