Field Criteria for Identifying a Die-Off Site

We have, as yet, no molecular or organismic markers for sword fern die-off.
Instead, I propose these six easily applied macroscopic site criteria.  These were derived inductively from Seward Park's original ground zero site.  They are strict, intentionally hard to meet, a heuristic useful until molecular markers are found.

1. at least 400 square feet in area
2. approximately symmetrical in shape (a circle or a square)
3.  understory previously dominated  by sword ferns (few or no Oregon grape, salal or shrubs)
4. has 25-40 dead crowns approximately evenly distributed across the 400 sq ft area
5. very few (<5) or no surviving ferns.
6. the affected area grows larger with each passing year