"Rupert" writes:

Where is the root system on a tree fern.

I ask because the tree ferns I have seen for sale all appear to be saw
across at the base and appear to be just a stump stuck in a small pot.
I have been told by one garden centre that the root system is near to the
crown so that the trunk is irrelevant

Depends on the species but they certainly run through the trunk, and
the Dicksonia Antarctica is normally transplanted by cutting it near
the ground. The root system will re-establish outside the trunk in a
year or two and some fern nurseries will grow on recent imports for a
year to ensure they will establish.

Anthony