The only exception to this is the large number of big-leaf maple seedlings which appear briefly each spring, and which are all dead within a matter of weeks. This year, due to unprecedented amounts of spring time rain, these seedlings are still doing well. I will report on their survival at ground zero over the summer months.
In addition to the ad hoc nitrogen sampling reported earlier on this blog, and the tree canopy Lobaria oregana nitrogen sources reported by Bill Dennison from the Andrews Experimental Forest, there has been related research by the Reimchen lab at the University of Victoria, suggesting - in some circumstances - that salmon can be a nitrogen source.
I live in the south sound where I haven't noticed fern die off aside from one failed transplant. If indeed lack of tree debris is the suspected culprit, clearly one needs to test this by introducing different mulches and debris. But I'd also look for toxins, natural and manufactured.
ReplyDeleteI'm dubious about placing blame on missing debris only because of how successful sword ferns are in groomed gardens where the plants are cut back to their base every spring and all mulch removed. This doesn't address the regeneration question, but certainly ferns can survive for a long time without mulch.
Hi Glen,
ReplyDeleteI think you are right: the current absence of coarse woody debris probably plays a negligible role - or no role at all. And any benefits from restoring traditional old-growth forest ground conditions would take years, if not decades, to appear.
The lack of natural regeneration is puzzling. Seattle Parks has offered a little funding for soil testing, and we hope to get results soon from comprehensive assays of a few different locations: at ground zero, at the edge of the spreading die-off, in parts of Seward's forest with healthy fern communities.
Be sure to let us know if you have more insights, or any field observations which help us figure this out.