Things only thrive when there is something the soil has excessive amounts of, or lacks.
For instance here we have smooth bedstraw which thrives in highly acidic soil. To get rid of it, a person just needs to get the PH level up with lime. Here Smooth Bedstraw came when the only limestone plant in New England, decided they would no longer
sell lime for agricultural farms. When the PH level dropped, stressed the other grasses in the sward, Smooth Bedstraw came in!
In one of my fields I had a problem with milkweed, but that thrives when potash is low. A decent amount of potash got rid of all of it...in a weeks time!
I have successfully used sheep to graze-out poison ivy (their favorite food), as well as raspberries.
I would think there is something African Fern really likes, and just change it so that other species can compete with it.