If you want to apply Optimizations on multiple forest objects then You can do the following:
1. Select 1st forstpack object,
2. Pin Selection object
3. Select all forest Pack objects
4. Press Optimize Materials
5. Chose settings and press "Optimize"
We will edit optimizer a bit, so progress bar resets if You do optimization again. Now it does not reset progress bar if You press Optimize more than once one the same object.
Hope this helps.