I just went to a lecture on pruning given by a botanist and expert plantsman. He made some specific remarks on Birch trees.

Birches are one of the very worst trees for pruning, because they do not heal well from the wounds. According to this botanist, the latest and greatest science on pruning says you actually want to prune your Birch when they are actively growing and not dormant, even if they "bleed", because the bleeding is a healing response by the tree. Pruning when dormant means the cut takes longer to heal.

However, because of the Birch weakness where healing is concerned, you want to avoid pruning them at all (except for dead wood, or course) if possible. Try to keep cuts to an absolute minimum. Trees need a good amount of energy to heal from cuts, so you weaken them somewhat when you do cut.

Incidentally the tree that handles pruning better than any other is the Apple tree. Scientific experiments show that the healing for Apple trees is almost instantaneous. This is why commercial Apple orchards can be productive for at least 100 years, because the Apple can heal itself so easily.

In contrast, Peach trees are nearly as weak as Birch trees, and the typical commercial Peach orchard lasts only 12-15 years.

The guy gave a great talk.