Air layering roots?

I found some nice trees that I wish to collect but they grow in rocky soil and it seems that I am not able to get any fine roots with them.
So I was wondering if I could air layer the major roots.
With apple tree I think it would work but what about an oak?
Can I air layer oaks tap root?

I have heard of folks ground layering roots for such trees by digging a trench around the tree and putting in better soil to develop finer roots. I the most extreme environments it can be done over a number of years and they will sometimes set up a system to drip irrigate during the driest seasons. The rap root on an oak will generally be directly below the trunk. I would think it better to get some good lateral roots and then cut the tap when you collect. That being said, my only experience so far is with some seedlings that are now in about their 4th year in which removal of the tap root is a minor operation.

Thank you for responding Marty Weiser.
Ground layering! Thanks for the correct term and thing to feed for the search engine.
I actually did this already for big maple stump with a monstrous surface roots just for try it out.
I cutted biggest roots and placed some spaghnum moss at the cutted ends.
I'm thinking to cut some of the abundant shoots off and then I will leave it alone until next spring.