What sort of evergreens are you planting? Are they native? I replanted a clearcut a year or so ago and even with an abnormally hot summer and a dry fall I'm looking at 30%, tops.
If you haven't yet, you may want to hire a professional forester. At 70% loss they'd likely pay for themselves many times over and save a lot of headache.
These are seedling trees, less than a foot high. They're expected to fail at a pretty high rate. In the future I'll be updating to 2nd year trees which seem to have a better cost/survival rate.