In campaign mission 1-4, I need to supply wood for an item as one of my quests. In order to do this, I need to build a Sawmill. The production chain ingame recommends a Tree Nursery for a Sawmill, but I'm wondering how necessary it is to have a Tree Nursery if I'm placing the Sawmill in an area that is currently fully forested.
Will there be a negative effect on my Sawmill's productivity if I don't build a Tree Nursery for it? What bonuses will I get if I do choose to build a Tree Nursery?