Maple is best
Most trees actually don't have sap runs like maples do. Boxelder works because it is in the maple family. Like maples they need a freeze to make the pressure for the sap to come out. Birch trees make pressure from the roots that makes the sap run. Most other trees don't have sap that comes pouring out if you try to tap them.
There is some kind of syrup made from hickory but it is made from the bark. If you check on the Internet you will be able to read about this information.
First year 2009
18 taps on 12 trees
boiled in 3 gal. pot on electric stove in garage
111 taps on 93 trees
boiling in 200 gal. stainless tank, wood fire
3 sided sugar shack