First evaluations of our short term data on fern groups relative migration revealed an average movement of 800 meters per years for the entire test group, with some species even moving up to 1,4 km per year.
basic map data: Google maps, manipulations by author
As the data shows some fast spreading species of our test group in Osmundaceae displayed a 4 times faster movement then the average. While Osmunda regalis seems to be more resitent to relative change in their environment Osmunda claytoniana performed at a top speed of 2km per year.
Relative spreading of Osmundaceae in constant environments is estimated at 20 meters per year at max.