Question
I have a paper birch tree in my yard that has tan/brown oblong and circular stains on the bark.

Could you tell me what it might be and if possible the remedy?

Thanks,
Pete  

Answer
Sounds like lichens--These are a combination of a fungi and algea that grow on plants but cause little problems. If the tree is heatly looking (foliage green and no die back) then I would not be concerned with a remedy. Here is a web site that will give more information on lichens:
http://helios.bto.ed.ac.uk/bto/microbes/lichen.htm