Precommercial thinning

[TREEFARMER at webtv.net]

Make room for a lurker-

We've got an 18 year old walnut/white pine Tree Farm in west central
Illinois and need some ideas on the following:

-Will a stand always respond to release, or can it be locked up so long
that dbh won't increase 
even if released?
-Should trees even be thinned if they're doing well but closely spaced.
-How big a hole is needed in the canopy of a 
mature forest to provide sufficient light for a pine seedling.

FYI-For TSI we don't use brushcutters (pinch and kickback) or herbicides
(flash), just 12"
Echo chainsaws at groundlevel with chaps and
headgear. In a year it's fuelwood.