Fungi propagate through spores.

Or do you believe every island independently evolved its own, entirely unique, species of trees, grass, fungi, toads, etc.?

Pollen and spores float in the air. That's why many people suffer from hay-fever. (Including me.) They're spread hither and yon by the winds.

Whether humanity was involved in introducing the fungi or not is therefore irrelevant: *any* species which has such a fragile grip on existence is most likely doomed in the long run. Whether that fungus was introduced by man, or by a passing breeze, the result would have been the same.

We can't protect 'em all. Nor should we. Natural selection has the word "natural" in it for a reason.