OK, so here's to explain the replanting of trees, which was just added.
You begin by crafting yourself a treeplanter's pot, burning it in a kiln, and filling it with four pieces of clay (as a representation of soil) and 1 liter of water. Then you pick a cone from a fir, and put in into the pot as well. You can now put this pot with a planted tree on a Herbalist's Table, where it will take them between 4 and 16 in-game hours to germinate, depending on your nature/industry alignment. Depending on your nature/industry alignment, it will have a lesser or larger chance to actually sprout (if it doesn't, it dies). A sprouted tree will die in 24 in-game hours unless planted.
Holding a pot with a sprouted tree, you can right-click on the ground to plant the tree. The tree will then grow. It will grow vastly faster on forest terrain than it will anywhere else. Depending on when you cut it down, you will get different stuffs from it.
I think that's all.
EDIT: Edited to reflect the germination time and spontaneous death.
UPDATE: Apple trees now grow faster on grassland than in forests, and they yield much less resources when cut down. Firs, on the other hand, will spread tiny amounts of forest terrain around them when they grow, so that they can be "used" to regain spoiled forests (but they still grow slowly on anything but forest terrain).