I was mostly talking about establishing a non native tree as far as fertilization. I've got Bur Oak, English Oak, and Chinese Chestnut that were planted last fall on our land and plan on planting some Chinkapin Oak and Sawtooth plus a bunch more Chinese Chestnuts and the Dunstans i got at Wal Mart this fall. When I planted those last fall I put 20-10-05 365 day slow release in the backfill, That tree will be fed slowly for a year. I don't plan on feeding them again until next spring so they go actually a year and a half on that one initial feeding. A healthy tree will be less likely to get fungus or insect damage that would injure or kill the tree or make it less productive. And more likely to recover from various problems.
I fertilize the Post Oak & Blackjack trees and all the shrubs and forbs around my food plots. I do it in hope that they will put on more and or bigger acorns, most established native trees are fine without fertilizer but providing additional nutrients is good not only for the trees but for everything growing under them too. A lot of browse gets woody and hardened off if it doesnt put on new growth. Fert will help to keep it putting on new growth and provide more browse.
Granual fertilizer on a small oak tree has the potential of killing it because it releases the nutrients very fast.
I use Osmocote slow release for trees 0-2 at a tablespoon or so for the growing season. Then 2 tablespoons for 3 and 4 year old trees. It works well sprinkled on the surface or worked into the dirt around the base of the tree. I also use it when transplanting a tree from a pot to the field. Been using it for 10 years and have yet to burn a tree. Results are a very healthy tree with several growth spurts during the season where the trees are watered regularly. It is pricey and I switch to granular (triple 12), a little at a time after the tree is 6 foot tall or so.
For mature trees, I apply granular at rate as if I were fertilizing the lawn. The slow release fertilizer spikes work well for young trees 4 to 8 years old. One member here suggested 3 holes in the ground at the drip line and a handful of triple 10. I tried it with triple 12 and experienced a little burning of the leaves early this spring. I cannot provide results for this method as we have only had one good rain in my area since May 7!