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.
