Question
I am removing a group of scrub oak from the east side of my house in Boise, Idaho. I would like to know what kind of tree I can plant in the soil as I am concerned about the effects of acids or tannins from the oaks on any new trees. The oaks were healthy, just too many acorns to deal with. I would like something fast growing, shady, drought tolerant.

Answer
I think you are concerned about something that does not exist/ It is true that the oak wood contains tannic acid but this is not transferred to the soil. So any tree species you want to plant is fine.
As to the species it will depend on what you want and the site as to the size tree needed. I would suggest you contact the Idaho State Forestry agency and ask one of their Foresters to advice you. Here is the web link to their Urban foresters contact page.
http://www.idl.idaho.gov/Bureau/community_forestry/contacts/index.htm