Oak shavings will reduce the pH of your soil for a while, but as it
decomposes they will tend toward neutral pH. In the process they will
tie up nitrogen, so you will have to fertilize. In general, the more
finely divided the wood is, the faster it will take up nitrogen and
decompose. Sticks won't hurt, but sawdust is a problem. Shavings could
be a problem.

If your soil is in the range ph 5.5-7.0, I wouldn't worry about it
unless you are trying to grow something like blueberries, which need
acid. If it's above 7.0, sulfur is a way to produce a more lasting acid
reaction without affecting soil nutrients.