Carlos in Spain wrote that he wanted to move a
50 year old Acer pseudoplatanus, Sycamore Maple,
and asked what he might expect in terms of root
size and the chances of success in moving the
tree to his garden.
Fabius answered saying that he had heard that the
roots would be about as deep as the tree is high and
that the roots would have a spread of about as wide
as the tree canopy.
There are lots of books showing the shape of the root mass
as essentially the mirror image of the canopy but this is
really not accurate. The roots mostly go out rather than
down. Some trees have a relatively small and compact root
ball while others have a shallow and spreading root ball.
The tree will be difficult to move because of the spread of
the roots more than the depth.
I would think the best bet would be to root prune on one
side of the tree one year and to do the other side the year
after. My guess that it would also take a bit of luck to get
that large a tree to really handle a move without some expert
movers.