Hi, welcome, all questions are good especially those that don't have a straight answer as it gets everyone thinking even if they have answered it before.
It will probably need some drying, unless it is a ghost, i.e. died while standing and fell later in which case it will depend!
There are ways to speed it up...
e.g.
- Rough turn bowls to about 1" thick
- Plank it to 1" or 2" thick
- Gently heat it
The key ingredient is air, always stack it with spacers to let the air get to all surfaces, the other key is to seal the end grain to even out the drying (PVA, old emulsion paint, wax, even cling film) which will generally give you a better crop of un-split timber.
If you have a lot then go to the local turning club see if you can swap it for some of last years timber which is dried, you would need to negotiate an exchange rate to cover the storage.
IF you rough turn it, please remember to clean and re-oil your tools as required lots of water does lathes and HSS no favors.
Bottom line is if you have a tree to play with and some space to play then try lots of different things. Oak is not good for spalting as the tannin stops most fungus, but if you have excess timber cover some in garden compost, give it a year then see what happens.
Avoid where possible the first few feet of any branches, that is best kept for firewood. the weight of the branch will compress the grain on the bottom and stretch the top so as it dries it tends to split.. except sometimes that can be a good piece to play with...
Depending on many factors the principle one is space, consider yourself lucky and timber rich, all you need now is time and space