Tree farming can be extremely successful.
I will dedicate a plot to farming each type of tree that I want. After the initial rush to get the steeloaks and ironbarks planted in the first spring, I'll set them to only plant in Autumn / Winter. That way my farmers aren't delaying planting surface crops in Spring / Summer. But let the farmer plant all of the initial crops first in order to further increase their level. That way the planted acorn is more likely to produce multiple saplings, thereby generating more seeds after processing.
The sawmill generates the seeds (beyond the generic wood ones) and I've never had a problem with the tree farm output increasing when starting with only a limited number of acorns. Usually only 4 is what I start with. Unless I am in a tree scarce area, I don't bring normal tree acorns and will get them from creating the smooth wood at the chopping block or sawmill. There is only a 10% chance that a seed will be generated per sapling.
In my last fort, I had a few hundred steeloak saplings waiting to be processed, but no need to do so since I had a 100+ steel bars laying around already.
