When the problem of routing multicast connections in networks has been
previously considered, the emphasis has been on
 the  source transmitting to a fixed set of
destinations (the multicast group).
There are some applications where destinations will join and leave the
multicast group.
Under these conditions,
computing an ``optimal'' spanning tree after each modification
  may not be the best way to proceed.  An alternative is to make
modest alterations to an existing spanning tree to derive a new one.
An extreme, though non-optimal, variation of this is to use minimal cost source to destination
routing for each destination, effectively ignoring the existing multicast 
tree.
We examine just how non-optimal these trees are in random 
general topology networks and conclude
that they are worse by only a small factor. 
The factor is reduced still further if a hierarchy is imposed upon the random
network to give a more realistic model.