  Based on a general theory of descendant trees of finite p-groups and the
virtual periodicity isomorphisms between the branches of a coclass subtree, the
behavior of algebraic invariants of the tree vertices and their automorphism
groups under these isomorphisms is described with simple transformation laws.
For the tree of finite 3-groups with elementary bicyclic commutator quotient,
the information content of each coclass subtree with metabelian mainline is
shown to be finite. As a striking novelty in this paper, evidence is provided
of co-periodicity isomorphisms between coclass forests which reduce the
information content of the entire metabelian skeleton and a significant part of
non-metabelian vertices to a finite amount of data.
