That's our native western sword fern, Polystichum munitum, and nothing bothers it!! Not deer, not slugs, not diseases and not summer droughts. Just won't grow in consistently wet or saturated soils.

The brown fronds are just last year's left overs (or the year before or before that). Even evergreen plants will develop foliage that ages, browns and dries eventually. Many NW gardeners trim the plant back to the ground in late February/early March before it sends out new fiddleheads. You will have a clean, fully regenerated plant in just a matter of a few weeks.

Or you can go the more laborious route and individually prune out all the brown or dead fronds - your choice :-)

Thank you! Glad to hear that they are hardy - I think they are really beautiful.

I, too, thought that sword ferns were pretty invulnerable, and yours don't look any different from some of mine. However, recently I heard that there has been a big sword fern die-off in the Seattle area: Seward Park ferns

So, we'll all see if this develops into a wider problem...