According to my sometimes sketchy internet reference tools, during the years of the Lamps only trees grew "Yet no birds or flowers had sung or bloomed for these things were still awaiting their time in the bosom of Yavanna", but the trees must have continued growing during the years of the trees, even when there was little light in the eastern parts of Arda, because when the elves awoke at Cuivienen they were in the woods. Also, if Orome was out hunting there must have been sufficient plant life to support animals.
Buy a nice new copy of Silm. is at the top of today's To Do List, as my younger brother (wspauldo12) absconded with my first copy and has now lost it.
After that I can get more exact quotes on the subject.
Sophia