At risk of offering a suggestion that has more than likely already been examined as obvious, the photos in your blog appear as if we might be dealing with a mycelium complex in the soil that has made the edaphic environment hydrophobic.
It appears as if nothing is regenerating, making it seem evident that the pathogen is not conspecific to Polystichum but simply establishing in Polystichum-friendly habitat.
Have any observations been made of fungal fruiting bodies on the outer edge of the infection sites or have soil samples been examined for the presence of mycelia? This has the gestalt of a ‘fairy ring’ in a lawn. Has anyone attempted to mechanically aereate the Hatchery Creek site to see if something will again begin to grow? The dead zone can seemingly only point to a hydrophobic condition, or to an unlikely pathogen that kills everything in its wake and disallows anything to reestablish.
This is a very interesting hypothesis. Hydrophobic soils are underappreciated (under-loathed might be a better word) and are common where there is a build up of organic matter.
ReplyDeleteIt is very easy to check, though. This coming winter, after we've had 10+ inches of rain, dig down into the soil and see what the water penetration looks like. Dig several test holes in the die off zone and several in non-die off zones and compare. If it's hydrophobic soil, the answer will be obvious.
I should say that while the hypothesis is very interesting (and possible), I think it's unlikely. Hydrophobic soils are very common in Seattle, but the do eventually get wet in our long, rainy winter. The frequent light rains are ideal for eventually wetting them.
David Perasso (not sure how to "log in" to this site, so I'm adding my name to this post).
I was just at Seward park and there are areas of die off where other species are doing fine. They are areas outside of ground zero that, I believe, began to show the problem within the last couple of years.
ReplyDeleteI saw Oxalis oreganum, Rubus ursinus, Acer macrophylum (seedlings), Symphorocarpos sp, Mahonia sp, Gaultheria shallon growing happily next to dead sword ferns. Maybe they will die at some point, but no sign of it yet.
Ground zero is indeed bleak with not much growing, but ground zero is a pure stand of red cedar and not much grows under red cedar anyway, even less will germinate there.
The other thing I noticed is that the organic layer is very thin in most places and there are plenty of spots where mineral soil is exposed. I think it's unlikely for the fungus type of hydrophobia to develop in such conditions.
I don't mean to be negative about Dan Hinkley making such a hypothesis. I've seen the problem myself (especially where too much mulch has been applied), so it's a very reasonable hypothesis. I appreciate very much his and anyone's suggestions about this problem.
I also think its a good idea to test the hypothesis this winter by digging into the soil in several places as I suggested in my earlier comment.