There has been discussion here in the past of whether decorative trees, when planted, drop seeds. Oftentimes, decorative trees may be planted just here and there, rather than altogether in a mass planting, such as the woodlots I use until I can afford to just buy wood from traders. One post I read stated that in order to drop seeds, there must be four or more of a particular tree in the locale in question, within a tile or two of each other. I have two such mass plantings of decorative oaks, because they are by far the fastest-growing. I am transitioning those sites to either farmland or for building, and have not replanted there in two game-years. Yet there are stage 1 oak trees sprouting up in the woodlots. Seems to me those oak trees have been dropping seeds.
Yes I have had this as well when I have planted a mass of oak trees together. But it doesn’t happen every time. Maybe it could be that you need to leave them as mature trees for a while before chppoing them down. Maybe if you chop them down to quickly they don’t drop seeds.
Well, those little stage 1 trees are coming from somewhere, and I didn’t plant them. Perhaps it is as @rhygar states, above, that it takes time for them to start dropping the seeds. I didn’t have to harvest from my woodlots every year, and I also staggered when I did (from one woodlot one year, and the other the next year). And now that I have enough gold coming in that I can just buy wood from the traders, I hadn’t planted in or harvested from my woodlots in 2-3 game-years. And there were all those little size 1 trees.
Devs have said that decor trees do not drop seeds
Any land that is conducive to tree growth will naturally have growth over time. The longer you allow that growth to go untouched, the more seeds that will drop as a result, and the thicker the growth becomes.
The Devs have directly answered the question of whether decorative trees drop seeds, however, and they have declared no. They have however, tweaked the natural growth of trees in the latest version 15f , to allow a more robust natural tree growth than past versions have had.
As for planting decorative trees for the value of the wood, don’t plant them in the forest, away from your village. Place them as close as you can to both the homes of your residents and a stockyard (or use the cargo wagon). You’ll get the best value for growth in three years time for oak trees, at 7 logs per tree.
I plant in 5x5 squares early on at $25 gold each year (25 trees), and then expand from there as the village grows, rotating 3 batches. Planting trees like this is labor intensive for your builders, so make sure you have sufficient numbers of them. I start with 10 builders and then as I plant more trees I increase the number of builders. That enables the builders to keep up with the building maintenance too.
The math equates to every $25 investment producing 175 logs. You can then use those 175 logs for your village consumption, or to trade. The average price for logs that I’ve seen is $3-$5 and there’s usually a trader hard up for them early on. That $25 investment can turn into $500-$850 profit. That’s a minimum 700% return on your money annually. 
They dont spread seeds at anytime. They could, otherwise, improve desirability since its “useless” from the point of view of decoration itself, and from the point that they dont serve for arboring because they dont produce other trees.
I know. My current first woodlot is right in front of my Town Center. The other is over by my crop fields and barns. I currently have over 100 laborers and 50 builders, and at that, my factories and processors and other venues are fully staffed, with multiples of many of the buildings.
Nice! Except that, early on, I keep running out of wood. But after that first push to build the basic buildings and housing, this certainly sounds like a plan! Thank you.
Well, then, I don’t know where all these little stage 1 seedlings are coming from, but they are there in my woodlot.
I think tree’s might spawn if there’s a lot of trees present without seeds being involved due to how the game models tree’s growing.
in real life i work with carpentry, and i have a huge love for oak trees.
so naturally once i’ve cleared an area, made the living quarters, decoration and such, i pop in some oak trees for decoration - and they do spread in my town.
the tree with the red arrow i planted next to the statue, all the others came by themself…